Biologists in the Gulf of Alaska are expanding their studies of the struggling Pacific cod after all-time low numbers in 2017 prompted the North Pacific Fisheries Management Council (NPFMC) to slash the 2018 quota by 80 percent.
Counts on last summer’s Pacific cod in the Gulf represented a 71 percent drop from 2013 and an 83 percent drop from 2015, prompting alarm among biologists and hand-ringing for fishermen who depend on cod, a major fishery in the Gulf of Alaska.
Mike Litzow, a researcher for the University of Alaska Fairbanks who is based in Kodiak, is now hoping to get a fuller picture of the Pacific cod life cycle by building on studies done by biologists from the Alaska Fisheries Science Center (AFSC), who have been tracking cod numbers for the past 12 years.
Litzow said AFSC research indicates that warmer water temperatures have boosted the species’ metabolism and caused them to starve.
“The data (AFSC’s) Steve Barbeaux has put together suggests really strongly that food availability for those juvenile age classes that did survive was down," Litzow said. “The hypothesis is that cod’s metabolic demands go up as the water temperature goes up. The two are linked together and as a result they couldn’t reach those increased energetic demands with the available forage.”
Litzow pointed out that AFSC counts have been limited to the summer season at just two sites near Kodiak. He and other colleagues in Alaska will look at the winter conditions for juvenile cod and expand the scope of the summer monitoring to stretch across the heart of the commercial fishing grounds.
“As we build that study out, it will help us understand the dynamics in those young fish over a bigger spatial scale. In general with ground fish we look to recruitment, the ability for existing fish to create more young fish to come in and get fished. That’s what really keeps these populations going, because when you fish them you tend take all the older fish out and you truncate the age structure, creating a population that’s skewed toward younger adults,” he said.
With the blob all but moved on, Litzow said recruitment in 2017 looked better than in previous years, but his optimism about a pending recovery is tempered.
“I don’t think we have any indication that Pacific cod are resilient to the temperatures we’re seeing. What started as the warm blob and sort of evolved into the marine heat wave of 2014 through 2016 are the warmest temperatures ever observed in the North Pacific over a very large area, and those temperature anomalies went very deep into the water column. They’re unprecedented,” he said. “We don’t know what’s going to happen with Pacific cod, but they’re fairly long-life fish and it will take them a while to recover from this event, even if it’s just one-off perturbation, which it’s clearly not. It’s a manifestation of global warming. The long-term prognosis is not great if the gulf continues to warm up.”
Around 16 percent of the world’s cod is caught in Alaska.
