June 28, 2024 — During recent periods of unusually warm water in the Gulf of Alaska, young Pacific cod in near shore safe havens where they typically spend their adolescence did not experience the protective effects those areas typically provide, a new Oregon State University study found.
Instead, during marine heat waves in 2014–16 and 2019, young cod in these near shore “nurseries” around Kodiak Island in Alaska experienced significant changes in their abundance, growth rates and diet, with researchers estimating that only the largest 15–25% of the island’s cod population survived the summer. Even after the high temperatures subsided, the cod have yet to return to pre-heat wave size and diet.
The findings, published today in the journal Scientific Reports, may have broader implications for marine fish populations worldwide, as marine heat waves become longer and more frequent with climate change, the researchers said.
“These coastal habitats aren’t supporting fish in the same way that they used to as a result of marine heat waves,” said lead author Hillary Thalmann, a graduate student in OSU’s Department of Fisheries, Wildlife and Conservation Sciences. “That’s a novel finding, because we don’t always look at the nurseries as a place where size-selective mortality could be occurring rapidly.”