Table of Contents Executive Summary Introduction Methods Results Discussion Acknowledgements References Cited Appendix
Northeast Fisheries Science Center Reference Document 13-05
A Brief Description of Northeast Region Fish and Invertebrate Discard Estimation for the 2013 Update to the National Bycatch Reportby J. Blaylock1, S.E. Wigley2, P.J. Rago2, M. Mood1, and M.C. Palmer2
1 Integrated Statistics, 16 Sumner St., Woods Hole, MA 02543
2NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543
Web version posted April 24, 2013Citation: Blaylock J, Wigley SE, Rago PJ, Mood M, Palmer MC. 2013. A brief description of Northeast region fish and invertebrate discard estimation for the 2013 update to the National Bycatch Report. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 13-05; 38 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/nefsc/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.
List of Acronyms and Abbreviations
AA = access area
B = B-day program
CV = coefficient of variation
d/k = discard/kept
GEN = general
HOOK = haddock longline hook sector
lg = large
LIM = limited
MA = Mid-Atlantic
NBR = National Bycatch Report
NE = New England
NEFOP = Northeast Fisheries Observer Program
NEFSC = Northeast Fisheries Science Center
NMFS = National Marine Fisheries Service
OPEN = non-access area
sm = small
USCAN = US/Canada Resource Sharing Area
VMS = Vessel Monitoring System
VTR = Vessel Trip Report
xlg = extra large
This report describes the discard estimation analysis performed for the 2013 Update to the National Bycatch Report. Estimates of discards that occurred during the January to December 2010 period in all federally managed fisheries in the northeast United States were derived for 34 species of finfish and invertebrates using a combined discard-to-kept ratio estimator. Based on this analysis, approximately 64,557 mt (live weight) of discards occurred across the 34 species and 29 fleets considered. The predominant species groups discarded were skates, Atlantic sea scallops and dogfish. 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.
In 2011, the National Marine Fisheries Service (NMFS) published the First Edition of the National Bycatch Report (NBR; Wigley et al. 2008, NMFS 2011), which summarizes estimates of discards, by species, that occurred in 2005 in all federally managed fisheries in the United States. New comprehensive editions of the NBR are scheduled to occur every six years, with online updates produced on a biennial basis, starting in 2013. This document describes the methods used to estimate the 2010 discards of finfish and invertebrates in fisheries of the Northeast region that will be included in the 2013 Update to the NBR. The Northeast regional analysis involved 34 species and 63 fleets (Table 1 and Table 2). The analysis did not consider stock components and only included fleets with sufficient data to derive discard estimates.
The discard estimation process used a stratification approach broad enough to encompass all species, and employed a combined ratio method using a discard-to-kept weight ratio. The discard estimates reported in this document will not necessarily correspond directly with those contained in individual stock assessments due to differences in stratification and data. However, the various estimates should be of the same order of magnitude.
Data Sources and Stratification
The data used include January through December 2010 data from the Northeast Fisheries Observer Program (NEFOP) database, the Vessel Trip Report (VTR; including logbooks from the surfclam and ocean quahog fishery) database, the Vessel Monitoring System (VMS) and the Northeast Fisheries Science Center (NEFSC) commercial landings (i.e., Dealer) database.
Northeast Fisheries Observer Program (NEFOP)
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; NEFOP 2011). 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, "set only" trips, carrier trips, and trips associated with a groundfish sentinel fishery (NEFOP program code = 127) were excluded from the analysis. Additionally, offwatch hauls, hauls with missing fleet information (e.g., unknown gear/mesh/area), and hauls with missing catch reported were excluded. Records of species hail weight with discard reason "039" ("previously discarded"), unknown species, or unknown catch disposition, were also excluded, as was any catch of non-living items.
A broad stratification scheme was used in this analysis, with trips partitioned into fleets using six classification variables: calendar quarter, gear type, access area, trip category, area fished, and mesh size. Calendar quarter was based on landed date and used to capture seasonal variations in fishing activity and discard rates. Gear type was based on Northeast fishing gear codes (negear). Some gear codes were combined: troll line and longline, handline and auto jig handline, scallop trawl and twin trawl, sink, anchored, and drift gillnets, herring and other purse seines, single and paired mid-water trawls, and clam and quahog dredges. Two access area categories were formed based on gear and program code: access area (AA) and open (OPEN). Additional categories referring to the US/Canada Resource Sharing area (USCAN) and Haddock longline hook sector (HOOK) that were used in First Edition of the NBR (NMFS 2011) were discontinued in this analysis because Special Access Programs were difficult to identify and were deemed outdated with the onset of groundfish sector-based management. The B-day access area category (B) was also discontinued due to minimal occurrence of such trips. Trips associated with the US/Canada access area, and B-day category have been grouped by other stratification variables (e.g., gear and mesh size). The sea scallop fishery was divided into General (GEN) and Limited (LIM) category trips based on trip length as a surrogate for permit category (single day is general category, multi-day is limited access). All other fisheries were combined into a trip category called "all." Two regional areas were defined based on area fished: New England (NE), which includes statistical reporting areas < "600" (encompassing Southern New England, Georges Bank, and the Gulf of Maine), and Mid-Atlantic (MA), comprised of statistical areas >= "600." This area fished definition applied to all trips except shrimp trawl trips fishing in Southern New England (statistical areas 530-539), which were assigned to the MA area to separate shrimp trips using a Nordmore grate in the northern shrimp fishery from other trips using turtle excluder devices in the Mid-Atlantic. Mesh size groups were defined for otter trawl and gillnet gear types. For otter trawls, two mesh groups were formed: small (sm; mesh less than 5.5 inches) and large (lg; 5.5 inch mesh and greater). For gillnets, three mesh groups were formed: small (sm; mesh less than 5.5 inches), large (lg; mesh between 5.5 and 7.99 inches), and extra large (xlg; mesh 8 inches and greater). All other fisheries were classified into a mesh category called "all."
Vessel Trip Report (VTR)
The VTR data constitute the basis of the fishing activity of the commercial fleets and are used for defining the sampling frame. Dealer data do not contain mesh size and area fished information and thus could not be used for this purpose in the analyses. The VTR data were used as a surrogate for Dealer data to expand the NEFOP discard ratios to total discards by fleet. VTR data are self-reported and all federally permitted vessels are required to file a VTR for each fishing trip. For this analysis, all 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. However, access area determination for VTR trips using scallop gear (negear 052 and 132) was based on Vessel Monitoring System (VMS) activity declaration code. A description of the methods used to assemble the VMS analytical dataset is provided in the Appendix; VMS trip information was linked to VTR trip data based on matching trip identifier (tripid). Trips with VMS program code "SAA" (Special Access Area) and "SCG" (Limited Access General Category) were assigned to access area category (AA). When linking the VTR and VMS databases, only 76% of scallop trawl trips (negear 052) and 87% of scallop dredge trips (negear 132) could successfully be matched to determine VMS activity code and access area classification. Trips without VMS activity code were classified as OPEN.
Other Data Sources
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.
As mentioned above, the VMS data were used to stratify VTR data into fleets. See the Appendix for further details.
The Dealer data (i.e., NEFSC commercial landings) for federally managed species were used only in the validation stage of the analysis.
Total discards of each of the 34 federally managed species were estimated for the January-December 2010 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 zero or one 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 the annual level. 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 which case discard estimates for the fleet were not derived.
Total discarded pounds for species j is defined as:
whereis total discarded pounds for species j; Kh is VTR total kept pounds in stratum h; rc,j is the combined ratio of species j; djih is discards of species j from trip i in stratum h; kih is kept pounds of all species on trip i in stratum h; Nh is the number of VTR trips in stratum h; and nh is the number of observed trips in stratum h. In Eq. 2 the summation over strata h = 1 to Q is over calendar quarters and the other strata values are held constant. Equation 3 (below) requires a more explicit definition of the stratum designation since the summation over quarter relies on an annual average ratio defined in Eq. 2.
Variance of for species j is defined as:
where is total discarded pounds for species j; Kqh is VTR total kept pounds in quarter q and stratum h; rc,j is the combined ratio of species j; djiqh is discards of species j from trip i in quarter q and stratum h; kiqh is kept pounds of all species on trip i in quarter q and stratum h; Nqh is the number of VTR trips in quarter q and stratum h; and nqh is the number of observed trips in quarter q and stratum h.
Coefficient of variation (CV) of is defined as:
For each species and fleet, the landings from the VTR and clam logbook are presented to provide perspective for the discard estimates.
Validation of the approach used to estimate total discards was performed by using the same approach to estimate the landings of each of the species in 2010, and comparing these estimates to the landings included in the VTR and Dealer databases.
To estimate landings using the NEFOP data, the same estimation method as described above was used; however, the species-specific poundage discarded (dj) was replaced with species-specific kept pounds (kj).
Total landed pounds for species j is defined as:
where is total kept pounds of species j; Kh is VTR total kept pounds in stratum h; rc,j is the combined ratio of species j; kjih is the total kept pounds of species j from trip i in stratum h; kih is kept pounds of all species on trip i in stratum h; Nh is the number of VTR trips in stratum h; and nh is the number of observed trips in stratum h. In Eq. 6 the summation over strata h = 1 to Q is over calendar quarters and the other strata values are held constant. Equation 7 (below) requires a more explicit definition of the stratum designation since the summation over quarter relies on an annual average ratio defined in Eq. 6.
The variance of for species j is defined as:
where is total discarded pounds for species j; Kqh is VTR total kept pounds in quarter q and stratum h; rc,j is the combined ratio of species j; kjiqh is the kept pounds of species j from trip i in quarter q and stratum h; kiqh is kept pounds of all species on trip i in quarter q and stratum h; Nqh is the number of VTR trips in quarter q and stratum h; and nqh is the number of observed trips in quarter q and stratum h.
The coefficient of variation of was defined as:
For each species, 95% confidence intervals were calculated for the point estimate of total landings.
The list of the 34 federally managed fish and invertebrate species analyzed for the 2013 Update to the NBR is given in Table 1. One species (Atlantic wolffish) was added to the analysis since the First Edition of the NBR (Wigley et al. 2008, NMFS 2011).
There were 63 fleets identified during the January-December 2010 time period (Table 2). There were three new fleets added to the analysis since the First Edition of the NBR (Wigley et al. 2008, NMFS 2011): NE large mesh Ruhle trawl (Row 16), NE large mesh haddock separator trawl (Row 17), and NE hagfish pots and traps (Row 45). Seventeen fleets present in the NBR First Edition are no longer present: NE HOOK longline, MA harpoon, MA B large mesh otter trawl, NE B small mesh otter trawl, NE B large mesh otter trawl, MA USCAN small mesh otter trawl, MA USCAN large mesh otter trawl, NE USCAN small mesh otter trawl, NE USCAN large mesh otter trawl, NE LIM AA scallop trawl, NE GEN OPEN scallop trawl, NE LIM OPEN scallop trawl, MA Danish seine, NE pots and traps, MA diving gear, MA Scottish seine, and NE Scottish seine.
Of the 63 fleets examined, 34 fleets had little or no observer data: 4 fleets had sparse observer data across all quarters, while 30 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 these 34 fleets (Table 2). For the 29 remaining fleets, estimates of discards and their associated CV were derived. Of the 29 fleets, there were 13 fleets (Rows 12, 14, 19, 22, 23, 24, 29, 30, 31, 33, 35, 41, and 45) where the simple imputation was applied (Table 2).
A total of 4,370 NEFOP trips was observed during January and December 2010. When these trips were stratified, some trips were partitioned between strata resulting in 5,008 trips (Table 2). There appears to be minor misreporting of gear type associated with trips in the NE large mesh Ruhle trawl fleet (Row 16; Table 2). The percentage of observed trips varied by fleet and calendar quarter. On an annual basis, the percentage of observed trips by fleet ranged between 0.03% (MA handline fleet, Row 3) to 63.82% (NE large mesh haddock separator trawl fleet, Row 17; Table 2). Over all fleets, the percentage of observed trips was 4.66%.
The 2010 VTR landings (all species combined, live weight, by fleet and quarter) used to expand the discard ratios are presented in Table 3. Total annual landings varied by fleet, with a range from 0.2 mt in the MA mussel dredge fleet (Row 58) to 181,450 mt in the MA ocean quahog/surfclam dredge; total landings over all 63 fleets was 658,765 mt.
Total 2010 estimated discards (live, metric tons, assuming 100% discard mortality), with associated CVs and combined d/k ratios, by species and fleet, are presented in Table 4. Because discards were not estimated for all fisheries (due to data limitations), the values in Table 4 underestimate the actual total discards by species in 2010.
Based on this analysis, approximately 64,557 mt (live weight) of discards of the 34 species occurred in the 29 fleets considered during the January to December 2010 period. The majority (78%) of the discards were comprised of three species groups: skates (49%), Atlantic sea scallops (19%), and spiny dogfish (10%); the remaining species each represented less than 4% of the total discards (Table 4). No discards occurred for Atlantic salmon. Almost half (45%) of the discards came from two fleets: NE large mesh otter trawl (Row 11; 25%), and MA LIM OPEN scallop trawl (Row 36; 20%); the remaining fleets each represented less than 10% of the total discards (Table 4). Two fleets had zero discards estimated for all 34 species under consideration: NE fish pots and traps (Row 41), and hagfish pots and traps (Row 45).
The combined d/k ratio varied among the 34 species and 29 fleets (Table 4). Among species, skates generally had the highest combined d/k ratios, followed by Atlantic sea scallop and spiny dogfish. Fleets with the highest combined d/k ratios included the MA GEN OPEN scallop trawl (Row 14) and MA Shrimp Trawl (Row 18).
The CV of the discard estimate also varied by species and fleet (Table 4). Of a total of 986 cells (where a cell is a species-fleet combination), over half (53%) had a value for CV; 463 cells had a null CV due to a zero discard estimate. Among the 523 cells with a CV value, 33% had a CV < 0.30, 35% had a CV between 0.31 and 0.60, 27% had a CV between 0.61 and 1.10, and 5% had CV >1.11, with a maximum CV value of 3.46 (windowpane in MA extra-large mesh gillnet [Row 24]). Ocean quahog, Atlantic surfclam, and offshore hake typically had the highest CV on discard estimates, while monkfish and skates had the lowest. The fleets with the highest CV values overall were the NE purse seine (Row 29) and NE GEN OPEN scallop dredge (Row 35), while the NE large mesh otter trawl (Row 11), NE large mesh haddock separator trawl (Row 17) and NE large mesh Ruhle trawl (Row 16) had the lowest overall CV values.
For most species, the VTR and Dealer databases provide similar values for the 2010 landings (Table 5, Figure 1). VTR landings exceeded Dealer landings in only five of the 33 species listed in Table 5: Atlantic herring, ocean pout, ocean quahog, offshore hake, and red hake. Four species (Atlantic halibut, bluefish, white hake, and windowpane flounder) had VTR landings below Dealer landings by more than 30%. However when potentially mixed species (i.e., longfinned and shortfinned squids, and offshore, red and white hakes) were combined, the resulting VTR landings were closer to the dealer data.
The results of the validation exercise (Table 5, Figure 1) show that the estimated landings derived using the NEFOP dataset do not differ significantly from the VTR values for ten species: the 95% confidence intervals of the estimated landings encompass the VTR landings for Acadian redfish, Atlantic herring, Atlantic mackerel, Atlantic wolffish, bluefish, haddock, offshore hake, silver hake, summer flounder, and winter flounder. Several species had 95% confidence intervals of the estimated landings relatively close to the VTR landings: American plaice, Atlantic cod, Atlantic halibut, Atlantic sea scallop, monkfish, ocean pout, pollock, shortfinned squid, skates, spiny dogfish, windowpane flounder, witch flounder, and yellowtail flounder. The ten remaining species (Atlantic surfclam, black sea bass, butterfish, deep see red crab, longfinned squid, ocean quahog, red hake, scup, tilefish, and white hake) had 95% confidence intervals of the estimated landings that differed substantially from VTR landings.
There was no observer coverage for the 2010 fisheries for five species (Atlantic surfclam, deep sea red crab, ocean quahog, and tilefish) so the estimated landings of these species do not approximate the VTR landings. For the three hake species (red, white and offshore hake) and the two squid species (longfinned and shortfinned), reporting of "mixed" species results in landings at the individual species level that do not compare as favorably as at the combined (i.e., "mixed hakes" or "mixed squid") level (Table 5 and Figure 1).
At the group level corresponding to fishery management plans, estimated landings did not differ significantly from the VTR for the Groundfish-small mesh, and Squid-Butterfish-Mackerel groups; these values were close for the Groundfish-large mesh group. The Fluke-Scup-Black Sea Bass and Atlantic surfclam-ocean quahog groups had more significant differences between estimated landings and VTR landings.
The analysis presented in this document used a broad stratification and a combined ratio method to estimate the 2010 discards of 34 federally managed finfish and invertebrate species in commercial fisheries of the Northeast region of the United States. Species-specific stock assessment discard estimation may differ from this report due to differences in stratification and data used (VTR landings versus Dealer landings). It is expected, however, that estimates would be in the same order of magnitude. The discard estimates presented here are not definitive estimates, but are indicative of where discarding occurred among commercial fleets.
This analysis used VTR data. Dealer (CFDERSyyyy) data do not contain mesh or area fished information until the trip-based allocation is performed. 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.
New fleets were added to reflect VTR activity in the time period examined. The Ruhle trawl (negear code 054) and haddock separator trawl (negear code 057) were used by vessels fishing in the NE region. These gear types are required in the US/Canada resource sharing area and their use is expected in both access and non-access areas to reduce discards of New England groundfish under sector management. Outreach and education via permit holder letters to industry members should emphasize the proper use of these two gear codes since underreporting does occur (i.e., VTR trips < NEFOP trips; Row 16; Table 2).
The NEFOP, VTR, and VMS databases do not contain the requisite information to directly match trips (i.e., one to one match) across databases, and hence ad-hoc methods were developed to accomplish this. Some misclassification of trips to various fleets is therefore inevitable and may also occur due to the limited auditing of the VTR data resulting in overlapping trip dates, incorrect gear codes, and/or incorrect area fished. In addition, misclassification of trips into access area categories was possible for trips using scallop gear (negear 052 and 132), due to limitations associated with the use of the VMS activity code.
Qualitative comparisons of the 2010 discard estimates (using both the annual totals and the totals for specific gear) with other recent discard estimates available for the same species indicated a similarity in order of magnitude. That is, the 2010 estimates approximate those derived from: (a) the 2009, 2010, and 2011 Standardized Bycatch Reporting Methodology analysis (Wigley et al. 2011a); (b) the 2012 discard estimation analysis (Wigley et al. 2012); (c) the 2012 Northeast groundfish stock assessment updates (NEFSC 2012); and (d) various Stock Assessment Workshop analyses.
Discard estimates in Table 4 assumed 100% discard mortality, i.e., we did 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 spiny dogfish, summer flounder, southern New England and Gulf of Maine stocks of winter flounder, southern New England yellowtail flounder, and Atlantic sea scallop. In addition, survival ratios are currently under consideration for the Georges Bank and Gulf of Maine Atlantic cod stocks.
The annual imputation approach may not be appropriate for all fleets and species and, in some cases, quarterly d/k ratios were based on very small sample sizes. This contributed to the lower precision (higher CVs) associated with several of the discard estimates (Table 4).
The validation analysis indicated that the VTR and Dealer estimates are generally comparable and the discard estimation method is appropriate. Where they exist, differences in VTR and Dealer landings reflect the different nature of the data, where VTR data report the good-faith hail weights whereas Dealer data provide actual landings weight. Some of the cases where the dealer landings exceeded the VTR landings (such as Atlantic halibut, black sea bass, bluefish, scup, and windowpane flounder) are likely discrepancies resulting from the inability to partition out the mandatory reporting landings (reflective of the VTR) from the state landings. The difference for monkfish likely reflects misreporting of monkfish product forms (i.e., tails vs. whole fish) in the VTR database.
Estimated landings using NEFOP data were similar to VTR landings in most species, although several species had significantly different estimates. Five species (Atlantic surfclam, deep sea red crab, ocean quahog, and tilefish) have targeted fisheries that were not observed, and it is therefore not surprising that the estimated landings of these species do not approximate the VTR landings. Other factors related to the onset of sector-based management for New England groundfish in May 2010 may also be contributing to these differences. For example, changes in regulations that enacted a "no possession" status for Atlantic wolffish, ocean pout, windowpane flounder, and winter flounder (Southern New England and Mid-Atlantic stocks only) likely result in inflated discard estimates and landing estimates (from the validation analysis).
In summary, a very broad stratification was used to encompass all species in the Northeast regional analysis. Discard estimates provided in this report will differ from discard estimates developed separately in stock assessments because of differences in estimation methods and in spatial/temporal/fleet stratification schemes.
We wish to thank all the NEFOP observers for their diligent efforts to collect the data used in this report. We also thank Mark Terceiro and other reviewers for their helpful comments on this report.
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 A comparison of discard rates derived from observer and at-sea monitor data revealed there were generally no statistical differences in discard rates between the two data collection programs for 18 species associated with Amendment 16 to the Northeast Multispecies Fishery Management Plan for four gear types (longline, large-mesh otter trawl, large-mesh gillnet, and extra-large-mesh gillnet) where at-sea monitor data exist (Wigley et al. 2011b). See NEFOP (2011) for more information on at-sea monitoring.
 In this document, "live" is equivalent to "round" grade.
 See Wigley et al. 2007 for more details on self-reported VTR data.
 The format of a VMS activity declaration code is: CCC-PPP-AADGTB, where PPP represents the program code description. For more details about VMS activity declaration codes, see http://www.nero.noaa.gov/nero/vms/doc/DECLARATION%20CODE%20FORMAT%20NOV%202012.pdf .
 The "combined d/k ratio" used in this analysis to estimate discards should not be confused with the NBR "bycatch ratio," which is defined as the ratio of bycatch to total catch where total catch equals landings plus bycatch (NMFS 2011).
 For more information on Amendment 16 to the Northeast Multispecies Fishery Management Plan, see http://www.nero.noaa.gov/nero/hotnews/mulamend16pr/