Salmon sharks appear to be turning up in fishermen’s nets, and washing up on public beaches around Kodiak Island in greater frequency this summer. But there isn’t enough data to determine if the shark population is growing off the coast of Alaska.
Earlier this week on Aug. 25 a Kodiak resident stumbled upon a salmon shark washed up on Boy Scout beach, near the Buskin River. And a few fishermen around Kodiak have reported seeing or catching more sharks than usual in their fishing gear this summer too.
The species is a cousin to the much larger Great White. It looks menacing but is harmless, to humans that is.
“Historically they were called salmon sharks because they were seen at the river mouths up in Alaska eating salmon," Alexandra McInturf, a researcher with Oregon State University, said.
McInturf researches salmon sharks, among others species, with the Big Fish Lab at Oregon State University. Even though Kodiak Island has seen dwindling runs of pink salmon and Chinook this summer, McInturf said salmon sharks are known to eat a variety of forage fish, mainly ones that are commercially viable like Pollock, herring, and even squid. Salmon sharks’ eating habits also depend on how old the sharks are, if they are juvenile or mature, female or male, etc.
“They do not seem to be salmon specialists," McInturf stated. "And so if there are poor salmon runs, then they might have to shift their foraging patterns to exploit other resources and that could be why they are being encountered by different fisheries (fishermen) than previously.”
Research over the last decade, from 2016-2021, suggests these predators play a role in the dwindling Chinook salmon numbers. But the direct link between king salmon declines and salmon shark predation is unclear.
Similarly, it’s difficult to determine the total number of salmon sharks in Alaska waters and the differences between stocks migrating from place to place up and down the West Coast, along the California current to places like Baja, and into the Gulf of Alaska and Bering Sea. More data is being gathered on the animals' habitat range as the Alaska Department of Fish & Game is tracking the movements of salmon sharks like Ada, an 8-foot female, tagged in the Northern Bering Sea a couple years ago.
McInturf also points out that even if more sightings of salmon sharks are being reported around Kodiak Island this summer, the sharks could have already been in the area in greater numbers.
“They don’t occupy two-dimensional space, right? Like they could be around but at depth. So in addition to thinking about their distribution geographically, we also have to think about their distribution throughout the water column," McInturf explained. "So even if we haven’t been seeing them at the surface, they could have been around but perhaps feeding on something more at depth.”
Salmon sharks have been seen as far north as the Bering Strait, around the Nome area, in recent years and could continue to migrate further as climate change pushes their prey into colder waters. This species of shark can regulate its own body temperature but is classified as a warm-blooded shark according to McInturf.
Fisheries biologist Cindy Tribuzio, with the Alaska Fisheries Science Center which is part of the National Marine Fisheries Service, agrees with McInturf; there is not enough catch data to support the idea that the amount of salmon sharks being caught in fishermen’s nets, as bycatch, is increasing in the Bering Sea and Gulf of Alaska.
“What’s being observed [in Kodiak] could represent population changes. It could also just represent the stocks being condensed in a certain area because of a certain food source. There are so many different things that could be leading into this observation that is going on right now," Tribuzio stated.
Tribuzio works at the Auke Bay Lab in Juneau and handles the stock assessments for sharks in the Bering Sea. She said it’s hard to estimate the number of salmon sharks, and other shark species overall in Alaska, partially due to a lack of data coming from the state’s commercial fisheries.
Since salmon sharks are not targeted for a specific commercial fishery, the latest research suggests there is no overfishing occurring in the Bering Sea or Gulf of Alaska (Aleutian Islands region).
The last stock assessment of salmon sharks in Alaska, and others like Pacific spiny dogfish, Pacific sleeper shark, was released in 2022 and the next one won’t be completed until 2026. In the meantime, a new forage study about salmon sharks’ diet from McInturf’s team at Oregon State University is expected to be released later this year.
