Summit County Citizens Voice

New study suggests shipping traffic a smaller factor

A pod of orcas in the Pacific. PHOTO COURTESY NOAA.

By Summit Voice

SUMMIT COUNTY —Recovering Chinook salmon populations in the Pacific Northwest is probably the key to killer whale conservation efforts, according to new research based on measurements of hormone levels in the marine mammals.

The southern resident killer whales, living in coastal waters of the Pacific Northwest, have been struggling and some researchers think it’s primarily because of increase ship traffic in the region.

According to the National Oceanic and Atmospheric Administration, they are also  threatened by pollution and other human activities in many parts of their range.

But new research suggests the marine mammals are struggling mainly because of inadequate prey.The study was led led by Katherine Ayres, who completed the work while at University of Washington in Seattle.

Ayres measured two different hormone levels, fecal thyroid and glucocorticoid, to distinguish between two different theories for the whale’s decline.

Both measures supported the inadequate prey hypothesis, which suggests that the killer whale is primarily limited by the decrease in the population of Chinook salmon, its major food source, more than the vessel impact hypothesis, which suggests that the animals are psychologically stressed from the high number of vessels in the area.

“The data support Chinook salmon being a more important driver of physiology than vessel traffic for the Southern resident killer whale population, however vessel traffic may cause added physiological stress during times of low prey availability,” Ayres said.

“Recovering their Chinook salmon prey is critical to assure long-term killer whale recovery. Everything, including boats and toxins, matters more when prey is low,” said researcher Samuel Wasser concurs.

Both nutritional and psychological stress lead to an increase in glucocorticoid levels, while only nutritional stress affects thyroid hormone levels, so measuring both of these levels allowed the researchers to identify which of the two models is correct. The results suggest that whale conservation efforts should focus on salmon population recovery, the authors said.

From the abstract of the study:

“Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability. Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.”

The study was published  June 6 in the open access journal PLoS ONE.

Filed under: biodiversity, endangered species, Environment, Marine biology Tagged: | Chinook salmon, Katherine Ayres, killer whales, Orcas, Pacific Northwest, southern resident killer whales