Annual reproductive rates of weddell seals in eastern antarctica from 1973 to 2000

This study is based on mark and re-sight observations of Weddell seals Leptonychotes weddelli at the Vestfold Hills (68° S, 78° E), which form a considerable time series (1973 to 2000) pertaining to Prydz Bay in eastern Antarctica. We use multi-strata modeling to estimate annual rates of reproduction and survival whilst taking into account annual and breeding state-specific re-sight probability. Inter-annual variation in both the proportion of females producing pups and the proportion of pups surviving juvenile years reveals the indefinite outcome of each reproductive opportunity for this species of the high Antarctic. In contrast, the relatively high and stable survival rates of breeding females lead to long life span and a spreading-out of reproductive bouts so that individuals sample a number of environments and, given environmental uncertainty, increase the probability of reproducing in a good season when pups are more likely to survive. Lack of evidence for costs of reproduction suggests that Weddell seals prudently select years for reproduction to conserve energy by pre-empting unsuccessful attempts. We propose terminating pregnancy is the Weddell seal's primary physiological mechanism to endure and buffer fluctuations in the environment. The time-series of reproductive rates signals ecosystem change. From 1973 to 2000, annual reproductive rates ranged from 53 to 88%. More recent (1990s) low reproductive rates were not linked to El Nino Southern Oscillation (ENSO) events compared to earlier decades. © Inter-Research 2008.