Journal of the Marine Biological Association of the United Kingdom

Diet

Feeding ecology of striped dolphins, Stenella coeruleoalba, in the north-western Mediterranean Sea based on stable isotope analyses

A.M. Meissnera1a2a3 c1, C.D. MacLeoda1, P. Richarda2, V. Ridouxa2 and G. Piercea4a5

a1 Institute of Biological and Environmental Sciences (IBES), University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen, AB24 3JG, UK

a2 Littoral, Envinnement et Sociétés, UMR 6250 CNRS-Université de La Rochelle, 17000 La Rochelle, France

a3 Centre de Recherche sur les Cétacés-Marineland, 306 Avenue Mozart, 06600 Antibes, France

a4 Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, PO Box 1552, 36200, Vigo, Spain

a5 Oceanlab, University of Aberdeen, Main Street, Newburgh, Aberdeenshire, AB41 6AA UK

Abstract

The feeding ecology of striped dolphin, Stenella coeruleoalba, in the north-western Mediterranean Sea was studied using stable isotope analyses. Carbon and nitrogen stable isotope ratios were measured in skin and muscle tissues of stranded and by-caught dolphins from six geographical areas in the Mediterranean Sea and Atlantic Ocean. Variation in δ15N in relation to dolphin size is attributed to changes in diet. Nursing calves have a higher trophic level than weaned animals and their δ15N values decrease progressively until weaning, estimated to be at a body length of around 155 cm. δ15N values then increased for larger individuals which suggests changes in diet for mature dolphins. Geographical differences in diet were apparent between the Atlantic and the Mediterranean, although no clear differences were apparent between the five Mediterranean areas. Comparisons of the nitrogen isotope ratios of skin and muscle highlighted a higher fractionation in skin compared to the muscle tissue. Values of δ13C also increased with body length although it appears that this is not only driven by trophic level enrichment. δ13C increases before weaning and the difference in trophic level between newly-weaned and mature dolphins was twice as high for carbon as for nitrogen. Ontogenetic changes in carbon isotope composition may therefore be driven by feeding on deep water prey and dolphin movements outside the coastal feeding grounds. Indeed, seasonal variations in δ13C are suspected to be driven by migration within the Mediterranean basin.

(Received July 27 2009)

(Accepted July 04 2011)

(Online publication September 13 2011)

Keywords

  • striped dolphin;
  • Stenella coeruleoalba ;
  • feeding ecology;
  • nitrogen and carbon stable isotopes;
  • skin;
  • muscle;
  • north-western Mediterranean Sea