Breeding chronology and the dynamics of male harem dominance in Southern elephant seals (Mirounga leonina) at the South Shetland Islands.

CARLINI AR,. POLJAK S, DANERI G.A., MÁRQUEZ M.E.I, NEGRETE J.

Curitiba

Simposio; IX SCAR Biology Symposium; 2005

The breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, King George Island (Isla 25 de Mayo), principally by extensive field census work during the 2003 breeding season. Males were individually tagged and their size estimated by the photogrammetrical method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in 10 harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6 respectively. A total of 33 males were identified associated to harems. Male size, measured as nose to hind flipper length, conferred an advantage in terms of dominance hierarchy, since dominant males (4.91± 0.15m) were significantly longer than subordinate males (4.63 ± 0.19). Harems were dominated by an average of 4.5 (range 2-7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations. Male displacement among harems suggests that important differences in mating success among males could be achieved through their different behaviours.