Parker et al.: Diet of Caretta caretta in the central North Pacific 



143 



60 N 



40 C N 



20° N 



0°N 



20°N 



40'N 



O less than 50 cm CCL 

 • 50 cm CCL or greater 



120°E 



160°E 



160W 



120°W 



80°W 



Figure 1 



Distribution of loggerhead sea turtles {Caretta caretta) incidentally captured in the 

 international high seas driftnet fishery in the central North Pacific Ocean. Turtles 

 smaller than 50 cm curved carapace length (CCL) are shown as open diamonds 

 and those larger than 50 cm CCL are shown as black circles. 



(TZCF), is an area of concentrated phytoplankton that 

 also collects and attracts a variety of neustonic and oce- 

 anic organisms — many of which may be potential prey 

 times, as well as predators, of oceanic-stage loggerhead 

 sea turtles in the Pacific. Polovina et al. (2000, 2004) 

 have suggested that the turtles are foraging along the 

 TZCF. 



The duration of the juvenile oceanic stage for logger- 

 head sea turtles in the Pacific is currently unknown. In 

 the Atlantic, juvenile turtles inhabit the oceanic zone 

 for approximately 10 years (Bjorndal et al., 2000). Based 

 on growth analyses (Zug et al., 1995; Chaloupka, 1998), 

 it is probable that this sea turtle from the Pacific can 

 have a similar extended oceanic stage, which in some 

 cases may last until sexual maturity (30+ years). 



Understanding the diets of sea turtles is important 

 for their conservation. Foraging studies have been done 

 with oceanic-stage turtles in the Atlantic (Van Nierop 

 and den Hartog, 1984). However, there is a paucity of 

 information regarding the foraging ecology of oceanic- 

 stage loggerhead sea turtles in the Pacific. Such infor- 

 mation can help identify important food resources and 

 foraging areas necessary for guiding decisions regarding 

 the management of endangered sea turtle populations 

 (Bjorndal, 1999). The objective of the present study is to 

 determine the diet composition of loggerhead sea turtles 

 from the central North Pacific Ocean and to discuss the 

 possibility of interactions between these turtles and 

 commercial fisheries that may occur as a result of the 

 foraging behavior of these sea turtles. 



Method 



National Marine Fisheries Service (NMFS) observers 

 between 1990 and 1992 obtained 52 dead loggerhead 

 sea turtles. These specimens were taken as bycatch 

 in the international high-seas driftnet fishery, which 

 targeted squid and albacore (Wetherall et al., 1993). 

 NMFS observers recorded capture position and sea sur- 

 face temperature aboard commercial driftnet vessels. 

 Samples were collected between latitude 29.5°N and 

 43°N and longitude 150°E and 154°W (Fig. 1). A total of 

 10 whole specimens and 42 excised stomachs were frozen 

 and transported to a Honolulu laboratory for analysis. 

 Stomachs were removed from whole specimens and all 

 stomachs were examined from anterior to posterior. 

 Gross observations of stomach contents were made and 

 the contents were sorted to the lowest identifiable taxo- 

 nomic level by using a dissecting microscope. Major fauna 

 were identified, quantified by volume, and the percent 

 contribution (to stomach contents) of each major organ- 

 ism was calculated (Forbes, 1999). Presence of jellyfish 

 or other jellies were identified by presence of tentacles, 

 nematocysts, and whole or partial individuals. Planes 

 spp. were identified from descriptions of Spivak and Bas 

 (1999). Frequency of occurrence of major components was 

 calculated by dividing the number of stomachs in which 

 the prey item occurred by the total number of turtle 

 stomachs examined. Percent sample volume was calcu- 

 lated for all prey items by summing the total volume of 

 each prey item and dividing it by the total volume of all 



