A study conducted by Oregon State University shows that the number of gray whales off the Pacific Northwest has decreased significantly since 2000; This points to potential wider environmental problems and underlines the urgent need for further research into the factors affecting their decline.

A recent study from Oregon State University found that gray whales feeding in the shallow coastal waters of the Pacific Northwest during the summer months have experienced a marked decrease in body length since about 2000. The smaller size could have serious consequences for the health and reproductive success of affected whales, raising concerns about the state of the food web in which they coexist, the researchers said.

“This could be an early warning sign that this population is declining or not healthy,” said C.C. Bierlich, study co-author and associate professor at OSU’s Marine Mammal Institute in Newport. “And whales are considered guardians of the ecosystem, so if the whale population is not doing well, that can say a lot about the environment itself.”

In a study published in the journal Global Change Biologylooked at the Pacific Coast Feeding Group (PCFG), a small subgroup of about 200 gray whales within the larger Eastern North Pacific (ENP) population of about 14,500 individuals. This subgroup stays closer to shore along the Oregon coast and feeds in shallower, warmer waters than the Arctic seas, where the majority of the gray whale population spends most of the year.

Recent OSU research has shown that whales in this subgroup are smaller and in overall poorer body condition than their ENP counterparts. Current research shows that these have decreased in recent years.

Technological progress in measuring whales

The Marine Mammal Institute’s Geospatial Ecology of Marine Megafauna (GEMM) Laboratory has been studying this subset of gray whales since 2016, including flying drones over the whales to measure their sizes. Using images of 130 whales with known or estimated ages from 2016 to 2022, the researchers found that an adult gray whale born in 2020 had an adult body length of 1.65 meters (about 5 feet 5 inches) shorter than a gray whale born earlier. determined that it should reach its length. 2000. For PCFG gray whales, which reach 38-41 feet in length at full maturity, this represents a loss of more than 13% of their total length.

If the same trend were observed in humans, it would be similar to the average American woman’s height dropping from 5’4″ to 4’8″ in 20 years.

“Size is very important for animals in general,” said Enrico Pirotta, the study’s lead author and a researcher at the University of St Andrews in Scotland. “It affects their behavior, their physiology, their life history, and it has a cascading effect on the animals and the community they are a part of.”

According to Pirotta, baby whales that shrink at weaning age may not be able to cope with the uncertainty surrounding their new independence, which may affect their survival rates.

One of the biggest challenges for adult gray whales is reproductive success.

“Because they are smaller, questions arise about how efficiently these PCFG gray whales can store and allocate energy to grow and maintain their health. What matters is whether they can expend enough energy to reproduce and sustain population growth.” said Birlich.

Scars on PCFG whales from boat strikes and entanglement in fishing gear raise the team’s concern that their smaller body size with lower energy reserves may make the whales less resilient to injury.

The impact of the environment on food resources

The study also looked at patterns in the ocean environment that regulate food availability for these gray whales off the Pacific coast, tracking “swell” and “slack” cycles in the ocean. Upwelling moves nutrients from deeper areas to shallower areas, while periods of relaxation allow these nutrients to remain in shallower areas; here the light allows plankton and other small organisms, including gray whale prey, to grow.

“Without a balance between upwelling and relief, 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 Laboratory at OSU.

Pirotta said the data showed that the whale’s size decreased simultaneously with changes in the balance between uplift and relaxation.

“We haven’t looked specifically at how climate change affects these patterns, but we know that in general, climate change affects the oceanography of the Northeast Pacific through changes in wind patterns and water temperatures,” he said. “And these and other factors influence the dynamics of upwelling and relief in the region.”

Now that they know that PCFG gray whales are shrinking in body size, researchers say they have many new questions about the consequences of this decline and the factors that may contribute to it.

“We are entering our ninth field season studying this subset of the PCFG,” Bierlich said. “This is a powerful data set that allows us to detect changes in body condition from year to year, so we are now investigating the ecological drivers of these changes.”