NOTE Polovina et al.: Dive-depth distribution of Ccrretta carretta and Lepidochelys olivacea in the central North Pacific 



193 



tribution of two loggerhead sea turtles between nesting 

 periods off Japan indicated that virtually all their dives 

 were shallower than 30 m (Sakamoto et al., 1993). The 

 deeper-dive distribution of olive ridley sea turtles is also 

 consistent with their oceanic habitat, which is south of 

 the loggerhead habitat in the central portion of the sub- 

 tropical gyre. The oceanography of this region is char- 

 acterized by a warm surface layer, a deep thermocline 

 depth, and an absence of strong horizontal temperature 

 gradients and physical or biological fronts. It is likely 

 that the deeper diving seen in the olive ridley sea turtles 

 results from foraging at depths associated with the deep 

 scattering layer 



Acknowledgments 



We wish to acknowledge the NMFS observers who at- 

 tached the transmitters to the turtles; we also wish to 

 thank Shawn K. K. Murakawa and Shandell Eames who 

 assisted in observer training and logistics. 



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