Population characteristics and seasonal migrations of leatherback sea turtles at high latitudes

Efforts to model populations of the leatherback sea turtle Dermochelys coriacea and design appropriate conservation measures for this endangered species have been hindered by a lack of information on in-water (vs. nesting) population characteristics. We present the first synthesis of population characteristics of leatherbacks at high latitudes. During 8 seasons of fieldwork (1999 to 2006) off Nova Scotia, Canada, we collected biological data from 152 turtles, including 127 live-captured individuals. The size-class distribution mainly represented large sub-adult and adult individuals (mean curved carapace length = 148.1 cm). Mean body mass was 392.6 kg (range: 191.9 to 640 kg). We found a significantly female-biased sex ratio (1.86 females: 1 male) among mature turtles. We expect that there may be geographical variation in sex ratios of foraging populations reflecting breeding periodicity, distance from nesting areas, and associated migration patterns. Tag recoveries from 25 leatherbacks captured off Canada reveal nesting origins throughout South and Central America and the Caribbean. Recapture data suggest that although some female turtles proceed to Canadian waters within several months of nesting (in the same calendar year), entry into high-latitude coastal waters of the western Atlantic may more regularly occur later in the nesting remigration interval. Comparison of data from leatherbacks off Canada with those from a foraging population at similar latitudes off France reveals unequal size-class distributions, which may reflect the different thermal regimes in these areas.