Smaller longer, larger shorter: energy budget calculations explain intrapopulation variation in remigration intervals for loggerhead sea turtles (Caretta caretta)

Abstract

Adult female loggerhead sea turtles ( Caretta caretta (L., 1758)) show a size-related behavioural and trophic dichotomy within several populations: oceanic planktivory by small females and neritic benthivory by large females. Within a Japanese population, smaller females have longer remigration intervals (the intervals between successive nesting years) than larger females. We hypothesized that this is attributed to the size-related foraging dichotomy, and calculated energy budgets and food requirements for the small and large females. Total reproductive energy costs for the small and large females were 1003 and 434 MJ, equivalent to 4043 kg of planktonic items and 275 kg of benthic items, respectively. The minimum durations necessary for accumulating the total reproductive energy for the small and large females were 430 and 26 days, equivalent to remigration intervals of 2 years and 1 year taking into account the nesting and migration durations and seasonal reproduction. Therefore, it was theoretically demonstrated that the intrapopulation variation in remigration intervals for Japanese loggerheads could be caused by the difference in their feeding habits, implying that remigration dynamics in a sea turtle population that shows a foraging dichotomy is regulated by feeding conditions not in a single habitat but in multiple habitats.

Movement Patterns for a Critically Endangered Species, the Leatherback Turtle (Dermochelys coriacea), Linked to Foraging Success and Population Status

“…A trophic dichotomy has similarly been identified in adult female loggerhead turtles, where oceanic planktivory occurred in small females and neritic benthivory by large females [51]. Energy budget calculations indicated the small oceanic females required almost 17 times longer to accumulate the necessary energy for reproduction than the large benthivorous females, which accounted for the intrapopulation variation in remigration intervals [51]. The relatively small size, long remigration intervals, and oceanic foraging of the EP leatherback females [5], suggests that this may also apply to this population and that the less energetically profitable oceanic strategy is currently dominant.…”

“…This implied differences in their choice of feeding habitats, with an offshore North Atlantic group and a more coastal West African group. A trophic dichotomy has similarly been identified in adult female loggerhead turtles, where oceanic planktivory occurred in small females and neritic benthivory by large females [51]. Energy budget calculations indicated the small oceanic females required almost 17 times longer to accumulate the necessary energy for reproduction than the large benthivorous females, which accounted for the intrapopulation variation in remigration intervals [51].…”

Dispersal and dive patterns during the post-nesting migration of olive ridley turtles from French Guiana

“…In other Chelonidea species, intra-population phenotypic differences have been related to variation in migration patterns: larger turtles perform neritic migrations, whereas smaller turtles perform oceanic migrations (Hatase et al 2002, Hawkes et al 2006, Hatase & Tsukamoto 2008, Zbinden et al 2011, Richardson et al 2013). In our study, the lack of relation between individual biometrics and migration patterns may have resulted from the fact that all turtles shared the same neritic pattern.…”

“…Yet it is still unclear how sea turtles assess and/or compensate for such environmental forcing processes (Gaspar et al 2006, Galli et al 2012. Furthermore, post-nesting migration patterns may vary intra-specifically, in relation with phenotypic factors such as gender (Shaver et al 2005, Van Dam et al 2008 or body size (Hawkes et al 2006, Hatase & Tsukamoto 2008, Zbinden et al 2011, Rees et al 2012, Richardson et al 2013.…”

Environmental and anthropogenic impacts on intra-specific variation in leatherback turtles: opportunities for targeted research and conservation

“…A possible analogy to this scenario was reported by Caut et al (2008), who used stable isotope analyses to assign leatherbacks from 1 nesting colony in French Guiana to 2 distinct foraging groups that differed according to their remigration intervals. Similarly, in a Japanese nesting rookery of loggerhead turtles Caretta caretta, individual turtles with 3 yr remigration intervals were associated with relatively poorer quality foraging grounds and prey availability, while turtles with 2 yr remigration intervals occupied higher quality foraging habitats (Hatase & Tsukamoto 2008). Thus, variation in environmental conditions, differences in migratory strategies among individual leatherbacks, and anthropogenic pressures can be manifested in observed differences in life history traits within and among conspecific populations.…”