Koen Alonso et al : Food habits of Otana flavescens 



257 



into classes below the organism's level of discrimi- 

 nation (Petraitis, 1979). However, one cannot eval- 

 uate the interaction between sources of variation 

 with these analyses. For this reason, as in any sta- 

 tistical test, the lack of a difference for a particular 

 source of variation does not indicate the absence of 

 a difference, it means only that there is not enough 

 information to affirm that this source of variation is 

 significant. 



The marine communities for both areas in this 

 study comprise the same species and are considered to 

 be relatively homogeneous along the entire geograph- 

 ical areas range covered by the study area (Fig. 1) 

 (Menni, 1983; Menni and Lopez, 1984; Angelescu and 

 Prenski, 1987). In addition, the trend of sea lion 

 stocks in northern and central Patagonia has fol- 

 lowed a pattern of decline and recovery during recent 

 decades. The northern Patagonia stock declined to 

 one fifth of its original population size between 1930 

 and the mid-1960s as a consequence of intense har- 

 vesting. Then it remained stable between 1972 and 

 1990, when it began to recover (Crespo and Pedraza, 

 1991 ). The central Patagonia stock had not been har- 



vested but declined in a similar proportion during 

 the mid-century and has shown evidence of popula- 

 tion increase in recent years — a fact that suggests 

 a strong connection and interchange of individuals 

 between these regions (Reyes et al., 1999). In addi- 

 tion, preliminary results based on electrophoresis 

 analysis of blood enzymes and proteins codified by 10 

 loci have indicated that nine of these loci are mono- 

 morphic, suggesting that South American sea lions 

 from both areas have had a strong gene flux between 

 them and possibly constitute an unique biological 

 population (Crespo"*). 



Regarding the two sampling periods, the differ- 

 ences in the diet detected with the SO are surely 

 associated with the absence of Argentine anchovy 

 in the 1982-1987 samples. The SO indicated that 

 the utilization curve of food resources of the period 

 1990-1998 could not be drawn from the utilization 



^ Crespo, E. A. 1998. Laboratorio de Mami'feros Marines, 

 Centre Nacional Patagonico ( CONICET). Boulevard Brown 3600, 

 (9120) Puerto Madryn, Chubut, Argentina. Personal commun. 



