200 



Distribution and relative abundance of 

 sea turtles caught incidentally by the 

 U.S. pelagic longline fleet in the western 

 North Atlantic Ocean, 1992-1995 



Wayne N. Witzell 



Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



75 Virginia Beach Drive 



Miami, Florida 33149-1099 



E-mail address wayne witzellm'noaa gov 



aboard selected longline vessels 

 (Lee et al., 1995; Gerrior, 1996). Sea 

 turtle species identifications from 

 the logbook data were edited to in- 

 clude only leatherback, Dermochelys 

 coriacea, and loggerhead, Caretta 

 caretta, sea turtles. This decision 

 was based on the known distribu- 

 tion, abundance, and biology of sea 

 turtles in the area, and the fact that 

 some vessel captains and NMFS 

 observers were unable to identify 

 accurately all turtles encountered. 



The distribution and abundance of 

 threatened and endangered species 

 of sea turtles in offshore waters are 

 not well understood. Early oceano- 

 graphic flights designed to record 

 sea surface temperatures along the 

 Atlantic continental shelf by the 

 U.S. Coast Guard illustrated that 

 aerial surveys for large pelagic fish, 

 marine mammals, and sea turtles 

 were possible ( Deaver' ). Aerial sur- 

 veys have since proven a cost-effec- 

 tive method of obtaining observa- 

 tional data on sea turtles and have 

 helped researchers understand 

 basic distributional patterns (Hoff- 

 man and Fritts, 1982; Fritts et al.. 

 1983; Schroeder and Thompson, 

 1987; Shoop and Kenney, 19921. 

 Additional sources of pelagic sea 

 turtle data are fishery observer and 

 vessel logbook programs. The U.S. 

 Atlantic pelagic longline fishery for 

 tuna, Thunnus spp., and swordfish, 

 Xiphias gladius, incidentally cap- 

 tures threatened and endangered 

 sea turtles, which have either in- 

 gested baited hooks or become en- 

 tangled or hooked externally, or 

 both. This paper examines the sea- 

 sonal distribution and relative 



' Deaver, J. W. 1975. Aerial oceano- 

 graphic nb.servation.s, July 1969-.Junc 

 1970, Cape Cod, Massachusetts to Miami, 

 Florida. U.S. Dep. Trans., Coast Guard 

 Oceanogr. Unit, Oceanogr. Rep. CG .373- 

 68, 27 p. INTIS Accession No. AD-A014 

 415.1 



abundance of these turtles caught 

 incidentally by the U.S. Atlantic 

 pelagic longline fleet from 1992 

 through 1995. 



Materials and methods 



The fishery data used in this analy- 

 sis are from the National Marine 

 Fisheries Service (NMFS) pelagic 

 logbook program managed by the 

 Southeast Fisheries Science Cen- 

 ter, Miami Laboratory. The logbook 

 program was initiated in 1991 and 

 requires U.S. Atlantic longline ves- 

 sels to report daily catch and effort 

 data. Specific longline information 

 from the pelagic logbooks includes 

 target species, type of bait, set and 

 haulback dates and positions, 

 length of mainline, number and 

 lengths of gangions and floatlines, 

 and numbers of light sticks and 

 hooks set (Cramer, 1996). Sea turtle 

 bycatch information was added to 

 the logbook data form in 1992. Only 

 sets targeting tuna or swordfish, or 

 both, are analyzed here because the 

 shark longline fishery is signifi- 

 cantly different temporally, spa- 

 tially, and geographically. NMFS 

 logbook data for 1992-95 were ana- 

 lyzed by nine geographic fishing 

 areas established by the NMFS 

 Miami Laboratory (Fig. 1). Biologi- 

 cal data of captured turtles were pro- 

 vided by NMFS observers placed 



Results and discussion 



The typical Lf.S. pelagic tuna and 

 swordfish longline consists of a 

 mainline, suspended horizontally 

 by floats at a set depth, that has a 

 series of baited hooks hanging ver- 

 tically. The gears used for both tar- 

 get species are essentially the 

 same. However, swordfish fisher- 

 men generally work at night using 

 chemical light sticks suspended 

 above the hooks to attract bait fish 

 and tuna fishermen generally fish 

 during the day without light sticks. 

 Still, there are indications from log- 

 book data that some of the longline 

 fleet apparently target both tunas 

 and swordfish and alter fishing 

 strategies and gear configurations 

 depending on the main target spe- 

 cies, geographic location, and sea- 

 son (Hoey, 1983; Sakagawa et al., 

 1987). The U.S. pelagic longline 

 fishery has evolved over the years 

 from cumbersome New England 

 style gears to lighter Florida style 

 gears (Berkeley etal., 1981)andare 

 significantly different from the 

 gears used by the Japanese who 

 targeted bluefin tuna in the west- 

 ern Atlantic (Lopez et al., 1979; 

 Witzell, 1984). The gears currently 

 in use on U.S. vessels vary consid- 

 erably; they average about 47 km 

 long and have 429 hooks suspended 

 by 174 floats 54 m below the sur- 



Manuscript accepted 24 April 1998. 

 Fish. Bull. 97:200-211 (19991. 



