Abstract. — In this study of the 

 feeding habits of the dusky dolphin, 

 Lagenorhynchus obscurus, stom- 

 ach content samples were collected 

 from dolphins caught by an 

 artisanal fishery operating along 

 the central coast of Peru. Collec- 

 tions were made from three fish- 

 ing ports, Pucusana, Ancon, and 

 Cerro Azul, during the summers 

 and winters of 1985 and 1986. 

 Overall, the anchoveta, Engraulis 

 ringens, the most abundant verte- 

 brate in Peruvian coastal waters, 

 was the principal prey of dusky 

 dolphins with respect to each of 

 four different measures of dietary 

 importance. Anchoveta was also 

 the dominant prey in both seasons 

 of both years, and for all reproduc- 

 tive classes of dusky dolphins. 

 Other prey species commonly found 

 in dolphin stomachs were horse 

 mackerel, Trachurus symmetricus, 

 hake, Merluccius gayi, sardine, 

 Sardinops sagax, Patagonian 

 squid, Loligo gahi, and jumbo fly- 

 ing squid, Dosidicas gigas. Regres- 

 sions of body size on otolith or squid 

 beak dimensions were used to es- 

 timate lengths and weights of an- 

 choveta and some other prey. All 

 prey species averaged less than 30 

 cm in estimated length and 300 g 

 in weight. Estimated total lengths 

 of anchoveta consumed as prey in- 

 creased between seasons in 1985 

 and between years, paralleling the 

 lengths of anchoveta taken by the 

 purse-seine fishery. However, esti- 

 mated total lengths of anchoveta 

 eaten by dusky dolphins were con- 

 sistently smaller than lengths of 

 those caught by the fishery. 



Feeding habits of the dusky 

 dolphin, Lagenorhynchus obscurus, 

 \n the coastal waters of central Peru 



Jeff McKinnon 



Department of Zoology, The University of Guelph 

 Guelph, Ontario, Canada NIG 2W1 



Present address The Biological Laboratories, Harvard University 



1 6 Divinity Ave, Cambridge, MA 02 1 38 



Manuscript accepted 11 November 1993. 

 Fishery Bulletin 92:569-578 ( 1994). 



The dusky dolphin, Lagenorhyn- 

 chus obscurus, is common in the 

 coastal waters of New Zealand, 

 South America, and South Africa, 

 but like most species of small 

 cetacea from the Southern Hemi- 

 sphere, its feeding habits are poorly 

 described (Gaskin, 1982; Goodall 

 and Galeazzi, 1985). The squid, 

 Nototodarus sloanei, and fish have 

 been reported as prey in New 

 Zealand waters (Gaskin, 1972), 

 whereas in Argentina Wiirsig and 

 Wiirsig ( 1980) observed dusky dol- 

 phins feeding on southern anchovy, 

 Engraulis anchoita. Prior to the 

 present study, little was known of 

 the feeding habits or natural history 

 of the dusky dolphin in Peruvian 

 waters, although large numbers of 

 dusky dolphins were being taken in 

 an artisanal fishery ( Read et al., 1988; 

 Van Waerebeek and Reyes, 1990). 



In Peru, the dusky dolphin is 

 found in the waters of the coastal 

 upwelling system (McKinnon, 

 1988), which has been extensively 

 studied by those involved in man- 

 aging the system's various fisheries 

 (Pauly and Tsukayama, 1987; Pauly 

 et al., 1989). The cool waters of the 

 coastal upwelling region constitute 

 one of the most productive areas of 

 the world ocean (Ryther, 1969), but 

 oceanographic conditions and the 

 abundance and distribution of 

 fishes can vary greatly within and 

 between years, especially when El 

 Nino's occur (Pauly and Tsukaya- 

 ma, 1987; Pauly et al., 1989). 



The objective of the present study 

 was to characterize, in terms of both 

 species composition and prey size, 

 the feeding habits of the dusky dol- 

 phin in Peruvian waters. Seasonal 

 and annual variation in feeding 

 habits was also investigated and 

 compared with abundance data for 

 important prey species during the 

 same periods. In addition, potential 

 dietary differences among dolphins 

 of different reproductive states were 

 examined, as feeding habits of lac- 

 tating females differ from those of 

 nonlactating females and males in 

 some small cetaceans (Bernard and 

 Hohn, 1989; Recchia and Read, 

 1989). 



Methods 



Data on feeding habits were ob- 

 tained by analysis of undigested 

 hard parts of prey, specifically fish 

 otoliths and squid beaks, from stom- 

 ach content samples collected 

 through the fishery. Dolphins were 

 usually captured by artisanal fish- 

 ermen in gill nets set from dusk to 

 dawn within the coastal upwelling 

 zone (Read et al., 1988; Van Waere- 

 beek and Reyes, 1990), but six stom- 

 ach samples from a single landing 

 by a purse seiner, in the summer of 

 1985, were also included. 



All samples were collected at 

 ports along the central coast of 

 Peru, where the largest dolphin 

 catches occurred during the present 



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