SS1.06 The Ecological Impacts of Pelagic Longline Fisheries
Date: Monday, June 10, 2002
Time: 2:15:00 PM
Location: Carson A
 
BaumJK, Dalhousie University, Halifax, Canada, baum@mscs.dal.ca
Kehler, D, , Dalhousie University, Halifax, Canada, kehler@mscs.dal.ca
Myers, R, A, Dalhousie University, Halifax, Canada, myers@mscs.dal.ca
 
COLLAPSE OF PELAGIC AND LARGE COASTAL SHARKS IN THE NORTHWEST ATLANTIC
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Pelagic and large coastal sharks are caught incidentally in considerable numbers in pelagic longline fisheries. While generally assumed to be vulnerable to exploitation, determining the status of shark populations is hindered by the lack of direct research surveys, and is consequently unknown for most species. To address this problem, we analysed logbook data from pelagic longline fishing vessels from the U.S. Atlantic, the Gulf of Mexico and the Caribbean between 1986 and 2000. Since zeros were not recorded in these data, we examined an approach for obtaining unbiased estimates of trends in abundance for shark species, when missing values cannot be distinguished from real zeros. We used generalized linear models (GLMs) with truncated negative binomial distributions, assuming only that if the sharks caught in a set were recorded that it was the true number. The observed trends in abundance were robust to models based on different distributions. Our results indicate that almost all recorded shark species have declined. The substantial declines in hammerhead sharks (Sphyrna mokarran, S. lewini, S. zygaena) represent a critical conservation concern that had been previously overlooked.