Northeast Fisheries Science Center Reference Document 09-20

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northeast Fisheries Science Center

Woods Hole, Massachusetts

December 2009

River Herring Discard Estimation, 

Precision and Sample Size Analysis 

by S.E. Wigley, J. Blaylock and P.J. Rago

NOAA’s National Marine Fisheries Serv., 166 Water St., Woods Hole MA 02543
Northeast Fisheries Science Center Reference Documents

This series is a secondary scientific series designed to assure the long-term documentation and 

to enable the timely transmission of research results by Center and/or non-Center researchers, 

where such results bear upon the research mission of the Center (see the outside back cover for 

the mission statement). These documents receive internal scientific review, and most receive 

copy editing. The National Marine Fisheries Service does not endorse any proprietary material, 

process, or product mentioned in these documents.

All documents issued in this series since April 2001, and several documents issued prior to 

that date, have been copublished in both paper and electronic versions. To access the electronic 

version of a document in this series, go to http://www.nefsc.noaa.gov/nefsc/publications/. The 

electronic version is available in PDF format to permit printing of a paper copy directly from 

the Internet. If you do not have Internet access, or if a desired document is one of the pre-April 

2001 documents available only in the paper version, you can obtain a paper copy by contacting 

the senior Center author of the desired document. Refer to the title page of the document for 

the senior Center author’s name and mailing address. If there is no Center author, or if there is 

corporate (i.e., non-individualized) authorship, then contact the Center’s Woods Hole Laboratory Library (166 Water St., Woods Hole, MA 02543-1026).

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.

This document may be cited as:

Wigley SE, Blaylock J, Rago PJ. 2009. River Herring Discard Estimation, Precision 

and Sample Size Analysis. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 09-

20; 15 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/
Table of Contents 

Executive Summary........................................................................................................... iv 

Introduction......................................................................................................................... 1 

Methods............................................................................................................................... 1 

Discard Estimation.......................................................................................................... 1 

Sample Size Analysis...................................................................................................... 2 

Results and Discussion ....................................................................................................... 3 

Discard Estimation.......................................................................................................... 3 

Sample Size Analysis...................................................................................................... 3 

Conclusions......................................................................................................................... 6 

Acknowledgements............................................................................................................. 7 

References........................................................................................................................... 7 

Table 1. Number of Vessel Trip Report and Northeast Fisheries Observer Program 

trips, by fleet and calendar quarter for the July 2007 to June 2008 time 

period ............................................................................................................. 8 

Table 2. River herring discards and coefficient of variation, the number of baseline 

trips, baseline sea days, and filtered sea days needed to achieve a 30% CV 

for river herring, number of filtered sea days needed to achieve a 30% CV 

for the 15 SBRM species groups, and the number of sea days accepted via 

the 2009 SBRM Prioritization process, by fleet for the July 2007 to June 

2008 time period ............................................................................................ 9 

Table 3a. Number of baseline trips needed to achieve discard estimates for river 

herring over a range of precision levels, for the six fleets where estimated 

river herring discards are greater than zero.................................................. 10 

Table 3b. Number of baseline sea days needed to achieve discard estimates for river 

herring over a range of precision levels, for the six fleets where estimated 

river herring discards are greater than zero.................................................. 10 

Table 4. River herring discards, fraction of total discards, cumulative fraction of total 

discards, fraction of total discard filter, discard mortality ratio, fraction of 

total mortality due to discards, cumulative fraction of total mortality due to 

discards, fraction of total mortality due to discards filter, unlikely cell filter, 

and importance filter, by fleet for 22 fleets with no discards estimated, 16 

fleets with discard equal to zero, and six fleets with discard estimates greater 

than zero....................................................................................................... 11 

Figure 1. Relationship between sample size and precision of river herring discards for 

six fleets where estimated river herring discards are greater than zero ....... 12 

Appendix 1. Equations used in discard estimation and sample size analysis................... 13 

iii
iv

Executive Summary 

A total of 106,455 pounds (149% CV) of river herring was discarded during the 

12-month period from July 2007 through June 2008. The river herring discards occurred 

primarily in the New England small mesh otter trawl fleet, and to a lesser extent in the 

New England shrimp trawl, New England large mesh trawl and Mid-Atlantic small mesh 

otter trawl fleets. 

The total number of sea days (9,002 days) needed to achieve a 30% CV for river 

herring discard estimates is 40% less than those needed for the 15 Standardized Bycatch 

Reporting Methodology (SBRM) species groups (15,125 days). On a fleet by fleet basis, 

the number of sea days needed to achieve a 30% CV for river herring discard estimates 

was either the same or less than for the 15 SBRM species groups with the exception of 

one fleet: New England large mesh otter trawl where the river herring species group 

needed 2,827 more sea days than the 15 SBRM species groups. 

The low number of observed trips in the Mid-Atlantic gillnet fleets and the 

limitations of observing all discards associated with the fishing practices of the highvolume fisheries are two sources of uncertainty in the discard estimation and sample size 

analysis. 
Introduction 

Concerns have been expressed by governmental and non-governmental groups 

regarding the discarding of river herring by commercial fishing fleets operating off the 

northeastern coast of the United States. River herring is a species group comprising two 

individual species: alewife, Alosa pseudoharengus, and blueback herring, Alosa 

aestivalis. This document provides estimates of river herring discards, with associated 

precision, and the number of sea days needed to achieve discard estimates over a range of 

precision levels. This document then compares the number of sea days needed for river 

herring with sea days needed for the 15 Standardized Bycatch Reporting Methodology 

(SBRM) species groups for the same time period derived in the 2009 SBRM analysis1

. 

The SBRM is an omnibus amendment to the 13 fishery management plans in the 

Northeast region that establish review and reporting requirements for bycatch monitoring 

and observer coverage as well as a process for prioritizing observer coverage when there 

is a shortfall in funding (NMFS 2007). 

River herring is managed by the Atlantic States Marine Fisheries Commission 

(ASMFC). Background information on river herring is available on the ASMFC web site: 

http://www.asmfc.org/

Methods 

Discard Estimation 

The 2009 SBRM analysis data set was expanded to include the river herring 

species group. This data set includes data from the Northeast Fisheries Observer 

Program (NEFOP), 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 Information 

Program (MRIP) recreational landings from July 2007 through June 2008. 

This analysis used the discard estimation methods described in the SBRM 

analysis (Wigley et al. 2007). Total discards of river herring from July 2007 through June 

2008 were estimated using a combined d/k ratio estimator (Cochran 1963), where d = 

discarded pounds of river herring and k = the kept pounds of all species. Total discards 

(in weight) of river herring, 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. In this report, the term coefficient of variation (CV) is defined as the ratio of 

the standard error of the total discards divided by the total discards. Appendix 1 presents 

the equations used in the analysis. We assumed 100% mortality for all discarded fish. 

In the analysis, the sampling unit was a fishing trip. The same broad stratification 

scheme used in the SBRM was employed, where trips were partitioned into fleets using 

 

1 2009 SBRM Prioritization documents are available on-line at 

http://www.nefsc.noaa.gov/femad/fishsamp/fsb/ (under DATA/REPORTS, click on ‘SBRM Annual 

Discard Report’). 

1
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 departure2

; 

ports located from Maine to Rhode Island constituted the NE region and ports located 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, (Table 1), and 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). Trips participating in the US/Canada access area, ‘B-day’ 

category and other quota monitoring programs could not be identified in the VTR 

database, and hence these trips were grouped by the other stratification variables and 

therefore not partitioned separately. The sea scallop fishery was divided into General 

(GEN) and Limited (LIM) category trips. All other fisheries were combined into a 

category called ‘all’. 

Of the 44 fleets examined in the analysis, 22 fleets had little or no observer data 

(all quarterly cells were missing for a fleet, or sparse observer coverage existed across all 

quarters for a fleet). No discard estimation was performed for these fleets, and all 22 

fleets were designated as in need of pilot coverage (Table 1). Pilot coverage is defined as 

a minimum level of observer coverage 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). For each of the remaining 22 fleets, estimates of river 

herring discards were derived. Eight fleets had limited observer data (i.e., one or no 

observed trips in a calendar quarter), and an imputation approach was used to ‘fill in’ the 

missing (or incomplete) information using data from an adjoining stratum. In this 

imputation procedure, only the temporal stratification (i.e., calendar quarter) was relaxed 

to half year or entire year, recognizing that seasonal variations may occur that will thus 

not be accounted for. For 14 fleets, sufficient observer data existed to estimate discards 

without imputation (Table 1). 

Sample Size Analysis 

A sample size analysis was conducted to estimate the number of baseline trips and 

sea days needed to monitor river herring discards in each fleet. As described in the 

SBRM analysis (and given in Appendix 1), the number of trips and sea days needed to 

achieve a given precision level was based on the variance of the total river herring 

discard estimates. Sample size (trips and sea days) associated with the SBRM precision 

standard for discard estimates (30% CV) were derived along with 5 other precision 

levels: 10%, 20%, 40%, 50% and 60% CV. The sample size analysis was performed 

using trips as the sampling unit of the analysis, and then converting the number of trips to 

 

2

 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. 

2
sea days by multiplying by the weighted mean trip length (Table 2) - where the weighting 

factor was the quarterly number of VTR trips. 

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 is the same as used in 

the 2009 SBRM analysis. 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. The pilot coverage may 

result in too much coverage in cases where little or no observer coverage may actually be 

needed. 

Importance filters were used in SBRM 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. Three filters (i.e., unlikely cell filter; fraction of 

discard filter; and fraction of mortality due to discards filter) are applied simultaneously. 

The unlikely cell filter eliminates sea days associated with fleets where species and gear 

combinations are unlikely or infeasible. The unlikely cell filter can act as an ‘override’ 

mechanism in situations where pilot coverage is evoked due to no variance (observer 

coverage indicates zero discards). A detailed description of the SBRM importance filters 

is given in Wigley et al. (2007). As in the 2009 SBRM analysis, the baseline sea days for 

river herring were filtered using a 95% cut-point in the discard mortality filter, and a 98% 

cut-point for the total mortality filter due to discards. The unlikely cell filter was not 

updated to include the river herring species groups as all fleets were considered ‘likely’ to 

discard river herring. 

Results and Discussion 

Discard Estimation 

River herring discards were estimated for 22 of the 44 fleets (Table 2). Of the 22 

fleets with discard estimates, 6 fleets had discard estimates greater than zero and 16 fleets 

had discard estimates equal to zero. A total of 106,455 pounds of river herring was 

discarded during the 12-month period from July 2007 through June 2008. By fleet, 

discards of river herring ranged between 0 and 95,744 pounds, with largest amount 

occurring in the New England small mesh otter trawl fleet. The coefficient of variation 

of the total river herring discard estimate was 149%. For the six fleets where estimated 

river herring discards were greater than zero, the coefficient of variation ranged between 

31% and 166% (Table 2). 

Sample Size Analysis 

Sample size coverage levels (baseline trips and sea days) to assess river herring 

discards are presented in Table 2. To achieve a 30% CV on river herring discards, a total 

of 6,923 baseline trips and 15,395 baseline sea days would be needed (Table 2). In six 

3
fleets, sample sizes (5,317 trips and 12,107 days) were based on the variance of total 

discards, while sample sizes for 38 fleets (1,606 trips and 3,288 days) were based on pilot 

coverage. The sample size based on pilot coverage (due to no data or no variance) 

contributed 23% and 21% to the total baseline trips and sea days, respectively. By fleet, 

the total number of baseline trips ranged between 6 and 1,662 trips while the total number 

of baseline sea days ranged between 10 and 4,060 days (Table 2). 

For the six fleets where estimated river herring discards were greater than zero, 

the number of baseline trips and sea days needed to estimate discards over a range of 

precision levels are presented in Tables 3a and 3b and Figure 1. The sample sizes 

reported in Tables 3a and 3b are subtotals associated with the six fleets. To obtain a 

grand total, the subtotal must be added to the pilot coverage subtotal given in the text 

above. For example, to achieve a 20% CV based on river herring discards, a total of 

11,423 baseline trips [9,817 trips (Table 3a) + 1,606 trips based on pilot coverage] and 

25,454 days [22,166 days (Table 3b) + 3,288 days based on pilot coverage] would be 

needed. 

The importance filter eliminated the sea days associated with the 16 fleets with 

zero discards of river herring. As well, three other fleets (MA large mesh otter trawl, MA 

small mesh otter trawl, and New England mid-water trawl) were eliminated from 

coverage because these fleets contributed to less than 5% of total discards and less than 

2% of the total mortality due to discards. The total number of filtered sea days needed to 

achieve a 30% CV is 9,002 days (Table 2). By fleet, the number of filtered sea days 

needed to achieve a 30% CV for the total discards of river herring ranged between 0 and 

4,060 days (Table 2). 

The total number of filtered sea days needed for river herring may be an 

overestimate due to the inclusion of sea days associated with fleets that would have been 

eliminated had the unlikely cell filter been updated for river herring. The sea days 

associated with the clam dredge fleets, handline fleets, and the fish, conch, lobster, and 

crab pot fleets would most likely have been eliminated as these gear types rarely capture 

river herring. The total number of filtered sea days needed for river herring will be 

improved when observer data are available for all the fleets (no sea day estimates based 

on pilot coverage) and the unlikely cell filter is updated for this species group. In 2011, 

a three-year evaluation of the SBRM will occur and, at that time, bycatch information and 

estimation methods will be evaluated including an evaluation of the unlikely cell filter for 

all species. 

This analysis used the SBRM Omnibus Amendment cut-points of 95% and 98% 

to eliminate sea days associated with fleets that contribute the smallest amount to total 

discards and total mortality due discards for river herring, respectively. Table 4 reveals 

that had another cut-point been used for the total discard filter, for example 93% instead 

of 95%, eliminating fleets contributing to the lower 7% of total discards instead of the 

lower 5% of total discards, then the 4,060 days associated with the NE large mesh otter 

fleet would have been filtered out and the total number of filtered sea days for river 

herring would have been 4,942 days instead of 9,002 days. 

River herring is not a species group included the SBRM analysis3

, thus the 

number of sea days needed to monitor the river herring species group can be compared 

 

3

 SBRM only considers federally managed species and turtles. 

4
with the 15 SBRM species groups. A comparison of the filtered sea days for river 

herring and the 15 SBRM species groups (Table 2) reveals fewer total sea days would be 

needed to monitor only river herring (Table 2). However, on a fleet basis, only the NE 

large mesh otter trawl fleet needed more sea days for river herring than for the 15 SBRM 

species groups. As noted above, if the SBRM cut-point for total discards was relaxed to 

93% and eliminated the sea days associated with the lower 7% of the total river herring 

discards, then the sea days from the NE large mesh otter trawl would be filtered out and 

the total number of sea days needed to monitor the 15 SBRM species groups would be 

greater than the sea days needed to monitor river herring for all fleets. 

The total number of sea days needed for the 15 SBRM species groups (15,125 

days) and for river herring (9,002 days) exceed the total number of sea days that the 

Northeast Fisheries Science Center (NEFSC) has funding to support. The NEFSC has 

funds to support a total of 6,283 days [4,283 days (Table 2) plus 1,940 US/Canada QuotaMonitoring sea days and 60 Discovery days; NEFSC 2009b]. When a funding shortfall 

exists, the SBRM Sea Day Prioritization Process (NEFMC 2007; NMFS 2007; NEFSC 

2009b) is invoked; the resulting 2009 sea days, by fleet, are given in Table 2. 

Misreporting of gear code in the VTR database is evident for the NE shrimp trawl 

fleet. The seasonal nature (December to April) of the northern shrimp fishery contributes 

to the inadvertent misreporting of gear code (OTS = otter trawl, shrimp and OTF = otter 

trawl fish) by fisherman who switch between these two fisheries. Thus caution is 

warranted when interpreting results regarding the NE shrimp trawl fleet. There is a need 

for improved data auditing and the identification of Special Access Program trips within 

the VTR database. Additionally, the low number of observed trips in Mid-Atlantic gillnet 

fleets contribute to uncertainty in the river herring discard estimates. Increased observer 

coverage will confirm the extent to which these fleets encounter river herring. 

From 2005 onwards, the NEFOP has informally collected information to 

characterize unique fishing practices (fish pumping, use of sorting grates at the pump 

entrance and on deck, and net release) of high-volume fisheries like the paired and single 

mid-water trawl fleets. In 2010, the NEFOP manual describing data collection will be 

formally expanded to include sampling protocols designed to systematically characterize 

the fishing practices of high-volume fisheries. It is important to emphasize that only 

information systematically collected has been used in the current discard estimation 

analysis. Thus, discards associated with underwater net release or those associated with 

sorting grate at the pump entrance have not been included. Therefore, the discard 

estimates presented here may underestimate river herring discards associated with the 

high-volume fisheries. In the future, discard estimation methods may be able to 

incorporate the expanded data collection information and summarize the frequency of 

underwater net releases. 

River herring is a non-targeted species group captured in various commercial 

trawl fleets. The 2009 SBRM Annual Discard Report4

 (NEFSC 2009a) summarizes 

where and when (statistical area and calendar quarter) observers have recorded the 

disposition of catch (kept or discarded) and the weight (pounds) of alewife and blueback 

herring among the commercial fleets (NEFSC 2009a, Section II, Tables 4c and 5c). 

Some trawl fleets that encounter river herring are retaining these species while other 

 

4

 SBRM Annual Discard Report is a data summary of the information collected by NEFOP observers, no 

extrapolation of observations (discard estimation) is performed in this summary. 

5
fleets are discarding them. Generally, the mid-water trawl fleets are retaining river 

herring, while the otter trawl fleets are not. 

Nominal catch (landings only) estimates of river herring during 2005 to 2007 

have been derived by Cieri et al. (2008). In their study, a ratio estimator of observed 

river herring bycatch (kept) to Atlantic herring landings was developed based upon 

NEFOP observer data, Maine Department of Marine Resource portside sampling data, 

and VTR data. A stratification scheme was also used that included: year, calendar 

quarter, area, and gear type. Estimates of the annual nominal catch of river herring 

during 2005-2007 were 285,833, 171,973 and 1,686,617 pounds, respectively. It is 

important to note that the Cieri et al. (2008) estimates are for nominal catch of river 

herring as a non-targeted (hence their use of the term ‘bycatch’) species in four 

commercial fishing fleets. In this context, the ‘bycatch’ estimates are not equivalent to 

the discard estimates derived in the present analysis. In the present analysis, discards 

represent the component of total catch that are not retained; total catch = landings (target 

and non-target) + discards. 

Conclusions 

This analysis indicates that during the July 2007 through June 2008 time period, 

river herring were primarily discarded in the NE small mesh otter trawl fleet, and to a 

lesser extent in the NE shrimp trawl, NE large mesh trawl and MA small mesh otter trawl 

fleets. 

The baseline sea days needed to attain a 30% CV for discard estimates of river 

herring are slightly higher than the total filtered sea days needed to monitor 15 SBRM 

species groups. When the importance filter is applied to the river herring species group, 

the sea days associated with 19 of the 22 fleets with estimated discard were eliminated, 

indicating that the discarding of river herring is a minor component of total discards and 

total catch of river herring in the majority of fleets. The total number of filtered sea days 

needed to monitor river herring is 40% less than those needed to monitor the 15 SBRM 

species groups. On a fleet by fleet basis, the number of filtered sea days needed to 

monitor river herring was either the same (due to pilot coverage) or less than for the 15 

SBRM species groups with the exception of one fleet: NE large mesh otter trawl where 

the river herring species group needed 2,827 more sea days than the 15 SBRM species 

groups. 

The low number of observed trips in the Mid-Atlantic gillnet fleets and the 

limitations of observing all discards associated with the fishing practices of the highvolume fisheries are two sources of uncertainty in this analysis. More observer coverage, 

particularly in the Mid-Atlantic region, is needed to derive discard estimates and sample 

sizes. Direct discard estimation will reduce the dependency on pilot coverage for sample 

sizes estimates. 

The discard estimation used a broad stratification approach designed to 

encompass all species groups considered in the SBRM analysis. The discard estimates 

reported here may not necessarily correspond directly with the discard estimates derived 

specifically for river herring due to differences in stratification. It is expected, however, 

that estimates would be in the same order of magnitude. 

6
7

Acknowledgements 

We wish to thank all the NEFOP observers for their diligent efforts to collect the 

discard information used in this analysis. We thank Jeff Hansen for his technical 

assistance and our reviewers for their helpful comments on this report. 

References 

Cieri, M, G. Nelson, and M. Armstrong. 2008. Estimates of river herring bycatch in the 

directed Atlantic herring fishery. Report prepared for the Atlantic States Marine 

Fisheries Commission, Washington, DC. September 23, 2008. 17 p. 

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). 2007. 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. pages 4736-4758. Available on-line at: 

http://www.gpoaccess.gov/fr/retrieve.html

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. 642p. Available on-line at: 

http://www.nefmc.org/issues/sbrm/index.html 

Northeast Fisheries Science Center (NEFSC). 2009a. 2009 Standardized Bycatch Report 

Methodology Annual Discard Report (Section I and II). Presented in the NEFMC 

and MAFMC. February 2009. 1560 p. Available on-line at: 

http://www.nefsc.noaa.gov/femad/fishsamp/fsb/ 

Northeast Fisheries Science Center (NEFSC). 2009b. Standardized Bycatch Reporting 

Methodology Proposed 2009 Observer Sea Day Allocation Consultation and 

Prioritization Process Response to Comments from New England and Mid 

Atlantic Fishery Management Councils and the Northeast Regional Office. 

Presented to Northeast Regional Coordinating Committee 1 April 2009. 15 p. 

Available on-line at: http://www.nefsc.noaa.gov/femad/fishsamp/fsb/ 

Wigley S.E, P.J. Rago, K.A. Sosebee, and D.L. 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., NortheastFish. Sci. Cent. Ref. Doc. 07-09; 156 p. Available online: http://www.nefsc.noaa.gov/publications/crd/crd0709/index.htm
Table 1. Number of Vessel Trip Report (VTR) and Northeast Fisheries Observer Program (NEFOP) trips, by fleet and calendar quarter 

June 2008 time period. Remarks indicate where discard estimation was possible, where imputed data were used for discard es

were designated as in need of pilot coverage (no discard estimation) in this analysis and the 2009 SBRM analysis. See text for 

Row Gear Type

Access 

Area

Trip 

Category 

(generallimited) Region Mesh Group Q3 Q4 Q1 Q2 TOTAL Q3 Q4 Q1 

1 Longline OPEN all MA all 28 37 36 31 132 11 .

2 Longline OPEN all NE all 140 226 577 133 1,076 10 56 10 

3 Hand Line OPEN all MA all 1,625 894 181 884 3,584 ...

4 Hand Line OPEN all NE all 1,267 276 197 354 2,094 . . .

5 Otter Trawl OPEN all MA lg 1,988 1,065 1,187 1,850 6,090 78 31 17 

6 Otter Trawl OPEN all MA sm 1,082 1,307 666 1,096 4,151 76 41 33 7 Otter Trawl OPEN all NE lg 3,202 2,706 2,984 2,500 11,392 165 164 170 8 Otter Trawl OPEN all NE sm 1,193 801 671 991 3,656 33 12 8 

9 Scallop Trawl AA GEN MA all 40 17 26 10 93 . .2

10 Scallop Trawl AA LIM MA all . 1 6 7 14 . .111 Scallop Trawl OPEN GEN MA all 380 60 53 311 804 . . . 

12 Scallop Trawl OPEN LIM MA all 35 36 6 7 84 ...

13 Shrimp Trawl OPEN all MA all 293 346 37 186 862 ...

14 Shrimp Trawl OPEN all NE all 19 363 2,252 72 2,706 . . 16 

15 Sink,Anchor,Drift Gillnet OPEN all MA lg 158 322 135 224 839 37 .

16 Sink,Anchor,Drift Gillnet OPEN all MA sm 786 478 275 421 1,960 11 3 . 

17 Sink,Anchor,Drift Gillnet OPEN all MA xlg 148 1,088 516 1,154 2,906 . 10 12 

18 Sink,Anchor,Drift Gillnet OPEN all NE lg 2,756 2,115 1,770 1,506 8,147 47 44 23 

19 Sink,Anchor,Drift Gillnet OPEN all NE sm 68 4 3 5 80 . . .20 Sink,Anchor,Drift Gillnet OPEN all NE xlg 1,249 927 385 1,118 3,679 86 48 11 

21 Purse Seine OPEN all MA all 144 32 . 51 227 .1 . 22 Purse Seine OPEN all NE all 231 62 . 50 343 8 2 . 

23 Scallop Dredge AA GEN MA all 86 40 330 460 916 2 3 68 

24 Scallop Dredge AA GEN NE all 120 5 2 63 190 29 . . 

25 Scallop Dredge AA LIM MA all 77 70 93 169 409 18 7 16 

26 Scallop Dredge AA LIM NE all 117 51 49 96 313 34 26 27 

27 Scallop Dredge OPEN GEN MA all 2,887 1,477 1,667 2,648 8,679 972

28 Scallop Dredge OPEN GEN NE all 1,400 584 559 1,012 3,555 612

29 Scallop Dredge OPEN LIM MA all 344 266 281 452 1,343 13 11 6 30 Scallop Dredge OPEN LIM NE all 570 345 291 431 1,637 23 11 19 31 Mid-water paired/single Trawl OPEN all MA all . . 41 3 44 . .1 32 Mid-water paired/single Trawl OPEN all NE all 2 105 133 62 302 . 9 23 

33 Fish pots/Traps Fish OPEN all MA all 429 419 74 361 1,283 . . .

34 Fish pots/Traps Fish OPEN all NE all 515 179 . 154 848 . . .35 Fish pots/Traps Conch OPEN all MA all 89 287 129 136 641 ...

36 Fish pots/Traps Conch OPEN all NE all 272 238 . 169 679 ...

37 Fish pots/Traps Hagfish OPEN all MA all 9 . 5 9 23 1 .138 Fish pots/Traps Hagfish OPEN all NE all 66 36 19 36 157 . .239 Lobster Pots OPEN all MA all 1,327 535 232 715 2,809 ...

40 Lobster Pots OPEN all NE all 13,437 9,344 2,298 4,135 29,214 ...41 Crab Pots OPEN all MA all 64 34 17 11 126 . . .42 Crab Pots OPEN all NE all 51 18 5 32 106 ...

43 Clam/Quahog Dredge OPEN all MA all 1,040 850 844 991 3,725 ...44 Clam/Quahog Dredge OPEN all NE all 920 514 472 838 2,744 ...

Total 40,654 28,560 19,504 25,944 114,662 653 495 470 

Number of VTR trips Number of NEFOP trip
Table 2. River herring discards (in pounds) and coefficient of variation (CV), the number of baseline trips, baseline sea days, and filter

achieve a 30% CV for river herring, number of filtered sea days needed to achieve a 30% CV for the 15 SBRM species groups

days accepted via the 2009 SBRM Prioritization process, by fleet for the July 2007 to June 2008 time period. Note: where est

discards equal zero (no CV), the baseline trips and sea days are based on pilot coverage. See text for abbreviation; IF = industr

River Herring 15 SBRM species gr

Row Gear Type

Access 

Area

Trip Category 

(generallimited) Region Mesh Group

Weighted 

Mean Trip 

Length (days) 

Discards 

(lbs) CV

Baseline 

Trips

Baseline 

Sea Days 

Filtered 

Sea Days

Filtered 

Sea Days

2009 SB

Prioritizat

1 Longline OPEN all MA all 9.023 12 108 108 108 

2 Longline OPEN all NE all 1.401 0 22 31 0 456 

3 Hand Line OPEN all MA all 1.110 72 80 80 80 

4 Hand Line OPEN all NE all 1.059 42 44 44 44 

5 Otter Trawl OPEN all MA lg 1.893 883 0.917 1,400 2,651 0 1,459 

6 Otter Trawl OPEN all MA sm 2.135 2,128 0.579 636 1,358 0 1,495 

7 Otter Trawl OPEN all NE lg 2.443 3,178 0.492 1,662 4,060 4,060 1,233 

8 Otter Trawl OPEN all NE sm 2.353 95,744 1.661 1,441 3,390 3,390 4,027 

9 Scallop Trawl AA GEN MA all 2.215 12 27 27 27 

10 Scallop Trawl AA LIM MA all 5.571 9 46 46 46 

11 Scallop Trawl OPEN GEN MA all 1.947 20 39 39 39 

12 Scallop Trawl OPEN LIM MA all 7.345 12 97 97 97 

13 Shrimp Trawl OPEN all MA all 4.225 20 80 80 80 

14 Shrimp Trawl OPEN all NE all 1.032 3,692 0.314 23 23 23 61 

15 Sink,Anchor,Drift Gillnet OPEN all MA lg 1.054 0 17 18 0 139 

16 Sink,Anchor,Drift Gillnet OPEN all MA sm 1.036 0 39 41 0 1,155 

17 Sink,Anchor,Drift Gillnet OPEN all MA xlg 1.358 0 58 79 0 1,273 18 Sink,Anchor,Drift Gillnet OPEN all NE lg 1.144 0 163 186 0 187 

19 Sink,Anchor,Drift Gillnet OPEN all NE sm 1.000 12 12 12 12 

20 Sink,Anchor,Drift Gillnet OPEN all NE xlg 1.492 0 74 110 0 171 21 Purse Seine OPEN all MA all 1.110 9 10 10 10 

22 Purse Seine OPEN all NE all 2.213 0 11 24 0 24 23 Scallop Dredge AA GEN MA all 1.641 0 22 36 0 36 

24 Scallop Dredge AA GEN NE all 1.732 0 12 26 0 26 

25 Scallop Dredge AA LIM MA all 7.900 0 12 98 0 271 

26 Scallop Dredge AA LIM NE all 8.236 0 12 102 0 233 

27 Scallop Dredge OPEN GEN MA all 1.556 0 174 270 0 167 28 Scallop Dredge OPEN GEN NE all 1.607 0 71 114 0 43 29 Scallop Dredge OPEN LIM MA all 8.712 0 27 234 0 398 30 Scallop Dredge OPEN LIM NE all 10.244 0 33 335 0 254 

31 Mid-water paired/single Trawl OPEN all MA all 5.136 6 41 41 41 

32 Mid-water paired/single Trawl OPEN all NE all 4.036 830 0.611 155 625 0 433 

33 Fish pots/Traps Fish OPEN all MA all 1.029 27 28 28 28 

34 Fish pots/Traps Fish OPEN all NE all 1.026 17 17 17 17 35 Fish pots/Traps Conch OPEN all MA all 1.022 15 15 15 15 

36 Fish pots/Traps Conch OPEN all NE all 1.022 14 14 14 14 

37 Fish pots/Traps Hagfish OPEN all MA all 11.348 9 106 106 106 38 Fish pots/Traps Hagfish OPEN all NE all 4.140 0 12 55 0 55 

39 Lobster Pots OPEN all MA all 1.226 56 69 69 69 40 Lobster Pots OPEN all NE all 1.259 329 430 430 430 

41 Crab Pots OPEN all MA all 1.833 12 28 28 28 

42 Crab Pots OPEN all NE all 3.745 12 70 70 70 

43 Clam/Quahog Dredge OPEN all MA all 1.643 75 122 122 122 

44 Clam/Quahog Dredge OPEN all NE all 0.845 55 46 46 46 

Total 106,455 1.494 6,923 15,395 9,002 15,125 
Table 3a. Number of baseline trips needed to achieve discard estimates for river herring over a range of precision levels, fo

estimated river herring discards are greater than zero. To obtain the total number of baseline trips needed across 

trips to the six fleet subtotals.

10% 20% 30% 40% 

5 Otter Trawl OPEN all MA lg 6,403 2,736 1,400 831 

6 Otter Trawl OPEN all MA sm 2,949 1,248 636 377 

7 Otter Trawl OPEN all NE lg 7,372 3,221 1,662 990 

8 Otter Trawl OPEN all NE sm 3,740 2,340 1,441 937 

14 Shrimp Trawl OPEN all NE all 195 51 23 13 32 Mid-water paired/single Trawl OPEN all NE all 298 221 155 109 

Six fleet subtotal 20,957 9,817 5,317 3,257 

Access Coefficient of variation (CV

Area

Trip 

Category 

(generalRow Gear Type limited) Region Mesh Group

Table 3b. Number of baseline sea days needed to achieve discard estimates for river herring over a range of precision level

where estimated river herring discards are greater than zero. To obtain the total number of baseline sea days neeadd 3,288 sea days to the six fleet subtotals. 

10% 20% 30% 40% 

5 Otter Trawl OPEN all MA lg 12,123 5,181 2,651 1,574 

6 Otter Trawl OPEN all MA sm 6,297 2,664 1,358 805 

7 Otter Trawl OPEN all NE lg 18,014 7,871 4,060 2,420 

8 Otter Trawl OPEN all NE sm 8,800 5,505 3,390 2,204 

14 Shrimp Trawl OPEN all NE all 201 52 23 13 32 Mid-water paired/single Trawl OPEN all NE all 1,201 893 625 440 

Six fleet subtotal 46,636 22,166 12,107 7,457 

Coefficient of variation (CV

Row Gear Type Region

Mesh 

Group

Access 

Area

Trip 

Category 

(generallimited)
Table 4. River herring discards (in pounds), fraction of total discards, cumulative fraction of total discards, fraction of tota

mortality ratio, fraction of total mortality due to discards, cumulative fraction of total mortality due to discards, f

mortality due to discards filter5, unlikely cell filter, and importance filter, by fleet for 22 fleets with no discards e

discard equal to zero, and six fleets with discard esti

mates greater than zero. A 95% cut-point has been used in th

98% cut-point for the total mortality due to discards filter; filter value of 1 indicates the sea days associated with 

indicates the sea days associated with the fleet are eliminated. 

Total Discard

Row Gear Type

Access 

Area

Trip 

Category 

(generallimited) Region Mesh Group Discard (lbs) Fraction Cumulative Fraction Filter

Discard 

Mortality 

Ratio Fraction

Cumulative 

Fraction 

22 fleets with no discards 

16 fleets with discards = 0 0 0.00% 0.00% 0 0 0.00% 0.00% 

32 Mid-water paired/single Trawl OPEN all NE all 830 0.78% 0.78% 0 0.003 0.32% 0.32% 

5 Otter Trawl OPEN all MA lg 883 0.83% 1.61% 0 0.003 0.34% 0.66% 

6 Otter Trawl OPEN all MA sm 2,128 2.00% 3.61% 0 0.008 0.82% 1.48% 

7 Otter Trawl OPEN all NE lg 3,178 2.98% 6.59% 1 0.012 1.22% 2.70% 

14 Shrimp Trawl OPEN all NE all 3,692 3.47% 10.06% 1 0.014 1.42% 4.12% 

8 Otter Trawl OPEN all NE sm 95,744 89.94% 100.00% 1 0.368 36.81% 40.92% 

106,454 0.409

Total Mortality due to Disca

5 Fraction of total mortality due to discards is defined as the ratio of discards of species group j in fleet 

h (

Djh) to the sum of commercia

recreational landings (

Rjh), and discards (

Djh) summed of h; river herring commercial landings equaled 136,908 pounds and recreationa

pounds from July 2007 through June 2008. 
River Herring 

Number of observed trips

0 1000 2000 3000 4000 5000 6000 

CV of river herring discards

0.00.10.20.30.40.50.60.70.80.91.0

NE Otter Trawl large-mesh (Row NE Otter Trawl small-mesh (Row MA Otter Trawl small mesh (Row MA Otter Trawl large-mesh (Row NE Shrimp Trawl (Row 14)NE Mid-water Trawl (Row 32)

Figure 1. Relationship between sample size (number of observed trips) and precision (coefficient of variation, CV) of river 

fleets where estimated river herring discards are greater than zero. The solid (red) curves represent fleets that are importance filter process; patterned (black) curves represent fleets that are not eliminated. 
Appendix 1. Equations used in discard estimation and 

sample size analysis 

Total discarded pounds for species j is defined as: 

(1) jc

Q

h

j hrKD ,

1

ˆ 



where 

(2) 







  h

h

n

i h

ih

Q

h

h

n

i h

jih

Q

h

h

jc

n

k N

n

d

N

r

11

11

, 

where is 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; 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. 

Dj ˆ

Variance of for species j is defined as: Dj ˆ

(3) 

   























 























 















    



 1

2 1 ) ˆ ( 1 ,

2 2

,

2

2

1

4

1

2

qh

n

i iqhjiqhjciqhjcjiqh

qh

n

i iqh

qhqh

qhqh

q

j qh n

kdrkrd

n

k

Nn

nN

KDV

qh

h

 

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; nqh is the number of 

observed trips in quarter q and stratum h. 

Dj ˆ

Coefficient of variation (CV) of is defined as: Dj ˆ

13
(4) 

j

j

j D

DV

DCV ˆ

) ˆ ( ) ˆ ( 

The number of sea days and trips needed to achieve a 30% CV are derived based on the 

variance of the total discards using the combined ratio method and the d/k discard ratio 

(Eq 3). 

From Eq 3, let 

 (5) 

   























  

 

1

2 ˆ 1 ,

2 2

,

2

2

qh

n

i iqhjiqhjciqhjhcjiqh

jqh n

kdrkrd

S

qh

 and 

 (6) 







4

q 1 qh

qh

qh

n

n



where qh is the fraction of the trips in quarter q in stratum h; rc,jh is the combined annual 

ratio of species j in stratum h; djiqh is discards of species j from trip i in stratum h in 

quarter q; kiqh is kept pounds of all species on trip i in stratum h in quarter q; and nqh is 

the number of observed trips in stratum h in quarter q. The rc,jh in Eq. 5 is defined in Eq. 

2 where the summation is over quarters within a given strata defined by gear, region, 

access area, trip type and so forth. 

The number of trips necessary to achieve a 30% CV based on the variance of the 

composite annual total discards for species group j in stratum h is defined as 

(7) 

h

jqh

q qh

qh

jh

q qh

jqh

qh

qh

jh

N

S

k

K

D

S

k

K

DT

2 4

1 2

2

2

4

1

2

2

2

30

ˆ

)09.0(

1 ˆ

ˆ





 



















  

where 0.09 = 0.302

, the square of the 30% CV, the given precision level. 

The number of sea days necessary to achieve a 30% CV based on the variance of the 

composite annual total discards for species group j in stratum h is defined as 

(8) jh jh

* DADTDS h ˆ ˆ 30  30

14
where AD h is the weighted average trip length of VTR trips in stratum h (weighted by 

the number of VTR trips in each quarter) . 

When total discards could not be estimated due to little or no observer coverage (no data) 

or when total discards are zero (no variance), sample size was determined by pilot cover, 

where 2% of the quarterly VTR trips for a fleet were multiplied by the quarterly mean 

VTR trip length. 

(9) jhq hq

*DATS hq ˆ ˆ ,30 

 

where is 2% of the VTR trips in stratum h and quarter q, and 3 <= <= 100 trips; Thq

ˆ Thqˆ

AD hq is the average trip length of VTR trips in stratum h and quarter q.

The quarterly trips and sea days were then summed for annual number of trips and sea 

days. 

15

Procedures for Issuing Manuscripts

in the

Northeast Fisheries Science Center Reference Document (CRD) Series

Clearance

All manuscripts submitted for issuance as CRDs 

must have cleared the NEFSC’s manuscript/abstract/

webpage review process. If any author is not a federal 

employee, he/she will be required to sign an “NEFSC 

Release-of-Copyright Form.” If your manuscript 

includes material from another work which has been 

copyrighted, then you will need to work with the 

NEFSC’s Editorial Office to arrange for permission 

to use that material by securing release signatures on 

the “NEFSC Use-of-Copyrighted-Work Permission 

Form.” 

For more information, NEFSC authors should see 

the NEFSC’s online publication policy manual, “Manuscript/abstract/webpage preparation, review, and dissemination: NEFSC author’s guide to policy, process, 

and procedure,” located in the Publications/Manuscript 

Review section of the NEFSC intranet page.

Organization

Manuscripts must have an abstract and table of 

contents, and (if applicable) lists of figures and tables. 

As much as possible, use traditional scientific manuscript organization for sections: “Introduction,” “Study 

Area” and/or ”Experimental Apparatus,” “Methods,” 

“Results,” “Discussion,” “Conclusions,” “Acknowledgments,” and “Literature/References Cited.” 

Style

The CRD series is obligated to conform with the 

style contained in the current edition of the United 

States Government Printing Office Style Manual. That 

style manual is silent on many aspects of scientific 

manuscripts. The CRD series relies more on the CSE 

Style Manual. Manuscripts should be prepared to 

conform with these style manuals. 

The CRD series uses the American Fisheries Society’s guides to names of fishes, mollusks, and decapod 

crustaceans, the Society for Marine Mammalogy’s 

guide to names of marine mammals, the Biosciences 

Information Service’s guide to serial title abbreviations, 

and the ISO’s (International Standardization Organization) guide to statistical terms. 

For in-text citation, use the name-date system. A 

special effort should be made to ensure that all necessary bibliographic information is included in the list 

of cited works. Personal communications must include 

date, full name, and full mailing address of the contact.

Preparation

Once your document has cleared the review process, the Editorial Office will contact you with publication needs – for example, revised text (if necessary) and 

separate digital figures and tables if they are embedded 

in the document. Materials may be submitted to the 

Editorial Office as files on zip disks or CDs, email 

attachments, or intranet downloads. Text files should 

be in Microsoft Word, tables may be in Word or Excel, 

and graphics files may be in a variety of formats (JPG, 

GIF, Excel, PowerPoint, etc.).

Production and Distribution

The Editorial Office will perform a copy-edit of 

the document and may request further revisions. The 

Editorial Office will develop the inside and outside 

front covers, the inside and outside back covers, and 

the title and bibliographic control pages of the document.

Once both the PDF (print) and Web versions of 

the CRD are ready, the Editorial Office will contact 

you to review both versions and submit corrections or 

changes before the document is posted online.

A number of organizations and individuals in the 

Northeast Region will be notified by e-mail of the 

availability of the document online. 
Research Communications Branch

Northeast Fisheries Science Center

National Marine Fisheries Service, NOAA

166 Water St.

Woods Hole, MA 02543-1026

Publications and Reports

of the

Northeast Fisheries Science Center

The mission of NOAA’s National Marine Fisheries Service (NMFS) is “stewardship of living marine resources 

for the benefit of the nation through their science-based conservation and management and promotion of the 

health of their environment.” As the research arm of the NMFS’s Northeast Region, the Northeast Fisheries 

Science Center (NEFSC) supports the NMFS mission by “conducting ecosystem-based research and assessments of living marine resources, with a focus on the Northeast Shelf, to promote the recovery and long-term 

sustainability of these resources and to generate social and economic opportunities and benefits from their use.” 

Results of NEFSC research are largely reported in primary scientific media (e.g., anonymously-peer-reviewed 

scientific journals). However, to assist itself in providing data, information, and advice to its constituents, the 

NEFSC occasionally releases its results in its own media. Currently, there are three such media:

NOAA Technical Memorandum NMFS-NE -- This series is issued irregularly. The series typically includes: data reports of 

long-term field or lab studies of important species or habitats; synthesis reports for important species or habitats; annual reports 

of overall assessment or monitoring programs; manuals describing program-wide surveying or experimental techniques; literature 

surveys of important species or habitat topics; proceedings and collected papers of scientific meetings; and indexed and/or annotated 

bibliographies. All issues receive internal scientific review and most issues receive technical and copy editing.

Northeast Fisheries Science Center Reference Document -- This series is issued irregularly. The series typically includes: data 

reports on field and lab studies; progress reports on experiments, monitoring, and assessments; background papers for, collected 

abstracts of, and/or summary reports of scientific meetings; and simple bibliographies. Issues receive internal scientific review and 

most issues receive copy editing.

Resource Survey Report (formerly Fishermen’s Report) -- This information report is a regularly-issued, quick-turnaround report on 

the distribution and relative abundance of selected living marine resources as derived from each of the NEFSC’s periodic research vessel surveys of the Northeast’s continental shelf. This report undergoes internal review, but receives no technical or copy editing.

TO OBTAIN A COPY of a NOAA Technical Memorandum NMFS-NE or a Northeast Fisheries Science Center Reference Document, 

either contact the NEFSC Editorial Office (166 Water St., Woods Hole, MA 02543-1026; 508-495-2350) or consult the NEFSC webpage 

on “Reports and Publications” (http://www.nefsc.noaa.gov/nefsc/publications/). To access Resource Survey Report, consult the Ecosystem 

Surveys Branch webpage (http://www.nefsc.noaa.gov/femad/ecosurvey/mainpage/).

ANY USE OF TRADE OR BRAND NAMES IN ANY NEFSC PUBLICATION OR REPORT DOES NOT IMPLY ENDORSEMENT.

MEDIA

 MAIL