Calf sightings are on the decline as ocean temperatures continue to rise.
Baleen whales can change migratory patterns and target new food sources more readily than toothed whales. That, experts suggested, gave species like humpbacks, fin, and blue whales a theoretical edge against climate change and dwindling food supplies. But new data now say the opposite is true for humpback whales.
A new study, published in the journal Global Change Biology found decreased numbers of young humpback whale populations between 2004-2018. The researchers observed the whales in the Gulf of St Lawrence in Canada, known as one of the whale’s key feeding grounds. It’s also been experiencing rising temperatures in recent years.
The researchers say those rising temperatures contributed to year-over-year changes in the mammals’ reproductive success. The teams tracked pregnancy and calving success, noting a 39 percent failure rate during the study period.
“[T]his research shows [the humpback whales’] ability to respond in these ways may not be enough to prevent their reproductive success from being impacted by environmental change,” Dr Joanna Kershaw, University of St Andrews researcher of marine mammals and study author, told the Independent.
“Together, these data suggest 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 meet the energetic demands of lactation in years of poorer prey availability rather than solely an inability to become pregnant,” said Kershaw.
Without the energy reserves, the whales can’t hunt for enough food to carry on pregnancies or feed their calves.
“Humans are changing the ecosystem,” Kershaw notes, “and whale populations are showing a slow in their recovery [from previous human pressures such as hunting].”