Koen Alonso et al : Food habits of Otaria flavescens 



259 



of dead, beached males with entan- 

 gled males did not show any signifi- 

 cant difference. 



The only difference in diet found 

 between subsamples was that shown 

 by sexes. In this case differences in 

 behavior and feeding habits could 

 reflect differences in diet. Even if each 

 sample source may have had differ- 

 ent potential biases and the overlap 

 analysis between them did not detect 

 differences, we consider our sample to 

 be, even with its limitations, a reason- 

 able approximation of the diet of South 

 American sea lions in Patagonia. 



The diversity of prey species (Table 

 3) found in the diet of the South 

 American sea lion indicates that it is 

 a broad-spectrum predator. Some of 

 these prey species (Argentine hake, 

 Argentine shortfin squid, and Ai'gen- 

 tine anchovy) are abundant key spe- 

 cies in the Patagonian continental 

 shelf ecosystem and have commercial 

 value (Angelescu, 1982 ;Angelescu and 

 Prenski, 1987; Brunetti, 1990; Bezzi 

 etal., 1994). 



Argentine hake and Argentine short- 

 fin squid are the two major target spe- 

 cies of the Argentine fleet (Anonymous, 

 1996), and Patagonian squid is also 

 exploited in the Falkland (Malvinas) 

 Islands (Hatfield, 1996). Sea lions ate 

 these prey species at both commercial 

 and noncommercial sizes (Fig. 4). 



The fishery catches Argentine hake 

 with length modes between 35 and 

 40 cm TL (Caiiete et al., 1986), and 

 the minimum commercial size of this 

 species is 30 cm TL. Mostly noncom- 

 mercial sizes of Argentine hake (less 

 than 30 cm TL) were consumed by 

 South American sea lions (Fig. 4). 

 Estimates of stock number by age by 

 using virtual population analysis indi- 

 cated that the most abundant Argen- 

 tine hakes are those of age-1 and age-2 

 year classes (approximately 30 cm or 

 less in TL), which represent around 

 56% in number of the estimated hake 

 stock (Bezzi et al., 1994). These data 

 indicate that sea lions are feeding on 

 this species according to prey-size dis- 

 tribution and availability in the envi- 

 ronment. Hakes smaller than 10 cm 



Red octopus 



8000 

 7000 

 6000 



3 5000 



f" 4000 



- 3000 



u 



> 



^ 2000 



1000 

 



20 



a 16 



I 12 

 I 8 



<§ ' 



32 

 28 



a 24 



20 



% '6 



12 

 8 



I 



Male Sea lions Female Sea lions 



Patagonian squid 



Male Sea lions Female Sea lions 



Raneya 



Male Sea lions 



Female Sea lions 



Min-Max 



25%-75% 



Median value 



Figure 5 



Box plots of regression-estimated size of red octopus (Enteroctopuf; megalo- 

 cvathiis). Patagonian squid iLoligo gahi), and "raneya" (Raneya hrasilwn- 

 sis) consumed by male and female South American sea lions collected in our 

 study. 



