Pacific gray whales have seen their size shrink by 13% in two decades, according to a recent study that offers new insights into the effects of climate change on marine mammals.
This reduction in size could have a major impact on these whales’ ability to reproduce and survive, and could also affect their feeding systems, scientists warn.
In this study published in the journal Global Change Biology, the research team focused on a small group of around 200 gray whales (Eschrichtius robustus) from the northeast Pacific Ocean, which are part of a larger population of around 14,500 individuals.
Considered “sentinels of the ecosystem,” these cetaceans stay close to shore and feed in shallower, warmer waters than other populations of gray whales that inhabit colder, deeper Arctic seas.
A warning sign of decline?
Previous studies have shown that this group of whales, smaller and thinner, is in worse shape than the others: “Now we know that their bodies have shrunk over the last 20 to 40 years, which is perhaps -be a warning sign that the population is at risk of decline,” explains Kevin Bierlich, co-author of the study.
Researchers analyzed drone images taken between 2016 and 2022 of 130 whales whose ages were estimated or known, and found an average decrease of 13% in the adult size of the whales, between individuals born in 2000 and those born in 2000. born in 2020, a reduction of 1.65 m on individuals of around 13 meters (read box).
The shrinkage is even more pronounced in females, which were historically larger than males and are now the same size. This would be the equivalent of seeing the average height of an American woman drop from 1.63 to 1.42 meters in the space of two decades! However, “size is essential for animals”, points out Enrico Pirotta, researcher and main author of thestudy.
“It affects their behavior, their physiology, their life cycle and has cascading effects on the animals and the population of which they are part,” he notes. Reproduction is particularly affected, with chances of survival potentially lower for smaller young.
Smaller size can not only hinder whales’ ability to thrive, but also make them more vulnerable to threats such as boat strikes and entanglement in fishing gear, which can be fatal.
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