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Diet of dusky dolphins, 
Lagenorhynchus obscurus, 
in waters off Patagonia, Argentina 
Mariano Koen Alonso 
Enrique Alberto Crespo 
Nestor Anibal Garcia 
Susana Noemi Pedraza 
Mariano Alberto Coscarella 
Centro Nacional Patagonico (CONICET) 
Universidad Nacional de la Patagonia and Fundacion Patagonia Natural 
Boulevard Brown s/n, (9120) Puerto Madryn, Chubut, Argentina 
E-mail address (for M. Koen. Alonso): koen@cenpat.edu. ar 
The dusky dolphin, Lagenorhyn- 
chus obscurus, is probably the best 
known species of the genus Lagen- 
orhynchus in the Southern Hemi- 
sphere. It is common in temperate 
waters of New Zealand, South Af- 
rica, Peru, northern Chile, and Ar- 
gentina (Crespo, 1991; Van Waere- 
beek, 1992; Crespo et al., in press). 
Incidental catches have been re- 
corded in coastal and offshore fish- 
eries of Argentina (Corcuera et al., 
1994; Crespo et al., 1994a, 1994b; 
Dans et al., in press), whereas di- 
rected captures have occurred off 
Peru (Read et al., 1988; Van Waere- 
beek and Reyes, 1990; Reyes, 1992). 
The biology of dusky dolphins has 
been studied in Argentina since the 
1970’s (Wiirsig and Wiirsig, 1980; 
Wiirsig and Bastida, 1986; Dans et 
al., 1993). A detailed behavioral study 
was carried out at Peninsula Valdes 
(Wiirsig and Wiirsig, 1980), and 
preliminary information about the 
reproductive biology of females was 
obtained by Dans et al. ( 1993, 1997). 
Feeding habits have been briefly 
described for dusky dolphins from 
New Zealand (Gaskin, 1972), Pata- 
gonia (Dans et al., 1993; Crespo et 
al., 1994c), and Antarctic and sub- 
Antarctic waters (Goodall and Ga- 
leazzi, 1985). In Patagonia, the be- 
havior of dusky dolphins feeding on 
Argentine anchovy, Engraulis 
anchoita, schools has been de- 
scribed by Wiirsig and Wiirsig 
(1980). A more recent and detailed 
study of their feeding habits by 
stomach content analysis was car- 
ried out in coastal waters of central 
Peru (McKinnon, 1994). The Peru- 
vian sample consisted of animals 
caught mostly in gill nets (McKin- 
non, 1994). Peruvian anchoveta, 
Engraulis ringens, was the most 
important prey species for Peru- 
vian dusky dolphins, accounting for 
92.5% in number and 83.8% in 
weight of the total sample, and 
97.8% frequency of occurrence 
(McKinnon, 1994). Differences in 
diet between lactating and nonlac- 
tating mature females were not 
found, and the anchoveta was al- 
most the exclusive prey species in 
both sexes (McKinnon, 1994). 
The objective of the present study 
is to describe the diet of the dusky 
dolphin in Patagonia in terms of 
both species composition and prey 
size. Seasonal and annual compo- 
sition were not investigated be- 
cause the sample size was small 
when subdivided along these lines. 
Materials and methods 
The sample consisted of 25 dolphins 
(6 males and 19 females) caught 
incidentally between November 
1989 and April 1994 by the trawl- 
ing fishery that operates over the 
Patagonian Continental Shelf. All 
dolphins were caught in the area 
between 43°S and 46°30'S and be- 
tween the coastline and the 100-m 
isobath. Most individuals were fro- 
zen onboard to -20°C when they 
were caught. 
The total weight, standard length, 
and other body measurements (Nor- 
ris, 1961) were recorded for each 
dolphin before dissections were 
made. Stomach contents were col- 
lected and then stored, either fro- 
zen or in 70% alcohol. They were 
separated with several sieves with 
a mesh size between 25 mm and 0.5 
mm. Flesh material from the sieved 
contents was placed in a deep, wa- 
ter-filled plastic tray, enabling re- 
moval of the remaining flesh mate- 
rial. Otoliths, fish bones, and ceph- 
alopod beaks were identified with 
the aid of published catalogues 
(Clarke, 1962, 1980, 1986; Torno, 
1976; Menni et al., 1984; Roper et 
al., 1984; Boschi et al., 1992; Gosz- 
tonyi and Kuba 1 ) and a reference 
collection of otoliths, cephalopod 
beaks, and crustaceans belonging 
to the Marine Mammals Labora- 
tory, Centro Nacional Patagonico, 
CONICET. 
The number of individuals of a 
particular fish species (NF) found 
in a stomach was calculated as 
1 Gosztonyi, A., and L. Kuba. 1996. Atlas 
de huesos craneales y de la cintura 
escapular de peces costeros patagonicos. 
Plan de Manejo Integrado de la Zona 
Costera Patagonica (PMIZCP), Global En- 
vironmental Facility (GEF), Programa de 
las Naciones Unidas para el Desarrollo 
(PNUD), Wildlife Conservation Soc. 
(WCS), and Fundacion Patagonia Natu- 
ral (FPN) Informe Tecnico 4, 29 p. 
Manuscript accepted 6 August 1997. 
Fishery Bulletin 96:366-374 (1998). 
