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CONTENTS
Stock Unit
History of Management and Assessment
Commercial Fishery Landings
Commercial Fishery Discards
Recreational Fishery Landings
Recreational Fishery Discards
Total Catch Composition
Research Survey Indices of Abundance
Biological Data
2010 Updated Fishing Mortality Rate and Stock Size Estimates
Biological References Points
2010 Updated Stock Status
Projections
Major Sources of Assessment Uncertainty
Acknowledgments
Literature Cited

Northeast Fisheries Science Center Reference Document 10-14

Stock Assessment of Summer Flounder for 2010

Mark Terceiro
NOAA Fisheries, Northeast Fisheries Science Center, 166 Water Street, Woods Hole MA 02543

Web version posted July 29, 2010

Citation: Terceiro M. 2010. Stock assessment of summer flounder for 2010. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 10-14; 133 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://nefsc.noaa.gov/publications/

Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.

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EXECUTIVE SUMMARY

This assessment of the summer flounder (Paralichthys dentatus) stock along the Atlantic coast (Maine to North Carolina) is an update through 2009 of commercial and recreational fishery catch data, research survey indices of abundance, and the analyses of those data. Reported 2009 landings in the commercial fishery were 4,848 mt, about 1% under the commercial quota. Commercial discard losses in the otter trawl and scallop dredge fisheries are estimated from fishery observer data and have recently accounted for 5%-10% of the total commercial catch, assuming a discard mortality rate of 80%. Estimated 2009 landings in the recreational rod-and-reel fishery were 2,856 mt, about 12% under the recreational harvest limit.  Recreational discard losses have recently accounted for 15%-20% of the total recreational catch, assuming a discard mortality rate of 10%. Total commercial and recreational landings in 2009 were 7,704 mt, and total catch was estimated at 9,017 mt.

The summer flounder stock is not overfished and overfishing is not occurring relative to the biological reference points established in the 2008 SAW 47 assessment.  The stock is currently under a rebuilding program with a deadline of January 1, 2013 (corresponding to the November 1, 2012 estimate of SSB). Fishing mortality (F) calculated from the average of the currently fully recruited ages (3-7+) ranged between about 1.0 and 2.0 during 1982-1996. The fishing mor­tality rate has declined to below 1.0 since 1997 and was estimated to be 0.237 in 2009, below the threshold fishing mortality reference point FMSY = F35% =  0.310.  There is a 50% probability that the fishing mortality rate in 2008 was between 0.224 and 0.250.  Spawning stock biomass (SSB) decreased from about 25,000 mt in the early 1980s to about 7,000 in 1989, then increased to above 40,000 mt by 2002.  SSB was estimated to be 53,458 mt in 2009, about 89% of the SSBMSY = SSB35% target reference point = 60,074 mt.  There is a 50% chance that SSB in 2008 was between 50,560 and 55,998 mt.  The arithmetic average recruitment from 1982 to 2008 is 42 million fish at age 0.  The 1982 and 1983 year classes are the largest in the assessment time series, at 73 and 81 million fish; the 1988 year class is the smallest at 13 million fish. The 2008 year class is estimated to be about 49 million fish, 17% above the average. The 2009 year class is currently estimated to be about 82 million fish, about twice the average, and is the largest in the assessment time series.  The summer flounder stock assessment has historically exhibited a consistent retrospective pattern of underestimation of F and overestimation of SSB; the causes of this pattern have not been determined. A recent pattern of overestimation in recruitment is also evident. Over the last 7 years, the annual internal model retrospective error in fishing mortality has ranged from +11% in the 2006 terminal year to -35% in 2003, while the annual internal model retrospective error in SSB has ranged from -13% in 2006 to +45% in 2003. Over the last 3 terminal years, the annual internal model retrospective error in recruitment has ranged from +54% for the 2008 year class to +80% for the 2006 year class. Comparison of the estimates for SSB, R and F over the last three assessments indicates consistency of those estimates in line with the most recent internal retrospective pattern of the 2010 assessment model.

STOCK UNIT

The definition of Wilk et al. (1980) of a unit stock extending from Cape Hatteras north to New England has been accepted in this and previous assessments. A consideration of summer flounder stock structure incorporating tagging data concluded that evidence supported the existence of stocks north and south of Cape Hatteras, with the stock north of Cape Hatteras possibly composed of two distinct spawning aggregations, off New Jersey and Virginia-North Carolina (Kraus and Musick 2001). The conclusions of Kraus and Musick (2001) are consistent with the current assessment unit stock. The MAFMC and ASMFC joint Fishery Management Plan (FMP) defines the management unit for summer flounder as extending from the southern border of North Carolina north to the U.S.-Canadian border. A summer flounder genetics study revealed no population subdivision at Cape Hatteras (Jones and Quattro 1999), consistent with the definition of the management unit.

HISTORY OF MANAGEMENT AND ASSESSMENT

An overview of the history of the summer flounder FMP and assessment is provided in this section and the box below. Management of the summer flounder fishery began through the implementation in 1988 of the original Summer Flounder FMP, a time that coincided with the lowest levels of stock biomass for summer flounder since the late 1960s. The MAFMC and ASMFC cooperatively develop fishery regulations, with NMFS serving as the federal implementation and enforcement entity. Cooperative management was developed because significant catch is taken from both state (0-3 miles offshore) and federal waters (3-200 miles offshore). 

Amendment 1 to the FMP in 1990 established the overfishing definition for summer flounder as equal to Fmax, initially estimated as 0.23 (NEFC 1990). Amendment 2 in 1992 established target fishing mortality rates for summer flounder for 1993-1995 as F = 0.53, and Fmax = 0.23 for 1996 and beyond. Regulations enacted under Amendment 2 to meet those fishing mortality rate targets included 1) an annual fishery landings quota with 60% allocated to the commercial fishery and 40% to the recreational fishery based on the historical (1980-1989) division of landings, with the commercial allocation further distributed among the states based on their share of commercial landings during 1980-1989,  2) a commercial minimum landed fish size limit at 13 in (33 cm),  3) a minimum mesh size of 5.5 in (140 mm) diamond or 6.0 in (152 mm) square for commercial vessels using otter trawls that possess 100 lbs (45 kg) or more of summer flounder, with exemptions for the flynet fishery and vessels fishing in an exempted area off southern New England (the Northeast Exemption Area) during 1 November to 30 April, 4) permit requirements for the sale and purchase of summer flounder, and 5) annually adjustable regulations for the recreational fishery, including an annual harvest limit, closed seasons, a 14 in (36 cm) minimum landed fish size, and possession limits.

The results of stock assessments in the mid-1990s indicated that summer flounder abundance was not increasing as rapidly as projected when Amendment 2 regulations were implemented. In anticipation of the need to drastically reduce fishery quotas in 1996 to meet the management target of Fmax, the MAFMC and ASMFC modified the fishing mortality rate reduction schedule in 1995 to allow for more stable landings from between years, while slowing the rate of stock rebuilding. Amendment 7 to the FMP set target fishing mortality rates of 0.41 for 1996 and 0.30 for 1997, with a target of Fmax = 0.23 for 1998 and beyond. Total landings were to be capped at 8,400 mt (18.51 million lbs) in 1996-1997, unless a higher quota in those years provided a realized F = 0.23.  

Amendment 12 in 1999 defined overfishing for summer flounder as occurring when the fishing mortality rate exceeds the threshold fishing mortality rate of FMSY.  Because FMSY could not be reliably estimated for summer flounder, Fmax = 0.24 was used as a proxy for FMSY; FMSY was also defined as the target fishing mortality rate.  Under Amendment 12, the stock was defined to be overfished when total stock biomass fell below the biomass threshold of one-half of the biomass target, BMSY.  Because BMSY could not be reliably estimated, the biomass target was defined as the product of total biomass per recruit and contemporary (1982-1996) median recruitment, at that time estimated to be 153,350 mt (338 million lbs), with the biomass threshold defined as 76,650 mt (169 million lbs).  In the 1999 stock assessment (Terceiro 1999) the reference points were updated using new estimates of median recruitment (1982-1998) and mean weights at age (1997-1998), which resulted in a biomass target of 106,444 mt (235 million lbs) and minimum biomass threshold of 53,222 mt (118 million lbs). The Terceiro (1999) reference points were retained in the 2000 and 2001 stock assessments (NEFSC 2000, MAFMC 2001a) because of the stability of the input data. Concurrent with the development of the 2001 assessment, the MAFMC and ASMFC convened the Summer Flounder Overfishing Definition Review Committee to review these biological reference points. The work of this Committee was later reviewed by the MAFMC SSC in August 2001. The SSC recommended that using the FMSY proxy for Fmax = 0.26 was appropriate and should be retained for 2002, and endorsed the recommendation of SARC 31 (NEFSC 2000) which stated that “...the use of Fmax as a proxy for FMSY should be reconsidered as more information on the dynamics of growth in relation to biomass and the shape of the stock recruitment function become available” (MAFMC 2001b).

The 2002 SAW 35 assessment (NEFSC 2002) indicated the summer flounder stock was overfished and overfishing was occurring relative to the biological reference points. The fishing mortality rate had declined from 1.32 in 1994 to 0.27 in 2001, marginally above the overfishing reference point (Fthreshold = Ftarget = Fmax = 0.26). Total stock biomass in 2001 was estimated as 42,900 mt (94.6 million lbs), or 19% below the biomass threshold (53,200 mt; 117.3 million lbs).  The 2002 SAW35 Review Panel concluded that updating the biological reference points was not warranted at that time (NEFSC 2002). Subsequent updates to the stock assessment were completed in 2003 (Terceiro 2003), 2004 (SDWG 2004), and 2005 (NEFSC 2005). While the 2003 assessment found the summer flounder stock was not overfished and no overfishing was occurring, the 2004 and 2005 assessments found the stock again experiencing overfishing. The 2005 SAW 41 assessment recommended updating the values for the fishing mortality and stock biomass reference points (NEFSC 2005).

A peer review of the assessment occurred in 2006 by the NMFS Office of Science and Technology Division (S&T) (Terceiro 2006a, 2006b). This review made several recommendations, including modification of the definition of the overfished stock from the original definition under Amendment 2 to the FMP. Instead of using January 1 total stock biomass (TSB), the stock was considered overfished when November 1 spawning stock biomass (SSB) fell below one-half SSBMSY = 44,706 mt (98.6 million lbs).   The 2006 S&T assessment concluded that the stock was not overfished, but that overfishing was occurring relative to the updated reference points (Terceiro 2006b).

The 2007 assessment update (SDWG 2007) found that relative to the 2006 S&T assessment biological reference points, the stock was overfished and overfishing was occurring. The fishing mortality rate estimated for 2006 was 0.35, a significant decline from the 1.32 estimated for 1994 but above the threshold of 0.28.

The most recent peer review of the assessment occurred at the 2008 SAW 47 (NEFSC 2008).  In the 2008 SAW 47 assessment, the age-structured assessment model changed from an ADAPT virtual population analysis (VPA) model to a forward projecting, ASAP statistical catch at age (SCAA) model (NFT 2008a), and the fishery catch was modeled as two fleets: totals landings and total discards. A new value for the instantaneous natural mortality rate (M) was adopted, changing from a constant value of M = 0.20 to age- and sex-specific values that resulted in a mean value of M = 0.25. Biological reference points were therefore also revised; the proxy for FMSY changed from Fmax to F35%, and F40% was recommended as Ftarget.  The assessment concluded that the stock was not overfished and overfishing was not occurring in 2007, relative to the revised biological reference points.  Fishing mortality calculated from the average of the currently fully recruited ages (3-7+) ranged between 1.143 and 2.042 during 1982-1996. The fishing mor­tality rate was estimated to be 0.288 in 2007, below the fishing mortality reference point = F35% = FMSY = 0.310.  SSB was estimated to be 43,363 in 2007, about 72% of the SSB35% = SSBMSY reference point = 60,074 mt. The assessment exhibited a consistent retrospective pattern of underestimation of F and overestimation of SSB, but no consistent retrospective pattern in recruitment.

This 2010 assessment update uses the same model as the 2008 SAW 47 and 2009 updated (Terceiro 2009) assessments.  Fishery and survey catches have been updated through 2009.  Status determination is made by comparison to the 2008 SAW 47 biological reference points.

Summary of the history of the Summer Flounder, Scup, and Black Sea Bass FMP.

Year Document Plan Species Management Action
1988 Original FMP summer flounder - Established management plan for summer flounder
1991 Amendment 1 summer flounder - Established an overfishing definition for summer flounder
1993 Amendment 2 summer flounder - Established rebuilding schedule, commercial quotas, recreational harvest limits, size limits, gear restrictions, permits, and reporting requirements for summer flounder
- Created the Summer Flounder Monitoring Committee
1993 Amendment 3 summer flounder - Revised the exempted fishery line
- Increased the large mesh net threshold
- Established otter trawl retentions requirements for large mesh use
1993 Amendment 4 summer flounder - Revised state-specific shares for summer flounder quota allocation
1993 Amendment 5 summer flounder - Allowed states to combine or transfer commercial summer flounder quota
1994 Amendment 6 summer flounder - Set criteria for allowance of multiple nets on board commercial vessels for summer flounder
- Established deadline for publishing catch limits, commercial mgmt. measures for  summer flounder
1995 Amendment 7 summer flounder - Revised the F reduction schedule for summer flounder
1996 Amendment 8 summer flounder and scup - Incorporated Scup FMP into Summer Flounder FMP and established scup measures including commercial quotas, recreational harvest limits, size limits, gear restrictions, permits, and reporting requirements
1996 Amendment 9 summer flounder and black sea bass - Incorporated Black Sea Bass FMP into Summer Flounder FMP and established black sea bass measures including commercial quotas, recreational harvest limits, size limits, gear restrictions, permits, and reporting requirements
1997 Amendment 10 summer flounder, scup, and black sea bass - Modified commercial minimum mesh requirements, continued commercial vessel moratorium, prohibited transfer of fish at sea, and established special permit for party/charter sector for summer flounder
1998 Amendment 11 summer flounder, scup, and black sea bass - Modified certain provisions related to vessel replacement and upgrading, permit history transfer, splitting, and permit renewal regulations
1999 Amendment 12 summer flounder, scup, and black sea bass - Revised FMP to comply with the SFA and established framework adjustment process
2001 Framework 1 summer flounder, scup, and black sea bass -Established quota set-aside for research for all three species
2001 Framework 2 summer flounder - Established state-specific conservation equivalency measures for summer flounder
2003 Amendment 13 summer flounder, scup, and black sea bass - Addressed disapproved sections of Amendment 12 and included new EIS
2003 Framework 3 scup - Allowed the rollover of winter scup quota
- Revised start date for summer quota period for scup fishery
2003 Framework 4 scup - Established system to transfer scup at sea
2004 Framework 5 summer flounder, scup, and black sea bass - Established multi-year specification setting of quota for all three species
2006 Framework 6 summer flounder - Established region-specific conservation equivalency measures for summer flounder
2007 Amendment 14 scup - Established rebuilding schedule for scup
2007 Framework 7 summer flounder, scup, and black sea bass - Built flexibility into process to define and update status determination criteria for each plan species
- Scup GRAs made modifiable through framework adjustment process

COMMERCIAL FISHERY LANDINGS

Total U.S. commercial landings of summer flounder from Maine to North Carolina peaked in 1979 at nearly 18,000 mt (39.7 million lbs, Table 1, Figure 1). The reported landings in 2009 of 4,848 mt (10.69 million lbs) were about 1% under the final 2009 commercial quota. Since 1980, about 70% of the commercial landings of summer flounder have come from the Exclusive Economic Zone (EEZ; greater than 3 miles from shore). Large variability in summer flounder landings exist among the states, over time, and the percent of total summer flounder landings taken from the EEZ has varied widely among the states.

Northeast Region (NER; Maine to Virginia)

Annual commercial landings data for summer flounder in years prior to 1994 were obtained from detailed trip-level landings records contained in master data files maintained by the NEFSC (the “weighout system”; 1963-1993) and from summary reports of the Bureau of Commercial Fisheries and its predecessor the U.S. Fish Commission (1940-1962).  Prior to 1994, summer flounder commercial landings were allocated to NEFSC 3-digit statistical area according to interview data (Burns et al. 1983). Beginning in 1994, landings estimates were derived from mandatory dealer reports under the current NMFS Northeast Region (NER) summer flounder quota monitoring system. During 1994-2008, dealer landings were allocated to statistical area using fishing Dealer and fishing Vessel Trip Reports (VTR data) in a multi-tiered allocation procedure at the fishing-trip level (Wigley et al., 2007). Three-digit statistical areas 537-539 (Southern New England), 611-616 (New York Bight), 621, 622, 625, and 626 (Delmarva region), and 631 and 632 (Norfolk Canyon area) have generally accounted for over 80% of the NER commercial landings since 1992 (Table 2).

A summary of length and age sampling of summer flounder landings collected by the NEFSC commercial fishery port agent system in the NER is presented in Table 3.  For comparability with the manner in which length frequency sampling in the recreational fishery has been evaluated, sampling intensity is expressed in terms of metric tons of landings (mt) per 100 fish lengths measured.  The sampling is proportionally stratified by market category (jumbo, large, medium, small, and unclassified), with the sampling distribution generally reflecting the distribution of commercial landings by market category. Overall sampling intensity has improved markedly since 1995, from 165 mt per 100 lengths to 17 mt per 100 lengths, and temporal and geographic coverage has generally improved as well.

The age composition of the NER commercial landings for 1982-1999 was generally estimated semi-annually by market category and 1-digit statistical area (e.g., area 5 or area 6), using standard NEFSC procedures (market category length frequency samples converted to mean weights by length-weight relationships; mean weights in turn divided into landings to calculate numbers landed by market category; market category numbers at length apportioned to age by application of age-length keys). For 2000-2002, sampling was generally sufficient to make quarterly estimates of the age composition in area 6 for the large and medium market categories. For 2003-2009, sampling was generally sufficient to make quarterly estimates of the age composition in areas 5 and 6 for the jumbo, large, and medium market categories.  The proportion of large and jumbo market category fish (generally of ages 3 and older) in the NER landings has increased since 1996, while the proportion of small market category landings (generally of ages 0 and 1) has become very low (Table 4, Figure 2). The mean size of fish landed in the NER commercial fishery has been increasing since 1993, and was 0.9-1.1 kg (2.0-2.4 lbs) during 2000-2009, typical of an age 3 to 4 summer flounder (Table 5).

North Carolina

The North Carolina winter trawl fishery accounts for about 99% of summer flounder commercial landings in North Carolina. A separate landings at age matrix for this component of the commercial fishery was developed from North Carolina Division of Marine Fisheries (NCDMF) length and age frequency sample data. The NCDMF program samples about 10% of the winter trawl fishery landings annually, most recently (2006-2009) at rates of less than 10 metric tons of landings per 100 lengths measured (Table 6).  All length frequency data used in construction of the North Carolina winter trawl fishery landings at age matrix were collected in the NCDMF program; age-length keys from NEFSC commercial data and NEFSC spring survey data (1982-1987) and NCDMF commercial fishery data (1988-2009) were combined by appropriate statistical area and semi-annual period to resolve lengths to age. Fishery regulations in North Carolina also changed between 1987 and 1988, with increases in both the minimum mesh size of the codend and minimum landed fish size taking effect.  It is not clear whether the change in regulations or the change in keys, or some combination, is responsible for the decreases in the numbers of age-0 and age-1 fish estimated in the North Carolina commercial fishery landings since 1987.  Landed numbers at age and mean weight at age from this fishery are shown in Table 7 and Table 8.

COMMERCIAL FISHERY DISCARDS

In the 1993 SAW 16 assessment, an analysis of variance of  NER Fishery Observer data for summer flounder was used to identify stratification variables for an expansion procedure to estimate total landings and discards from the observer data kept and discard rates (weight per day fished) in the commercial fishery. Initial models included year, quarter, fisheries statistical division (2-digit area), area (divisions north and south of Delaware Bay), and tonnage class as main effects. Quarter and division consistently emerged as significant main effects without significant interaction with the year (NEFSC 1993).  The estimation procedure expands transformation bias-corrected geometric mean catch (landings and discards) rates in year, quarter, and division strata by total days fished (days fished on trips landing any summer flounder by any mobile gear, including fish trawls and scallop dredges) to derive fishery landings and discards. The use of fishery effort as the multiplier (raising factor) allows estimation of landings from the fishery observer data for comparison with dealer reported landings, to help judge the potential accuracy of the procedure.  For strata with no observer sampling, catch rates from adjacent or comparable strata were substituted as appropriate (except for Division 51, which generally has very low catch rates and negligible catch). Estimates of discard were stratified by 2 gear types (scallop dredges; trawls) for years when data were adequate (1992 and later years).   The NER Fishery Observer sample data aggregated on an annual basis for 1989-2009 are summarized in Table 9.

While estimates of catch rates from the NER Fishery Observer data were used in this assessment to estimate total discards, catch rate information is also reported in the NER Vessel Trip Report (VTR) data for 1994-2008 (Table 10). A comparison of discard to total catch ratios for the Fishery Observer and VTR data sets for trawl and scallop dredge gear indicates similar discard rates from the two data sources through the 1990s. Since about 2000, Overall Fishery Observer and VTR discard to total catch ratios have diverged, with the Fishery Observer data generally indicating higher discard rates. Discard rates of summer flounder in the scallop dredge fishery were generally much higher than in the trawl fishery.

The change in mid-1994 from the interview/weighout data reporting system to the VTR/mandatory dealer report system required a change in the estimation of effort (days fished) to estimate total discards.  An initial examination of days fished and catch per unit effort (CPUE; landings per day fished) for cod conducted at SAW 24 (NEFSC 1997a) compared these quantities as reported in the full weighout and VTR data sets (DeLong et al., 1997). This comparison indicated a shift to a higher frequency of short trips (trips with one or two days fished reported), and to a mode at a lower rate of CPUE.  It was not clear at SAW 24 if these changes were due to the change in reporting system (i.e., the units reported were not comparable), or real changes in the fishery, and so effort data reported by the VTR system were not used quantitatively in the SAW 24 assessments.  In the 1997 SAW 25 assessment for summer flounder (NEFSC 1997b), a slightly different comparison was made. The port agent interview data for 1991-1993 and merged dealer/VTR data for 1994-1996, which under each system serve as the “sample” to characterize the total commercial landings, were compared in relative terms (percent frequency).  For summer flounder, the percent frequency of short trips (lower number of days fished per trip) increased during 1991-1996, but not to the degree observed for cod, and the mode of  CPUE rates for summer flounder increased in spite of lower effort per trip.  For the summer flounder fishery, these may reflect actual changes in the fishery, due to increased restrictions on allowable landings per trip (trip landings limits might lead to shorter trips) and stock size increases (higher CPUE).  As for cod, however, the influence of each of these changes (reporting system, management changes, stock size changes) has not been quantified. Total days fished in the summer flounder fishery were comparable between the period from 1989-1993 and 1994. Since 1994, total days fished have ranged from 20,670 days in 1999 to 7,615 days in 2008 with a mean of about 12,000 days, a substantial decline relative to the 1989-1993 mean of 22,000 days. Because the effort measure is critical to the estimation of discards for summer flounder, the VTR data were used as the best data source to estimate summer flounder fishery days fished for 1994-2009.

The approach described above was based only on the day fished data for ports in the NER during 1989-1996, and so it was necessary to raise the discard estimate to account for discarding occurring outside the NER reporting system (i.e., NER state reporting systems such as Connecticut, Virginia and North Carolina). To determine the proper raising factor, landings accounted for by the NER reporting system (which result from the fishing effort on which the fishery observer discard estimate is based) were compared with total NER landings, plus that portion of North Carolina landings from the EEZ (it is assumed that only the North Carolina fishery in the EEZ would experience significant discard, as mesh regulations in state waters have resulted in very low discards in state waters since implementation of the regulation in 1989; R. Monaghan, NCDMF; personal communication, June 30, 1997).  As a result of this exercise, the total discard estimates were raised by 11 to 38% for 1989-1996.  Since 1996, all states’ landings and are included in the NER dealer reporting system, so no raising is necessary to account for missing landings.

Two additional adjustments were made to the dealer/VTR matched data subset days fished estimates to fully account for summer flounder fishery effort during 1994-2009.  First, the landings to days fished relationship in the matched set was assumed to be the same for unmatched trips, and so the days fished total in each discard estimation stratum (2-digit area and quarter) was raised by the dealer to matched set landings ratio. This step in the estimation accounted for days fished associated with trips landing summer flounder, and provided an estimate of discard for trips landing summer flounder. Given the restrictions on the fishery however, there is fishing activity which results in summer flounder discards, but no landings, especially in the scallop dredge fishery. The days fished associated with these trips was accounted for by raising strata discard estimates by the ratio of the total days fished on trips catching any summer flounder (trips with landings and discard, plus trips with discard only) to the days fished on trips landing summer flounder (trips with landings and discard). For this step, it is necessary to assume  that the discard rate (as indicated by the fishery observer data, which includes trips with discard but no landings, and which is used in previous estimation procedure steps) is the same for trips with only discards as for trips with both landings and discards.

Discard estimates are summarized in Table 11. Commercial fishery discard mortality in weight was highest in 1990-1991 and 1999, and lowest in 2009.  Scallop dredge fishery discard to landed ratios are much higher than trawl fishery ratios, purportedly because of closures and trip limits. Although the scallop dredge landings of summer flounder are less than 5% of the total, the discards of summer flounder are of the same order of magnitude as in the trawl fishery. Annual commercial fishery discards estimated for 2006-2009 were less than 20% of the annual reported commercial landings.

Table 12 presents a comparison of commercial fishery dealer reported landings of summer flounder with estimates of summer flounder commercial landings from landings rates of NEFSC Fishery Observer sampling and commercial fishing effort (days fished) reported on commercial NER Vessel Trip Reports (VTR) . Estimates of landings from observer data ranged from +53% (1999) to -77% (2007) of the reported landings in the fisheries, with discards ranging from 38% (1990) to 3% (2009) of the dealer reported landings. Since 2003, the estimate of landings from the Observer data has averaged about 65% below the reported landings. An alternative discard estimation approach explored for the 2008 SAW 47 assessment provided no improvement in precision or “accuracy” of discard estimates through 2003, but the recent consistent trend suggests the estimation procedure needs to be reconsidered in next benchmark assessment.

As recommended by SAW 16 (NEFSC 1993), a commercial fishery discard mortality rate of 80% was assumed to develop the final estimate of discard mortality (Table 11). The 2008 SAW 47 assessment (NEFSC 2008) considered some preliminary information from a 2007 Cornell University Cooperative Extension study which conducted ten scientific trips on inshore multispecies commercial trawling vessels to determine discard mortality rates relative to tow duration, fish size, and the amount of time fish were on the deck of the vessel. The median mortality for all tows combined was 78.7%, very close to the estimated overall discard mortality of 80% used in the assessment.. The 2008 SAW 47 Review Panel recommended additional work be conducted to understand factors affecting discard mortality rates and the difference between the inshore (day-trip) and offshore (multi-day) components of the multispecies trawl fishery to facilitate future application of this information at a broader scale.

Existing NER Fishery Observer data were used to develop estimates of commercial fishery discard for 1989-2009. However, adequate data (e.g., interviewed trip data, survey data) are not available to develop summer flounder discard estimates for 1982-1988.  Discard numbers were assumed to be very small relative to landings during 1982-1988 (because of the lack of a minimum size limit in the EEZ), but to have increased since 1989 with the implementation of fishery regulations in the EEZ.  It was recognized that not accounting directly for commercial fishery discards in 1982-1988 would result in an underestimation of fishing mortality and population sizes in these years.

Discard estimates at length and age were stratified by gear for 1994-2000 and 2002-2008, again due to sample size considerations (Table 13). Only 11 fish were sampled from the sea scallop dredge fishery 2001, and so the scallop dredge discards were assumed to have the same length and age composition as the trawl fishery discards in 2001. NER Fishery Observer length frequency samples were converted to sample numbers at age and sample weight at age frequencies by application of NEFSC survey length-weight relationships and Fishery Observer, commercial fishery, and survey age-length keys.  Sample weight proportions at age were next applied to the raised fishery discard estimates to derive fishery total discard weight at age.  Fishery discard weights at age were then divided by fishery observer mean weights at age to derive fishery discard numbers at age. Classification to age for 1989-1993 was done by semi-annual periods using Fishery Observer age-length keys, except for 1989, when first period lengths were aged using combined commercial landings (quarters 1 and 2) and NEFSC spring survey age-length keys. For 1994-2008, only NEFSC winter, spring, and fall survey age-length keys were used, since Fishery Observer age-length keys were not yet available and commercial landings age-length keys contained an insufficient number of small summer flounder (<40 cm = 16 inches) that comprise most of the discards. Estimates of discarded numbers at age, mean length and mean weight at age are summarized in Table 13, Table 14, and Table 15.

The reason for discarding in the trawl and scallop dredge fisheries has been changing over time. During 1989 to 1995, the minimum size regulation was recorded as the reason for discarding summer flounder in over 90% of the observed trawl and scallop dredge tows. In 1999, the minimum size regulation was provided as the reason for discarding in 61% of the observed trawl tows, with quota or trip limits given as the discard reason in 26% of the observed  tows, and high-grading in 11% of the observed tows.  In the scallop fishery in 1999, quota or trip limits was given as the discard reason in over 90% of the observed tows. During 2000-2005, minimum size regulations were identified as the discard reason in 40-45% of the observed trawl tows, quota or trip limits in 25-30% of the tows, and high grading in 3-8%. In the scallop fishery during 2000-2005, quota or trip limits was given as the discard reason for over 99% of the observed tows. During 2006-2009, minimum size regulations were identified as the discard reason in 15-20% of the observed trawl tows, quota or trip limits in 60-70% of the tows, and high grading in 5-10%. In the scallop fishery during 2006-2009, quota or trip limits was given as the discard reason for about 40% of the observed tows, with about 50% reported as “unknown.” As a result of the increasing impact of trip limits, fishery closures, and high grading as reasons for discarding, the age structure of the summer flounder discards has also changed, with a higher proportion of older fish being discarded (Table 13).

RECREATIONAL FISHERY LANDINGS

Summary landings statistics for the summer flounder recreational fishery (catch type A+B1) as estimated by the NMFS Marine Recreational Fishery Statistics Survey (MRFSS) are presented in Table 16 and Table 17.  Recreational fishery landings decreased 17% by number and 20% by weight from 2008 to 2009. and were about 12% under the 2009 recreational harvest limit.

The commercial fishery VTR system provides an alternative set of reported recreational landings by the party/charter boat sector. A comparison of VTR reports and MRFSS estimates indicates that MRFSS estimates are higher by a factor of 2-3 for the 1995-2009 period, with an increasing trend in recent years and ranging from a factor of 1.02 in 1998 to 5.47 in 2005 (Table 18). It is unclear if this is due mainly to under-reporting of party/charter boat recreational landings in the VTR system, or a systematic positive bias of MRFSS landings estimates for the party/charter boat sector.

Length frequency sampling intensity for the recreational fishery was calculated by MRFSS sub-regions (North - Maine to Connecticut; Mid - New York to Virginia; South - North Carolina) based on a metric tons of landings per hundred lengths measured basis (Burns et al.1983). For 2009, aggregate sampling intensity averaged 123 mt of landings per 100 fish measured (Table 19).  To convert the recreational fishery length frequencies to age, MRFSS sample length frequency data, NEFSC commercial and survey age-length data were examined in terms of number of fish measured/aged on various temporal and geographical bases. Correspondences were made between MRFSS intercept date (quarter), commercial quarter, and survey season (spring and summer/fall), and between MRFSS sub-region, commercial statistical areas, and survey depth strata to integrate data from the different sources. Based on the number, size range, and distribution of lengths and ages, a semi-annual, sub-regional basis of aggregation was adopted for matching of commercial and survey age-length keys with recreational length frequency distributions to convert lengths to ages. Limited MRFSS length sampling for larger fish resulted in a high degree of variability in mean length for older fish, especially at ages 5 and older during the first decade of the time series.  Attempts to estimate length-weight relationships from the MRFSS biological sampling data provided unsatisfactory results. As a result, the commercial fishery quarterly length (mm) to weight (g) relationships from Lux and Porter (1966) were used to calculate annual mean weights at age from the estimated age-length frequency distribution of the landings.

The recreational landings historically were dominated by relatively young fish. During 1982-1996, age 1 fish accounted for over 50% of the landings by number and fish of ages 0 to 3 accounted for over 95% of landings by number. No fish from the recreational landings were determined to be older than age 7. With increases in the minimum landed size since 1996 (to 14.5 in [37 cm] in 1997, 15 in [38 cm] in 1998-1999, generally 15.5 in [39 cm] in 2000, and various state minimum sizes from 14.0 [36 cm] to 21 in [53 cm] in 2001-2009) and a trend to lower fishing mortality rates, the age composition of the recreational landings now includes mainly fish at ages 3 and older, at mean weights of greater than 1 kg per fish (Table 20 and Table 21). The number of summer flounder of ages 3 and older landed by the recreational fishery in 2008-2009, at over 90% of the landings by number, was the highest in the time series (Table 20).

RECREATIONAL FISHERY DISCARDS

MRFSS catch estimates were aggregated on a sub-regional basis for calculation of the proportion of live discard (catch type B2) to total catch (catch types A+B1+B2) in the recreational fishery for summer flounder. The live discard has varied from about 18% (1985) to about 91% (2008) of the total catch during 1982-2008 (Table 22). To account for all removals from the summer flounder stock by the recreational fishery, some assumptions about the biological characteristics and discard mortality rate of the recreational live discard need to be made, because biological samples are not routinely taken of MRFSS catch type B2 fish. In previous assessments, data available from NYDEC surveys (1988-1992) of New York party boats suggested that nearly all (>95%) of the fish released alive from boats were below the minimum regulated size (during 1988-1992, 14 in [36 cm] in New York state waters), that nearly all of these fish were age 0 and age 1 summer flounder, and that these age 0 and 1 summer flounder occurred in about the same proportions in the live discard as in the landings. It was therefore assumed that all B2 catch would be of lengths below regulated size limits, and be either age 0 or age 1 in all three sub-regions during 1982-1996. Catch type B2 was allocated on a semi-annual, sub-regional basis in the same ratio as the annual age 0 to age 1 proportion observed in the landings during 1982-1996.  Mean weights at age were assumed to be the same as in the landings during 1982-1996.

The minimum landed size in federal and most state waters increased to 14.5 in (37 cm) in 1997, to 15.0 in (38 cm) in 1998-1999, and to 15.5 in (39 cm) in 2000. Applying the same logic used to allocate the 1982-1996 recreational released catch to size and age categories during 1997-2000 implied that the recreational fishery released catch included fish of ages 2 and 3. Investigation of data from the CTDEP Volunteer Angler Survey (VAS) for 1997-1999 and from the American Littoral Society (ALS) for 1999, and comparing the length frequency of released fish in these programs with the MRFSS data on the length frequency of landed fish below the minimum size, indicated this assumption was valid for 1997-1999 (MAFMC 2001a).  The CTDEP VAS and ALS data, along with data from the NYDEC Party Boat Survey (PBS), was used to validate this assumption for 2000. For 1997-2000 all B2 catch was assumed to be of lengths below regulated size limits, and therefore comprised of ages 0 to 3. Catch type B2 was allocated on a sub-regional basis in the same ratio as the annual age 0 to age 3 proportions observed in the landings at lengths less than 37 cm in 1997, 38 cm in 1998-1999, and 39 cm in 2000.

In 2001, many states adopted different combinations of minimum size and possession limits to meet management requirements. As a result, minimum sizes for summer flounder ranged from 15.5 in (39 cm) in federal, VA, and NC waters, 16 in (41 cm) in NJ, 16.5 in (42 cm) in MA, 17 in (43 cm) in MD and NY, to 17.5 in (44 cm) in CT, RI, and DE.  Examination of data provided by MD sport fishing clubs, the CTDEP VAS, the ALS, and the NYDEC PBS indicated that the assumption that fish released are those smaller than the minimum size remained valid for 2001, and so catch type B2 was characterized by the same proportion at length as the landed catch less than the minimum size in the respective states.  The differential minimum size by state has continued since 2001, and increased samples of the recreational fishery discards by state agency Volunteer Angler Surveys (VAS) and the MRFSS For Hire Survey (FHS) has allowed direct characterization the length frequencies of the discards from sample data (Table 23).

Studies conducted to estimate recreational fishery discard mortality for striped bass and black sea bass suggest a rate of 8% for striped bass (Diodati and Richards 1996) and 5% for black sea bass (Bugley and Shepherd, 1991).  Work by the states of Washington and Oregon with Pacific halibut (a potentially much larger flatfish species, but otherwise morphologically similar to summer flounder) found "average hooking mortality...between eight and 24 percent" (IPHC, 1988). An unpublished tagging study by the NYDEC (Weber MS 1984) on the survival of released sublegal summer flounder caught by hook-and-line suggested a total, non-fishing mortality rate of 53%, which included discard plus tagging mortality as well as deaths by natural mortality. Assuming deaths by natural mortality to be about 18%, (an instantaneous natural mortality rate of 0.20), an annual discard plus tagging mortality rate of about 35% can be derived from the NYDEC results. 

In the 1997 SAW25 (NEFSC 1997b) and earlier assessments of summer flounder, a 25% discard mortality rate was assumed for summer flounder released alive by anglers. However, two subsequent investigations of summer flounder recreational fishery discard, or hooking, mortality suggested that a lower rate was more appropriate. Lucy and Holton (1998) used field trials and tank experiments to investigate the discard mortality rate for summer flounder in Virginia, and found rates ranging from 6% (field trials) to 11% (tank experiments).  Malchoff and Lucy (1998) used field cages to hold fish angled in New York and Virginia during 1997 and 1998, and found a mean short term mortality rate of 14% across all trials. Given the results of these studies conducted specifically for summer flounder, a 10% discard mortality rate was adopted in the Terceiro (1999) stock assessment and has been retained in all subsequent assessments. Ten percent of the total B2 catch at age is therefore the basis of estimates of summer flounder recreational fishery discard at age (Table 24).  The mean weights at age of the recreational fishery discards are presented in Table 25.

TOTAL CATCH COMPOSITION

NER commercial fishery landings and discards at age, North Carolina winter trawl fishery landings and discards at age, and MRFSS recreational fishery landings and discards at age totals were summed to provide a total fishery catch at age matrix for 1982-2009 (Table 26; Figure 2). The percentage of age 3 and older fish in the total catch in numbers has increased during the last decade from only 4% in 1993 to 72% in 2008 and 68% in 2009.  Overall mean weight at age in the total catch was calculated as the weighted mean (by number in the catch at age) of the respective mean value at age from each fishery component (Table 27; Figure 3). The recreational fishery component of the total summer flounder catch has generally increased since 1995 (Table 28; Figure 4).  

RESEARCH SURVEY INDICES OF ABUNDANCE

NEFSC spring

Long-term trends in summer flounder abundance were derived from a stratified random bottom trawl survey conducted in spring by the NEFSC between Cape Hatteras and Nova Scotia since 1968 (Clark 1979). NEFSC spring survey indices suggest that total stock biomass last peaked during 1976-1977. The 2007 index (3.17 kg/tow) represented a time series high before falling by over half to 1.41 kg/tow in 2008 (Table 29, Figure 5).

The Fisheries Survey Vessel (FSV) Albatross IV (ALB) was replaced in Spring 2009 by the FSV Henry B. Bigelow (HBB) as the main platform for NEFSC research surveys, including the Spring and Fall bottom trawl surveys.  The size, towing power, and fishing gear characteristics of the HBB are significantly different from the ALB, resulting in different fishing power and therefore different survey catchability.  Calibration experiments to estimate these differences were conducted during 2008 (Brown 2009),  and the results of those experiments were peer reviewed by a Panel of three non-NMFS scientists during the summer of 2009 (Anonymous 2009, Miller et al. 2010). The terms of reference for the Panel were to review and evaluate the suite of statistical methods used to derive calibration factors by species before they were applied in a stock assessment context. Following the advice of the August 2009 Peer Review (Anonymous 2009), the beta-binomial model based calibration factors were used to convert 2009 HBB survey catch number and weight indices to 2009 ALB equivalents for use in this stock assessment update (Table 30).

Age composition data from the NEFSC spring surveys indicate a substantial reduction in the number of ages in the stock between 1976-1990 (Table 31, Figure 6). For the period 1976-1981, fish of ages 5-8 were captured regularly in the survey, with the oldest individuals aged 8-10 years. From 1982-1986, fish aged 5 and older were only occasionally observed in the survey, and by 1986, the oldest fish observed in the survey were age 5. In 1990 and 1991, only three age groups were observed in the survey catch, and there was an indication that the 1988 year class was very weak. Since 1996, the NEFSC spring survey age composition has expanded significantly, with increasing abundance of age-3 and older fish. Mean lengths at age from the NEFSC spring survey are presented in Table 32.

NEFSC autumn

Summer flounder are frequently caught in the NEFSC autumn survey at stations in inshore strata (< 27 meters = 15 fathoms = 90 feet) and at offshore stations in the 27-55 meter depth zone (15-30 fathoms, 90-180 feet) at about the same bathymetry as in the spring survey.  NEFSC autumn aggregate and at-age indices are presented in Table 29, Table 30, and Table 33. The NEFSC autumn survey catches age-0 summer flounder in abundance, providing an index of summer flounder recruitment (Table 33, Figure 7). NEFSC autumn survey indices suggest improved recruitment since the late 1980s, and an increase in abundance of age-2 and older fish since 1996. Mean lengths at age from the NEFSC autumn survey are presented in Table 34.

NEFSC winter

A series of NEFSC winter trawl surveys was initiated in February 1992 to provide improved abundance indices for flatfish, including summer flounder. The surveys targeted flatfish concentrated offshore during the winter. A modified trawl was used that differed from the standard trawl employed during the NEFSC spring and autumn surveys in that long trawl sweeps (wires) were added before the trawl doors to better herd fish to the mouth of the net, and the large rollers used on the standard gear were replaced on the footrope with a chain "tickler" and small spacing "cookies."  The design and conduct of the winter survey (timing, strata sampled, and the use of the modified trawl gear) resulted in greater catchability of summer flounder compared to the other surveys. Most fish were captured in survey strata 61-76 (27-110 meters; 15-60 fathoms) off the Delmarva and North Carolina coasts. Other concentrations of fish were found in strata 1-12, south of the New York and Rhode Island coasts, in slightly deeper waters. Significant numbers of large summer flounder were often taken along the southern flank of Georges Bank (strata 13-18).

Indices of summer flounder abundance from the winter survey indicate stable stock size during 1992-1995, with catch per tow values ranging from 10.9 in 1995 to 13.6 in 1993 (Table 29 and Table 35). For 1996, the winter survey index increased by 290% over 1995, from 10.9 to 31.2 fish per tow. The largest increases in 1996 occurred in the Mid-Atlantic Bight region (offshore strata 61-76), where increases up to an order of magnitude occurred in several strata, with the largest increases in strata 61, 62, and 63 off the northern coast of North Carolina. Most of the increased catch in 1996 consisted of age-1 summer flounder from the 1995 year class. In 1997, the index dropped to 10.3 fish per tow, due to the lower numbers of age-1 (1996 year class) fish caught. From 1998-2003, the winter trawl survey indices increased; with the 2003 winter survey number and weight per tow indices being the highest in the time series at 27.58 kg/tow (Table 29, Table 35, Figure 9). The winter survey index was lower from 2004-2007, and values ranged from 10.3 to 15.9 fish per tow. Similar to the other NEFSC surveys, there is strong evidence since the mid-1990s of increased abundance of age-3 and older fish relative to earlier years in the time series (Table 35, Table 36, Table 37).  The NEFSC winter survey series ended in 2007.

Massachusetts DMF

Spring and fall bottom trawl surveys conducted by the Massachusetts Division of Marine Fisheries (MADMF) show a decline in abundance in numbers of summer flounder from high levels in 1986 to record lows in 1990 and 1991 (MADMF fall and spring survey, respectively). In 1994, the MADMF survey indices increased to values last observed during 1982-1986, but then declined substantially in 1995, although the indices remain higher than the levels observed in the late 1980s. Since 1996, both the MADMF spring and fall indices have increased to record high levels (Table 38, Table 39, Figure 8). The MADMF also captures a small number of age-0 summer flounder in a seine survey of estuaries, and these data constitute an index of recruitment (Table 40, Figure 9).

Connecticut DEP

Spring and fall bottom trawl surveys are conducted by the Connecticut Department of Environmental Protection (CTDEP). The CTDEP surveys show a decline in abundance in numbers of summer flounder from high levels around 1986 to record lows in 1989. The CTDEP surveys indicate recovery since 1989, and evidence of increased abundance at ages 2 and older since 1995. The 2003 spring and 2002 autumn indices were the highest in the respective time series; although index values decreased in 2004-2008 (Table 41, Table 42, Figure 10). An index of recruitment from the autumn series is available (Figure 7).

Rhode Island DFW

Standardized bottom trawl surveys have been conducted since 1979 during the spring and fall months in Narragansett Bay and state waters of Rhode Island Sound by the Rhode Island Department of Fish and Wildlife (RIDFW). Indices of abundance at age for summer flounder have been developed from the autumn survey data using NEFSC autumn survey age-length keys. The autumn survey reached a time series high in 2009 (Table 43, Figure 8). An abundance index has also been developed from a set of fixed stations sampled monthly since 1990, which also reached a time series high in 2009 (Table 44). Recruitment indices are available from both the autumn (Figure 9) and monthly fixed station surveys.

New Jersey BMF

The New Jersey Bureau of Marine Fisheries (NJBMF) has conducted a standardized bottom trawl survey since 1988. Indices of abundance for summer flounder incorporate data collected from April through October (Table 45, Figure 11). The NJBMF survey mean number per tow indices and frequency distributions were converted to age using the corresponding annual NEFSC combined spring and fall survey age-length keys. Since 1998, most year classes are at or below average; however, the 2005 year class is above average (Figure 12).

Delaware DFW

The Delaware Division of Fish and Wildlife (DEDFW) has conducted a standardized bottom trawl survey with a 16 foot head-rope trawl since 1980 and with a 30 foot head-rope trawl since 1991.  Recruitment indices (age 0 fish; one index from the Delaware estuary proper for 1980 and later, one from the inland bays for 1986 and later) have been developed from the 16 foot trawl survey data (Table 46, Table 47, Figure 12).  Indices for age-0 to age-4 and older summer flounder have been compiled from the 30 foot head-rope survey (Table 48, Figure 11).  The indices use data collected from June through October (arithmetic mean number per tow), with age 0 summer flounder separated from older fish by visual inspection of the length frequency.

Maryland DNR

The Maryland Department of Natural Resources (MDDNR) has conducted a standardized trawl survey in the seaside bays and estuaries around Ocean City, MD since 1972.  Samples collected during May to October with a 16 foot bottom trawl have been used to develop a recruitment index for summer flounder (Table 49, Figure 13). This index suggests that weakest year class in the time series recruited to the stock in 1988 and the strongest in 1986.

Virginia Institute of Marine Science

The Virginia Institute of Marine Science (VIMS) conducts a juvenile fish survey using trawl gear in Virginia rivers since 1955. An index of recruitment developed from the VIMS survey suggests weak year classes (<0.2 fish per trawl) recruited to the stock in 1955, 1959, 1961-1962, 1966, 1968, 1970, and 1975, with strong year classes (>2.0 fish per trawl) recruiting in 1956-57, 1963, 1971, 1979-1983, 1990-1991, and 1994. Recruitment indices since 1994 have been below average (Table 50, Figure 13).

The VIMS ChesMMap survey was started in 2002, providing research survey samples from Chesapeake Bay.  The ChesMMap samples are dominated by age 0-2 summer flounder. Due to the brevity of the series, it has not yet been included in population models (Table 51, Figure 14).

The VIMS NEAMAP survey was started in Fall 2006, providing research survey samples along the Atlantic Coastal waters from Rhode Island to North Carolina, in depths of 20-90 feet (9-43 meters). Due to the brevity of the series, it has not yet been included in population models (Table 52, Figure 14).

North Carolina DMF

The North Carolina Divisions of Marine Fisheries (NCDMF) has conducted a stratified random trawl survey using two 30 foot headrope nets with 3/4" mesh codend in Pamlico Sound since 1987. An index of recruitment developed from these data suggests the weakest year class recruited to the stock in 1988, with strong year classes in 1987, 1996, 2001, 2002 and 2008 (Table 53, Figure 13). The survey normally takes place in mid-June, but in 1999 was delayed until mid-July. The 1999 index is therefore inconsistent with the other indices in the time series, and so the 1999 value has been excluded.

BIOLOGICAL DATA

Aging

Work performed for the SAW 22 assessment (NEFSC 1996b) indicated a major expansion in the size range of 1-year old summer flounder collected during the 1995 and 1996 NEFSC winter bottom trawl surveys. This also brought to light differences between ages determined by NEFSC and NCDMF fishery biology staffs; therefore, age structure (scale) exchanges were performed after the SAW 22 assessment to explore these differences. The results of the first two exchanges indicated low levels of agreement between age readers at the NEFSC and NCDMF (31 and 46%).  In 1996, research was conducted to determine inter-annular distances and to back-calculate mean length at age from scale samples collected on all NEFSC bottom trawl surveys (winter, spring and fall) for comparison with NCDMF samples. While mean length at age remained relatively constant from year to year, inter-annular distances increased sharply in the samples from the 1995-1996 winter surveys, and increased to a lesser degree in samples from other 1995-1996 surveys. As a result, further exchanges were suspended pending the resolution of an apparent aging problem.

Age samples from the winter 1997 bottom trawl survey, aged utilizing both scales and otoliths by only by one reader, indicated a similar pattern as the previous two winter surveys (i.e., several large age 1 individuals),  and some disagreement between scale and otolith ages obtained from the same fish.  Because of these problems, a team of five experienced NEFSC readers re-examined the scales aged from the winter 1997 survey. After reviewing several hundred scales, the team determined that re-aging all samples from 1995-1997 would be appropriate, including all winter, spring, and fall samples from the NEFSC and MADMF bottom trawl surveys and all samples from the commercial fishery. The age determination criteria remained the same as those developed at the 1990 summer flounder workshop (Almeida et al. 1992) and described in the aging manual utilized by NEFSC staff (Dery 1997). Only those fish for which a 100% agreement of all team members was attained were included in the revised database, however.  The data from the re-aged database were used in analyses in the SAW 25 assessment (NEFSC 1997b).

A third summer flounder aging workshop was held at the NEFSC in 1999 to continue the exchange of age structures and review of aging protocols for summer flounder (Bolz et al. 2000). Participants at this workshop concluded that the majority of aging disagreements arose from the interpretation of marginal scale increments due to highly variable timing of annulus formation, and from the interpretation of first year growth patterns and first annulus selection.  The workshop recommended regular samples exchanges between NEFSC and NCDMF, and further analyses of first year growth. Subsequently, Sipe and Chittenden (2001) concluded that sectioned otoliths were the best structure for aging summer flounder over the age range from 0 to 10 years. Since 2001, both scales and otoliths have routinely been collected in all NEFSC trawl surveys for fish larger than 60 cm, and studies are underway to determine the best structure to use for aging these large summer flounder. An exchange of NEFSC and NCDMF aging structures for summer flounder occurred again in 2006. This exchange examined samples from fish aged 1 to 9 (23-76 cm total length) and determined that the consistency of aging between NCDMF and the NEFSC was at an acceptable level.

Maturity

The maturity schedule for summer flounder used in the 1990 SAW 11 and subsequent stock assessments through 1999 was developed by the 1990 SDWG using NEFSC Fall Survey maturity data for 1978-1989 and mean lengths at age from the NEFSC fall survey (G. Shepherd, NEFSC, personal communication, July 1, 1990; NEFC 1990; Terceiro 1999).  The 1990 SAW 11 work indicated that the median length at maturity (50th percentile, L50) was 25.7 cm for male summer flounder, 27.6 cm for female summer flounder, and 25.9 cm for the sexes combined. Under the aging convention used in the 1990 SAW 11 and subsequent assessments (Smith et al. 1981, Almeida et al. 1992, Szedlmayer and Able 1992, Bolz et al. 2000), the median age of maturity (50th percentile, A50) for summer flounder was determined to be 1.0 years for males and 1.5 years for females. Combined maturities indicated that at peak spawning time in the autumn, 38% of age-0 fish are mature, 72% of age-1 fish are mature, 90% of age-2 fish are mature, 97% of age-3 fish are mature, 99% of age-4 fish are mature, and 100% of age-5 and older fish are mature.  The maturities for age-3 and older were rounded to 100% in the 1990 SAW 11 and subsequent assessments.

It has been noted that the NEFSC maturity schedules have been based on simple gross morphological examination of the gonads that may overestimate the true spawning potential of the summer flounder stock, especially for age-0 and age-1 fish. A research recommendation that the true spawning contribution of young summer flounder to the SSB be investigated was included in the 1993 SAW 16 assessment (NEFSC 1993). URI studies to address this research recommendation were completed in 1999 (Specker et al 1999, Merson et al 2000).  In light of the URI results, the NEFSC maturity data for summer flounder for 1982-1998 were examined in the 2000 SAW 31 assessment (NEFSC 2000) to determine if changes in the maturity schedule were warranted.

The URI work examined the histological and biochemical characteristics of female summer flounder oocytes to determine if age-0 and age-1 female summer flounder produce viable eggs, and to develop an improved guide for classifying the maturity of summer flounder collected in NEFSC surveys. The URI studies examined 333 female summer flounder (321 aged fish) sampled during the NEFSC Winter 1997 Bottom Trawl Survey (February 1997) and 227 female summer flounder (210 aged fish) sampled during the NEFSC Autumn 1997 Bottom Trawl Survey (September 1997) using radioimmunoassays to quantify the biochemical cell components characteristic of mature fish (Specker et al. 1999, Merson et al. 2000).

The NEFSC and URI maturity determinations disagreed for 13% of the 531 aged fish, with most (10%) of the disagreement due to NEFSC mature fish classified as immature by the URI histological and biochemical criteria.  The URI criteria indicated that 15% of the age-0 fish were mature, 82% of the age-1 fish were mature, 97% of the age-2 fish were mature, and 100% of the age 3 and older fish were mature.  When the proportions of fish mature at length and age were estimated by probit analysis,  median length at maturity (50th percentile, L50) was estimated to be 34.7 cm for female summer flounder, with the following proportions mature at age: age-0: 30%,  age-1: 68%,  age-2: 92%,  age-3: 98%, and age-4: 100%. Median age of maturity (50th percentile, A50) was estimated to be about 0.5 years. Based on this new information, the 2000 SAW 31 (NEFSC 2000) considered 5 options for the summer flounder maturity schedule for the assessment:

  1. No change, use the maturity schedule for combined sexes as in the 1990 SAW 11 and subsequent assessments (rounded to 0.38, 0.72, 0.90, 1.00, 1.00, and 1.00 as in the 1997 SAW 25 and Terceiro (1999) assessment analyses).
  2. Consider only age-2 and older fish of both sexes in the SSB.
  3. Knife edged, age-1 and older maturity for both sexes. This would eliminate age-0 fish of both sexes from the SSB, and assume that the proportions mature at age-1 “round” to 100%.
  4. NEFSC 1982-1989, 1990-1998 for both sexes, assuming a 1:1 sex ratio in deriving a combined schedule.
  5. NEFSC 1982-1989, 1990-1998 for males, URI study for females, assuming a 1:1 sex ratio in deriving a combined schedule.

The 5 options produce the following maturity schedules for both sexes combined:

Option

Age

0

1

2

3

4

5+

1

0.38

0.72

0.90

1.00

1.00

1.00

2

0.00

0.00

0.90

1.00

1.00

1.00

3

0.00

1.00

1.00

1.00

1.00

1.00

4

0.45, 0.45

0.88, 0.82

0.97, 0.93

1.00, 0.98

1.00, 0.99

1.00, 1.00

5

0.29, 0.31

0.74, 0.76

0.95, 0.94

0.99, 0.98

1.00, 1.00

1.00, 1.00

The 2000 SAW 31 assessment concluded that some contribution to spawning from ages 0 and 1 should be included, eliminating options 2 and 3. The differences among remaining options 1, 4, and 5 were considered to be relatively minor, and so the 1990 SAW 11 schedule (Option 1) was retained for subsequent assessments (MAFMC 2001a, NEFSC 2002b). The 2000 SAW 31 recommended that more biochemical and histological work should be done to verify that results of the URI studies would be applicable in the future. The 2000 SAW 31 also noted the need for research to explore whether the viability of eggs produced by young, first time spawning summer flounder is comparable to the viability of eggs produced by older, repeat spawning summer flounder (NEFSC 2000). In the 2005 SAW 41 work (NEFSC 2005), the maturity schedule was updated and broadened to include data from 1992-2004, covering the year range for individually measured and weighed fish sampled in NEFSC research surveys. The resulting combined sex maturity schedule (0.38, 0.91, 0.98, 1.00, 1.00, and 1.00; respectively for age-0 to 5+) was retained in the 2006 assessment and S&T peer review (Terceiro, 2006b). The 2008 SDWG examined the proportions of summer flounder mature at age from 1981-2007 as well as individual fish information on length and age at maturity from 1992-2007, and concluded that it was appropriate to retain the maturity schedule from the 2006 assessment for the 2008 SAW47 assessment (NEFSC 2008).  The 2006 schedule was retained in the 2009 (Terceiro 2009) and 2010 updated assessments.

Natural Mortality Rate (M)

In the 1996 SAW 20 assessment (NEFSC 1996a), estimates of M were derived using methods described by 1) Pauly (1980) using growth parameters derived from NCDMF age-length data and a mean annual bottom temperature (17.5oC) from NC coastal waters, 2) Hoenig (1983) using a maximum age for summer flounder of 15 years and 3) consideration of age structure expected in unexploited populations (5% rule, 3/M rule, e.g., Anthony 1982).  The 1996 SAW 20 concluded that M = 0.2 was a reasonable value given the mean (0.23) and range (0.15-0.28) obtained from the various analyses, and this value for M had been used in all assessments through 2007.

For the 2008 SAW 47 assessment (NEFSC 2008), sex and age-specific estimates of M were calculated from summer flounder age and growth data (1976-2007) from the NEFSC trawl surveys. Longevity based estimators of M are sensitive to underlying assumptions which include the terminal proportion of the population surviving to a given maximum age and the maximum observed age under no or low exploitation conditions. Using a maximum age of 15 years for summer flounder, the Hoenig (1983) and Hewitt and Hoenig (2005) longevity based estimates of M for combined sexes ranged from 0.20 to 0.36, depending on whether terminal proportion of 1.5% or 5% was assumed. Other life-history based models were examined and included Pauly (1980), Jensen (1996), Gunderson and Dygert (1988), and Gunderson (1997), with estimates ranging from 0.20 to 0.45. Age-specific and size variable estimates of M, based on the work of Peterson & Wroblewski (1984), Chen & Watanabe (1989), Lorenzen (1996), and Lorenzen (2000), ranged from 0.19 to 0.90, with the highest values obviously associated with age-0-1 fish (fish at smaller lengths). While these exercises provided a wide range of methods and M estimates to be considered, each estimate involved a suite of underlying assumptions which were debated. In addition, the assessment modeling frameworks considered in the 2008 SAW 47 assessment (ADAPT VPA, ASAP SCAA, and SS2 SCAA) allowed for log-likelihood profiling of M to determine which M estimate provided the best model fit. The M that minimized the log-likelihood was 0.35, 0.20, and 0.25 under the ADAPT VPA, ASAP SCAA, and SS2 SCAA models, respectively. The estimate of M that resulted in the best diagnostic value was sensitive to model selection and configuration, as the data inputs were similar across the three models.

The 2008 SAW47 Review Panel considered the different approaches to estimating M and after lengthy discussion assumed a natural mortality rate (M) of 0.20 for females and 0.30 for males, based mainly on recently observed maximum ages in the NEFSC survey data of 14 years (76 cm, in NEFSC Winter Survey 2005) for females and 12 years (63 cm, in NEFSC Spring Survey 2007) for males, and the expectation that larger and older fish would likely be observed if future fishing mortality rates are maintained near current rates (< F = 0.3). A combined sex M-schedule at age was developed by assuming these initial M rates by sex, an initial proportion of females at age 0 of 0.40 derived from the NEFSC Fall survey indices by age and sex, and population abundance decline over time at the sex specific M rates. The final abundance weighted combined sex M-schedule at age ranged from 0.26 at age 0 to 0.24 at age 7+, with a mean of 0.25.   This M-schedule was retained in the 2009 (Terceiro 2009) and 2010 updated assessments.

2010 UPDATED FISHING MORTALITY RATE AND STOCK SIZE ESTIMATES

Fishing mortality rates and stock sizes were estimated using the ASAP statistical catch at age model (NFT 2008a). The catch at age, mean weights at age, maturity at age, and survey index calibration time series were input as in the 2008 SAW 47 assessment. An age-specific instantaneous natural mortality rate providing an average M = 0.25 was assumed for all years. Winter, spring, and mid-year survey indices and all survey recruitment (age-0) indices were compared to population numbers of the same age at the beginning of the same year. Fall survey indices were compared to population numbers one year older at the beginning of the next year.  Lognormal error distributions were assumed for the total catch in weight, research survey catch at age calibration indices, internal Beverton-Holt stock-recruitment relationship and parameters, selectivity parameters, annual fishing mortality parameters, survey catchability parameters, and estimated stock numbers at age. A multinomial distribution was assumed for fishery catch at age. A number of additional initial model settings including specification of likelihood component emphasis factors (lambdas), size of deviation factors expressed as standard deviations, and penalty functions for extreme fishing mortality estimates were set at consensus values by the 2008 SDWG after multiple sensitivity runs to evaluate a range of inputs.

The annual selection of age-1 fish decreased from about 0.5 during the first time block of selectivity estimation (1982-1994) to about 0.2 during the second block, 1995-2008. The annual selection of age-2 fish decreased from about 1.0 during the first time block of selectivity estimation (1982-1994) to about 0.7 during the second block, 1995-2008. These decreases in selection at age are in line with expectations given changes in commercial and recreational fishery regulations.  For these reasons, summer flounder are currently considered to be fully recruited to the fisheries at age 3, and fully recruited fishing mortality is expressed as the un-weighted average of fishing mortality at age for ages 3 to 7+.

Summary estimates for the 2010 updated assessment are provided in Table 54, and population number and fishing mortality estimates at age are provided in Table 55 and Table 56. The 2010 update indicates that fishing mortality ranged between 1.0 and 2.0 during 1982-1996. The fishing mor­tality rate has declined to below 1.0 since 1997 and was estimated to be 0.237 in 2009 (Figure 15).  There is a 50% probability that the fishing mortality rate in 2008 was between 0.224 and 0.250 (Figure 16). The summer flounder stock assessment has historically exhibited a retrospective pattern of underestimation of F; the causes of this pattern have not been determined (Figure 17). Over the last 7 years, the annual internal model retrospective error in fishing mortality has ranged from +11% in the 2006 terminal year to -35% in 2003.

Spawning stock biomass (SSB) decreased from about 25,000 mt in the early 1980s to about 7,000 in 1989, then increased to above 40,000 mt by 2002.  SSB was estimated to be 53,458 mt in 2009, about 89% of the SSBMSY = SSB35% reference point = 60,074 mt (Table 54, Figure 18, Figure 19).  There is a 50% chance that SSB in 2009 was between 50,560 and 55,998 mt (Figure 20). The assessment has historically exhibited a retrospective pattern of overestimation of SSB; the causes of this pattern have not been determined (Figure 21). Over the last 7 years, the annual internal model retrospective error in SSB has ranged from -13% in the 2006 terminal year to +45% in 2003.

The arithmetic average recruitment from 1982 to 2009 is 42 million fish at age 0. The 1981 and 1982 year classes are the largest in the historical assessment time series, at 73 and 81 million fish; the 1988 year class is the smallest at 13 million fish. The 2008 year class is estimated to be about 49 million fish, 17% above the average. The 2009 year class is currently estimated to be about 82 million fish, about twice the average, and is the largest in the assessment time series (Table 54, Figure 18, Figure 19). A recent pattern of overestimation in recruitment is evident (Figure 22). Over the last 3 years, the annual internal model retrospective error in recruitment has ranged from +54% for the 2008 year class to +80% for the 2006 year class. Comparison of the estimates for SSB, R and F over the last three assessments indicates consistency of those estimates in line with the most recent internal retrospective pattern of the 2010 assessment model (Figure 23, Figure 24, Figure 25).

BIOLOGICAL REFERENCE POINTS (BRPs)

Background

The calculation of biological reference points for summer flounder based on yield per recruit analysis using the Thompson and Bell (1934) model was first detailed in the 1990 SAW 11 assessment (NEFC 1990). The 1990 analysis estimated that Fmax = 0.230.   In the 1997 SAW 25 assessment (NEFSC 1997b), an updated yield per recruit analysis reflecting the partial recruitment pattern and mean weights at age for 1995-1996 estimated that Fmax = 0.240. The Overfishing Definition Review Panel (Applegate et al. 1998) recommended that the MAFMC base MSY proxy reference points on yield per recruit analysis, and this recommendation was adopted in formulating the FMP Amendment 12 Overfishing Definition (MAFMC 1999).  These reference points were based on the 1999 assessment (Terceiro 1999) and followed what would later be described as the Anon-parametric approach@  (i.e., biomass reference points calculated as the product of biomass per recruit and a reference period recruitment level; NEFSC 2002a).   The analysis in the Terceiro (1999) assessment, reflecting partial recruitment and mean weights at age for 1997-1998, indicated that Fthreshold = Ftarget= Fmax = 0.263,  yield per recruit (Y/R) at Fmax was 0.55219 kg/recruit,  and January 1 Total Stock Biomass per recruit (TSB/R) at Fmax was 2.8127 kg/recruit. The median number of summer flounder recruits estimated from the 1999 assessment for 1982-1998 was 37.8 million age-0 fish.  Based on this median recruitment level, maximum sustainable yield (Ymax as a proxy for MSY) was estimated to be 20,897 mt (46 million lbs) at a Total Stock Biomass (TSBmax as a proxy for BMSY) of 106,444 mt (235 million lbs). The biomass threshold, one-half TSBmax as a proxy for one-half BMSY, was therefore estimated to be 53,222 mt (118 million lbs).  The Terceiro (1999) reference points were retained in the 2000 SAW 31 assessment (NEFSC 2000) because of the stability of the input data and resulting biological reference point estimates.

The MAFMC SSC conducted a peer review of the summer flounder Overfishing Definition in concert with the 2001 assessment update (MAFMC 2001a, b). The 2001 SSC reviewed six analyses to estimate biological reference points for summer flounder conducted by members of the Summer Flounder Biological Reference Point Working Group. After considerable discussion, the 2001 SSC decided that although the new analyses conducted by the Working Group had resulted in a wide range of estimates, they did not provide a reliable alternative set of reference points for summer flounder.  The 2001 SSC therefore recommended that Ftarget remain at the Terceiro (1999) estimate of Fmax = 0.263 because a better estimate had not been established by any of the new analyses. The 2001 SSC also reviewed the biomass target (BMSY) and threshold (one-half BMSY) components of the Overfishing Definition and concluded that the new analyses did not justify an alternative estimate of the BMSY proxy. The 2001 SSC endorsed the recommendations of the 2000 SAW 31 which stated that Athe use of Fmax as a proxy for FMSY should be reconsidered as more information on the dynamics of growth in relation to biomass and the shape of the stock recruitment function become available@ (NEFSC 2000).  The 2001 SSC agreed that additional years of stock and recruitment data should be collected and encouraged further model development, including model evaluation through simulation studies.  They also encouraged the evaluation of alternative proxies for biological reference points that might be more appropriate for an early maturing species like summer flounder and the development and evaluation of management strategies for fisheries where BMSY is unknown. The 2001 SSC indicated that as the stock size increases, population dynamic processes that could reflect density dependent mechanisms should be more closely monitored and corresponding analyses should be expanded, i.e., rates of size and age, maturity, fecundity, and egg viability should be closely monitored as potential indicators of compensation at higher stock sizes.  Finally, the 2001 SSC recommended that potential environmental influences on recruitment, including oceanographic changes and predation mortality, should be reevaluated as additional recruitment data become available. As a result of the 2001 SSC peer review (MAFMC 2001a) the Terceiro (1999) reference points were retained in the 2001 stock assessment (MAFMC 2001b).  In the review of the 2002 stock assessment (NEFSC 2002b), SAW 35 concluded that revision of the reference points was not warranted at that time due to the continuing stability of the input data and resulting reference point estimates.  The Terceiro (1999) reference points were subsequently retained in the 2003 (Terceiro 2003) and 2004 (SDWG 2004) assessment updates. 

The biological reference points for summer flounder were next peer-reviewed by the 2005 SAW 41, using fishery data through 2004 and research survey data through 2004/2005 (NEFSC 2005).  The SAW 41 Panel noted that the Beverton-Holt (Beverton and Holt, 1957; Mace and Doonan 1988; BH) model fit the observed stock-recruitment data well, and provided reference points comparable to those derived from a non-parametric (yield and biomass per recruit) approach.  The SAW 41 Panel noted, however, that the quantity of observed stock-recruitment data was limited (22 years), and the data during the early part of the time series, when the SSB was at the lowest observed levels, indicated a level of recruitment near the estimated Rmax, and exerted a high degree of leverage on the estimation of the model parameters. This leverage resulted in a high value (0.984) for the calculated steepness of the BH curve, outside of the + one standard error interval of the estimate for Pleuronectid flatfish (0.8 + 0.1) indicated by Myers et al. (1999).  The BH model results suggested that summer flounder SSB could fall to very low levels (<2,000 mt) and still produce recruitment near that produced at SSBMSY.  The SAW 41 Panel concluded a) that this result might not be reasonable for the long term, given the recent stock-recruitment history of the stock (i.e., production of a very poor year class in 1988), b) the BH model estimated parameters might prove to be sensitive to subsequent additional years of S-R data, especially if they accumulated at higher levels of SSB and recruitment in the near term, and c) the BH model fit might also be sensitive to the magnitude of recently estimated spawning stock and recruitment, given the recent retrospective pattern of overestimation of stock size evident in the assessment. Given these concerns, the SAW 41 Panel advised that the BH model estimates were not suitable for use as biological reference points for summer flounder, and recommended continued use of reference points developed using the non-parametric model approach.  FMP biological reference points from the 2005 assessment were Fmax = FMSY = 0.276, Ymax = MSY = 19,072 mt (42.0 million lbs), TSBmax = BMSY = 92,645 mt (204.2 million lbs), and biomass threshold of 0.5*TSBmax = 46,323 mt (102.1 million lbs; NEFSC 2005).

The biological reference points for summer flounder were peer-reviewed again in 2006 by the National Marine Fisheries Service (NMFS) Office of Science and Technology (S&T) (Methot 2006). The 2006 S&T Peer Review recommended using SSB, rather than TSB as in previous assessments, as the metric for the biomass reference point proxy. The product of the mean recruitment (37.0 million fish) and Y/R at Fmax was 21,444 mt = 47.276 million lbs (as the proxy for MSY); the product of the mean recruitment and SSB/R at Fmax was 89,411 mt = 197.118 million lbs (as the proxy for BMSY; Terceiro 2006a, b). The 2006 S&T Peer Review Panel (Methot 2006) recommended adoption of these biological reference points from the non-parametric approach for summer flounder, advising: 

“The low level of recruitment observed in 2005 is essentially the same as the low 1988 recruitment, so it is within the range of recruitment fluctuation used in calculating the expected time to rebuild this stock. The Panel finds that the most representative approach to calculating BRPs and rebuilding rates would be to use the entire set of recruitments from 1982-2005.  The average, not median, of these recruitments should be used for calculation of biological reference points because much of the stock’s accumulated biomass comes from the larger recruitments.  Random draws from this set of recruitments would provide a probability distribution of rebuilding rates that is consistent with the occasional occurrence of small recruitments (1988 and 2005) and large recruitments (1982-1987).  There is no documented and obvious reason why recruitments were higher during 1982-1987.  If such recruitment levels become more common as the stock rebuilds, then the stock may rebuild to an even higher level than is currently targeted.  If such recruitment levels do not occur during the next few years of the rebuilding, then the rebuilding target may be not be achieved by the target time to rebuild.  More precise forecasts than this are not feasible.”

The two biological reference point estimation approaches previously used in the 2005 SAW 41 (NEFSC 2005) and 2006 S&T Peer Review (Terceiro 2006b) assessments were again applied in the 2008 SAW 47 assessment work (NEFSC 2008), so as to be potentially complementary and supportive and because using both should build confidence in the results.  Objective application of either approach is often compromised by lack of sufficient observation on stock and recruitment over a range of biomass to provide suitable contrast.  Thus, it is often necessary to extrapolate beyond the range of observation and to infer the shape of the stock-recruit relationship from limited and variable observations (NEFSC 2002a). The 2001 MAFMC SSC review of summer flounder reference points also noted this concern (MAFMC 2001a).

The non-parametric approach was to evaluate various statistical moments (mean, variance, percentiles) of the observed series of recruitment data and apply the estimated spawning stock biomass and yield per recruit associated with common F reference points to derive the implied spawning stock biomass and equilibrium total yield (landings plus discards).  The biomass and yield per recruit models were fit using the NOAA Fisheries Toolbox (NFT) YPR version 2.7.2 software (NFT 2008b).  The full time series of recruitment during 1982-2007 as estimated in the 2008 SAW47 assessment was used in the yield and spawning stock biomass calculations at fishing mortality reference points, as per the 2006 S&T Peer Review Panel recommendation. The non-parametric approach assumes that compensatory mechanisms such as impaired growth, maturity, or recruit survival are negligible over the range of biomass considered (NEFSC 2002a).  Once the Fmax reference point (i.e., the Fmax proxy for FMSY) was determined, a long-term (100 year) stochastic projection of stock sizes and catches was done to provide better consistency between the estimated medians of the BRP calculations and shorter-term (e.g., 1-5 year) projections (Legault 2008).

The parametric approach used fitted parametric stock-recruitment models along with yield and spawning biomass per recruit information to calculate MSY-based reference points following the procedure of Sissenwine and Shepherd (1987).  Stock-recruitment models were fit using the NFT SRFIT version 6.3 software (NFT 2008c).  Since a wide range of models (Beverton-Holt [BH] and Ricker [RK] models, incorporating autoregressive error, and Bayesian priors for various parameters) had been tested in the 2005 SAW 41 work, the 2008 SAW47 parametric model exercise was limited to the simple Beverton-Holt and Ricker models (Beverton and Holt 1957, Mace and Doonan 1988, Ricker 1954).

2008 SAW 47 Biological Reference Points (BRPs)

For the 2008 SAW 47 assessment, the ASAP SCAA model provided the basis for the 2008 biological reference points and stock status. Average values of mean weights at age in the catch and stock, maturity schedule, and partial recruitment pattern for the period 2005-2007 were used as input for ages 0-7+ for BRP calculations. In previous assessments (NEFSC 2005 and earlier) for older aged fish (ages 8-15) with very limited or missing samples, Gompertz functions based on younger ages were used to estimate mean weights for the older ages in the BRP calculations.  However, the practice of extending the age structure to age 15 and use of Gompertz weights for the older ages resulted in inconsistency between the BRP biomass estimates based on long-term stochastic projections and shorter-term (e.g., 1-5 year) projections used for Total Allowable Landings (TAL) calculations (NEFSC 2002a, Legault 2008). Therefore, to increase consistency between these two types of projections, the age range of the BRP and projection calculations was set at 0-7+, with 8 additional ages (to age 15) included in the plus group calculation of yield and spawning biomass per recruit (NFT 2008b).  The mean weight at age for the plus group (ages 7+) was updated for the 2008 SAW47 assessment in a new way, by using a weighted average of mean weights for ages 7-15 (observed catch weights for ages 7-10; calculated Gompertz weights for ages 11-15 as estimated from observed ages 0-10) based on the relative proportions at age given a 2007 total mortality rate of 0.55 (mean M = 0.25 + 2007 F = 0.30; this value is coincidently consistent with the F35% proxy for FMSY). The combined effects of the new assumption for M and the modeling of landings and discards as distinct fleets (which resulted in a slightly domed-shaped combined fishery selectivity pattern) resulted in higher estimates of F reference points, lower estimates of MSY, lower estimates of SSB reference points, and improved stock status with respect to both the F and SSB reference points, as compared to the S&T 2006 assessment.

The reference points estimated from the parametric approach were suspect because the Beverton-Holt function steepness parameters were always very near 1.0.  Therefore Fmax, F40%, and F35% (and their corresponding biomass reference points) from the non-parametric approach were considered as candidate proxies for FMSY and BMSY.  Fmax had been used in previous assessments as the proxy for FMSY.  The estimate of Fmax using mean M = 0.25 and updated fishery selectivity and mean weights at age was relatively high (0.558) and the YPR to F relationship did not indicate a well defined peak.  As a result, little gain in YPR (<5%) was realized at fishing mortality rates higher than F35% = 0.310.  However, the corresponding decline in SSBR between F35% = 0.310 (~1.48 kg/r) and Fmax = 0.558 (~0.93 kg/r) was about 37%.  The 2008 SAW47 concluded that F40% = 0.254 and F35% = 0.310 were candidate proxies that provided sufficient YPR (F40% YPR = 92% of Fmax YPR; F35% YPR = 97% of Fmax YPR) to allow for productive fisheries while also providing for substantial SSBR (F40% SSBR = 176% of Fmax SSBR; F35% SSBR = 155% of Fmax SSBR) to buffer against short-term declines in recruitment.   Recommended proxies for FMSY and SSBMSY were F35% = 0.310 and the associated MSY (13,122 mt) and SSBMSY (60,074 mt) estimates from long-term stochastic projections.  F40% (= 0.254) was recommended as a fishing mortality rate target for management.   These 2008 SAW47 BRPs were subsequently adopted by the NMFS and MAFMC in the 2009 fishery regulation specification process, and have retained in the 2009 (Terceiro 2009) and 2010 updated assessments to evaluate stock status.

2010 UPDATED STOCK STATUS

Based on the 2008 SAW 47 assessment biological reference points the summer flounder stock was not overfished and overfishing was not occurring in 2009. The fishing mor­tality rate was estimated to be 0.237 in 2009, below the threshold fishing mortality reference point = F35% = FMSY = 0.310. Spawning stock biomass (SSB) was estimated to be 53,458 in 2009, about 89% of the SSB35% = SSBMSY target reference point = 60,074 mt (Table 54, Figure 26).

PROJECTIONS

Stochastic projections were made to provide forecasts of stock size and catches in 2010-2012 consistent with the 2008 SAW47 biological reference points. The projections do not explicitly account for the recent retrospective pattern in the assessment, as per the 2006 S&T Peer Review advice (Methot 2006, Terceiro 2006a, b).  The projections assume that recent (2007-2009) patterns of discarding will continue over the time span of the projections.  Different patterns that could develop in the future due to different trip and bag limits and fishery closures have not been evaluated. One hundred projections were made for each of the 1000 MCMC realizations of 2010 stock sizes using NFT AGEPRO version 3.1.3 (NFT 2008d).  Future recruitment at age 0 was generated randomly from a cumulative density function of the updated recruitment series for 1982-2009 (mean recruitment = 42.0 million fish). The projected catch estimates in the following text-tables are percentile intervals of the catch distributions for fixed F.

If the landings in 2010 equal the TAL = 10,038 mt = 22.13 million lbs and the 2010 discards are 1,720 mt = 3.79 million lbs, the projections estimate a median (50% probability) F in 2010 = 0.241 and a median SSB on November 1, 2010 of 72,367 mt, above the biomass target of SSBMSY = SSB35% = 60,074 mt. Fishing at Ftarget = F40% = 0.255 during 2011-2012 is projected to maintain the stock above SSBMSY = SSB35% = 60,074 mt.  The projections indicate that fishing at Ftarget = 0.255 in 2011 could provide landings that exceed MSY (13,122 mt landings = 28.93 million lbs).

Landings, Discards, and Spawning Stock Biomass (SSB) in metric tons
2011
Ftarget =  0.255 Landings Discards SSB

25%ile 12,663 1,904 72,433
50%ile 13,371 2,028 76,201
75%ile 14,304 2,176 80,973

Fishing at Fthreshold = F35% = 0.310 during 2011-2012 is projected to maintain the stock above SSBMSY = SSB35% = 60,074 mt.  The projections indicate that fishing at Fthreshold = 0.310 in 2011 could provide landings that exceed MSY (13,122 mt landings = 28.93 million lbs).

Landings, Discards, and Spawning Stock Biomass (SSB) in metric tons
2011
Fthreshold =  0.310 Landings Discards SSB

25%ile 15,055 2,274 70,034
50%ile 15,899 2,422 73,678
75%ile 17,008 2,598 78,271

Fishing at 75% of Fthreshold = 0.233 during 2011-2012 is projected to maintain the stock above SSBMSY = SSB35% = 60,074, with landings about 6% less than MSY (13,122 mt landings = 28.93 million lbs) in 2011.

Landings, Discards, and Spawning Stock Biomass (SSB) in metric tons
2011
0.75* Fthreshold =  0.233 Landings Discards SSB
       
25%ile 11,674 1,752 73,420
50%ile 12,327 1,867 77,237
75%ile 13,186 2,003 82,085

MAJOR SOURCES OF ASSESSMENT UNCERTAINTY

  1. The landings from the commercial fisheries used in this assessment assume no under reporting of summer flounder landings. Therefore, reported landings and associated effort from the commercial fisheries should be considered minimal estimates.
  2. The recreational fishery landings and discards used in the assessment are estimates developed from the Marine Recreational Fishery Statistics Survey (MRFSS).  While the estimates of summer flounder catch are considered to be among the most reliable produced by the MRFSS, they are subject to error. The MRFSS program is being redesigned in light of the outcome of the NRC Review of the MRFSS methodology (NRC 2000).
  3. The length and age composition of the recreational discards are based on data from a limited geographic area (MRFSS, MRFSS For-hire survey, ALS, Connecticut (CTDEP Volunteer Anglers), Maryland (MD-DNR Volunteer Anglers), except for the most recent years. Future sampling of recreational fishery discards on an annual, synoptic basis is needed.
  4. The current estimate of M remains an ongoing source of uncertainty. M is highly influential on the assessment results and has a “rescaling affect” on SSB, F, R, point calculations, and the associated perception of current stock status.
  5. Estimation of the mean weight at age for older fish (i.e. age 10+) remains an ongoing source of uncertainty.
  6. Sex specific differences in life history parameters may have an affect on the results of the assessment model.

ACKNOWLEDGMENTS

Special thanks to Jay Burnett and the staff of the NOAA Fisheries NEFSC Population Biology Branch for their timely preparation of the 2009 summer flounder ages used in this assessment update.

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