St Andrews Research Finds Climate Change May be Leading to a Decline in Humpback Whale Breeding

Researchers from The University of St Andrews have found that warming in the North Atlantic over the last 15 years may be causing humpback whales to struggle to breed, as a result of a depletion in their food sources.

The scientists took biopsy samples from female humpback whales in the Gulf of St Lawrence in the North Atlantic, a significant feeding ground for humpback whales, to discover pregnancy and breeding rates in humpback whales by observing 457 individuals between 2004 and 2018. 

Researchers have confirmed that although there has been no overall decline in pregnancy rates during the 15 years of observation, there has been a significant decline in the number of humpback whale calves born every year. The study found that around 39% of the pregnancies that were identified in the whales were unsuccessful.

The study states that, “the declines in reproductive success could be, at least in part, the result of females being unable to accumulate the energy reserves necessary to maintain pregnancy and/or meet the energetic demands of lactation in years of poorer prey availability rather than solely an inability to become pregnant”. 

 The study found that the environmental changes in the north Atlantic, including a rapid temperature increase, changes in circulation patterns, ocean acidification and declining sea ice, has impacted the availability of herring, a crucial source of prey for the whales. 

Humpback whales are widely viewed as a vital part of our ocean’s ecosystem health. The correlation between climate change ‒ and the subsequent loss of herring availability ‒ and the decline in calving rates, “over a period of major environmental variability”, the study suggests, may mean that the population of humpback whales, “has limited resilience to such ecosystem change.”