Annual reproductive rates of Weddell seals in eastern Antarctica from 1973 to 2000

Abstract

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 Niño Southern Oscillation (ENSO) events compared to earlier decades.KEY WORDS: Weddell seal · Ecosystem monitoring · Antarctic · Reproductive rate · Mark and re-sight · MARK Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 366: [259][260][261][262][263][264][265][266][267][268][269][270] 2008 forsteri at Terre Adélie (66°30' S, 141°01' E) (Woehler et al. 2002). Monitoring single-predator populations has potential to show changes over time in demographic rates, which are in themselves quantitative measures of population status. As part of a suite of parameters from various populations, the same time series may provide 'snap-shots' of the state of the environment. Ultimately, simultaneous interpretation of multiple time series could provide a basis for ecosystem models (Constable et al. 2003).This approach to ecosystem monitoring is conceptually focused on the predator's 'perspective' of the environment (Fraser & Hofmann 2003). Nevertheless, there are many examples where Antarctic predator time series are congruent with large scale physical phenomena (e.g. Whitehead et al. 1990, Testa et al. 1991, Fraser & Hofmann 2003, Jenouvrier et al. 2003, 2005. In the Southern Hemisphere, it is common for signals of reduced productivity to coincide with El Niño events (Trillmich & Ono 1991). One of the first studies to propose such a link cited a reproduction time series from Weddell seals in McMurdo Sound (Testa et al. 1991). A decade later, scientists documented ENSO forcing of physical parameters in the Southern Ocean (Kwok & Comis...

Evaluating the demographic buffering hypothesis with vital rates estimated for Weddell seals from 30 years of mark–recapture data

“…Accordingly, the vital rate estimates reported here provide useful baselines that can be compared with what is found under contrasting circumstances for Weddell seals or other closely related species in the Southern Ocean. Estimates of adult survival rates and breeding probabilities for Weddell seals in eastern Antarctica are available for 26 recent years (Lake et al 2008). Similar to what we report here, Lake et al (2008) found that breeding females had consistently high annual survival rates but variable breeding probabilities and used a flexible breeding strategy to avoid reproductive costs to survival.…”

“…Estimates of adult survival rates and breeding probabilities for Weddell seals in eastern Antarctica are available for 26 recent years (Lake et al 2008). Similar to what we report here, Lake et al (2008) found that breeding females had consistently high annual survival rates but variable breeding probabilities and used a flexible breeding strategy to avoid reproductive costs to survival. Results from studies of other pinnipeds in the Southern Ocean indicate that there might be some interspecific consistency in this pattern.…”

Maternal characteristics and environment affect the costs of reproduction in female mountain goats

“…We also previously reported a positive association between age at first reproduction and longevity (Hamel et al 2009b). Similar to our results, most studies of large mammals found that reproduction did not affect female survival , Packer et al 1998, Testa 2004, Beauplet et al 2006, Lake et al 2008, Weladji et al 2008. Survival costs of reproduction, however, have been reported in two ungulate populations (Tavecchia et al 2005, Moyes et al 2006 and are also occasionally reported in other long-lived species (Boyd et al 1995, Golet et al 1998), but we currently do not have an explanation for these differences.…”

Recovery Trends in Marine Mammal Populations

“…Many Antarctic true seal populations have relatively recent population estimates and are thought to have healthy populations, but they lack longer time series or historical estimates due to the inaccessibility of their remote breeding habitats until recently [24]. Abundance monitoring of Antarctic species may become more important for assessing and managing the effects of climate change and expanding Antarctic fisheries [64], [65], [66].…”