Demographic implications of alternative foraging strategies in juvenile loggerhead turtles Caretta caretta of the North Pacific Ocean

摘要

To assess the potential demographic consequences of alternative juvenile foraging strategies in loggerhead sea turtles Caretta caretta, we compared habitat selection, movement, size frequency, and diet of juvenile loggerheads in neritic versus oceanic habitats of the North Pacific. Forty juveniles satellite-tracked from neritic habitat revealed utilization distributions 2 orders of magnitude smaller than those of 26 juveniles of the same size class tracked for similar durations from oceanic habitat. Oceanic juveniles traveled significantly further, faster and straighter, experienced lower sea surface temperature and productivity, and consumed prey of much lower energy density, strongly suggesting that the neritic foraging strategy is energetically favorable. These findings combined with those from other studies suggest that the neritic strategy would result in higher growth and eventually higher fecundity. Manipulation of a loggerhead demographic model indicated that small disadvantages in survivorship for neritic juveniles could balance the relatively large advantages in growth and fecundity of the neritic strategy. The oceanic strategy may persist as a slower but safer life history strategy. Our findings underscore the importance of elucidating variation in the ecology and corresponding vital rates of juveniles for modeling, managing, and conserving migratory megafaunal populations.