Why are killer whales changing their hunting behavior?

By Mark Waghorn via SWNS

Endangered killer whales are changing their hunting behavior and one of the reasons could be disturbance from shipping, reveals new research.

Seasonal use of the inland Salish Sea has also changed dramatically due to shifts in their preferred salmon prey.

The area spans from Olympia, Wash., in the south to the Campbell River, British Columbia in the north, and west to Neah Bay - and includes the cities of Seattle and Vancouver.

Lead author Dr. Monika Wieland Shields, director of the Orca Behavior Institute in Washington State, said: "Their endangered status has prompted a wide array of additional studies focused on topics such as their diet, hormone levels, body condition and responses to vessel disturbance.

"Current presence or absence is key to consider for short-term and immediate protection measures such as vessel exclusion zones or area-based fisheries closures."

She added: "The fish-eating Southern Resident killer whales (Orcinus orca) of the northeastern Pacific are listed as endangered in both the USA and Canada.

"The inland waters of Washington State and British Columbia, a region known as the Salish Sea, are designated as Southern Resident critical habitat by both countries."

The whales have historically had regular monthly presence in the Salish Sea, with peak abundance occurring from May through September.

Dr. Wieland Shields said: "In recent years, at least partially in response to shifting prey abundance, habitat usage by the Southern Residents has changed.

"As conservation measures aim to provide the best possible protection for the whales in their hopeful recovery, it is key that policies are based both on historic trends and current data."

The study shares 2018–2022 daily occurrence data to build upon and compare to previously published whale presence numbers and to demonstrate more recent habitat shifts.

Dr. Wieland Shields said: "These changes correspond to identified shifts in prey availability, with the continued decline of spring and summer Fraser River Chinook, the increasing importance of Columbia River Chinook in the diet and the overall increased abundance of fall and winter chum in Puget Sound."

Based on reports from an extensive network of community scientists as well as online streaming hydrophones, every Southern Resident occurrence was confirmed
either visually or acoustically.

Dr. Wieland Shields said: "Documented here are the first-ever total absence of the Southern Residents in the Salish Sea in the months of May, June, and August, as well
as their continued overall declining presence in the spring and summer, while fall and winter presence remains relatively high.

"It is key that management efforts consider these shifting presence patterns when setting both seasonal and regional protection measures aimed at supporting population recovery."

Whales are intelligent apex predators that capture our imagination. They can cooperate - following prey more than a mile beneath the waves in complete darkness. They rely on sound.

Dr. Wieland Shields has observed orcas in the Salish Sea since 2000 - conducting non-invasive behavioral and acoustic research on Southern Residents and the mammal-eating Bigg’s killer whales.

She said: "I have been studying, photographing, writing about, and advocating for these whales for over 20 years, and am the author of the 2019 book “Endangered Orcas: The Story of the Southern Residents”.

The analysis in PeerJ Life & Environment found historic Southern Resident habitat use of this area has essentially reversed.

Dr. Wieland Shields said: "Protecting habitats is a key component of endangered species recovery.

"But to be biologically meaningful, any geographic or temporal protection zones need to overlap in space and time with how the target species is currently using the habitat, rather than based on historic trends.

"Both Canada and the U.S. have implemented regional and seasonal protection measures aimed at supporting population recovery, but it is important that they are regularly updated to reflect shifting habitat usage by the Southern Residents.

"This study fills that data gap by demonstrating how these endangered orcas are utilizing the Salish Sea over the last five years and how that has shifted from previous trends."

Previous studies have documented how new behaviors spread among killer whales over time through cultural transmission.

Orcas are the iconic great white shark's only predator apart from humans. The huge marine mammals can reach up to 30ft in length and weigh over six tons, feeding on fish, squid, seals and sea birds.