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Table of Contents
Executive Summary
Background
Methods
Results
Discussion
Acknowledgements
References Cited
Appendix

Northeast Fisheries Science Center Reference Document 12-17

2012 Discard Estimation, Precision, and Sample Size Analyses for 14 Federally Managed Species Groups in the Northeast Region

by Susan Wigley1, Jessica Blaylock2, Paul Rago1, and Gina Shield1
1National Oceanic Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA, 02543 USA
2Integrated Statistics, 16 Sumner St., Woods Hole, MA 02543 USA

Web version posted September 17, 2012

Citation: Wigley SE, Blaylock J, Rago PJ, Shield G. 2012. 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 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 report describes the analysis of the expected coverage needed by at-sea observers for Northeast fisheries for the April 2012 through March 2013 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 2011 3-year Review Report. The sea days needed to achieve the precision-based performance standard (30% coefficient of variation of the discard estimate) were updated using July 2010 through June 2011 data. To monitor 14 federally managed fish and invertebrate species groups across 55 fleets, a total of 18,822 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 and dogfish. 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 is needed.

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 Part 2 (Wigley et al. forthcoming 2012).

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 differs 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 2010 through June 2011 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 Fisheries Marine Recreational Fisheries Statistics Survey[4] (MRFSS) 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, "set only" trips, and trips associated with a groundfish sentinel fishery (program code = 127) were excluded from this analysis. 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, where 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[7] 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 comprising each species group, is given in Table 1. This analysis does not include sea turtles. 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.

Discard Estimation

Total discards of each of the 14 federally managed species groups were estimated for the July 2010 through June 2011 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 for fish) 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 half year (or annual) 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. 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 1. 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.

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 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 3 trips per quarter (12 trips per year) and a maximum of 100 trips per quarter (400 trips per year). The 2% pilot coverage level[8] was the same as was used in 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.

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. forthcoming 2012). Thus, in this analysis, all cells in the unlikely filter were set to 1 (all cells are likely).

The 2012 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 98% of the total mortality.

To determine the number of sea days (referred to as the "2012 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 will be based on pilot coverage to maintain monitoring coverage for that fleet. 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 55 fleets identified during the July 2010 through June 2011 period (Table 2 and Table 3). There were three new fleets compared to the 2011 sea day analysis (NEFSC 2011b, NEFSC and NERO 2011): MA large mesh Ruhle trawl (Row 13), NE small mesh Ruhle trawl (Row 14), and MA large mesh haddock separator trawl (Row 16). New fleets, those that have not been identified in previous analyses, have been identified with a plus (+).

Of the 55 fleets examined, 29 fleets had little or no observer data: 6 fleets had sparse observer data across all quarters, while 23 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 23 fleets with no observer coverage and they were designated as fleets in need of pilot coverage (Table 2 and Table 3). The 6 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 26 remaining fleets (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 26 fleets, there were 9 fleets (Rows 11, 15, 19, 22, 23, 24, 29, 31, and 35) where the simple imputation was applied.

Thus, for discard estimation and precision analysis, 23 fleets had no discard estimation and 32 fleets had discards estimated. For the sample size analysis, 26 fleets had sample sizes derived from the discard variances and 29 fleets had sample sizes based upon pilot coverage.

A total of 5,444 trips (14,174 days) was observed during July 2010 through July 2011. When these trips were stratified, some trips were partitioned between strata resulting in 5,558 trips (15,018 days; Table 2 and Table 3) in the VTR. There appears to be minor misreporting of gear type associated with trips in the NE Ruhle trawl fleet (Row 15) and MA Mid-water trawl (Row 38; Table 2 and Table 3; Quarter 3). For Ruhle trawl, the incidence of misreporting gear (bottom otter trawl versus Ruhle trawl) is less than in previous years.

The percentages of observed trips varied by fleet and calendar quarter. On an annual basis, the percentage of observed trips by fleet ranged between 0.1% (MA handline fleet, Row 3) to 72% (MA Mid-water trawl fleet, Row 38; Table 2). Over all fleets, the percentage of observed trips was 5.5%.

Annual VTR landings and estimated discards (live pounds) with associated precision are summarized for 53 fleets (Rows 1-19, 21-43, 45-55 and "Other fleets" with landings only) for each of the 14 species groups and the individual species that comprise those species groups (Table 4A and Table 4B; Figure 1A and Figure 1B). The landings associated with the "minor" fleets not uniquely identified in this analysis have been aggregated into a single fleet labeled "Other fleets." Due to confidentially rules, the landings associated with MA Floating Trap (Row 20) and MA Hagfish Pots and Traps (Row 44) have been combined with the landings of other minor fleets (labeled as "Other fleets") that have not been not uniquely identified within this analysis. As a consequence, the fleet row numbers within Table 4A and Table 4B are sequential but there are gaps in the row numbers. The landings associated with the various minor fleets aggregated into "Other fleets" generally contribute less than 0.5% of the total landings across all fleets for each of the 14 species groups (Table 4A). As mentioned above, there are 23 fleets (Rows 10, 13, 14, 20, 21, 25, 28, 40-55) that have no discard estimation due to no NEFOP coverage (dark shaded fleets in Table 4A and Table 4B, with Rows 20 and 44 included in "Other fleets"). In Table 4A, 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 4B) were not used in the sample size analysis.

Based upon this analysis, over 71,000 mt (live wt) of discards of the 14 species groups occurred during the July 2010 through June 2011 period. The majority (77%) of the discards were comprised of three species groups: skates (49%), scallops (16%), and dogfish (12%); the remaining species groups comprised less than or equal to 5% (Table 4A).

The percentage of discards to total catch varied among the 14 species groups (Table 4A; Figure 1A) and individual species (Table 4B; 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; three species groups (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 five species groups (MONK, RCRAB, 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 (75%), dogfish (62%), and red crab (62%; Figure 1A). For individual species, most notable are the high percentages of discards to total catch of wolffish (99%) and ocean pout (99%) due to the no possession regulations for these two species.

The reasons for discarding varied among the 14 species groups (Appendix Table 2A) and individual species (Appendix Table 2B). Overall, for the 14 species groups, the majority (74%) of discards occurred due to "No Market," "Regulation" (due to size, quota, and other), "Poor Quality," and "Other" contributed 21%, 3%, and 1%, respectively (Appendix Table 2A).

The percentages of discard to total catch were also summarized by fleet for 26 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 one fleet (Row 29) where discards were less than 1% of the total catch in the fleet; four fleets (Rows 4, 23, 38, and 39) where the percentages of discards ranged between 1% and 10%; 13 fleets (Rows 2, 7, 15, 19, 22, 24, 26, 27, 32, 33, 35, 36, and 37) where the percentages of discards ranged between 11% and 25% of total catch; five fleets (Rows 5, 8, 17, 31, and 34) where the percentages of discards ranged between 26% and 50% of the total catch; and three fleets where discards were greater than 50% of the total catch (Row 6, 11, and 16).

The number of species groups discarded within a fleet also varied among fleets. The majority of fleets (17 of the 26 fleets) were comprised of two or three discarded species groups. Eight of these fleets (Rows 2, 4, 15, 16, 31, 33, 35, and 38) had 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 another five fleets (Rows 22, 29, 32, 34, and 39) where the "Non-FMP" species group comprised the majority of the discards. There was one fleet (Row 23) where discards were evenly split between with "Other FMP" and "Non-FMP" species groups. There were 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 skate, small mesh groundfish, and dogfish (Rows 11, 19, and 26 respectively).

The remaining fleets (9 of the 26 fleets) had between four and nine discarded species groups. The skate species group dominated the discards in five of these fleets (Rows 6, 8, 17, 24, and 27) while "Non-FMP" species group dominated the discards in two fleets (Rows 36 and 37). Two fleets (Rows 5 and 7) had a mix of discarded species groups.

The dominant "Non-FMP" species in the scallop dredge fleets (Rows 32, 33, 34, 35, and 36) were: sand dollar, sponge, and starfish. Menhaden and jellyfish were the dominant "Non-FMP" species in the MA small mesh gillnet fleet (Row 22). "Fish, not known" was the dominant species in the NE purse seine fleet (Row 29).

The precision of the discard estimates varied by species group and fleet (Table 4A and Table 4B). Of the 14 species groups, 11 species groups had an overall CV that was less than 30%, two species groups (BLUE and SCOQ) 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 4A; Figure 1A).

The numbers of sea days needed for each species group and fleet, as well of the number of sea days needed for the fleet (referred to as "2012 Sea Days Needed"), are summarized in Table 5. A total of 18,822 days are needed for all fleets. As mentioned previously, 29 fleets had insufficient observer information to estimate discards and the sea days for these fleets have sea days based on pilot coverage. The number of sea days needed associated with fleets with the pilot coverage designation was 1,638 days (9% of 18,822; Table 5). There are 10 fleets where the sea days for all species groups were filtered out via the importance filter and pilot days was used to maintain some coverage (Rows 2, 4, 15, 16, 22, 23, 29, 31, 35, and 38; Table 5). The sea days needed associated with these fleets was 377 days (2% of 18,822; Table 5). The sea days needed for the remaining 16 fleets (16,807 days representing 89% of the total sea days needed) were derived using the variance of the discard estimate (Table 5). Of the 16,807 days, 12,661 days (75%) were associated with three fleets (Rows 5, 6, and 8).

The sample size (in terms of number of sea days, number of trips, and percentage of trips based upon the VTR trips in July 2010 through June 201) needed to achieve a 30% CV of the discard estimate in these 16 fleets is given in Table 6. 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 three fleets (Rows 5, 6, and 8) and the penultimate (next largest) value was used in each of the three fleets, then the total number of sea days needed across all fleets would be 7,827 days (a 42% decrease from the 18,822 days). Using the penultimate value, the expected achieved precision of red crab discards in Rows 5, 6, and 8 would be 92% CV, 140% CV, and 72% 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. 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 of 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 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. 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 in response to VTR activity in the time period examined. The Ruhle Trawl (negear code 054) and Haddock Separator Trawl (negear code 057) were used by vessels departing from the MA 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. Due to the low number of VTR trips reported for these fleets in the July 2010 through June 2011 period, the number of sea days needed is lower than what may be realized. Additional outreach and education via permit holder letters to industry members have emphasized the proper use of these two gear codes.

There are several fleets with high sea day requirements (> 3,000 sea days). The Northeast Fisheries Observer Program data associated with the trips within these fleets were reviewed to rule out any data "irregularities." The high coverage for New England and Mid-Atlantic otter trawl fleets (Rows 5, 6, and 8; Table 5) was due to high variability associated with red crab discards. In this analysis, as well as in the 2011 SBRM analysis (NEFSC 2011a; NEFSC 2011b; NEFSC and NERO 2011; Wigley et al. 2011), the high variability arises from observing some trips that are fishing in deep-water portions of statistical areas as well as observing other trips that are 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 2A), these vessels do not generally have permits to land red crab, 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) where 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 for their diligent efforts to collect the data used in this report. We thank Jiachen Tang for her assistance with the figures. We thank our reviewers for their helpful comments on this report.

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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 Science Center (NEFSC) and Northeast Regional Office (NERO). 2011. Standardized bycatch reporting methodology proposed 2011 observer sea day allocation consultation and prioritization process response to comments. April 1, 2011. Internal document presented to the Northeast Regional Coordinating Committee. 16p. Available on-line at: http://www.nefsc.noaa.gov/femad/fsb/SBRM/2011/2011_Re-Prioritization_and_Response_to_Comments_04012011.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, Drew K. Forthcoming 2012. Standardized bycatch reporting methodology 3-year review report 2011- part 2. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 238 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026 or online at http://nefsc.noaa.gov/publications/.

Wigley SE, Blaylock J, Rago PJ, Tang J, Haas HL, 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, Rago PJ, Sosebee KA, Palka DL. 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/index.htm


Endnotes

[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/fsb/SBRM/2012/Proposed_2012_Observer_Sea_Day_Allocation_3-23-2012_v3.pdf

[3] 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 the 14 fish species groups for four gear types (longline, large-mesh otter trawl, large-mesh gillnet and extra-large-mesh gillnet) where at-sea monitor data exist. See Northeast Fisheries Observer Program (2011) for more information on at-sea monitoring.

[4] Marine Recreational Fisheries Statistics Survey (MRFSS) was replaced with Marine Recreational Information Program (MRIP) in 2012.

[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.

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

[7] The trip-based allocation of Dealer (CFDETT/SyyyyAA) data are conducted annually and were not available when the annual discard estimation and sample size analyses were conducted.

[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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