Predation on fish by the southern elephant seal, Mirounga leonina, at King George Island, South Shetland Islands, as reflected by stomach lavage

Between november and february of the years 1993/94, 1995/96, 1996/97, 1997/98, 1998/99 and 1999/2000, one hundred and fifty three specimens of southern elephant seals, Mirounga leonina, were stomach lavaged at King George Island in order to analyse their diet. The two major prey types were cephalopods and fish which ocurred respectively in 98,1% and 14% of stomachs containing prey remains. The aim of the present paper was to report data on fish prey obtained from seal stomachs throughout the whole study period. One hundred and forty five sagittal otoliths were removed from 16 stomachs containing fish remains. Of these stomachs, 9 belonged to adult females, 6 to juvenile males and 1 to a subadult male. The identification of otoliths revealed the predominance of myctophids as fish prey of seals, representing 76,5% of the fish predated. The most frequent (75%) and abundant prey species was Gymnoscopelus nicholsi which constituted in number 69% of the otoliths found. This species was followed by the nototheniid Pleuragramma antarcticum which represented 11,7% in number and 31,3% in frequency of occurrence. Based on the great distances travelled by seals from their foraging grounds to their hauling sites and the differential rate of passage of fish and cephalopod remains through their gastrointestinal tract, an underrepresentation of the consumption of fish is highly probable. Moreover, according to the movements at sea of southern elephant seals tracked from King George Island we suggest that while myctophids may be their dominant fish prey in areas close to their hauling sites, they are probably replaced by the Antarctic silverfish P. antarcticum as seals migrate southward towards higher latitudes where this species is highly abundant.