189 



Dive-depth distribution of 



loggerhead (Carretta carretta) 



and olive ridley iLepidochelys olivacea) 



sea turtles in the central North Pacific: 



Might deep longline sets catch fewer turtles? 



Jeffrey J. Polovina 



Honolulu Laboratory 



Southwest Fisheries Science Center 



National Manne Fisheries Service, NOAA 



2570 Dole Street 



Honolulu, Hawaii 96822 2396 



E mail address: Jeffrey Polovinarainoaa gov 



Evan Howell 



Denise M. Parker 



Joint Institute for Marine and Atmospheric Research 

 University of Hawaii 

 1000 Pope Road 

 Honolulu, Hawaii 96822 



George H. Balazs 



Honolulu Laboratory 



Southwest Fisheries Science Center 



National Manne Fishenes Service, NOAA 



2570 Dole Street 



Honolulu, Hawaii 96822-2396 



The Hawaii-based longline fishery oper- 

 ates over a large area in the central 

 North Pacific, from the equator to lat- 

 itude 45°N, between longitudes 130°W 

 and 180°W. In 2000, 125 vessels were 

 active in the fishery, producing total 

 landings estimated at 24 million 

 pounds and exvessel (wholesale) reve- 

 nues of $50 million. The target species 

 include bigeye tuna (Thunnus obesus), 

 yellowfin tuna (7^ albacares), and alba- 

 core tuna (T! alalunga), and swordfish 

 (Xiphias gladius ). 



Caught incidentally with these target 

 species are leatherback (Dermochelys 

 coriacea ), loggerhead ( Carretta carretta), 

 olive lidley iLepidochelys olivacea), and 

 green iChelonia mydas) sea turtles. 



Over the period 1994-99, it was es- 

 timated that an annual average of 418 

 loggerhead, 112 leatherback, 146 olive 

 ridley, and 40 green sea turtles were 

 caught in the Hawaii-based longline 

 fishery (McCrackenM. 



Historically, the Hawaii longline 

 fishery has set longlines considerably 

 shallower than 100 m to target sword- 

 fish (Xiphias gladius) or substantially 

 deeper than 100 m to target bigeye 

 tuna. Incidental bookings of logger- 

 head turtles have been reported in 

 the Hawaii longline fishery observer 

 data, which cover about 5% of the 

 total annual effort. Analyses of these 

 data found that loggerhead turtles 

 were caught only when gear was set 

 shallow enough to target swordfish, 

 primarily in the northern portion of 

 the fishing ground. No loggerhead sea 

 turtles were caught when longline gear 

 was set deep to target bigeye tuna, 

 primarily in the southern portion of 

 the fishing ground. These analyses sug- 

 gest that a ban of shallow sets in the 

 fishery since 1 April 2001 may reduce 

 future incidental catches of loggerhead 

 sea turtles. However, analyses based 

 only on observer data suffer from the 



limited observer coverage and the de- 

 pendence between depth of setting and 

 area fished. For example, swordfish are 

 targeted at night in the north, whereas 

 tuna are targeted during the day in the 

 south. To better understand the depths 

 inhabited by sea turtles, we used div- 

 ing depth distributions collected from 

 satellite-linked dive recorders attached 

 to two loggerhead and two olive ridley 

 sea turtles caught and released in 

 the Hawaii-based longline fishery. Al- 

 though other studies on the dive depths 

 of olive ridley and loggerhead sea tur- 

 tles have been conducted in the Pacific, 

 these have been conducted with sea 

 turtles in coastal areas rather than in 

 the oceanic central Pacific (Sakamoto et 

 al, 1993; Beavers and Cassano, 1996). 



Materials and methods 



We attached Wildlife Computer Argos 

 satellite-linked depth recorders (SDR- 

 TIO) to two loggerhead and two olive 

 ridley sea turtles that had been caught 

 with commercial longline fishing gear. 

 One loggerhead and one olive ridley 

 were hooked in the mouth and were 

 released after the hook and line had 

 been removed. The other loggerhead 

 and olive ridley sea turtle had deeply 

 ingested hooks, and for both of these 

 turtles the fishing line was cut close 

 to the mouth but the hook was not 

 removed. Trained observers on the 

 fishing vessel attached transmitters 

 to the carapace of each of the four sea 

 turtles, using fiberglass cloth strips 

 and polyester resin patterned after 

 the method presented in Balazs et al, 

 (1996). The observers noted that all 

 four sea turtles swam vigorously away 

 after release. 



' McCrackca, M. L. 2000. Estimation of 

 sea turtle take and mortality in the Ha- 

 waiian longline fisheries. Southwest Fish. 

 Sci. Cent. Admin. Rep. H-00-06. 29 p. 

 Southwest Fish. Sci. Cent., Honolulu Lab., 

 Natl. Mar. Fish. Serv., NOAA, Honolulu, 

 HI 96822-2396. 



Manuscript accepted 20 September 2002. 

 Fish. Bull. 101 (1):189-193 (2003). 



