Gray whales that feed in the shallow waters off the Pacific Northwest coast have shrunk in size by 13% over the past 20 to 30 years, an Oregon State University study found.

Once reaching maturity, gray whales belonging to the Pacific Coast Feeding Group located in the more shallow coastal waters along Oregon and California can grow up to 49 feet long. However, the Marine Mammal Institute’s Geospatial Ecology of Marine Megafauna collected photos via drones of 130 individual whales with known or estimated age. Researchers found that a full-grown whale born in 2020 is expected to reach an adult body length of about 5 feet, 5 inches shorter than a gray whale born before 2000. This accounts for more than a 13% loss in their total length.

To put that into perspective, this would be the equivalent to the average height of a woman going from 5’4″ to 4’8″ in the span of just 20 years. 

There are about 200 gray whales that reside in the shallow waters of Oregon’s coastline. They belong to a larger North Pacific gray whale population of around 14,500.

Studies from Oregon State reveal that whales belonging to the Pacific Coast Feeding Group are smaller and in overall worse body condition than gray whales inhabiting deeper waters of the Eastern Northwest.

“In general, size is critical for animals,” Enrico Pirotta, lead author of the study and a researcher at the University of St. Andrews in Scotland, told Oregon State’s newsroom. “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.”

Smaller gray whale sizes will have a negative impact on reproductive success.

With whales being smaller, there are questions about how effectively these Pacific Coast Feeding Group gray whales can store and allocate energy toward growing and maintaining their health.

“Are they able to put enough energy toward reproduction and keep the population growing?”, KC Bierlich, co-author of the study, said. 

With the gray whales’ shrunken size, researchers are led to question their ability to recover from injuries. 

Researchers are also concerned about what the whales’ diminished size may reveal about the ocean’s ecosystem. The study tracked the Pacific coast’s cycles of upwelling and relaxation which regulate food availability. Upwelling sweeps nutrients from deeper to shallower regions, whereas relaxation periods will keep those nutrients in shallower areas where light allows for the growth of plankton, a food source for gray whales. Data show that whale size declined concurrently with changes in the balance between upwelling and relaxation.

While it’s not clear to researchers if climate change is affecting these patterns, researchers say it is impacting wind patterns and water temperature of the Northeast Pacific.

Shrunken sizes have also been recorded in the North Atlantic within right whale populations. A 2021 study found that 5-year-old and 10-year-old whales were about the size of 2-year-old whales.

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Joshua Stewart, a quantitative conservation ecologist with the National Oceanic Atmospheric Administration, told the New York Times that he attributes the shrunken size to the thousands of fisherman traps that are along the route of the whales migratory patterns, causing some to get stuck. 

“What we think is going on here is that dragging these big trailing heaps of gear is creating all this extra drag, which takes energy to pull around, and that’s energy that they would probably otherwise be devoting to growth,” Stewart told the outlet.