408 



Abstract— The U.S. East Coast pe- 

 lagic longline fishery has a history 

 of interactions with marine mam- 

 mals, where animals are hooked 

 and entangled in longline gear. Pilot 

 whales (Globicephala spp.) and Risso's 

 dolphin (Grampus griseus) are the 

 primary species that interact with 

 longline gear. Logistic regression was 

 used to assess the environmental and 

 gear characteristics that influence 

 interaction rates. Pilot whale inter- 

 actions were correlated with warm 

 water temperatures, proximity to the 

 shelf break, mainline lengths greater 

 than 20 nautical miles, and damage to 

 swordfish catch. Similarly, Risso's dol- 

 phin interactions were correlated with 

 geographic location, proximity the 

 shelf break, the length of the main- 

 line, and bait type. The incidental 

 bycatch of marine mammals is likely 

 associated with depredation of the 

 commercial catch and is increased by 

 the overlap between marine mammal 

 and target species habitats. Alter- 

 ing gear characteristics and fishery 

 practices may mitigate incidental 

 bycatch and reduce economic losses 

 due to depredation. 



Interactions between marine mammals 



and pelagic longline fishing gear 



in the U.S. Atlantic Ocean between 1992 and 2004 



Lance P. Garrison 



Email address: Lance.Garrison@noaa.gov 



National Marine Fisheries Service 

 Southeast Fishenes Science Center 

 75 Virginia Beach Dr. 

 Miami, Florida 33149 



Manuscript submitted 11 December 

 2006 to the Scientific Editor's Office. 



Manuscript approved for publication 

 27 March 2007 by the Scientific Editor. 



Fish. Bull. 105:408-417 (2007). 



Marine mammal mortalities and inju- 

 ries occur in gillnet fisheries (Perrin 

 et al., 1994), trawl fisheries (Fertl and 

 Leatherwood, 1997), and longline fish- 

 eries (e.g.. Garrison, 2005; Kock et al., 

 2006). The U.S. East Coast pelagic 

 longline fishery targeting swordfish, 

 tunas, and sharks has long been the 

 focus of bycatch reduction efforts for 

 nontarget fish species (e.g., billfish; 

 Goodyear, 1999) and for marine tur- 

 tles (Watson et al., 2005). In addition, 

 marine mammal bycatch in the pelagic 

 longline fishery is common, particu- 

 larly of pilot whales (Globicephala 

 spp.) and Risso's dolphins (Grampus 

 griseus). An estimated average of 132 

 (CV [coefficient of variation] = 0.49) 

 pilot whales and 45 (CV=0.38) Ris- 

 so's dolphins either died or were seri- 

 ously injured because of interactions 

 with pelagic longline gear each year 

 between 1999 and 2003 (Waring et al., 

 2006). These numbers account for 63% 

 of the total commercial fishery-related 

 mortality for pilot whales and 88% for 

 Risso's dolphins along the U.S. East 

 Coast. The total fishery mortality for 

 pilot whales approaches the potential 

 biological removal (PER) benchmark 

 (PBR = 249 for pilot whales and 129 

 for Risso's dolphins), and it exceeds 

 the requirement that mortality caused 

 by commercial fishing approach insig- 

 nificant levels as mandated by the 

 U.S. Marine Mammal Protection Act 

 (MMPA) (Waring et al, 2006). 



In addition to marine mammal con- 

 servation concerns, the occurrence of 

 depredation, or marine mammals feed- 

 ing on the catch or bait from commer- 

 cial fishing gear, is an emerging global 

 issue. Depredation has been observed 



on both bottom and pelagic longlines 

 by killer whales (0/-cinus orca; Sec- 

 ciii and Vaske, 1998: Kock et al., 

 2006), false killer whales (Pseudorca 

 crassidens), pilot whales, and sperm 

 whales (Physeter macrocephalus; Kock 

 et al., 2006). Fishermen in the Atlantic 

 longline fleet indicate that damage to 

 commercial catch by pilot whales is 

 common (Angliss and DeMaster, 1998). 

 Depredation has a direct economic im- 

 pact on commercial fishermen by re- 

 moving commercially valuable catch. 



Identification of the fishing prac- 

 tices and environmental processes 

 that drive interactions between ma- 

 rine mammals and longline fishing 

 gear is important to understanding 

 and reducing both incidental mortal- 

 ity and depredation. In this study, 

 pelagic longline fishery observer da- 

 ta collected between 1992 and 2004 

 were analyzed to describe the number 

 of interactions, seasonal and spatial 

 patterns, and the types of interac- 

 tions associated with serious injuries 

 and mortalities of marine mammals. 

 Logistic regression was used to exam- 

 ine factors affecting the probability 

 of interactions with pilot whales and 

 Risso's dolphins. The results of these 

 analyses will help managers make 

 informed decisions to reduce both ma- 

 rine mammal bycatch and economic 

 losses due to depredation. 



Materials and methods 



Pelagic observer program 



The U.S. East Coast pelagic longline 

 fishery has been observed since 1992. 



