Six months ago, biologist Mike Litzow was so pessimistic about the numbers of Pacific cod in the Gulf of Alaska that he was wondering what compensatory species might move in to replace them.
“Jellyfish taste pretty good with some barbecue sauce,” he joked grimly.
Litzow, a researcher for the University of Alaska Fairbanks based in Kodiak, deepened monitoring of Gulf cod this year after the species exhibited a troubling implosion, which biologists believe was mostly caused by warmer water temperatures in the Pacific Ocean. The 2017 count on Gulf cod represented a 71 percent drop from 2013 and an 83 percent drop from 2015, a huge blow for the seminal Gulf fishery.
But after a summer of observing young cod, Litzow sees a glimmer of hope.
“I’d say we’re optimistic in a really guarded way. We did go out and catch what seems like a lot of cod, but we don’t have anything to compare it with. It’s certainly much better than going out and not being able to find any age-zero cod,” Litzow said.
Ben Laurel, a research biologist from the Alaska Fisheries Science Center (AFSC), has been studying Pacific cod close to Kodiak since 2005. Litzow and his team expanded on Laurel’s area of research, making over 130 beach seine sets on the west side of Kodiak island and out the Alaska peninsula to Sand Point, scooping up 18,000 age-zero cod, which “seems like a lot”, according to Litzow.
The research team also used baited cameras to assess the abundance of age-one cod, which are a little deeper than the year-zero cod.
High mortality rates could still kill the fish off before they reach a harvestable age, but Laurel too was cautiously optimistic about recent counts on young fish.
“In 2017, the ocean temperatures started to get back to normal and we did see signs of some fish, which is good because we hadn’t seen fish earlier. In 2018, we also are seeing some young fish. But again, we’re just looking at one year in one area and it might not be reflective throughout the Gulf, so we are not sure what it means,” Laurel told National Fisherman recently.
Data put together by biologists like Laurel and Steve Barbeaux, also an AFSC researchers, suggest that the warm Pacific water mass known as the blob that sat in the Gulf from 2014 through 2016 is responsible for the precipitous decline in local cod populations. The problem is twofold: Warmer waters lower the levels of plankton that cod feed on while they raise their metabolism, causing the fish to starve out.
While water temperatures have cooled over the last couple years, Litzow said they are still far warmer than historic averages, and this is part of the reason his optimism is so guarded.
“We’re still well above average temperatures. We’ve dropped down from the peak in 2016, which around 1.8 degrees warmer than average, but we’re still somewhere between half-a-degree to a degree over historic averages,” Litzow said.
If a one-degree change in water temperature doesn’t seem like much, Litzow points to the recent past to show how significant it can be. Kodiak has come to depend on the cod fishery over the past 25 years, but it was a shrimp and crab town before 1977, when water temperatures rose a degree and drastically altered the marine population.
While Litzow jokes about eating jellyfish, his idea of a compensatory species is not far-fetched. For now, though, biologists hope water temperatures keep dropping, and the young cod they observed this summer survive.
Photo courtesy of Mike Litzow
