Northeast Fisheries Science Center Reference Document 07-20
Estimates of Cetacean and Pinniped Bycatch
in the 2006 Northeast Sink Gillnet
and Mid-Atlantic Coastal Gillnet Fisheries
by Dana Belden1,2 and Christopher D. Orphanides1
1 NOAA Fisheries, Northeast Fisheries Science Center, 166 Water Street, Woods Hole MA 02543-1026
2 Current contact information: Office of Naval Research, Marine Mammals & Biological Oceanography Program, One Liberty Center, Code 322 – Rm 1072C, 875 N. Randolph St., Arlington, VA 22203-1995. beldend@onr.navy.mil
Print
publication date December 2007;
web version posted January 9, 2008
Citation: Belden D, Orphanides CD. 2007. Estimates of Cetacean and Pinniped Bycatch
in the 2006 Northeast Sink Gillnet
and Mid-Atlantic Coastal Gillnet Fisheries. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 07-20; 18 p.
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Abstract
This report provides incidental take estimates for six
marine mammal species taken in the 2006 Northeast Sink Gillnet (NESG) and
Mid-Atlantic Coastal Gillnet (MACG) fisheries and documents the methodology
used to produce the estimates. For the NESG fishery, the estimated take was 20
common dolphins (CV = 105%), 514 harbor porpoises (CV = 31 %), 41 Atlantic
white-sided dolphins (CV = 71%), 248 gray seals (CV = 47%), 87 harbor seals (CV
= 58%), and 65 harp seals (CV = 66%). For the MACG fishery, the estimated 2006
takes was 512 harbor porpoises (CV = 32%), 11 common dolphins (CV = 103%), and 26
harbor seals (CV = 98%).
INTRODUCTION
Pursuant to the 1994 amendments of the Marine Mammal
Protection Act (MMPA), Section 117 states that estimates of annual human-caused
mortality and serious injury to marine mammal stocks must be reported in annual
stock assessment reports (SAR) for each stock of marine mammal that occurs in
waters under U.S jurisdiction.
The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer
Program (SSOP), presently known as the Northeast Fisheries Observer Program
(NEFOP), was initiated in 1989 to document the bycatch of marine mammals taken
incidentally to commercial fishing operations (Waring et al. 2004). Since the
initiation of the observer program, the estimation of total takes for harbor
porpoise (Phocoena phocoena) has been the focus of much attention due to frequent
observations of incidental takes occurring in the NESG fishery (NMFS 1998). This attention led to the development of a
stratification method designed to estimate the total annual takes of harbor
porpoise (Bisack 1993; Smith et al. 1993; Bravington and Bisack 1996; Bisack
1997; Rossman and Merrick 1999; Bisack 2003). The regional scope of the SSOP was expanded into the Mid-Atlantic (MA)
region in 1995 in an effort to learn more about marine mammal interactions
occurring in MA gillnet fisheries.
Rossman and Merrick (1999) documented the methods used to
estimate harbor porpoise bycatch in the NESG and MACG fisheries. These methods
have also been used by the NEFSC to estimate the bycatch of other marine
mammals observed bycaught in the NESG and MACG fisheries (Blaylock et al. 1995;
Waring et al. 1997; Waring et al. 2004; Belden et al. 2006; Belden 2007).
Historically, the NESG fishery extended from Maine to Connecticut
and was dominated by bottom-tending sink gillnets. Less than 1% of the fishery
utilized a drift gillnet (not tending the ocean bottom). Monofilament twine was
typically used with stretched mesh sizes ranging from 6 to 12 inches. String
lengths ranged from 600 to 10,500 feet. Mesh size and string lengths varied by the primary fish species targeted
for catch.
The MACG fishery ranged from Connecticut to North Carolina
and utilized both drift and sink gillnets. These nets were most frequently
attached to the bottom, although unanchored drift or sink nets were also
utilized to target specific species. Monofilament twine was again the dominant
material and was used with stretched mesh sizes ranging from 2.5 to 12 inches.
String lengths ranged from 150 to 8400 feet. The mesh size and string lengths
varied by the primary fish species targeted for catch (Waring et al. 2004). Due to recent fishing patterns, the division
between the Northeast and Mid-Atlantic has changed from Connecticut to Rhode
Island. This will be discussed further in
this report.
The same ratio estimator methodology was used to calculate
cetacean and seal bycatch for the 2006 NESG and MACG fisheries as was used in
Belden et al. (2006) and Belden (2007). However, there were a few changes in the
stratification; these changes and the resulting bycatch estimates are described
in this report. As in previous years, bottlenose dolphin bycatch was not
estimated in this document. Bottlenose dolphin estimates can be found in the
upcoming 2008 U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessment
Report (Waring et al. in prep.), and in an upcoming paper by Rossman (in
prep.).
METHODS
Data Sources
Three databases were used to estimate the total marine mammal
takes in 2006: the NEFOP database, Northeast (NE) Dealer Reports, and Northeast
Vessel Trip Reports (VTR). First, the
NEFOP database provided data on the observed bycatch of marine mammals. The
NEFOP has two types of sampling protocols when observing fishing trips: (1)
complete fish sampled trips where the observer samples the catch for fish discard
information (the observer is not able to watch the net as it is being hauled),
and (2) limited fish sampled trips where the observer watches the net for
incidental takes as it is being hauled. In the NESG fishery only, hauls
observed from both trip sampling protocols were used to estimate the bycatch
rates from observed incidental takes. Only limited fish sampling trips were
used in the MACG fishery to estimate the bycatch rates of most species.
Second, the NE Dealer Report landings database was used to
determine the total landings in 2006 of all finfish caught in the Northeast and
Mid-Atlantic gillnet fishery.
Lastly, the NE VTR database was used to assign (prorate) the
NE Dealer Report landings from the NESG fishery to spatial and temporal strata
historically used to estimate takes of harbor porpoise in the NESG fishery
(Rossman and Merrick 1999; Bisack 2003).
For purposes of this report, a “take” is defined as any
observed incidental take where the animal’s condition was recorded as either
alive with injuries or dead (fresh or under various stages of decomposition).
All incidental takes are identified to species by the fishery observer whenever
possible. There were several incidental
takes that were not identified to species: two unknown porpoise/dolphin species
and eight unknown seal species. These animals were not included in the bycatch
estimates for the strata in which they were caught..
The level of sampling (observer coverage) for each stratum
was calculated by dividing the observed metric tons (mtons) of fish caught by
the prorated metric tons of fish recorded in the dealer database. This value
represented the fraction of total landings that were sampled.
Analysis
Data Stratification
The strata defined in Rossman and Merrick (1999) were used
to estimate takes in 2006. The NESG data were stratified temporally by season,
spatially by port group-area and time/area closures, and by bycatch avoidance
techniques via the use of pingers (Table
1). Seasons are defined as winter
(January to May), summer (June to August), and fall (September to December).
Connecticut (CT) gillnet fishing effort has historically
been included in the Mid-Atlantic region bycatch analyses. Spatial analysis of
2005 and 2006 VTR and observer data indicated that CT vessels are currently fishing
in the same time and area as vessels from the Northeast region fishing in the
South of Cape Cod port group (Figure
1). Therefore, CT trips were included in
the 2006 Northeast South of Cape Cod port group bycatch estimates (Table
1). This
change affected the estimated bycatch of harbor porpoise, common
dolphin, gray seal, harbor seal, and harp seal.
As indicated in Belden et al. (2006), until 2004 MACG
bycatch estimates have been calculated by month for each state. In 2005 and
2006, observer and VTR trip locations indicate New Jersey (NJ) MACG trips
during January to April fished in a similar area (Figure
2). So, a winter season (January to April) was
used for the 2006 analyses (Table
2) of harbor porpoise and harbor seal takes
in New Jersey waters.
In January 2006, a common dolphin take was observed off the
coast of NJ. Rather than creating a winter category as we had done for harbor
porpoise and harbor seal, we calculated a bycatch rate for only the month of
January, due to uncertainty about the distribution of common dolphins during
that time of year. The take was observed on a complete sampling trip. No common
dolphin bycatch was observed on limited sampling trips. Historically, MA cetacean
bycatch estimates have been calculated using only limited trips (Rossman and
Merrick 1999; Belden et al. 2006; Belden 2007), but since the observed bycatch
occurred on a complete trip, we used both complete and limited trips to
estimate bycatch for common dolphins. Use
of both types of trips is likely more representative of bycatch than complete
trips alone, since the observer on complete trips is not able to watch the net
as it is being hauled. Using both trip types
also increased the sample size of observed hauls from 38 to 106, providing a
more robust estimate.
New York (NY) gillnet fishing effort has historically been
included in the MA region bycatch analyses. Spatial analysis of 2006 VTR and observer data
indicated that some NY vessels, including a vessel on which takes were observed,
fished in the same time and area as vessels from the Northeast region fishing
in the South of Cape Cod port group or time/area closure (Figure
3). Therefore,
the NY observed trips that were east of the 72º30’W line were included in the
2006 Northeast South of Cape Cod port group or time/area closure bycatch
estimates (Table
1). This fits in well with the List of Fisheries definition
for NESG fisheries, which states that the MA area is from 72º30’W south to
36º33’03”N. This change affected the estimated bycatch of harbor porpoise,
common dolphin, gray seal, harbor seal, and harp seal.
The VTR effort for NY was divided between the NE and MA regions
using the 72º30’W line, as was the observer data. Next, the proportion of NY VTR
tons assigned to the South of Cape Cod port group or area was calculated for
each month. These proportions were then applied to the NY dealer data to get
the prorated dealer tons to be used in the bycatch estimates for the appropriate
port group or area in the NE region. Thus, the NY data from the observer and
VTR databases were divided into the NE region (Table
1 and Table
2) and MA region
(Table
3).
Bycatch Rates
The number of marine mammal takes (B) is the product of the
observed bycatch rate multiplied by the total effort in each stratum (S). The observed
bycatch rate for each stratum is defined as the number of observed takes divided
by the observed mtons (effort) of fish landed.
There is a possibility that strings could be either equipped
or not equipped with pingers in the NESG fishery. Therefore, a weighted bycatch
rate was calculated for strata where there were hauls with and without pingers. Within a stratum, the weighted bycatch rate
was calculated as the sum of two weighted bycatch rates, one from hauls with pingers
and one from hauls without pingers. Each bycatch rate was weighted by the
proportion of hauls sampled with or without pingers within its respective
stratum.
Standard bootstrapping techniques were used to derive the
confidence intervals and coefficients of variation (CV) for the bycatch
estimates for each stratum. The re-sampling unit used was an entire trip rather
than individual hauls to ensure that any within trip dependence was carried
over into the bycatch estimate’s CV (Bisack 2003).
RESULTS
Northeast Region
The overall observer coverage in the NESG was 3.6%, ranging
from 1.3% in the summer to 6.0% in the winter (Table
1). This level is lower than in 2005, which was
7.3%, ranging from 4.2% in the fall to 11.5% in the winter (Belden 2007). One
common dolphin, 26 harbor porpoises, 2 white-sided dolphins, 2 unknown
porpoise/dolphins, 9 gray seals, 3 harbor seals, 3 harp seals, and 8 unknown
seals were observed taken in the 2006 NESG fishery. Unidentified animals were
not included in this analysis.
The 2006 estimated total takes of cetaceans in the NESG
fishery included 20 (CV = 105%) common dolphins (Table
4), 514 (CV = 31%)
harbor porpoises (Table
5), and 41 (CV = 71%) white-sided dolphins (Table
6). The 2006 estimated total takes of pinnipeds
in the NESG fishery included 248 (CV = 47%) gray seals (Table
7), 87 (CV = 58%)
harbor seals (Table
8), and 65 (CV = 66%) harp seals (Table
9).
Mid-Atlantic Region
The 2006 observer coverage for the MACG fishery using only
limited trips was 3.7% (Table
2) and using both complete and limited trips was 4.3%
(Table
3). The 2006 observer coverage for the winter off of NJ was 3.9% (Table
10).
The 2006 observer coverage for January off of NJ was 9.0% (Table
11). There
were 20 harbor porpoises, 1 common dolphin, and 1 harbor seal observed taken in
the MACG fishery in 2006.
The 2006 estimated total takes for cetaceans in the MACG
fishery included 512 (CV = 32%) harbor porpoises (Table
12) and 11 (CV = 103%)
common dolphins (Table
13). The 2006
estimated total takes for pinnipeds in the MASG fishery was 26 (CV = 98%)
harbor seals (Table
14).
REFERENCES
Belden, DL, Orphanides CD, Rossman MC, Palka DL. 2006.
Estimates of cetacean and seal bycatch in the 2004 Northeast sink gillnet and
Mid-Atlantic coastal gillnet fisheries. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 06-13; 24 p. Available
from: NOAA Fisheries, 166 Water St, Woods Hole MA 02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/crd/crd0613/crd0613.pdf.
Belden, D. 2007. Estimates of cetacean and seal bycatch in
the 2005 Northeast sink gillnet and Mid-Atlantic coastal gillnet
fisheries. US Dep Commer, Northeast Fish
Sci Cent Ref Doc. 07-08; 16 p. Available from: NOAA Fisheries, 166 Water St,
Woods Hole MA 02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/crd/crd0708/crd0708.pdf.
Bisack KD. 1993. Estimates of total US harbor porpoise bycatch in the Gulf of Maine sink
gillnet fishery. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 93-11; 23 p.
Available from: NOAA Fisheries, 166 Water St, Woods Hole MA 02543-1026.
Bisack KD. 1997. Harbor porpoise bycatch estimates in the New England multispecies sink
gillnet fishery: 1994 and 1995. Rep int
Whal Commn. 47:705-714.
Bisack KD. 2003. Estimates of marine mammal bycatch in the Northeast (New England)
multispecies sink gillnet fishery in 1996. US Dep Commer, Northeast Fish Sci
Cent Ref Doc. 03-18; 18 p. Available from: NOAA Fisheries, 166 Water St, Woods
Hole MA 02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/crd/crd0318/
Blaylock RA, Hain JW, Hansen LJ, Palka DL, Waring GT. 1995.
US Atlantic and Gulf of Mexico Marine Mammal Stock Assessments. NOAA Tech Mem. NMFS-SEFSC-363; 211 p.
Bravington MV, Bisack KD. 1996. Estimates of harbor porpoise bycatch in the
Gulf of Maine sink gillnet fishery, 1990-1993. Rep int Whal Commn. 46:567-574.
National Marine Fisheries Service [NMFS]. 1998. Taking of marine mammals incidental to
commercial fishing operations; harbor porpoise Take Reduction Plan regulations.
Fed Regis. 63(231):66464-66490.
Rossman MC, Merrick RL. 1999. Harbor porpoise bycatch in the Northeast
multispecies sink gillnet fishery and the Mid-Atlantic coastal gillnet fishery
in 1998 and during January-May 1999. Northeast Fish Sci Cent Ref Doc. 99-17; 36 p. Available from: NOAA Fisheries, 166 Water St,
Woods Hole MA 02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/crd/crd9917.pdf
Rossman, MC. [in
prep.] Estimating bycatch of coastal bottlenose
dolphin (Tursiops truncatus) in U.S. Mid-Atlantic gillnet fisheries during
2001-2006. NOAA NMFS Northeast Fisheries
Science Center, 166 Water St, Woods Hole MA 02543.
Smith TD, Palka DL, Bisack KD. 1993. Biological significance of bycatch of harbor
porpoise in the Gulf of Maine demersal gillnet fishery. US Dep Commer, Northeast Fish Sci Cent Ref
Doc. 93-23; 15 p. Available from: NOAA Fisheries, 166 Water St, Woods Hole MA
02543-1026.
Waring GT, Palka, DL, Mullin KD, Hain JHW, Hansen LJ, Bisack
KD, Editors. 1997. US Atlantic and Gulf of Mexico marine mammal stock
assessments – 1996. NOAA Tech Mem NMFS-NE-114; 250 p. Available from: NOAA Fisheries, 166 Water St,
Woods Hole MA 02543-1026.
Waring GT, Pace RM, Quintal JM,
Fairfield CP, Maze-Foley K, Editors. 2004. US Atlantic and Gulf of Mexico
marine mammal stock assessments -- 2003. US Dep Commer, NOAA Tech Memo NMFS NE
182; 287 p. Available from: NOAA Fisheries, 166 Water St, Woods Hole MA
02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/tm/tm182/tm182.pdf
Waring, GT, Josephson E, Fairfield-Walsh CP, and Maze-Foley
K. [in prep.] U.S. Atlantic and Gulf of Mexico marine
mammal stock assessments – 2007(8). NOAA
Fisheries, 166 Water St, Woods Hole MA 02543.
| Acronyms |
| CV = |
coefficient of variation |
| MA= |
Mid-Atlantic |
| MACG = |
Mid-Atlantic Coastal Gillnet |
| MMPA = |
Marine Mammal Protection Act |
| mtons = |
metric tons |
| NE = |
Northeast |
| NEFOP = |
Northeast Fisheries Observer Program |
| NEFSC = |
Northeast Fisheries Science Center |
| NESG = |
Northeast sink gillnet |
| NMFS = |
National Marine Fisheries Service |
| NOAA = |
National Oceanic and Atmospheric
Administration |
| SAR = |
stock assessment report |
| SSOP = |
Sea Sampling Observer Program |
| VTR = |
Vessel Trip Report |
