372 
Fishery Bulletin 96(2), 1998 
1994). Dolphins in this study were caught off central 
Patagonia throughout the year between 43°S and 
46°30'S; thus dusky dolphins appear to feed on Ar- 
gentine anchovies from the Patagonian stock. The 
absence of a well-defined seasonal migration pattern 
in Argentine dusky dolphins (Wtirsig and Wiirsig, 
1980) could be related to predation on the Patagonian 
stock of Argentine anchovy. However, long-distance 
movements of two dusky dolphins have been recorded 
after several years in Argentine waters (Wiirsig and 
Bastida, 1986). 
The Argentine shortfin squid is a neritic-oceanic 
species, distributed from 30°S to 54°S (Rodhouse and 
Hatfield, 1990). At least three spawning stocks, 1) 
the bonaerensis to north Patagonian (early winter), 
2) the south Patagonian (winter), and 3) the sum- 
mer spawning stock (Nigmatullin, 1989; Brunetti et 
al., 1991; Brunetti and Ivanovic, 1992) have been 
described over the Argentine Continental Shelf. The 
latter spends its entire life cycle over the continen- 
tal shelf, the former two have their spawning grounds 
on the shelf break and in oceanic waters. Their lar- 
vae and juveniles grow and mature over the conti- 
nental shelf (Nigmatullin, 1989; Rodhouse and 
Hatfield, 1990; Brunetti and Ivanovic, 1992). The 
shortfin squids captured by dolphins could belong to 
any of the spawning stocks because their distribu- 
tions overlap in the area where dolphins were caught. 
In addition, the size of squids eaten by dolphins cor- 
responds with that for juvenile squids from all spawn- 
ing stocks. These juvenile squids are pelagic (Brunetti 
and Ivanovic, 1992; Ivanovic and Brunetti, 1994) and 
can be found mostly between the 50- and 100-m 
isobaths (Brunetti and Ivanovic, 1992). 
The Patagonian squid is a neritic species and its 
life cycle is associated with the Malvinas Current 
over the continental shelf and slope (Hatfield et al., 
1990). Its spawning grounds are in shallow and 
coastal waters, and it migrates to deeper waters to 
grow, reaching maturity at sizes larger than 10 cm 
of DML (Hatfield et al., 1990). Patagonian squids 
eaten by dusky dolphins were mostly of small size; 
thus feeding on this species could occur as juveniles 
migrate from the coastal area to deeper feeding 
grounds beyond the shelf break. 
The main TL peak for Argentine hake eaten by 
dolphins corresponds to the age-0 group. This group 
exhibits pelagic schooling behavior (Angelescu and 
Prenski, 1987). Moreover, juveniles do not follow the 
adult hake migration pattern but remain in their 
nursery grounds (south of the Golfo San Jorge and 
Isla Escondida area) (Angelescu and Prenski, 1987). 
In sum, these results indicate that dusky dolphins 
of Patagonia feed mostly on species whose stages 
exhibit pelagic and schooling behavior. 
Finally, Argentine hake, Argentive anchovy, and 
squids are key species in the trophic web of the Pata- 
gonian Continental Shelf ecosystem and seem to 
present some degree of association (Angelescu and 
Prenski, 1987). Peneid crustaceans, like the shrimp, 
appear to be associated with these species in the study 
area even when their abundance is comparatively less 
(Angelescu and Prenski, 1987). Shrimp were not found 
in dolphins stomachs, even when they were caught in- 
cidentally in shrimp hauls. There are no data about 
the behavior of the dolphins at the moment of the catch, 
but the absence of shrimp in the diet suggests that dol- 
phins avoid shrimp as a prey. 
Acknowledgments 
The authors are indebted to Silvana L. Dans for her 
critical readings and helpful comments on an earlier 
version of this paper; Pablo Yorio for his critical read- 
ing, editorial suggestions, and help with translations; 
Maria del Carmen Falcon for help with English; 
Pablo Mariotti, Laura Reyes, and Barbara Beron 
Vera for assistance in the field and laboratory; and 
to all the fishermen for their help at sea and con- 
stant interest in our work. Kimberly Murray, John 
B. Pearce, and three anonymous reviewers made in- 
teresting and useful comments that enhanced the 
validity of results. Sharyn Matriotti gave us impor- 
tant help with this article. This work was carried 
out with the financial support of the National Geo- 
graphic Society (grant 4249/90 to E.A. Crespo and 
A.C.M. Schiavini), the Whale and Dolphin Conser- 
vation Society, the Patagonian Coastal Zone Man- 
agement Plan (GEF/PNUD), and the Programa de 
Cooperacion Cientifica con Iberoamerica (BOE 29- 
III-96). The University of Patagonia, CENPAT- 
CONICET, and Fundacion Patagonia Natural pro- 
vided logistical support. An earlier version of this 
paper was presented by E.A. Crespo as SC/48/SM19 
in the 48 th Annual Meeting of the International Whal- 
ing Commission, Aberdeen, Scotland, 5-17 June 
1996; he attended the meeting with support from the 
IWC and Cetacean Society International. Thanks are 
also given to Tony Martin and Kate O’Connell. 
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Contrib. Inst. Nac. Invest. Des. Pesq. (INIDEP) 409, 83 p. 
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