Variability in the diet of common dolphins (Delphinus delphis) in Galician waters 1991- 2003 and relationship with prey abundance

No abstracts are to be cited without prior reference to the author.

Analyses of marine mammal diets in Galician waters have been carried out over the last 13 years as part of four consecutive European funded projects. The species that is best represented in samples from stranded animals is the common dolphin Delphinus delphis, for which 414 non-empty stomachs were analysed during 1991-2003. We quantified interannual and seasonal variation in the diet, as well as differences between the diets of male/female and juvenile, sub-adult and adult dolphins. Although sampling is based on stranded dolphins, the majority showed evidence of having died as a consequence of interactions with fisheries (by-catch). The influence of cause of death on stomach contents was examined. The most important prey species were (small) blue whiting (Micromesistius poutassou), sardine (Sardina pilchardus) and scad (Trachurus sp.), all of high commercial importance in Galician waters, and (in the first quarter of the year), sand smelt Atherina sp. Interannual trends in the importance of sardine in the diet of common dolphins appear to track trends in spawning stock biomass. Preliminary estimates are also made for the amount of fish removed by the common dolphin population in Galician waters.