Whale, Where's My Salmon? Southern Residents Forced to Forage Elsewhere

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Salmon Shortage Sends Southern Resident Killer Whales Searching Elsewhere

Endangered whales alter feeding habits due to diminishing food supply in Salish Sea

As the once-abundant Chinook salmon dwindle in numbers, the endangered Southern Resident killer whales, who have long frequented the Salish Sea off the coasts of Washington and British Columbia, are finding themselves forced to spend far less time in their beloved feeding grounds, reveals a new study.

For generations, the San Juan Islands in the Salish Sea have served as a mecca for these majestic marine mammals. The Southern Residents would flock to the area during the summer months, feasting on the Fraser River's Chinook salmon stock as it passed through the islands en route to their spawning grounds upriver. But as the Chinook salmon populations have plummeted, so too has the time spent by the Southern Residents around the San Juan Islands – a staggering decline of over 75%, according to Joshua Stewart, the study's lead author and an assistant professor with Oregon State University’s Marine Mammal Institute.

The study, recently published in the journal Marine Mammal Science, paints a worrying picture of the Southern Residents' need to seek alternative food sources, as their primary summer feeding grounds become increasingly unreliable and unproductive. With only 73 whales remaining in the population, prey limitation is emerging as a crucial factor in their decline.

Comprised of three matriarchal pods – J, K, and L – the Southern Resident killer whale population has traditionally been spotted in the Salish Sea region between April and October. While the J pod frequents the Salish Sea year-round, the K and L pods venture further afield, especially during winter and spring.

Research utilizing drone technology to assess the whales' body condition has demonstrated the importance of the summer feeding period, when the Southern Residents gorge on returning salmon before facing the leaner winter months. The Fraser River Chinook salmon, the largest and highest quality salmon in the Southern Residents' foraging range, plays a vital role in helping the whales build up blubber stores to survive the winter and early spring.

Stewart's analysis of nearly two decades of whale sighting data, collected through reports from naturalists and researchers throughout the Salish Sea, has shown a strong relationship between the Southern Residents' presence in the San Juan Islands and the return of Chinook salmon to Fraser River tributaries. In years with higher salmon returns, the whales were more frequently present in the area; conversely, when salmon returns were lower, the Southern Residents spent less time in the vicinity.

With the health of the Southern Resident killer whales already impacted by the loss of salmon, the situation is further exacerbated by other stressors such as pollutants and vessel disturbances. As the search for alternative food sources continues, understanding the foraging