343 



Abstract — We documented depreda- 

 tion by bottlenose dolphins (Turaiops 

 tJ-uncatiis) in the Florida king mack- 

 erel (Scomberomorus cavalla) troll 

 fishery. Between March and June 

 2003, we conducted 26 interviews of 

 charter and commercial fishermen 

 in Islamorada, Florida, and 23 along 

 Florida's east coast from Fort Pierce 

 south to Lake Worth Inlet. All fish- 

 ermen indicated they had observed 

 bottlenose dolphins depredating 

 bait or catch — king mackerel being 

 the species most often taken by dol- 

 phins. During on-board observations 

 of depredation between March and 

 June 2003, we found that dolphins 

 took 6% of king mackerel caught by 

 charter fishermen and 207^ of fish 

 caught by commercial fishermen. We 

 concluded that depredation by bottle- 

 nose dolphin occurs commonly in this 

 fishery and has the potential to incur 

 a significant economic cost to king 

 mackerel fishermen. To address this 

 concern, we conducted preliminary 

 tests of a gear modification designed 

 to reduce depredation in the king 

 mackerel fishery between December 

 2003 and January 2004. These tests 

 demonstrated that a modification to 

 the outrigger planer will successfully 

 deter bottlenose dolphins from engag- 

 ing in depredation, without causing 

 a reduction in catch. 



Depredation of catch by bottlenose dolphins 

 (Tursiops truncotus) in the Florida king mackerel 

 {Scomberomorus cavalla) troll fishery 



Erika A. Zollett 



Andrew J. Read 



Duke University Marine Laboratory 



Nicholas School of the Environment and Earth Sciences 



135 Duke Marine Lab Road 



Beaufort, North Carolina 28516 



Present address: University of New Hampshire 



Ocean Process and Analysis Laboratory 



Institute for the Study of Earth, Oceans, and Space 



142 Morse Hall 



Durham, New Hampshire 03824 

 E-mail address for Enka Zollett, enkazollettia'unti edu 



Manuscript submitted 16 September 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



16 September 2006 by the Scientific Editor. 



Fish. Bull. 104;343-349 (2006). 



Depredation is the removal of or 

 damage to captured fish or bait caused 

 by marine predators. Evidence of 

 depredation exists for several pinni- 

 ped and cetacean species (Yano and 

 Dahlheim, 1995; Reeves et al.'; NRC, 

 2003). A recent increase in the number 

 of reports of depredation by marine 

 mammals may reflect changes in fish- 

 ing effort, increased spatial overlap 

 between these predators and fisheries, 

 or behavioral learning among marine 

 mammals (Donoghue et al.-). With a 

 rapidly growing human population, 

 fishing effort in coastal regions will 

 likely continue to increase, causing 

 even greater conflicts between fisher- 

 ies and marine mammal populations 

 throughout the world's oceans (Read, 

 2005). 



Marine mammals engaging in dep- 

 redation cause damage to fishing 

 gear, decrease the value and quan- 

 tity of catches, and reduce catch by 

 dispersing fish (Reeves et al.M. Dep- 

 redation may benefit marine mam- 

 mals by increasing foraging success, 

 but the behavior, habitat, and distri- 

 bution of mammals may change as 

 they frequent areas of high fishing 

 effort (Reeves et al.M. Harmful con- 

 sequences of depredation to marine 

 mammals may include injury or mor- 

 tality from entanglement with fishing 

 gear or from the retaliatory measures 

 of angry fishermen. 



Our purpose in this study was to 

 document the extent, nature, and cost 

 of depredation by bottlenose dolphins 

 (Tursiops truncatus) in the king mack- 

 erel (Scomberomorus cavalla) charter 

 and commercial fisheries of Florida. 

 There have been previous anecdotal 

 reports of depredation by dolphins in 

 this fishery (Odell, 1975), but no sys- 

 tematic study of these interactions has 

 been conducted. We also worked with 

 fishermen to identify potential tools 

 that would deter dolphins from engag- 

 ing in depredation. Other studies have 

 employed this approach with consider- 

 able success. For example, Noke and 

 Odell (2002) modified the design of 

 crab pots, and thus prevented dolphins 



1 Reeves, R. R., A. J. Read, and G. Notar- 

 bartolo di Sciara (eds.). 2001. Report 

 of the workshop on interactions between 

 dolphins and fisheries in the Mediter- 

 ranean: evaluation of mitigation alter- 

 natives, 44 p. Istituto Centrale per 

 la Ricerca Applicata al Mare, Rome, 

 Italy. Website: http://www.cetaceanby- 

 catch.org/Papers/Reeves.pdf [acessed on 

 12 March 2004]. 



- Donoghue, M., R. R. Reeves, and G. 

 Stone. 2003. Report on the workshop 

 on interactions between cetaceans and 

 longline fisheries held in Apia, Samoa, 

 November 2002. New England Aquar- 

 ium Aquatic Forum Series Report 03-1, 

 44 p. Website: http://neaq2.securesites. 

 net/scilearn/conservation/Longline 

 Report2002.pdf [accessed on 17 Januarv 

 2004]. 



