Researchers have found an average decrease of 13% in the adult size of whales, which could have major implications for their ability to reproduce and survive.
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 Biologyresearchers focused on a small group of about 200 gray whales in the northeast Pacific Ocean.
Considered as “ecosystem sentinels”, these cetaceans stay close to the coast and feed in shallower and warmer waters than other populations of gray whales. Previous studies have shown that this group is in worse shape than other whales, which are smaller and thinner. “Now we know that their bodies have shrunk over the last 20 to 40 years, which may be an early sign that the population is at risk of decline.”explains to AFP Kevin Bierlich, co-author of the study.
More pronounced shrinkage in women
The 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 2020, a reduction of 1.65 m on individuals of around 13 meters. The shrinkage is even more pronounced in females, who were historically larger than males and are now the same height. Gold, “size is essential for animals”points out Enrico Pirotta, researcher and lead author of the study.
“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 explains. Reproduction is particularly affected, with chances of survival potentially lower for smaller young. Importantly, the study established a correlation link between this drop in size and the disruption of the ocean cycle caused by climate change, and in particular the currents which allow the growth of plankton, food for whales.
