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Table of Contents
List of Acronyms and Abbrievations
Executive Summary
Background
Methods
Results
Discussion
Acknowledgements
References Cited
Appendix

Northeast Fisheries Science Center Reference Document 13-15

2013 Discard Estimation, Precision, and Sample Size Analyses for 14 Federally Managed Species Groups in the Northeast Region

SE Wigley1, J Blaylock2, PJ Rago1, and G Shield1
1NOAA Fisheries, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543
2 Integrated Statistics, 172 Shearwater Way, Falmouth, MA 02540

Web version posted December 6, 2013

Citation: Wigley SE, Blaylock J, Rago PJ, Shield G. 2013. 2013 Discard estimation, precision, and sample size analyses for 14 federally managed species groups in the northeast region. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 13-15; 150 p., 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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List of Acronyms and Abbrievations

AA = Access area
ASM = At-Sea Monitoring Program
ASMFC = Atlantic States Marine Fisheries Commission
CV = coefficient of variation
d/k = discard/kept
FED = finfish excluder device
FMP = fishery management plan
GEN = General category
lg = large mesh
LIM = Limited access category
MA = Mid-Atlantic
MPC = minimum pilot coverage
MRFSS = Marine Recreational Fisheries Statistical Survey
MRIP = Marine Recreational Information Program
NE = New England
NEFOP = Northeast Fisheries Observer Program
NEFSC = Northeast Fisheries Science Center
NMFS = National Marine Fisheries Service
OPEN = Non-access area
SBRM = Standardized Bycatch Reporting Methodology
sm = small mesh
VTR = Vessel Trip Report
xlg = extra large mesh

Executive Summary

This report describes the analysis of the expected coverage needed by at-sea observers for Northeast fisheries for the April 2013 through March 2014 period using the Standardized Bycatch Reporting Methodology. Refinements to the procedure for filtering the needed sea days have been made based on analyses conducted for the SBRM 3-year Review Report - 2011 (Part 1 and Part 2).

The sea days needed to achieve the precision-based performance standard (30% coefficient of variation of the discard estimate) were updated using July 2011 through June 2012 data. Analyses revealed that observer coverage within a fleet corresponded well with the spatial and temporal patterns of fishing activity for fleets with observer coverage. To monitor 14 federally managed fish and invertebrate species groups across 56 fleets, a total of 11,499 sea days are needed. The discards reported in this document may not necessarily correspond directly with the discard estimates derived for individual stock assessments due to differences in stratification and data. Hence, the discard estimates are not definitive, but indicative of where discarding is occurring among commercial fleets and for which species groups. Based upon this analysis, the predominant species groups discarded are skates, dogfish and scallops. Across all species groups examined, "No Market' is the reason reported for the majority of discards.

Background

The Standardized Bycatch Reporting Methodology (SBRM) Omnibus Amendment (NEFMC 2007; NMFS 2008) was vacated by the US District Court of the District of Columbia on September 15, 2011 and the regulations implementing the SBRM were removed by the National Marine Fisheries Service (NMFS) on December 29, 2011 (NMFS 2011). While an SBRM is not currently required, the need to allocate observer sea days to monitor fisheries prosecuted off the northeast coast of the US remains and thus an analysis to estimate the number of sea days needed by each fleet was conducted.

The SBRM discard estimation methods described in Wigley et al. 2007 are still applicable. Refinements to the procedure for filtering the needed sea days have been made based on analyses conducted for the 2011 SBRM 3-year Review Report (Wigley et al. 2012a). The analyses conducted for 2013 are similar to those conducted in 2012 (Wigley et al. 2012b).

This document presents the estimated discards and associated precision, and the number of sea days needed to obtain a 30% coefficient of variation (CV) on the discard estimates for the 14 species groups associated with federal fishery management plans (FMPs) in northeast fleets[1]. Additionally, discard reasons associated with the discarded species are summarized. This document and Wigley et al. (2012b) differ from previous SBRM documents in that it does not include a sea day prioritization[2] and focuses on fish and invertebrate species groups; it does not include sea turtles.

Methods

Data Sources

The data sets used include July 2011 through June 2012 data from the Northeast Fisheries Observer Program[3] (NEFOP) database, the Vessel Trip Report (VTR; including logbooks from the surfclam and ocean quahog fishery) database, the Northeast Fisheries Science Center (NEFSC) commercial landings database, and the NOAA Marine Recreational Information Program[4] (MRIP) database.

The NEFOP is a comprehensive, multi-purpose program that collects a broad range of data on all species that are encountered during a fishing trip as well as gear characteristics data, economic information, and biological samples (NEFOP, 2010). The NEFOP employs trained sea-going observers and monitors to collect these data that also include weight, by species and disposition (retained and discarded), of the entire catch. Fish and invertebrate species are recorded in weight. Conversion factors were applied to convert any dressed weight data to live weight equivalents.

For this analysis, only observed hauls from NEFOP trips with a "complete" sampling protocol were used. A "complete" sampling protocol includes obtaining species weights for both kept and discarded portions of all species in the catch. NEFOP training trips have been included in the analysis. Aborted trips and "set only" trips were excluded from this analysis along with one trip fishing in a statistical area associated with the Southeast region (statistical area '702'), one trip landing outside the Northeast region, and 12 "carrier" trips (contarea = "050"; no fishing effort occurred on these trips). Additionally, hauls with no catch report and species hail weight with discard reason "039" ("previously discarded") were excluded.

The same broad stratification scheme used in SBRM analyses was employed in this analysis, in which trips were partitioned into fleets using six classification variables: calendar quarter, geographic region, gear type, mesh, access area, and trip category. Calendar quarter was based on landed date and used to capture seasonal variations in fishing activity and discard rates. Two broad geographical regions were defined: New England (NE) and Mid-Atlantic (MA) based on port of departure[5]; ports from Maine to Rhode Island constituted the NE region, and ports in states from Connecticut southward constituted the MA region. Gear type was based on Northeast gear codes (negear). Some gear codes were combined: sink, anchored, and drift gillnets, and single and paired mid-water trawls. Trips for which gear was unknown were excluded. Mesh size groups were formed for otter trawl and gillnet gear types. For otter trawls, two mesh groups were formed: small (mesh less than 5.5 inches) and large (5.5 inch mesh and greater). For gillnets, three mesh groups were formed: small (mesh less than 5.5 inches), large (mesh between 5.5 and 7.99 inches), and extra large (mesh 8 inches and greater). Two access area categories were formed: access area (AA) and open (OPEN). The sea scallop fishery was divided into General (GEN) and Limited (LIM) category trips. All other fisheries were combined into a category called "all."

Stratification abbreviations used are given below.

Abbreviation

Definition

MA

Mid-Atlantic ports (CT and southward)

NE

New England ports (RI and northward)

sm

Small mesh (less than 5.5 inches)

lg

Large mesh (5.5 to 7.99 inches)

xlg

Extra large mesh (8 inches and greater)

LIM

Limited access category

GEN

General category

OPEN

Non-access area

AA

Access area

The VTR data are used as a basis for defining the sampling frame, since all federally permitted vessels are required to file a VTR for each fishing trip (See NMFS-Northeast Regional Office http://www.nero.noaa.gov/ro/fso/vtr_inst.pdf ). These self-reported data[6] constitute the basis of the fishing activity of the commercial fleets. Because Dealer data do not contain mesh size and area fished information, the Dealer data could not be used to expand discard ratios by fleet for the annual analyses. The VTR data were used as a surrogate for Dealer data and were used to expand the NEFOP discard ratios to total discards. For this analysis, the commercial VTR trips (excluding NY state [non-federal] vessels) were used. Conversion factors were applied to convert various units of measure to pounds and all weight to live weight. VTR trip data were collapsed into fleets as defined above. Trips participating in the US/Canada access area, B-day category programs and other special access programs could not be identified in the VTR data. These trips have been grouped by the other stratification variables and have not been partitioned separately.

The clam fishery has a separate logbook system from the VTR logbook. The commercial clam logbook data were used to augment the VTR data for the clam dredge fishery. The commercial and recreational landings (in live weight) for the federally managed species were used only in sample size analysis.

A list of the 14 federally managed fish and invertebrate species groups analyzed, and the individual species that comprise each species group, is given in Table 1. Summaries of the data used, in terms of number of trips and number of sea days, by fleet, calendar quarter, and data source (NEFOP and VTR), are given in Table 2 and Table 3, respectively.

The spatial and temporal patterns of observer coverage within a fleet were evaluated. Rather than use a trip-based metric, the kept weight of all species reported in the VTR was used. The "kept weight with observer coverage" was derived as the kept weight of all species reported in the VTR summed by fleet, statistical area, and quarter where at least one observed trip occurred in the fleet-quarter-statistical area cell and at least three observed trips[7] occurred in the fleet-quarter stratum. The "kept weight" was derived as the kept weight of all species reported in the VTR summed over all statistical areas and quarters within a fleet. The percentages of "kept weight with observer coverage" were calculated by dividing the "kept weight with observer coverage" by the "kept weight." These percentages were derived for the 56 fleets (reported as 51 individual fleets and the five confidential fleets combined into "Confidential fleets"), "Other minor fleets" (that include the ten observed twin trawl trips), and all fleets combined. Additionally, as a relative measure of fleet activity among all fleets, the percentage of "kept weight" was derived by dividing the "kept weight" by the sum of the "kept weight" across all fleets.

Discard Estimation

Total discards of each of the 14 federally managed species groups were estimated for the July 2011 through June 2012 time period using a combined discard/kept (d/k) ratio estimator (Cochran 1963), where d = discarded pounds of a given species group, and k = the kept pounds of all species. Total discards (in weight ) were derived by multiplying the estimated discard rate of each fleet by the corresponding fleet landings in the VTR database, and then summing over fleets.

Simple imputation methods were used to fill quarterly cells for which there were one or no observed trips. Data from adjoining strata were pooled to impute estimates for cells with zero or one trip. In this imputation only the temporal stratification, calendar quarter, was relaxed to an annual aggregation recognizing that seasonal variation can occur for some species. This simple imputation could not be applied to fleets where observer coverage was low or missing throughout the year (i.e., too few data to support the simple imputation approach). In these cases, imputed values were not used, and the fleet was designated as a fleet in need of pilot coverage[8]. If some data were available, then discard estimates were derived, but these results were not used in sample size analyses.

The variances of the discard estimates were also derived. In this document, CV is defined as the ratio of the standard error of the total discards divided by the total discards. The appendix presents the equations used in the analysis.

For each species/species group and fleet, the landings from the VTR and clam logbook are presented to provide perspective for the discard estimates.

Discard Reasons

For each species group and fleet, the fish dispositions associated with discarding (as reported by the at-sea observer) have been grouped into the following six discard reason categories: no market, regulation (size), regulation (quota), regulation (other), poor quality, and other. The discard reason categories and the associated fish dispositions are summarized in Appendix Table 2. The discard reasons "No Market" and "Poor Quality" would be considered economic discards and not regulatory discards.

The observed (non-extrapolated) discards associated with each of the six discard reason categories were summed for each species group/species for the fleets where discards could be estimated. For individual fleets, the percentage of observed discards by discard reason category was derived by dividing the sum of the observed discards for each discard reason category by the sum of the total observed discards for each species group/species and fleet. The discard reason category percentages were taken from the observed discard reason category percentages. For the "Other fleets filtered out" (an aggregated fleet that represents fleets where the variance of the discard estimate was not used in the annual sample size analysis), the observed discard reason category percentages were then multiplied by the total estimated (extrapolated) discards for each species group/species and fleet to derive the estimated discards by discard reason category for each species group/species and fleet for each of the fleets associated with the aggregated fleet. For each "Other fleets filtered out," the total estimated discards by discard reason category were summed over the fleets that comprise the fleet aggregation for each species group/species. The estimated discard reason category percentage was derived by dividing the estimated discards for each discard reason category by the sum of the total estimated discards for each species group/species and fleet. In other words, the "Other fleets filtered out" represents the weighted percentage where the weighting factor was the fleet extrapolated discards.

Sample Size Analysis

The sample size analysis (also referred to as sea day analysis) was conducted to estimate the number of baseline trips and sea days needed to monitor the 14 federally managed species groups in each fleet. As described in Wigley et al. 2007 (and given in the appendix), the number of trips and sea days needed to achieve a given precision level was based on the variance of the total discard estimate for a species group. Sample size (trips and sea days) associated with the precision standard for discard estimates (30% CV) were derived. The sample size analysis was performed using trips as the sampling unit, and then converting the number of trips to sea days by multiplying by the weighted mean trip length, where the weighting factor was the quarterly number of VTR trips. The percentage of trips was derived by dividing the number of trips needed by the number of VTR trips that occurred in the fleet.

When total discards could not be estimated due to little or no observer coverage (no data), or when total discards were zero (no variance), the sample size (number of trips) was determined using a pilot coverage level set to 2% of the quarterly VTR trips for a fleet, with a minimum of three trips per quarter (12 trips per year) and a maximum of 100 trips per quarter (400 trips per year). The 2% pilot coverage was the same as was used in the 2012 sea day analysis (Wigley et al. 2012b) and the SBRM analyses (Wigley et al. 2007; Wigley et al. 2011). The quarterly trips were then multiplied by the quarterly mean VTR trip length to derive quarterly sea days. The quarterly trips and quarterly sea days were then summed for annual number of trips and sea days. It is recognized that pilot coverage may result in too much coverage in cases where little or no observer coverage may actually be needed or when effort changes sharply between years.

Some fleet/species combinations contribute very little to the total mortality or discard of the species, but may require significant resources to characterize the precision of the estimate. For example, a high variance estimate for a rare event within a fleet would require high levels of sampling, even though the total discard in that fleet was unimportant with respect to either the total discard or total mortality on the resource. To address this, a modification of the filtering approach developed for SBRM was employed. Similar to the SBRM analyses (Wigley et al. 2007), importance filters were used to provide a standardized protocol to further refine the number of baseline sea days based on: (a) the importance of the discarded species relative to the total amount of discards by a fleet, and (b) the total fishing mortality due to the discards. In the SBRM analyses, the importance filter was comprised of three filters (i.e., unlikely cell filter, fraction of discard filter, and fraction of total mortality due to discards filter) that were applied simultaneously. However, based on an evaluation of the use of the unlikely filter over a three-year period, it was found that no substantive changes in the determination of sea days would have resulted had the unlikely filter been removed from the importance filter (Wigley et al. 2012a). Thus, in this analysis, all cells in the unlikely filter were set to 1 (all cells are likely; this is equivalent to removing the unlikely filter from the importance filter).

The 2013 baseline sea days were filtered using a 95% cut-point in the discard filter, and a 98% cut-point for the total mortality filter due to discards. In other words, estimates of sea day coverage for a given species or species group were derived for those fleets where discards constituted 95% of the discard mortality and catch constituted 98% of the total mortality.

To determine the number of sea days (referred to as the "2013 sea days needed") and trips needed to achieve a 30% CV on the estimates of discards for each of the 14 species groups within a fleet, the maximum number of sea days for the 14 species groups (i.e., the maximum number of sea days in a row) was used. This ensures that all species groups will have a 30% CV or less. In the event that sea days for each species group within a fleet are filtered out, then the number of sea days for the fleet was based on minimum pilot days to maintain monitoring coverage for that fleet. Minimum pilot coverage represents a minimum threshold for the allocation of sea days and is defined as three trips per quarter for each quarter with industry activity. The quarterly number of trips are multiplied by the quarterly mean VTR trip length and then summed over quarters to derive the annual minimum pilot days for the fleet. These fleets are indicated with a "MPC."

If the fleet was designated as a pilot fleet, then pilot sea days were used. These fleets are indicated with a "P." The fleets with sufficient data to estimate sample size are referred to as non-pilot fleets.

Results

There were 56 fleets uniquely identified during the July 2011 through June 2012 period (Table 2 and Table 3; Appendix Table 1). Based upon the industry activity during this time period, the MA Danish seine fleet (Row 38) was added to the collection of fleets analyzed (fleets that have not been included in previous analyses are indicated with a "+"). The other minor fleets not uniquely identified in this analysis have been aggregated into a single fleet labeled "Other minor fleets." Due to confidentially rules, the landings associated with 5 unique fleets (MA GEN Access area scallop trawl [Row 10], MA large mesh haddock separator trawl [Row 16], MA floating trap [Row 20], MA Danish seine [Row 38], and MA hagfish pots and traps [Row 45]) have been aggregated into a single fleet labeled "Confidential fleets" for reporting purposes. Hence, the fleet row numbers within Table 2 and Table 3 are sequential, while the fleet row numbers in Tables 4 - 7 are ordered but there are gaps in the row numbers.

Of the 56 fleets examined, 34 fleets had little or no observer data: eight fleets had sparse observer data across all quarters, while 26 fleets were missing observer data in all quarterly cells. The fleets with no observer coverage were primarily pot and trap fisheries targeting particular species (e.g., lobster, crab, conch, shrimp, and hagfish). No discard estimation was performed for the 26 fleets with no observer coverage and they were designated as fleets in need of pilot coverage (Table 2 and Table 3). The eight fleets with sparse observer coverage were also designated as fleets in need of pilot coverage for the sample size analysis; however, discard estimation was performed using the sparse observer data. For the 22 remaining fleets (designated as non-pilot fleets), estimates of discards and their associated variance were derived and used to determine the sample sizes needed for a 30% CV. Of the 22 fleets, there were six fleets (Rows 19, 23, 24, 30, 34, and 35) where the simple imputation was applied.

Thus, for the discard estimation and precision analysis, 26 fleets had no discard estimation and 30 fleets had discards estimated. For the sample size analysis, 22 fleets had sample sizes derived from the discard variances and 34 fleets had sample sizes based upon pilot coverage.

A total of 5,155 trips (14,738 days) was observed during July 2011 through July 2012. When these trips were stratified, some trips were partitioned between strata resulting in 5,613 trips (15,622 days; Table 2 and Table 3) in the NEFOP. The number of trips and days do not include ten observed twin trawl trips in the MA and NE twin trawl fleets due to only two reported VTR trips for the MA twin trawl fleet and no trips reported for the NE twin trawl fleet. The information for these two fleets has been aggregated into "Other minor fleets." The apparent misreporting of gear types is further described in the discussion section of this report.

In terms of number of trips, the percentages of observed trips varied by fleet and calendar quarter. On an annual basis, for the 30 fleets with some observer coverage, the percentage of observed trips by fleet ranged between 0.01% (NE lobster pot fleet, Row 49) to 50% (MA AA LIM scallop trawl fleet, Row 10; Table 2). For the 22 non-pilot fleets, the percentage of observed trips ranged between 0.6% (MA large mesh gillnet fleet, Row 23) and 30% (NE mid-water trawl fleet, Row 40). Over all fleets, the percentage of observed trips was 5.6% (Table 2).

In terms of kept weight of all species, the percentage of observer coverage over all fleets was 56% (Table 4). For the 21 non-pilot fleets (excluding the one non-pilot confidential fleet aggregated into "Confidential fleets"), the percentage of observer coverage ranged between 34% and 99% (Table 4) with 18 of the 21 fleets having a percentage greater than or equal to 75% . This indicates that the majority of kept weight within the fleet was associated with statistical areas and quarters with observer coverage. Additionally, these 18 fleets comprised approximately 60% of the total kept weight across all fleets. The kept weight of all species was considered a surrogate for fishing effort and hence observer coverage spatially and temporally occurred where the majority of fishing effort occurred.

The combined fleet "Other minor fleets" had a percentage of observer coverage greater than zero due to the ten observed twin trawl trips that were not uniquely identified to a fleet. The landings associated with this combined fleet contributed less than 0.1% of the total landings across all fleets (Table 4).

Annual VTR landings and estimated discards (live pounds) with associated precision are summarized for 51 individual fleets (Rows 1-9, 11-15, 17-19, 21-37, 39-44, 46-56) and two combined fleets ("Confidential fleets," and "Other minor fleets" [with landings only] for each of the 14 species groups and the individual species that comprised those species groups (Table 5A and Table 5B; Figure 1A and Figure 1B). There were 23 fleets (Rows 1, 3, 13-14, 18, 21, 25, 28, 39, 41-44, 46-48, and 50-56) as well as the "Other minor fleets" that have no discard estimation due to no NEFOP coverage (dark shaded fleets in Table 5A and Table 5B). In Table 5A, the CVs associated with the cells (species group and fleet) that were not used in the sample size analysis (i.e., cells filtered out via the importance filter) are indicated in light shading. Precision of discards of individual species (Table 5B) were not used in the sample size analysis.

Based upon this analysis, 69,039 mt (152,203,992 pounds; live weight) of discards for the 14 species groups occurred during the July 2011 through June 2012 period. The majority (79%) of the discards were comprised of three species groups: skates (52%), dogfish (15%), and scallops (12%); the remaining species groups each accounted for less than or equal to 5% (Table 5A).

The percentage of discards to total catch varied among the 14 species groups (Table 5A; Figure 1A) and individual species (Table 5B; Figure 1B). There was one species group (SAL) with zero discards (this species group is not presented in Figure 1A); two species groups (HERR and SCOQ) where discards were less than 1% total catch; four species groups (RCRAB, SCAL, SBM, and TILE) where percentages of discards ranged between 1% and 10% of total catch; three species groups (BLUE, FSB, and GFL) where discards ranged between 11% and 25% of total catch; and four species groups (MONK, SKATE, GFS, and DOG) where discards were greater than 26% of total catch. The species groups with the highest percentage of total discards relative to total catch were: skates (69%), dogfish (63%), and monkfish (30%; Figure 1A). For individual species, most notable are the high percentages of discards to total catch of wolffish (>99%), ocean pout (>99%) and windowpane flounder (97%) due to the no possession regulations for these three species.

The reasons for discarding varied among the 14 species groups (Appendix Table 3A) and individual species (Appendix Table 3B). Overall, for the 14 species groups, the majority (72%) of discards occurred due to "No Market." "Regulation" (due to size, quota, and other), "Poor Quality," and "Other" contributed 22%, 4%, and 2%, respectively (Appendix Table 3A).

The percentages of discard to total catch were also summarized by fleet for 22 fleets (the non-pilot fleets; Figure 2). Discards of one or more of the 14 species groups that were filtered out via the importance filter have been aggregated into a species group labeled "Other FMP." Discards of non-federally managed species have been aggregated into a species group labeled "Non-FMP." The percentages of discard to total catch varied by fleet (Figure 2). There was two fleets (Rows 29 and 40) where discards were less than 1% of the total catch in the fleet; two fleets (Rows 4 and 35) where the percentages of discards ranged between 1% and 10%; 12 fleets (Rows 2, 7, 17, 19, 23-24, 27, 30, 32-33, and 36-37) where the percentages of discards ranged between 11% and 25% of total catch; four fleets (Rows 5, 8, 26, and 34) where the percentages of discards ranged between 26% and 50% of the total catch; and two fleets (Rows 6 and 16) where discards were greater than 50% of the total catch.

The number of species groups discarded within a fleet also varied among fleets. The majority of fleets (12 of the 22 fleets) were comprised of two or three discarded species groups. For six of these fleets (Rows 4, 16, 17, 24, 35, and 40), the "Other FMP" species group comprised the majority of the discards. This indicates that the majority of discards were filtered out via the importance filter. There were three fleets (Rows 29, 30, and 34) for which the "Non-FMP" species group comprised the majority of the discards. There were another three fleets where two of the three discarded species groups were "Other FMP" and "Non-FMP" and the other was the dominant species group of dogfish (Rows 2 and 23) and small mesh groundfish (Row 19).

The remaining fleets (10 of the 22 fleets) had between four and ten discarded species groups. The skate species group dominated the discards in four of these fleets (Rows 5, 6, 8, and 27) while "Non-FMP" species group dominated the discards in three fleets (Rows 32, 36, and 37). Three fleets (Rows 7, 26, and 33) had a mix of dominant discarded species groups that included small mesh groundfish, dogfish, and scallops.

The dominant "Non-FMP" species in the scallop dredge fleets (Rows 30, 32, 34, 36, and 37) were: sand dollar, sponge, and starfish. "Fish, not known" was the dominant "Non-FMP" species in the NE purse seine fleet (Row 29).

The precision of the discard estimates varied by species group and fleet (Table 5A). Of the 14 species groups, 10 species groups had an overall CV that was less than 30%, three species groups (BLUE, SCOQ, and TILE) had an overall CV that was greater than 30% CV, and one species group (SAL) had zero discards and consequently no CV. The discards of four species groups (BLUE, HERR, SCOQ, and TILE) were filtered out in all fleets indicating the discards of these species groups were a minor component of the total catch of these species (Table 5A; Figure 1A). The precision of the discard estimates for individual species are given in Table 5B; these were not used in the sample size analysis.

The numbers of sea days needed for each species group and fleet, as well of the number of pilot coverage days, minimum pilot coverage days, and the sea days needed for the fleet (referred to as "2013 Sea Days Needed"), are summarized in Table 6. A total of 11,499 days are needed for all fleets. As mentioned previously, 34 fleets had insufficient observer information to estimate discards and the sea days for these fleets were based on pilot coverage days. The number of sea days needed for fleets with the pilot coverage designation was 1,643 days (14% of 11,499; Table 6). There are eight fleets for which the sea days for all species groups were filtered out via the importance filter, and minimum pilot coverage days were used to maintain some coverage (Rows 4, 16, 17, 29, 30, 34, 35, and 40; Table 6). The sea days associated with these fleets was 238 days (2% of 11,499; Table 6). Of these eight fleets, there were two fleets (Rows 16 and 17) where pilot days equaled minimum pilot days, a result of low industry activity in these fleets. The sea days needed for the remaining 14 fleets (9,618 days, representing 84% of the total sea days needed) were derived using the variance of the discard estimate (Table 6). Of the 9,618 days, 6,698 days (70%) were associated with two fleets (Rows 5 and 8; Table 6).

The sample size (in terms of number of sea days, number of trips, and percentage of trips based upon the VTR trips in July 2011 through June 2012) needed to achieve a 30% CV of the discard estimate in these 14 fleets is given in Table 7. The relationship between sample size and precision, over a range of sample sizes, is shown in Figure 3 for species groups and fleets. If the precision standard (30% CV) was relaxed for the red crab species group in two fleets (Rows 5 and 8), resulting in the penultimate (next largest) value being used in each of the two fleets (e.g., using 583 days rather than 1,408 days for Row 5 and 496 days rather than 5,290 days for Row 8), then the total number of sea days needed across all fleets would be 3,999 days (a 65% decrease from the 11,499 days). Using the penultimate value, the expected achieved precision of red crab discards in Rows 5 and 8 would be 53% CV and 113% CV, respectively.

Discussion

A broad stratification was used to support the deployment of observers on commercial fishing trips among various fleets using attributes known prior to the trip departure. As discussed in previous discard estimation analyses (Wigley et al. 2007; Wigley et al. 2011), species-specific stock assessment discard estimation may differ from this report due to differences in stratification and data used (calendar year versus 12-month [July to June] time period; area fished versus region [port of departure]; and VTR landings versus Dealer landings). Region, based on port of departure, was used for the deployment observers. It is recognized that area fished would provide a better stratification for discard estimation. It is expected, however, that estimates would be in the same order of magnitude. The discard estimates presented here are not definitive estimates, but rather are indicative of where discarding occurred among the commercial fleets for the 14 federally managed species groups.

We have assumed 100% discard mortality, i.e., we do not account for potential survival of organisms returned to the water. When comparing discard estimates from this study with those from stock assessments, it is usefully to note that survival ratios are applied in stock assessments for Georges Bank and Gulf of Maine stocks of cod, Atlantic sea scallop, spiny dogfish, summer flounder, southern New England and Gulf of Maine stocks of winter flounder, and southern New England yellowtail flounder.

These analyses have used VTR data. Dealer (CFDERSyyyy) data do not contain mesh or area fished information until the trip-based allocation is performed (Wigley et al. 2008). The trip-based allocation of Dealer (CFDETT/SyyyyAA) data is conducted annually and was not available when this analysis was initiated. Given that the VTR landings estimates are usually less (VTR reports the good faith hails) than the dealer records for a given fleet, the corresponding estimates of discards will also be underestimated. The magnitude of the underestimation will vary by fleet and year.

During the data preparation for these analyses, some possible misreported gear types were encountered. Some of the possible misreporting was associated with the seasonal switch between fishing for groundfish and shrimp. For example, captains reported using a shrimp trawl ("OTS") with 6.5 inch mesh catching groundfish (in these cases, one would expect "OTF," otter trawl fish). And conversely, captains reported "OTF" with 1 7/8 inch mesh catching shrimp (in these cases, one would expect "OTS"). Generally, there are only a few trips with these possible reporting errors.

There also appeared to be some confusion in the proper use of the VTR gear code "OTS" (shrimp trawl), "OTT" (twin trawl), "OTC" (scallop trawl), and "OTF" (otter trawl). Some of the "OTS" trips have either squid or scallops as the predominant species reported (no shrimp reported) and it is not certain whether or not these trips used a shrimp trawl, scallop trawl, otter trawl, or twin trawl. Regarding the twin trawls trips, there were only 2 VTR trips that reported using twin trawl (VTR gear code "OTT") yet there were ten observed twin trawl trips that occurred during July 2011 through June 2012. When these ten observed trips were mapped back to the VTR data, it was found that the captains had reported "OTF" (otter trawl, bottom, fish) and hauled two nets. Due to this misreporting of twin trawl, the twin trawl fleet could not be included in this analysis (observed trips were greater than VTR trips). Caution should be used when interpreting results associated with these gear types as the implications of misreported gear types are variable among fleets and the true magnitude is unknown. Continued outreach and education to industry members emphasizing proper reporting of gear types is a critical need as well as improved data quality and data accuracy of the VTR data.

Since the northern shrimp fishery is closed during the calendar quarter 3, the VTR trips associated with NE shrimp trawl fleet (Row 19, Qtr 3; Table 2 and Table 3) were investigated. These trips reported catching herring using 2 inch mesh while a few trips reported catching squid. The captains of these vessels indicated that a finfish excluder device (FED) was not used. The northern shrimp fishery requires a FED; however, other small mesh exempted fisheries do not require a FED. Currently, there is not a data element within the VTR database that indicates whether or not a FED, or other bycatch reduction device, was used. Due to this limitation, the trips within the NE shrimp trawl fleet (Row 19) represent trips using shrimp trawl with and without a FED. An additional data element within the VTR database would be needed to partition these trips into separate fleets.

The analysis conducted for the spatial and temporal observer coverage used live weight. As a result, fleets using scallop dredge and clam dredge targeting species with shells have higher kept weight percentage than other fleets due the use of "live" weight rather than "landed meat" weight. However, the use of live weight does not distort the observed percentage (spatial or temporal pattern) within a fleet. It is important to remember that percent observer coverage is an indicator of where observed kept weight (or trips) occurred relative to unobserved kept weight (or trips). The percentage observed should not be confused with the precision of the discard estimate which is the metric used to describe discard variability and determine the sample size needed for monitoring purposes.

The use of minimum pilot coverage represents a refinement over previous years' analyses when pilot coverage was used. As depicted in Figure 4 of Wigley et al. 2012a, there were two cases in which pilot coverage had been invoked in the sample size analysis: (1) insufficient or no NEFOP data (no discard information is available), and (2) when all sea days were filtered out (discard information is available and discards found to be low relative to other fleets). By utilizing the minimum pilot coverage, the numbers of trips needed to monitor the fleet in the upcoming year are based upon the information obtained via the data analysis. It is important to note that in most cases, there are only minor differences in the number of the pilot days versus the minimum pilot days due to the low number of industry trips in the fleets where all species are filtered out. Thus, the use of minimum pilot coverage represents only a minor refinement in the sea day analysis.

There are two fleets with high sea day requirements (>1,400 sea days). The NEFOP data associated with the trips within these fleets were reviewed to rule out any data "irregularities." The high monitoring coverage for New England large mesh and Mid-Atlantic small mesh otter trawl fleets (Rows 5 and 8; Table 6) was due to high variability of red crab discards. In this analysis, as well as in previous analyses (NEFSC 2011a; NEFSC 2011b; Wigley et al. 2011; Wigley et al. 2012b), the high variability arose from observing some trips that were fishing in deep-water portions of statistical areas as well as observing other trips that were fishing in shallower portions of the same statistical areas. Red crabs were encountered during trips fishing in deep water. Although the discard reason reported for three fleets was "No Market" (Appendix Table 3A), these vessels do not generally have permits to land red crabs, thus the red crabs must be discarded. Currently, the analysis does not stratify these fleets further to account for depth because statistical area is the finest spatial resolution that defines a subtrip within the Vessel Trip Report (a subtrip within the VTR is a unique gear, mesh, and statistical area). While depth is a data element in the VTR, depth is not always reported and there are few QA/QC checks on this data element.

Fish may be discarded for economic reasons (e.g., "No Market" or "Poor Quality") or for regulatory reasons (size, quota, or other). When considering mechanisms to reduce discards, it may be useful to know why discarding is occurring. It is important to note that large discard percentages may be associated with a small quantity of discards. Additionally, it is important to note that for many species, the discards are associated with fleets that have been filtered out by the importance filter. Observers classify the discards by fish disposition based upon the NEFOP protocol (NEFOP 2010; NEFOP 2011) in which the observer asks the captain/crew why species are being discarded. Thus, these data should be considered a form of self-reported data and as such these data are difficult to verify and should be interpreted cautiously.

This analysis does not address the coverage needed for individual sectors or multiple stock components of a species. The analytical basis for the allocation of future sea day coverage in this analysis is a specified level of precision (i.e., 30% CV) and an expectation that the pattern of fishing activity observed in the prior year will be similar to that in the upcoming year.

Acknowledgements

We thank all the NEFOP observers and at-sea monitors for their diligent efforts to collect the data used in this report. We thank our reviewers for their helpful comments on this report.

References Cited

Cochran, W.L. 1963. Sampling Techniques. J. Wiley and Sons. New York.

National Marine Fisheries Service (NMFS). 2004. Evaluating bycatch: a national approach to standardized bycatch monitoring programs. U. S. Dep. Comm., NOAA Tech. Memo. NMFS-F/SPO-66, 108 p. On-line version, http://www.nmfs.noaa.gov/by_catch/SPO_final_rev_12204.pdf

National Marine Fisheries Service (NMFS). 2008. Magnuson-Stevens Fishery Conservation and Management Act Provisions; Fisheries of the Northeastern United States; Northeast Region Standardized Bycatch Reporting Methodology Omnibus Amendment. Federal Register, Vol. 73, No. 18, Monday, January 28, 2008. p. 4736-4758. Available on-line at: http://www.gpoaccess.gov/fr/retrieve.html

National Marine Fisheries Service (NMFS). 2011. Fisheries of the Northeastern United States; Removal of Standardized Bycatch Reporting Methodology Regulations. Federal Register, Vol. 76, No. 250, Thursday, December 29, 2011. p. 81844 - 81850. http://www.gpo.gov/fdsys/pkg/FR-2011-12-29/pdf/2011-33302.pdf

New England Fishery Management Council (NEFMC), Mid-Atlantic Fishery Management Council and National Marine Fisheries Service. 2007. Northeast Region Standardized Bycatch Reporting Methodology: An Omnibus Amendment to the Fishery Management Plans of the New England and Mid-Atlantic Fishery Management Councils. June 2007. 642 p. Available on-line at: http://www.nefmc.org/issues/sbrm/index.html

Northeast Fisheries Science Center (NEFSC). 2011a. Standardized Bycatch Report Methodology Annual Discard Report 2011 (Section 1 and 2). Internal document presented to the NEFMC and MAFMC. 1135 p. Available on-line at: http://www.nefsc.noaa.gov/fsb/SBRM/

Northeast Fisheries Science Center (NEFSC). 2011b. Standardized Bycatch Report Methodology Sea Day Analysis and Prioritization 2011. Internal document presented to the NEFMC and MAFMC on January 25, 2011. 25 p. Available on-line at: http://www.nefsc.noaa.gov/fsb/SBRM/2011/2011-SBRM-Sea-Day-Analysis-Prioritization.pdf

Northeast Fisheries Observer Program (NEFOP). 2010. Fisheries Observer Program Manual 2010. Northeast Fisheries Science Center, Woods Hole, MA 02543. 442 p. Available on-line at: http://www.nefsc.noaa.gov/fsb/manuals/2010/NEFOPM_010110_Bookmarks_Compressed.pdf

Northeast Fisheries Observer Program (NEFOP). 2011. At-Sea Monitoring Program Manual. Northeast Fisheries Science Center, Woods Hole, MA 02543. 502 p. Available on-line at: http://www.nefsc.noaa.gov/fsb/manuals/2011/ASM_program_manual_0611.pdf

Wigley SE, Blaylock J, Rago PJ, Murray KT, Nies TA, Seagraves RJ, Potts D, and Drew K. 2012a. Standardized Bycatch Reporting Methodology 3-year Review Report 2011- Part 2. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 12-27; 226 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026 or online at http://www.nefsc.noaa.gov/publications/crd/crd1227/

Wigley SE, Blaylock J, Rago PJ, Shield G. 2012b. 2012 Discard estimation, precision, and sample size analyses for 14 federally managed species groups in the northeast region. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 12-17; 146 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online http://www.nefsc.noaa.gov/publications/crd/crd1217/

Wigley SE, Blaylock J, Rago PJ, Tang J, Haas HL, and Shield G. 2011. Standardized Bycatch Reporting Methodology 3-year Review Report 2011- Part 1. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 11-09; 285 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/publications/crd/crd1109/

Wigley SE, Hersey P, Palmer JE. 2008. A description of the allocation procedure applied to the 1994 to 2007 commercial landings data. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 08-18; 61 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/publications/crd/crd0818/

Wigley SE, PJ Rago, KA Sosebee, and DL Palka. 2007. The analytic component to the Standardized Bycatch Reporting Methodology Omnibus Amendment: sampling design and estimation of precision and accuracy (2nd edition). U.S. Dep. Commer., Northeast Fish. Sci. Cent. Ref. Doc. 07-09; 156 p. Available on-line: http://www.nefsc.noaa.gov/publications/crd/crd0709/



[1] "fleet" is synonymous with "fishing mode."

[2] The Proposed 2012 Observer Sea Day Allocation (March 23, 2012) document is available on-line at: http://www.nefsc.noaa.gov/femad/fsb/SBRM/2012/Proposed_2012_Observer_Sea_Day_Allocation_3-23-2012_v3.pdf When available, the Proposed 2013 Observer Sea Day Allocation document will be posted on the SBRM website under Additional Documents.

[3] There were 3,124 At-Sea Monitoring Program (ASM) trips associated with NE handline, longline, otter trawl, and gillnet fleets during July 2011 through June 2012. A comparison of discard rates derived from observer and at-sea monitor data in 2010 and 2011 revealed there were generally no statistical differences in discard rates between the two data collection programs for the 18 fish species for four gear types (longline, large mesh otter trawl, large mesh gillnet, and extra large mesh gillnet) where at-sea monitor data exist, hence NEFOP and ASM data were pooled. See Northeast Fisheries Observer Program (2011) for more information on ASM. The Atlantic States Marine Fisheries Commission (ASMFC) funded 87 trips during July 2011 through June 2012. A comparison of discard rates derived from NEFOP-allocated and ASMFC-allocated trips reveals there were generally similar discard rates for the four fleets where ASMFC-allocated trips exist (MA small and large mesh otter trawl fleets and NE small and large mesh otter trawl fleets), hence these data have been pooled.

[4] Marine Recreational Information Program (MRIP) was implemented in 2012 and supersedes the NOAA Marine Recreational Fisheries Statistics Survey (MRFSS).

[5] Wigley et al. (2007) found that the majority (over 93%) of 2004 observed trips both originated and fished in the same region and exhibited the same general pattern as in the VTR data. An updated analysis using data collected during July 2007 through June 2011 found similar results (Wigley et al. 2012a).

[6] See Wigley et al. 2007 for more details on self-reported VTR data.

[7] The three trips for fleet-quarter correspond with a minimum threshold for allocating observer coverage.

[8] Pilot coverage is defined as a minimum level of observer coverage necessary to acquire bycatch information with which to calculate variance estimates that in turn can be used to further define the level of sampling needed (NMFS 2004).

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