344 



Fishery Bulletin 104(3) 



30'0'0"N- 



from opening pot doors and taking bait 

 fish. Melvin et al. (1999) demonstrated 

 a reduction in seabird depredation of 

 salmon gill nets by combining the use of 

 acoustic devices and mesh panels strate- 

 gically placed in the upper portion of the 

 gillnet as a deterrent to seabirds. 



King mackerel are distributed along 

 the east coast of the United States from 

 Massachusetts to the Gulf of Mexico 

 and Caribbean Sea (Gold et al., 2002). 

 Two stocks of king mackerel occur in 

 Florida, one that migrates along the At- 

 lantic coast and the other that is found 

 in the Gulf of Mexico (Schaefer and 

 Fable, 1994; Gold et al., 2002). 



King mackerel are captured primar- 

 ily by trolling, in which a fishing ves- 

 sel trails several fishing lines — either 

 from fishing poles (on charter vessels) 

 or from reels (on commercial boats). 

 Both charter and commercial vessels 

 use outriggers that help to prevent en- 

 tanglement of multiple lines. Trolling 

 is generally considered to be a "clean" 

 fishery with little bycatch. By varying 

 the size of hooks, lures, and choice of 

 bait, fishermen effectively target particular species and 

 limit the bycatch of undesired species (Alverson et al., 

 1994). Nontarget species are generally released and 

 have a high probability of survival. 



Commercial fishing operations in the United States 

 yielded over 4.8 million pounds of king and cero mackerel 

 {Scomberomorus regalis) during 2001. This commercial 

 fishery was valued at almost seven million dollars, more 

 than half of which was landed in Florida (O'Bannon, 

 2002). During 2001-02, commercial fishermen captured 

 more than two million tons of Atlantic king mackerel, 

 sixty percent of which was caught in Florida, whereas 

 recreational fishermen reported catching about four mil- 

 lion tons of fish from the same stock, and about fifty-eight 

 percent of this catch was taken in Florida (NMFS*). 



Materials and methods 



Study sites 



We selected two coastal regions of Florida: 1) Islamorada 

 in the Florida Keys and 2) along the eastern coast, from 

 Fort Pierce south to Lake Worth Inlet, for our study 

 (Fig. 1). These regions represent areas in which commer- 

 cial and charter fisheries for king mackerel exist during at 



80 O'O'W 



(riilj ofMcxico 



Lake Wortli Inlcl 



N 

 S 



IN 



lamoradn 



5n jiii) 21 )0 Miles 



30 00"N 



80°0'0"W 

 Figure 1 



Survey area for bottlenose dolphin ^Tiiisiops truncatus) depreda- 

 tion on the king mackerel i Scomberomorus cavalla) fishery in 

 Florida. (Source of map: Florida Fish and Wildlife Conservation 

 Commission; adapted by present authors.) 



3 NMFS (National Marine Fisheries Service). 2003. Stock 

 assessment analyses on Spanish and king mackerel stocks, 

 147 p. Prepared for the 2003 mackerel stock assessment 

 panel meeting. Sustainable Fisheries Division Contribu- 

 tion SFD/2003-0008, NMFS, Southeast Fisheries Science 

 Center, Sustainable Fisheries Division, 75 Virginia Beach 

 Drive, Miami, FL 33149. 



least part of the year. Islamorada draws thousands of tour- 

 ists each year to its charter fleet; the east coast of Flor- 

 ida boasts a thriving commercial king mackerel fishery. 



Interviews with fishermen 



From March through June 2003, we interviewed fisher- 

 men, using the face-to-face method of Rea and Parker 

 (1997). We selected captains of offshore fishing charter 

 boats or commercial king mackerel fishermen in the 

 study sites to participate in this study. Because of the 

 multi-use nature of fishing vessels, we included com- 

 mercial, charter, and recreational vessels as options of 

 vessel type on the survey. 



Observations of dolphins 



We conducted observations from the flying bridge of the 

 charter boats and from the stern of the commercial ves- 

 sels from March to June 2003. We recorded positional 

 coordinates every 30 minutes with a hand-held GPS 

 unit. During each 30-minute interval, we recorded vessel 

 activity (transit to and from fishing grounds, or active 

 fishing) and further categorized the fishing activity, 

 depending on the target species. 



For each 30-minute period, we recorded the behavior 

 and estimated the number of dolphins sighted during the 

 interval. We defined the following behavioral categories: 



Depredation a dolphin was observed consuming bait 

 or captured fish from the lines 



Begging a dolphin approached a vessel in order 



to obtain food 



