Somatic growth model of juvenile loggerhead sea turtles Caretta caretta: duration of pelagic stage

The pelagic juvenile stage of sea turtles is poorly studied. We present a g rowth model and estimates for duration of the pelagic juvenile stage for lo ggerhead sea turtles Caretta caretta in the North Atlantic based on length- frequency analyses and sizes of young-of-the-year stranded in the Azores. T he size-specific growth model is a monotonic, nonlinear, declining function . The growth model is consistent with growth rates calculated from recaptur es of tagged loggerheads. Loggerheads leave the pelagic habitat and recruit to neritic habitats over a range of sizes from 46 to 64 cm curved carapace length (CCL). From this size range and the growth model, we estimate the d uration of the pelagic stage varies from 6.5 to 11.5 yr. Nonparametric smoo ths of the size frequency distributions of loggerheads in pelagic (n = 1692 ) and neritic (n = 1803) habitats intersect at 53 cm CCL, which is equivale nt to an 8.2 yr duration for the pelagic stage. More growth data from logge rheads <2 yr old would strengthen the database for our growth model and per haps lengthen our estimates of the duration of the pelagic stage. Incorpora ting our estimates for duration of the pelagic juvenile stage into the stag e-based population model developed for North Atlantic loggerheads would hav e a major effect on estimates of population growth.