King salmon swim in a dangerous ocean
King salmon have been returning younger and in lower numbers than predicted in much of the state, which has biologists wondering what is happening to kings in the ocean -- and research that seems to indicate that a predator may be involved.
Kaitlyn Manishin, from the College of Fisheries and Ocean Sciences at the University of Alaska Fairbanks, caught everyone’s attention at the recent Alaska Marine Science Symposium when she showed data from one of the three-year ocean king salmon that her team caught and tagged to better understand what was happening to kings in the midst of the ocean.
"My lab put pop-up satellite tags on large immature salmon outside of Dutch Harbor, Alaska in both summer and winter months," Manishin said. "So, these tags record depth, temperature, and light, and we got some unexpected results.”
She pointed to a graph generated with data from one fish caught, tagged, and released Dec. 18. The graph shows a fish swimming up and down in the water with temperatures of 6 degrees Celsius in the Bering Sea, and normal changes in light.
“Then, all of a sudden on Dec. 27, the temperature jumps up to a balmy 26 degrees Celsius and the tag records complete darkness for over three days,” Manishin said
The question is what happened? What could warm the temperatures and turn off the light? Researchers looked at the temperature. It’s much warmer than that of cold-blooded fish, but not as warm as marine mammals.
“We concluded the tag is inside the stomach of a salmon shark,” Manishin said.
The team got the same results from close to half of the fish they released and retrieved tag data from. That’s a high percentage in anyone’s book, but after Manishin’s presentation, other scientists pointed out that these tags are so big that they may make it easier for sharks to capture the king salmon. Furthermore, because sharks can detect electromagnetic signals, her tags may have made it easier for sharks to track the kings, which could seriously skew her results.
“That is definitely a possibility,” Manishin said. “It’s a large tag on a fish, so it could be a lure.”
Manishin’s not stopping. She plans to look deeper and try to sort out the effects that predation, combined with earlier salmon maturity, may be having on the king salmon run.