Southern Right Whale (Eubalaena australis) Reproductive Success is Influenced by Krill (Euphausia superba) Density and Climate.

Elisa Seyboth,Luciano Dalla Rosa,Keith Reid,Paulo A C Flores,Eduardo R Secchi,Karina R Groch

doi:10.1038/srep28205

Abstract

The reproductive success of southern right whale (Eubalaena australis) depends on body condition and, therefore, on foraging success. This, in turn, might be affected by climatically driven change in the abundance of the species main prey, krill (Euphausia superba), on the feeding grounds. Annual data on southern right whale number of calves were obtained from aerial surveys carried out between 1997 and 2013 in southern Brazil, where the species concentrate during their breeding season. The number of calves recorded each year varied from 7 to 43 ( = 21.11 ± 11.88). Using cross-correlation analysis we examined the response of the species to climate anomalies and krill densities. Significant correlations were found with krill densities (r = 0.69, p = 0.002, lag 0 years), Oceanic Niño Index (r = −0.65, p = 0.03, lag 6 years), Antarctic Oscillation (r = 0.76, p = 0.01, lag 7 years) and Antarctic sea ice area (r = −0.68, p = 0.002, lag 0 years). Our results suggest that global climate indices influence southern right whale breeding success in southern Brazil by determining variation in food (krill) availability for the species. Therefore, increased frequency of years with reduced krill abundance, due to global warming, is likely to reduce the current rate of recovery of southern right whales from historical overexploitation.

Highlights

The reproductive success of southern right whale (Eubalaena australis) depends on body condition and, on foraging success
The positive correlation between the number of southern right whale calves in southern Brazil and krill densities near South Georgia, considered an important feeding ground for this whale population, suggests that the reproductive success of southern right whale is directly influenced by food availability during the early months of gestation
A relationship at a similar time scale was found between sea ice data and body condition of humpback whales

Summary

Introduction

The reproductive success of southern right whale (Eubalaena australis) depends on body condition and, on foraging success. Climate effects may be direct, through physiology, involving metabolic and reproductive processes, or indirect, through the ecosystem The latter includes the interactions between prey, predators and competitors through the impact on food availability and species distribution[3]. The strongest correlation observed was between the signal in the west Pacific (El Niño 4 region) and the SST around South Georgia with a delay of approximately three years[8] The manifestation of these physical effects can subsequently be seen in biological effects, often illustrated by the response of upper-trophic level predators[9,10]. In waters around South Georgia, krill abundance declined when SST was higher than normal, in www.nature.com/scientificreports/

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