Decline in Pacific Coast Gray Whale Size Raises Environmental Alarms, Study Finds

A new study from Oregon State University reveals that Pacific Coast gray whales have shrunk by over 13% since 2000. This alarming trend signifies potential crises in marine health and food network dynamics.

Gray whales that feed along the Pacific Northwest coast have seen a significant reduction in their body length since the turn of the century, according to a groundbreaking study from Oregon State University (OSU).

The findings could have profound implications for the whales’ health and reproductive success, as well as for the broader marine ecosystem they inhabit.

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

The study, published in the journal Global Change Biology, focused on the Pacific Coast Feeding Group (PCFG) of gray whales. This smaller subset of around 200 whales resides in shallow coastal waters off Oregon, in contrast to the larger Eastern North Pacific (ENP) population of about 14,500 whales that migrate to Arctic waters.

Drone surveys conducted from 2016 to 2022 revealed a startling decline in whale sizes. Researchers determined that a gray whale born in 2020 is expected to be 1.65 meters (approximately 5 feet, 5 inches) shorter as an adult compared to whales born before 2000. For whales that typically grow to 38-41 feet, this represents a more than 13% reduction in size.

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

The researchers emphasized that smaller body size affects whale calves’ survival chances. Calves weaned at a smaller size may struggle with the challenges of independence, potentially leading to lower survival rates. For adult whales, the reduced size raises concerns about their ability to store and utilize energy, impacting their health and reproductive success.

“With them being smaller, there are questions of how effectively these PCFG gray whales can store and allocate energy toward growing and maintaining their health. Importantly, are they able to put enough energy toward reproduction and keep the population growing?” Bierlich added.

Furthermore, scarring from entanglements with fishing gear and collisions with boats might exacerbate the situation. Researchers worry these smaller, less resilient whales may struggle more with injuries.

Exploring the underlying causes, the study tracked cycles of ocean “upwelling” and “relaxation” that regulate prey availability. Upwelling brings nutrients to shallower waters, fostering plankton growth, while relaxation allows nutrients to remain at depths where light facilitates further biological activity. Any imbalance in these cycles may impair the ecosystem’s capacity to support large whales.

“We haven’t looked specifically at how climate change is affecting these patterns, but in general we know that climate change is affecting the oceanography of the Northeast Pacific through changes in wind patterns and water temperature,” Pirotta explained. “And these factors and others affect the dynamics of upwelling and relaxation in the area.”

The research team is now pursuing further studies to understand the environmental drivers behind these changes in body condition.

“We’re heading into our ninth field season studying this PCFG subgroup,” Bierlich noted. “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.”

Other co-authors of the paper include Lisa Hildebrand, Clara Bird and Alejandro Ajó of OSU, as well as Leslie New from Ursinus College in Pennsylvania. The collective effort underscores the importance of ongoing research in addressing and mitigating the impacts of environmental changes on marine life.