Annual cycle of the southern elephant seal<i>Mirounga leonina</i> (Linn.) at Marion Island

Abstract

The annual cycle of southern elephant seals, Mirounga leonina, was studied at Marion Island (46°54'S, 37°45' E), between August 1973 and December 1976. Data on the breeding and moulting haul-out of different age and sex classes were obtained by conducting once weekly censuses in a selected study area. The haul-out sequence, characterized by a high degree of synchronization and annual regularity was similar to that occurring at other breeding grounds. Photoperiod, in particular the mean monthly increase in day length, appeared to act as an obligatory proximate factor initiating the haul-out to breed and onset of hair growth. Temperature and radiation appeared to act as obligatory ultimate factors initiating the haul-out to moult.

Die jaarlikse siklus van die suidelike olifantrob, Mirounga leonina is bestudeer op Marioneiland (46°54'S 37°45' O) vanaf Augustus 1973 tot Desember 1976. Inligting aangaande die teel en verharing aankoms- tydperke van verskillende ouderdoms- en geslagsgroepe is verkry deur die uitvoer van een-weeklikse volktellings in 'n geselekteerde studiegebied. Die aankomsvolgorde, gekenmerk deur'n hoe mate van sinkronisasie en jaarlikse gereeldheid, was soortgelyk aan di6 van ander teelbevolkings. Photoperiodisiteit, veral die gemiddelde maandelikse toename in daglengte, tree waarskynlik op as 'n onmiddelike verpligtende faktor wat die aankoms om te teel en die aanvang van haargroei inlei. Temperatuur en radiasie blyk om op te tree as 'n fundamentele verpligtende faktor wat die aankoms vir verharing reguleer.