346 



Fishery Bulletin 104(3) 



fasciata), blackfin tuna (Thunnus atlanticus). and Span- 

 ish mackerel {Scomberomorus maculatus) (Fig. 3). 



More than half of the fishermen we interviewed in- 

 dicated that the interactions with bottlenose dolphins 

 occurred either daily or several times a week. In Islam- 

 orada, fishermen indicated that winter was the season 

 with the highest number of interactions, and along the 

 east coast of Florida, most interactions occurred dur- 

 ing spring (Fig. 4). Most interviewees {lG.69c) indicated 

 they believed that bottlenose dolphin conflicts with fish- 

 ing efforts had increased over the past several years. 

 The vast majority (94%) of commercial fishermen indi- 

 cated that bottlenose dolphin depredation was causing 

 a significant economic loss, although a smaller number 



97.9 



100 



Amberjack 



Blackfin 

 tuna 



King 

 mackerel 



Spanisti Yellowfin 

 mackerel tuna 



Fish species reportedly depredated 



Figure 3 



Percent of surveyed fishermen identifying fish species that are 

 depredated by bottlenose dolphins (Tursiops truncatus) in the 

 Florida king mackerel (Scomberomorus cavalla) fishery. No 

 individuals reported depredation of yellowfin tuna [Thunnus 

 albacares), and all of the fishermen reported depredation of at 

 least one of the listed fish species. 



of charter fishermen held this view (Fig. 5). A Mann 

 Whitney test indicated a significantly higher perceived 

 economic loss from depredation for commercial fisher- 

 men than for charter fishermen (P<0.001). 



Observations of dolphins 



We made observations from five charter boats in Islamo- 

 rada and from four charter and four commercial boats 

 along the east coast. We spent 41 hours conducting field 

 observations in Islamorada and 85 hours along the east 

 coast. We observed dolphins taking or attempting to take 

 catch, following the boat, feeding or milling near boat 

 with no interactions, and passing by the boat (Fig. 6). All 

 the observations of bottlenose dolphins following 

 the vessel occurred when the vessel was fishing 

 for king mackerel. 



We observed 15 fish taken or damaged by 

 bottlenose dolphins. Depredation by bottlenose 

 dolphins was characterized by an abnormal 

 jerk on the line after a fish was known to have 

 taken the bait. For charter fishermen, 6% of the 

 king mackerel catches were taken or damaged 

 by bottlenose dolphins. Depredation events oc- 

 curred more frequently on commercial fishing 

 vessels, where bottlenose dolphins took almost 

 20% of the king mackerel. We observed thirteen 

 depredation events on commercial vessels and 

 single depredation events while aboard charter 

 vessels on Florida's east coast and off Islamo- 

 rada. All depredation events occurred during 

 fishing operations for king mackerel. Only one 

 event occurred in Florida's state waters (within 

 three nautical miles from shore); all others oc- 

 curred between three and twelve nautical miles 

 offshore. In both study areas, the number of 

 dolphins observed while depredation occurred ranged 

 from one to three dolphins, although other dolphins 

 were often in the same area, following or engaging in 

 depredation with nearby fishing vessels. 



It proved impossible to photograph bottlenose dolphin 

 dorsal fins during acts of depredation, because of the 

 nature of the interaction. Bottlenose dolphins typically 

 remained too far from the vessel to allow useful pho- 

 tographs to be obtained. When a fish was caught, the 

 dolphins would swim rapidly towards the boat with 

 their dorsal fins directly below the surface in order to 

 take the fish. After taking the fish, the dolphins would 

 surface well away from the boat. 



Impact on the king mackerel fishery 



During the fifteen depredation events, we observed lost 

 and damaged fish and loss of gear, including line, lures, 

 hooks, and occasionally planers. Fishermen typically 

 responded to depredation by leaving the area or by ignor- 

 ing the bottlenose dolphins. In one instance, we observed 

 a charter boat captain shooting a gun into the water to 

 protect his catch and fishing gear. We also observed the 

 use of bird bangers, sound-creating devices similar to a 



