NOTE Koen Alonso et a I.: Diet of Lagenorhynchus obscurus in waters off Patagonia 
371 
Total length (cm) 
Figure 4 
Length-frequency distribution of Argentine hake, Merluccius hubbsi, eaten by dusky 
dolphins in Patagonia. 
dolphin feed on ecologically simi- 
lar species, mostly schooling 
fishes. However, whereas ancho- 
veta represented 80% in weight 
of the diet of Peruvian dolphins, 
Argentine anchovy represented 
between 40% and 50% in weight 
of the diet of Argentine dolphins. 
Sample size in this study is 
relatively small and possibly bi- 
ased by age and sex (Dans et al., 
1997; in press). However, our 
sample included mature and im- 
mature dolphins of both sexes, 
and all the stomach contents 
were very similar in composition 
(Table 2). Moreover, dusky dol- 
phins had never been reported to 
be feeding around fishing vessels 
on discards and disturbed fish, 
even when the dolphins in this 
sample were caught by shrimp 
trawlers. Furthermore, the diet 
composition of Peruvian dusky 
dolphins did not show any differ- 
ence between sexes or reproduc- 
tive status (McKinnon, 1994). At 
Peninsula Valdes, dusky dolphin 
feeding groups consisted of indi- 
viduals of both sexes and of al- 
most all age classes (calves and 
small young could be excluded 
from the feeding group) (Wiirsig 
and Wiirsig, 1980). Therefore, 
considering the general similari- 
ties in diet composition between 
Argentine and Peruvian popula- 
tions, the absence of differences 
in the diet between sexes and 
reproductive status in the Peru- 
vian population, the lack of evi- 
dence to suggest that dolphins 
feed on discards and disturbed 
fishes, and the gregarious feed- 
ing behavior of patagonian dusky 
dolphins described by Wiirsig 
and Wiirsig ( 1980), we conclude 
that the sample analyzed in this 
study is a reasonable indicator of diet composition of 
dusky dolphins in Argentine waters. 
At least two populations of Argentine anchovy have 
been reported over the Argentine Continental Shelf: 
the bonaerensis (northern) and the Patagonian 
(southern) stocks (Brandhorst et al., 1974; Angelescu, 
1982; Angelescu and Anganuzzi, 1986; UNESCO, 
1990; Hansen, 1994). Preadults and adults of the 
bonaerensis stock migrate northwest from coastal 
spawning areas to offshore feeding grounds; avail- 
able information indicates that the Patagonian stock, 
however, does not show a seasonal migration 
(Brandhorst et al., 1974; Angelescu, 1982; Angelescu 
and Anganuzzi, 1986; UNESCO, 1990; Hansen, 
