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Evaluating the Accuracy of Trawl Logbook Estimates of Groundfish Discards

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  • The Enhanced Data Collection Project (EDCP), administered by the Oregon Department of Fish and Wildlife, collected data on discard rates for groundfish species and bycatch rates of prohibited species. From late 1995 to early 1999 EDCP observers collected discard data from 235 fishing trips by 25 trawl vessels that voluntarily participated in the program. Besides these observer data, vessels in the program kept enhanced logbooks that recorded retained and discarded catch. These logbooks had data from 866 trips by 44 vessels, including most of the trips with observers. Provided logbook data are acceptably accurate, collecting discard data using logbooks could be a cost-effective supplement to an observer program for measuring discard rates and total discards. Comparisons of tow-by-tow logbook discards with the corresponding observer discards indicated substantial inaccuracies in the logbook information. However, when averaged across tows, trips, and vessels, the discard rates (discard/catch) from the logbooks were lower than the observer discard rates, but predictably so. Generalized linear models were used to determine the major factors contributing to variability in the discard rates. The models indicated tremendous vessel-to-vessel variability in discard rates. Principal components analysis (PCA) was applied to trip-level landings and species compositions from the entire groundfish trawl fleet to summarize the fleet-wide characteristics of fishing trips. Analyses of the PCA scores from the trips that were in the EDCP compared to the scores from all other trips indicated that the EDCP trips probably were not representative of the fleet at large.
  • Keywords: observers, logbooks, Fisheries Economics, groundfish, trawl fishery, bycatch, discards, Theoretical and Empirical Bio-Economic Modelling
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  • Sampson, David B., Yong-Woo Lee. 2002. Evaluating the Accuracy of Trawl Logbook Estimates of Groundfish Discards. Peer Review: No. In: Proceedings of the Eleventh Biennial Conference of the International Institute of Fisheries Economics and Trade, August 19-22, 2002, Wellington, New Zealand: Fisheries in the Global Economy. Compiled by Ann L. Shriver. International Institute of Fisheries Economics & Trade, Corvallis, Oregon, USA, 2002. CD ROM.
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