MEPS 321:283-293 (2006)  -  doi:10.3354/meps321283

Importance of local production versus pelagic subsidies in the diet of an isolated population of bottlenose dolphins Tursiops sp.

Susan Mærsk Lusseau1,2, Stephen R. Wing1,*

1Department of Marine Science, PO Box 56, University of Otago, Dunedin, New Zealand
2Lighthouse Field Station, University of Aberdeen, School of Biological Sciences, George Street, Cromarty IV11 8YJ, UK
*Corresponding author. Email:

ABSTRACT: Isolated populations can be strongly influenced by patterns in the local production of food, and by subsidies from outside sources. We used stable-isotope analysis to investigate the relative importance of autochthonous food resources versus pelagic subsidies in the diet of the isolated population of bottlenose dolphins Tursiops sp. inhabiting Doubtful Sound, New Zealand. Samples of the primary carbon sources (macroalgae, phytoplankton and chemoautotrophs) as well as potential food sources (fish and squid) were collected from Doubtful Sound and analysed for δ13C and δ15N. Isotopic signatures of fishes fell along a gradient from very depleted values for deep benthic species, particularly hagfish Eptatretus cirrhatus13C –23.6, δ15N 6.3), to intermediate values for pelagic species (δ13C –18.1, δ15N 11.3) and more enriched values for reef-associated species (δ13C –16.1, δ15N 14.4). Exfoliated skin tissue was collected from live dolphins (n = 11) and used to estimate the isotopic signature of dolphin diet (δ13C –15.4, δ15N 14.2). The position of this estimate at the most enriched end of the range of isotopic signatures indicated that there was likely minimal mixing of resources from different habitats and that a majority of the dolphin population’s diet came from rocky reef and demersal habitats. Estimates of δ13C and δ15N for dolphin diet were compared with isotopic signatures of the different primary carbon sources using a multiple-source mixing model. Both results suggest that the diet of this population was primarily made up of autochthonous carbon production with a large contribution from benthic macroalgae, rather than pelagic subsidies from outside of the Sound.

KEY WORDS: Bottlenose dolphin · Diet · Fjord · Stable isotopes · Isolated population

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