King salmon are a staple for Bering Sea fishermen, but their population is dwindling. Could the salmon shark be one of the reasons for their decline?
The salmon shark got its name for a reason. They are one of the many creatures that feed on king salmon so it’s not surprising that researchers are studying the possibility that these animals are having an impact on the numbers of salmon in the Bering Sea.
According to a report, researchers have been using “pop-up” tags for about 15 years to monitor depth and temperature of salmon and can also estimate their location. The tags are designed to release its hold on the fish after a certain length of time and rise to the surface of the ocean.
Andy Seitz, of the University of Alaska School of Fisheries and Ocean Science, has tagged bluefin tuna, halibut, and even Dolly Varden in northwest Alaska. Having success with those species prompted Seitz to have a go at the king salmon.
After 10 kings were tagged, and eventually getting 5 of them back, he noted at least two different temperature changes that led him to believe that the salmon were eaten, and likely by a salmon shark.
Sharks can regulate their internal temperature to be warmer than the ambient water temperature in the Bering Sea, which is around 40-50 degrees. The tags indicated a temperature of 70-80 degrees which is considered warm enough for a shark but too cold for a sea lion or a whale. Seitz said;
It’s too early to tell if salmon sharks have any impact on abundance on king salmon in the ocean, but it’s certainly another factor that should be investigated.
Seitz hopes to tag 10 more salmon in 2015, noting that they would be larger fish that still had another year to live in the open ocean before making their spawning run. Knowing whether fish of this size are being predated upon is key to understanding if salmon sharks are contributing to the issue of declining king salmon numbers in the Bering Sea.