Decline in Southern Ocean Krill Due to Global Warming Threatens Whale Populations

Scientific Reports, 6 June 2023

Diminishing stocks of Antarctic krill in the Southern Ocean have decreased the average weight of southern right whales by 23% in the past three decades, reducing their ability to produce healthy offspring. This is the first study to measure the long-term bodily harm of decreasing Southern Ocean productivity on capital feeders (animals that only feed during specific periods in their life cycle) around Antarctica. Researchers monitoring whales near South Africa observed a sharp decline in body weight over the past decade as rising ocean temperatures and sea ice loss decreased the availability of Antarctic krill, their main source of food. Reduced food intake jeopardizes the health of mothers who lose weight as they support their young, decreases the number of calves born each season and delays the growth of juveniles. Together, these factors pose a grave threat to southern right whale populations, not just in South African waters but across wintering grounds in the Southern Hemisphere. Authors identify this species as “a sentinel for environmental change in their South Ocean foraging grounds” because their survival depends on the wellbeing of Antarctic krill and copepods. These findings raise serious concern for the continued reproductive success and population recovery of these whales, and make clear the urgency of reducing emissions to limit warming and reduce the negative impacts on marine species throughout Antarctic ecosystems.

https://www.nature.com/articles/s41598-023-30238-2