Overfishing of small pelagic fishes increases trophic overlap between immature and mature striped dolphins in the Mediterranean Sea

Gómez-Campos, Encarna; Borrell, Assumpció; Cardona, Luis; Forcada, Jaume ORCID: https://orcid.org/0000-0002-2115-0150; Aguilar, Alex. 2011 Overfishing of small pelagic fishes increases trophic overlap between immature and mature striped dolphins in the Mediterranean Sea. PLoS One, 9 (6), e24554. 9, pp. 10.1371/journal.pone.0024554

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Abstract/Summary

The interactions among diet, ecology, physiology, and biochemistry affect N and C stable isotope signatures in animal tissues. Here, we examined if ecological segregation among animals in relation to sex and age existed by analyzing the signatures of δ15N and δ13C in the muscle of Western Mediterranean striped dolphins. Moreover, we used a Bayesian mixing model to study diet composition and investigated potential dietary changes over the last two decades in this population. For this, we compared isotope signatures in samples of stranded dolphins obtained during two epizootic events occurring in 1990 and 2007–2008. Mean δ13C values for females and males were not significantly different, but age-related variation indicated δ13C enrichment in both sexes, suggesting that females and males most likely fed in the same general areas, increasing their consumption of benthic prey with age. Enrichment of δ15N was only observed in females, suggesting a preference for larger or higher trophic level prey than males, which could reflect different nutritional requirements. δ13C values showed no temporal variation, although the mean δ15N signature decreased from 1990 to 2007–2008, which could indicate a dietary shift in the striped dolphin over the last two decades. The results of SIAR indicated that in 1990, hake and sardine together contributed to 60% on the diet of immature striped dolphins, and close to 90% for mature striped dolphins. Conversely, the diet of both groups in 2007–2008 was more diverse, as hake and sardine contributed to less than 40% of the entire diet. These results suggest a dietary change that was possibly related to changes in food availability, which is consistent with the depletion of sardine stocks by fishing.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1371/journal.pone.0024554
Programmes:	BAS Programmes > Polar Science for Planet Earth (2009 - ) > Ecosystems
ISSN:	1932-6203
Additional Information. Not used in RCUK Gateway to Research.:	Open access article made available under a CC-BY Creative Commons Attribution license.
NORA Subject Terms:	Marine Sciences Biology and Microbiology
Date made live:	18 Oct 2011 11:02 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/15369

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