Grey whales in the northeastern Pacific are shrinking

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Author: Stuart Butler

A juvenile grey whale (Photo: jo Crebbin/Shutterstock)

A new study reveals that grey whales are rapidly shrinking and scientists fear this could have a significant impact on whale health


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The grey whale (Eschrichtius robustus, also spelt gray whale), was once known as the ‘devil fish’, for the ferocity with which they fought the whalers trying to harpoon them. Now that whalers have been replaced with whale watchers, they go by the far more appealing nickname of the ‘friendly whale’, as they are known for their curiosity and friendly behaviour towards humans, often gently approaching whale-watching boats and sometimes even allowing people to pet them.

However, a change of nickname isn’t the only thing that’s changed for grey whales. Recent studies have found that off the Pacific coast of North America, they’re also getting smaller.

Grey whales, which can weigh in at over four tonnes and grow to over fifteen metres in length, were once common throughout the Northern Hemisphere. They were driven to extinction in the Atlantic in the 18th Century and, by the 1930s hunting had reduced grey whale numbers to two extant populations, one in the Eastern and one in the Western North Pacific.

The Western Pacific population, around the Sea of Ohtosk, Japan and Korea remains very low, but the Eastern Pacific population has recovered to such an extent that it has been downgraded on the IUCN Red List of Threatened Species to being of ‘Least Concern’.

Within the larger Eastern Pacific population is a small sub-population numbering just over 200 animals, known as the Pacific Coast Feeding Group (PCFG). Studies in recent years have shown that the whales living in this subpopulation have undergone a significant decline in body length since around the year 2000, and new research by scientists from the University of St Andrews has found that this may be linked to changes in environmental conditions in the region they live.

Grey whales are friendly and inquisitive, often actively encouraging interactions (Photo: Andrea Izzotti/Shutterstock)

The Marine Mammal Institute’s Geospatial Ecology of Maine Megafauna (GEMM) Lab at Oregon State University (OSU) has been studying this subgroup of grey whales since 2016, including flying drones over the whales to measure their size.

Using images taken over a seven-year period between 2016-2022 of 130 individual whales with known or estimated ages, researchers determined that a fully-grown grey whale born in 2020 is expected to reach an adult body length that is 1.65 meters (5ft 5in) shorter than a grey whale born prior to 2000 . This amounts to them losing about 13 per cent of their overall length.

The worry is that the smaller size could have major consequences for the health and reproductive success of the affected whales, and also raises alarm bells about the state of the food web in which they coexist.

‘This could be an early warning sign that the abundance of this population is starting to decline, or is not healthy,’ said Dr K C Bierlich, co-author of the study and assistant professor at OSU’s Marine Mammal Institute. ‘Whales are considered ecosystem sentinels, so if the whale population isn’t doing well, that might say a lot about the environment itself.’

Study authors note that whale calves that are smaller at weaning age may be unable to cope with the uncertainty that comes with being newly independent, which can affect survival rates and that for adult grey whales being smaller might impact reproductive success.

‘In general, size is critical for animals,’ said Dr Enrico Pirotta, lead author of the study and a researcher at the University of St Andrews in Scotland. ‘It affects their behaviour, their physiology, their life history, and it has cascading effects for the animals and for the community they’re a part of.’

Now that they know the PCFG grey whales’ body size is declining, researchers say they have a lot of new questions about how that might affect the whales in the future, and what factors could be contributing to the change.

‘We’re heading into our ninth field season studying this PCFG subgroup,’ Dr Bierlich said. ‘This is a powerful dataset that allows us to detect changes in body condition each year, so now we’re examining the environmental drivers of those changes.’

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