Data spanning nearly half a century shows that endangered southern resident killer whales are spending less time in inland waters, whereas their larger cousins, Bigg’s killer whales, are increasingly present in Puget Sound.
The National Oceanic and Atmospheric Administration listed southern resident killer whales as endangered in 2005 after rapid population decline in the late 1990s. Now, just 74 remain, split into three pods: J, K and L. Bigg’s – sometimes referred to as transients – are more common, but difficult to count because they travel in smaller groups over wider ranges.
Looking at data from The Whale Museum‘s Sightings Archive between 1978 and 2022, University of Washington researchers modeled migratory trends based on observations from researchers, recreational boaters and whale watchers. They found that K and L pods are visiting Puget Sound less often, but the J pod remains well represented. The data on Bigg’s corroborates recent results showing a steady increase in inland waters.
The results were published June 24 in PLOS One.
“We do see increasing transient presence over time, but we don’t see a definitive decline or overall increase for the southern residents. Their presence here is much more variable,” said lead author Zoe Rand, a UW postdoctoral researcher of marine and environmental affairs.
Key behavioral and subtle physical differences separate the southern residents from Bigg’s. The southern residents eat salmon, while Bigg’s prey on seals, porpoises and other marine mammals. Seals and sea lions rebounded in Washington after the Mammal Protection Act, which may have drawn Bigg’s killer whales to inland waters, but that doesn’t explain the changing distribution of southern residents.
Because southern residents are organized into tight matriarchal societies led by female elders, researchers believe that social cues may play an important role.
“Does J pod know something that K and L don’t? Or vice versa? We like to think about which pods have really old grandmas left and whose teaching them where to go,” said co-author Laura Koehn, a marine mammal specialist at the National Oceanic and Atmospheric Administration (NOAA), West Coast Regional office.
Policies to protect southern residents typically apply to all pods. With K and L spending more time in coastal waters, NOAA expanded the critical habitat for southern residents in 2021 to include 16,000 square miles of marine waters between the U.S. and Canada border and Point Sur, California.
Measures like the Quiet Sound Program, which encourages commercial ships to slow down where whales are present, aim to mitigate the impact of noise. Boats are also forbidden from coming within 1,000 feet of the southern residents.
Indications of changing habitat have prompted some to question the need for such regulations in Puget Sound, but these results underscore their continued importance.
“Even though we’re seeing less of K and L pods, we still have to think about how our actions impact J pod. They’re still hanging around,” Koehn said.
The study also notes that southern residents and Bigg’s are sharing habitat more often, though it isn’t clear whether they mingle or avoid each other. This raises questions about their relationship and underscores the importance of accounting for both in management decisions.
“Having more transients around could be good for the southern residents, because they eat marine mammals that also eat salmon,” Rand said.
But if the southern residents avoid the transients, their increased presence could be disruptive. Researchers are actively studying threats to the southern residents – including prey availability – to support the imperiled population.
This analysis wouldn’t have been possible without consistent contributions from citizen scientists. People who report whale sightings using apps like Whale Alert help researchers provide data to policymakers, which can be consequential for the whales.
“This study quantitatively shows things that people have been suspecting,” Rand said. “There are more transients here in Washington, but the southern resident’s story is a bit more complicated.”
Additional co-authors include Alexis Morrigan of the Whale Museum and M. Bradley Hanson of NOAA Fisheries Northwest Fisheries Science Center.
This study was funded by Washington Sea Grant, NOAA Fisheries West Coast and the Puget Sound Partnership.
