Estimated Bycatch of Small Cetaceans in Northeast US Bottom Trawl Fishing Gear during 2000-2005

Abstract

The U.S. Marine Mammal Protection Act mandates monitoring of incidental marine mammal mortality and serious injury attributable to commercial fishing operations. Generalized linear models (GLM) applied to data collected on a sample of the fisheries were utilized to estimate incidental bycatch rates of pilot whales (Globicephela macrorhynchus and G. melas), white-sided dolphin (Lagenorhynchus acutus), and common dolphin (Delphinus delphis) in U.S. bottom trawl fisheries operating off the Northeast coast of the U.S. during 2000–2005. Spatial, habitat, environmental and fishing practice covariates were significant in the best fitting GLM models. Highest bycatch rates (observed bycatch per observed days fished) occurred in deeper waters with low sea surface temperature (whitesided dolphin), on vessels in the Mid-Atlantic region fishing in deeper waters (pilot whales), and in offshore waters (common dolphin). Estimated bycatch rates were expanded by total bottom trawl effort (days fished) to derive the mean annual bycatch mortality for each of the three species. The estimated mean annual bycatch during 2000–2005 for pilot whales, white-sided dolphin, and common dolphin in U.S. Atlantic bottom trawl fisheries is 72, 212 and 142 animals, respectively. These estimates are 29%, 42%, and 14%, respectively, of their current potential biological removal (PBR) levels for these three species. The importance of animal behavior in conjunction with vessel and gear characteristics associated with bycatch should be investigated further to learn more about potential mechanisms entrapping cetaceans in bottom trawl nets.