In a concerning discovery, a new study from Oregon State University (OSU) has revealed that gray whales spending their summers feeding in the shallow waters off the Pacific Northwest coast have undergone a significant decline in body length since around the year 2000.
This reduction in size could have major consequences for the health and reproductive success of these whales, while also serving as an alarming indicator of potential issues within their marine food web.
The study, published in the journal Global Change Biology, focused on the Pacific Coast Feeding Group (PCFG), a subset of approximately 200 gray whales within the larger Eastern North Pacific population.
This subgroup remains closer to shore along the Oregon coast, feeding in warmer, shallower waters compared to the Arctic seas frequented by most gray whales.
Researchers from OSU's Marine Mammal Institute and the Geospatial Ecology of Marine Megafauna (GEMM) Lab analyzed drone images of 130 individual PCFG whales from 2016 to 2022, with known or estimated ages.
The findings were startling: 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 before 2000. For PCFG gray whales that typically grow to 38-41 feet at maturity, this represents a loss of over 13% of their total length.
"In general, size is critical for animals," said lead author Enrico Pirotta from the University of St. Andrews. "It affects their behavior, physiology, life history, and has cascading effects for the animals and their community."
Smaller whale calves may struggle to survive independently after weaning, while adults could face challenges in allocating sufficient energy for reproduction and maintaining population growth. Additionally, scarring from boat strikes and fishing gear entanglements raises concerns about the resilience of smaller whales with lower energy reserves.
The study also examined the balance between "upwelling" and "relaxation" cycles in the ocean, which regulate food availability for these whales. Changes in this balance, potentially driven by climate change's impact on wind patterns and water temperatures, could disrupt the ecosystem's ability to produce enough prey to support the whales' large size.
"This could be an early warning sign that the abundance of this population is starting to decline, or is not healthy," said co-author K.C. Bierlich from OSU's Marine Mammal Institute. "And whales are considered ecosystem sentinels, so if the whale population isn't doing well, that might say a lot about the environment itself."
As researchers continue to investigate the causes and consequences of this decline, they plan to examine environmental drivers contributing to changes in the whales' body condition during their ongoing field studies of the PCFG subgroup.
This alarming trend highlights the urgent need for further research and potential interventions to mitigate the impacts of climate change and other human activities on these magnificent marine mammals and their ecosystem
