Decadal Decline in Maternal Body Condition of a Southern Ocean Capital Breeder

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Abstract The changing physical properties of the Southern Ocean are known to impact the recruitment and survival of Antarctic krill (Euphausia superba), with knock-on effects on oceanic top predators. Considering this relates to a reduced energy intake, population-level effects are likely preceded by alterations in the animal’s body condition. This is especially true for capital breeders, that rely on stored energy for successful reproduction. One such Southern Ocean capital breeder, the southern right whale (Eubalaena australis), has been monitored over the past 43 years in their South African wintering ground. Changes in the population have been documented in the past decade, including a decreased reproductive success and a shift in foraging strategy. Evaluating if a reduced foraging success is an underlying factor, we assessed the temporal variation in morphological body condition through aerial photogrammetry. Results showed a 23% reduction in maternal body condition, possibly contributing to the decreased reproductive success of the population. To the best of our knowledge, this is the first study to quantify a decadal reduction in the body condition of a capital breeder dependent on Southern Ocean productivity. Understanding the bioenergetic consequences of environmental change is vital to predicting a species’ resilience to climate change.

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