Feeding habits of two sympatric dolphin species off North Patagonia, Argentina

ROMERO, MARÍA ALEJANDRA; DANS, SILVANA L.; GARCÍA, NESTOR; SVENDSEN, GUILLERMO M.; GONZÁLEZ, RAÚL; CRESPO, ENRIQUE A.

MARINE MAMMAL SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2012 vol. 28 p. 364 - 377

0824-0469

The marine community of North Patagonia has undergone an increase in fishingeffort since the 1970s, with the development of several high-sea fisheries thattarget hake, Merluccius hubbsi, and squid, Ilex argentinus. When the first signs ofoverexploitation appeared at the end of the 1990s alternative target species like theArgentine anchovy, Engraulis anchoita, started to be explored. Even though the effortwas low, the use of mid-water trawls on this target led to the highest probability ofdolphin entanglement among all the types of fishing gear. Both common and duskydolphins were affected suggesting an overlap in time and space of these delphinids,their prey, and the fishery (Crespo et al. 2000).This paper provides an appraisal of the diet and feeding habits of common anddusky dolphins, two sympatric species inhabiting North Patagonia, in order toanalyze how these species are using the available food resources.For the diet analysis, 30 stomachs of common dolphins were collected in 1999and in 2003?2009 along the northern area off Patagonia. The animalswere obtained from two sources: strandings (6 females and 3 males) and fisheriesbycatch (7 females and 14 males). The bycatch was mostly by mid-water trawlerstargeting Argentine anchovy, but one dolphin was caught by a hake mid-waterlongline vessel. Eighteen were caught in January 1999, between 40◦30_?41◦30_Sand 61◦00_?61◦40_W. Diet composition of dusky dolphins was based on the analysis of contents of 31 stomachs. Information was available from the study of feeding habits of duskydolphins by Koen Alonso et al. (1998), as well as additional individuals collected morerecently. Analysis of the feeding strategy based on the Amundsen graphical method shows that common and dusky dolphins off North Patagonia exhibited a mixed feedingpattern with a dominance of Argentine anchovy. SA long-fin squid occurredat high frequency (%FO) but only accounted for a small proportion of the food whenpresent. Comparing the information about dusky dolphins feeding in Central Patagonia(Koen Alonso et al. 1998) with northern samples, some differences in feeding strategywere found. The southern dusky dolphins showed less preference forArgentine anchovy, with a more generalist feeding strategy. Opposite to that foundfor common and dusky dolphins in North Patagonia, the diet of southern dusky dolphinswas based on a mixture of fish and cephalopods in similar proportions (KoenAlonso et al. 1998). This study represents the first attempt at quantifying the diet and feeding habits of short-beaked common dolphins, D. delphis, off North Patagonia, the austral limit oftheir distribution. It goes beyond the description of the diet of this species addressingthe question of how it is sharing resources with a sympatric delphinid, the duskydolphin, L. obscurus. In spite of the small sample size of this species, the descriptionand brief quantification of the diet of dusky dolphin provides essential information fortheir conservation and management in an area where little is known about delphinidspecies