Researchers at Oregon State University have discovered a concerning trend among gray whales that frequent the Pacific Northwest coast. Since 2000, these whales have experienced a significant decline in body length.
This change could have detrimental effects on their health, reproductive success, and the overall balance of their shared ecosystem.
“This could be an early warning sign that the abundance of this population is starting to decline or is not healthy,” said K.C. Bierlich, co-author of the study and an assistant professor at OSU’s Marine Mammal Institute in Newport. “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 research, published in Global Change Biology, focused on the Pacific Coast Feeding Group (PCFG), a smaller segment of approximately 200 gray whales within the larger Eastern North Pacific (ENP) population of around 14,500. This subgroup is known for staying closer to the Oregon coast, where they feed in shallower, warmer waters compared to the Arctic seas, where the majority of the gray whale population spends most of the year.
Recent research conducted by OSU has indicated that whales in this subgroup are smaller and have poorer overall body condition compared to their ENP counterparts. The latest study shows that these whales have been decreasing in size over the past few decades.
The GEMM Lab at the Marine Mammal Institute has been researching a specific subgroup of gray whales since 2016, using drones to measure their size. By analyzing images of 130 individual whales from 2016-2022, researchers have discovered that a full-grown gray whale born in 2020 is expected to reach an adult body length 1.65 meters (about 5 feet, 5 inches) shorter than a whale born prior to 2000. This accounts for a loss of over 13% in total length for PCFG gray whales that reach 38-41 feet at full maturity.
To put this in perspective, if the same trend occurred in humans, the average American woman’s height would shrink from 5 feet, 4 inches to 4 feet, 8 inches over a 20-year period.
“In general, size is critical for animals,” said Enrico Pirotta, lead author of the study and a researcher at the University of St. Andrews in Scotland. “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.”
Whale calves with smaller body size at weaning age may struggle to handle the challenges of independence, impacting their chances of survival, according to Pirotta. Reproductive success is a major concern for adult gray whales.
“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 said.
The presence of scars on PCFG whales from boat strikes and fishing gear entanglement raises concerns about their resilience due to smaller body sizes and lower energy reserves.
The study also analyzed ocean patterns that influence food availability for gray whales off the Pacific coast by tracking cycles of “upwelling” and “relaxation” in the ocean. Upwelling brings nutrients from deeper to shallower regions, while relaxation periods sustain these nutrients in shallower areas, supporting the growth of plankton and other prey for gray whales.
“Without a balance between upwelling and relaxation, the ecosystem may not be able to produce enough prey to support the large size of these gray whales,” said co-author Leigh Torres, associate professor and director of the GEMM Lab at OSU.
The data show that whale size declined concurrently with changes in the balance between upwelling and relaxation, Pirotta said.
“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,” he said. “And these factors and others affect the dynamics of upwelling and relaxation in the area.”
Researchers have recently discovered a decline in the body size of PCFG gray whales. This has led to a myriad of new questions about the potential downstream consequences of this decline and the contributing factors behind it.
“We’re heading into our ninth field season studying this PCFG subgroup,” 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.”
Journal reference:
- Enrico Pirotta, K. C. Bierlich, Leslie New, Lisa Hildebrand, Clara N. Bird, Alejandro Fernandez Ajó, Leigh G. Torres. Modeling individual growth reveals decreasing gray whale body length and correlations with ocean climate indices at multiple scales. Global Change Biology, 2024; DOI: 10.1111/gcb.17366