Researchers now have a better idea of what’s eating king salmon in the open ocean. A new study from the University of Alaska Fairbanks College of Fisheries and Ocean Science found kings filling the bellies of salmon sharks, but that wasn’t the information they were after.
KDLL’s Shaylon Cochran spoke with Dr. Andy Seitz, who conducted the research, about what new questions these data raise and what it could mean for king salmon management.
The real goal in this study actually had very little to do with what happens to kings in the ocean. Any insight there would be sort of incidental. They were just trying to see if a satellite tagging method was going to work for future studies.
“The technology exists to study fish behavior and that’s the pop up satellite tags. They’ve been used on a variety of fish species, but never on king salmon. So the study was conceived as a small number of tags being put on king salmon to see if king salmon could carry a tag around on them, and then if so, we could get some preliminary behavior information on them," Seitz said.
But some of the tags started sending back information sooner than was expected and the data coming in didn’t really make sense coming off a king salmon. After the tags are inactive for three days, they automatically transmit their stored information about water depth and temperature. And some of the tags were showing huge movements up and down in the water column while maintaining a fairly constant temperature. Not what’s expected out of chinook, unless, that chinook is now being carried around the ocean in the stomach of a salmon shark. Seitz conducted his study out in Bering Sea and got data back from 35 of 43 fish tagged between 2013 and 2017.
“The big follow-up questions now are does this mortality occur throughout the year and regardless of whether it occurs throughout the year, we’re curious what are the spatial patterns of this mortality throughout the range for chinook salmon. So for the project, all of the tags were put out in the Bering Sea and so we know a lot about mortality and behavior about chinook salmon in the southeast Bering Sea, but what happens when a chinook salmon swims north into the northern Bering Sea or south and east into the Gulf of Alaska.”
Gaining some insight on some of that ocean behavior, which is where kings spend the majority of their lives, could help inform future management decisions.
“For instance, if the pollock fishery mainly fishes at a certain depth and king salmon mainly fish at a certain depth, does that make king salmon more or less susceptible to bycatch in a groundfish fishery? And if they’re more susceptible because of overlap in fishing depth, can there be fishing practices that are modified to try and avoid chinook salmon?”
If that sounds familiar, you know your local commercial fishing policy. That same principle was applied here in Cook Inlet several years ago when a similar study found kings swimming lower in the water than sockeye. Despite concerns from the Department of Fish and Game about that study, its findings were used to put some new rules in place for commercial setnetters fishing a second permit that limited the depth of their nets. How effective that rule has been for avoiding the catch of kings is still up for debate, but Seitz says there are other practical applications, including potentially for law enforcement.
As with so many scientific endeavors, this study raised at least as many questions as it answered. Seitz says they’re currently working on proposals to extend the work, which has been published in the Canadian Journal of Fisheries and Aquatic Sciences.