Diamond: Estimation of shrimp trawl bycatch 



485 



Bycatch is a major issue in the shrimp trawl fisheries 

 of the Gulf of Mexico and the South Atlantic Bight. These 

 fisheries are the most valuable fisheries in the southeast- 

 em United States; almost 136,000 metric tons of shrimp, 

 worth over $700 million, were landed in 2000 (NMFS^). It 

 is estimated that 60-80% of the catch by weight in these 

 fisheries is bycatch. Over 150 species have been reported in 

 shrimp trawl bycatch, including marine turtles (Grouse et 

 al., 1987) and juveniles of species that are highly valued as 

 adults in other fisheries, such as weakfish iCynoscion rega- 

 lis rVaughan et al.-'] ) and red snapper (Lutjanus campecha- 

 nus [Goodyear'*! ). 



Both types of statistical estimators have been used 

 to estimate bycatch in shrimp trawl fisheries. In the 

 South Atlantic, biologists have periodically partici- 

 pated as observers aboard commercial shrimp trawlers 

 since at least the 1950s to characterize bycatch and 

 estimate its magnitude (Fahy, 1966; Latham, ^ Lunz et 

 al.,6 Fahy,'' Fahy« Fahy,^ Wolff,"* Keiser.n Knowltoni^). 

 For most of the studies conducted between the 1950s and 



2 NMFS (National Marine Fisheries Service). 2002. Unpubl. 

 data Website: http://www.st.nmfs.gov/stl/comniercial/index. 

 html. 



^ Vaughan, D. S., R. J. Seagraves, and K. West. 1991. As assess- 

 ment of the status of the Atlantic weakfish stock, 1982-1988. 

 Special Report 21, 29 p. Atlantic States Marine Fisheries 

 Commission, 1444 Eye Street, N.W., Sixth Floor, Washington, 

 DC 20005. 



^ Goodyear, C. P. 1995. Redsnapper in US watersofthe Gulfof 

 Mexico. Contribution MlA-95/96-05, 171 p. Miami Laboratory, 

 Southeast Fisheries Science Center, NMFS,75 Virginia Beach 

 Drive, Miami. Florida 33149-1099. 



^ Latham, F F. 1951. Evidence of fish loss due to shrimping 

 in Pamlico Sound. Appendix B in The destruction of small 

 fish by the shrimp trawlers in Pamlico Sound, North Carolina 

 (G. R. Lunz, J. L.,McHugh, E. W. Roelofs, R. E. Tiller, and C. E. 

 Atkinson), p. 17-24. Committee Report to the Atlantic States 

 Marine Fisheries Commission, 1 November 1951. Atlantic 

 States Marine Fisheries Commission, 1444 Eye Street, N.W, 

 Sixth Floor, Washington. DC 20005. 



« Lunz. G. R.. J. L. McHugh, E. W. Roelofs, R. E. Tiller, and C. E. 

 Atkinson. 1951. The destruction of small fish by the shrimp 

 trawlers in Pamlico Sound, North Carolina. Committee Report 

 to Atlantic States Marine Fisheries Commission, 1 November 

 1951, 34 p. Atlantic States Marine Fisheries Commission, 

 1444 Eye Street, N.W., Sixth Floor, Washington, DC 20005. 



"Fahy, W. E. 1965a. Report of trash fish study in North Caro- 

 lina in 1962. Division of Commercial and Sports Fisheries, 

 NC Department of Conservation and Development, Special 

 Scientific Report 5. 20 p. NC Division of Marine Fisheries, 

 3441 Arendell St., Morehead City, NC 28557. 



8 Fahy, W. E. 1965b. Report of trash fish study in North Caro- 

 lina in 1964. Division of Commercial and Sports Fisheries, 

 NC Department of Conservation and Development, Special 

 Scientific Report 7, 13 p. NC Division of Marine Fisheries, 

 3441 Arendell St., Morehead City. NC 28557. 



3 FahyW.E. Unpubl.datacitedinBrown, J.,andE.McCoy 1969. 

 A review of the North Carolina scrap fishery. Division of Com- 

 mercial and Sports Fisheries. NC Department of Conservation 

 and Development. Information Series 1, 12 p. NC Division of 

 Marine Fisheries, 3441 Arendell St., Morehead City, NC 28557. 



1" Wolff, M. 1972. A study ofNorth Carolina scrap fishery. NC 

 Department of Natural and Economic Resources, Special Sci- 

 entific Report 20, 29 p. NC Division of Marine Fisheries, 3441 

 Arendell St., Morehead City, NC 28557. 



the 1980s, fisheries bycatch was estimated by using a ratio 

 estimator, that is to say by calculating the observed ratio of 

 fish (F) bycatch to shrimp (S) by weight and then multiply- 

 ing by the total pounds of shrimp landed by the fleet (the 

 F:S ratio estimator). The catch of shrimp was used as the 

 auxiliary variable primarily because better records were 

 kept of shrimp landings than of any measure of fleet effort. 

 By the late 1980s, the problem of shrimp trawl bycatch in 

 the United States was considered to be of such magnitude 

 that in 1990 the Magnuson Fishery Conservation and 

 Management Act (Magnuson Act) was amended to include 

 bycatch research. Beginning in 1992, observers trained 

 by the National Marine Fisheries Service (NMFS) to use 

 a standardized sampling protocol (NMFS'-*) rode aboard 

 paid volunteer commercial vessels in the South Atlantic 

 and Gulf of Mexico. The 1992-94 observation data collected 

 in the South Atlantic were used to estimate bycatch by spe- 

 cies with a mean-per-unit estimator, which was the weight 

 or number of fish caught per observed trip multiplied by 

 the total number of trips taken by the fleet (the CPUE- 

 mean-per-unit estimator). Trips were used as the auxiliary 

 variable because fleet effort data were available at the trip 

 level and this method was thought to be less variable than 

 the F:S ratio method (SEAMAP'"). 



To date, there have been no detailed studies on how 

 these different techniques compare to each other, or how 

 accurately they estimate bycatch. Vaughan and Nance''' in 

 a draft paper compared the estimated bycatch of mackerels 

 (Scomberomorus spp.) and cobia {Rachycentron canadum) 

 using both methods and found much higher estimates with 

 the F:S ratio estimator than with the CPUE-mean-per-unit 

 estimator. Because of the wide range of estimation meth- 

 ods used over the years, the discrepancy in the estimates 

 generated by the different methods, and the increasing im- 

 portance of bycatch estimation for shrimp trawl fisheries 



" Reiser, R. K. 1977. The incidental catch from commercial 

 shrimp trawlers of the South Atlantic states. Technical Report 

 26, 38 p. South Carolina Wildlife and Marine Resources Depart- 

 ment, South Carolina Department of Natural Resources, Rembert 

 C. Dennis Building, 1000 Assembly Street, Columbia, SC 29201. 



12 Knowlton, C. J. 1972. Fishes taken during commercial 

 shrimping in Georgia's close inshore ocean waters. Con- 

 tributed Series 21, 42 p. Georgia Department of Natural 

 Resources, Coastal Resources Division, One Conservation Way, 

 Suite 300, Brunswick, GA 31520. 



1-^ NMFS (National Marine Fisheries Service). 1992. Shrimp 

 trawl bycatch characterization. Sampling Protocol Manual 

 for Data Collection, 62 p. Galveston Laboratory, Southeast 

 Fisheries Science Center, NMFS, 4700 Avenue U, Galveston, 

 TX 77551-5997. 



''• SEAMAP (Southeast Area Monitoring and Assessment Pro- 

 gram ). 1996. Estimates of finfish bycatch in the South Atlan- 

 tic Shrimp Fishery, July 24, 1995 (R. Peuser, ed.), 64 p. Final 

 report of the Southeast Area Monitoring and Assessment Pro- 

 gram (SEAMAP), SEAMAP-South Atlantic Committee, Shrimp 

 Bycatch Work Group. Atlantic States Marine Fisheries Com- 

 mission, 1444 Eye Street, N.W., Sixth Floor, Washington, DC 

 20005. 



'^ Vaughan, D. and J. Nance. 1998. Estimates of bycatch of 

 mackerel and cobia in US South Atlantic shrimp trawls. Re- 

 port for Gulf of Mexico and South Atlantic Fishery Management 

 Councils, February 16, 1998, 26 p. NMFS -SEFSC, Beaufort 

 Laboratory, 101 Fivers Island Road, Beaufort NC 28516. 



