Publisher :
Place of publication :
Publication year : 2009
Thematic : Fisheries
Language : English
Note
For immature animals, diet quality and composition influence expression of life history traits such as growth
rates and ultimately life stage duration and age to maturity. Circumglobally distributed loggerhead turtles
(Caretta caretta) exhibit a multi-decade immature stage that generally occupies neritic habitats and is
characterized by slow growth and an omnivorous diet. Although adult nesting populations are geographically
distinct, foraging areas for immature loggerheads show a high degree of mixing of individuals that originate
from multiple nesting stocks. Furthermore, despite their generalist foraging ecology, immature loggerheads
have been observed to supplement their natural diets with fish from fishery discards and/or caught in fishing
gear. However, whether trophic opportunism results in variation in loggerhead growth rates within or among
feeding areas has not been investigated. In Core Sound, North Carolina (NC), USA, immature loggerheads
demonstrate highly variable size-specific growth rates, in contrast to other studies that report discernible
somatic growth functions in immature marine turtles. To determine whether inter-individual variation in
growth rates at this site was due to variation in diet composition, and specifically variation in consumption of
fish, we analyzed carbon and nitrogen stable isotope ratios of loggerhead blood plasma and of tissue samples
of putative loggerhead prey, as well as commercially important fish species. Our results indicated that growth
rates were not related to trophic levels at which individual turtles fed, but rather probably reflected interindividual
variation in overwintering or foraging behavior (i.e. nearshore vs. offshore). Furthermore,
loggerhead diets were highly diverse, and comprised mainly blue crabs and/or whelks, as well as small
proportions of cannonball jellies. Fish were unimportant dietary components for loggerheads. Although
loggerheads in NC do not appear to feed on fish catch or discards, immature turtles showed dietary
preferences for prey items that are also valuable to or are commonly taken as bycatch in commercial fisheries
(e.g. blue crabs and whelks, respectively) in the region. Thus, the status of these prey items/fishery stocks as
well as trends in loggerhead populations should be monitored to mitigate potential competitive interactions
between fisheries activities and loggerhead turtles.
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Keywords : marine-conservation
Encoded by : Pauline Carmel Joy Eje
