November 18, 2023 — When scientists estimated that more than 10 billion snow crab had disappeared from the Eastern Bering Sea between 2018 and 2021, industry stakeholders and fisheries scientists had several ideas about where they’d gone.
Some thought bycatch, disease, cannibalism, or crab fishing, while others believed it could be predation from other sea animals like Pacific cod.
But now, scientists say they’ve distinguished the most likely cause for the disappearance. The culprit is a marine heatwave between 2018 and 2019, according to a new study authored by a group of scientists with the National Oceanic and Atmospheric Administration.
Mike Litzow is a co-author of the study and the director for NOAA’s Kodiak lab. He said starvation mediated by increased temperatures caused the collapse.
“Really the crab were not able to get the food they needed,” Litzow said. “They were just outstripping the resources that were available to them.”
According to Litzow and his fellow researchers, the crab faced a number of compounding factors: First, higher temperatures meant increased metabolism so they needed more food; on top of that, there was less space for the crab to forage that food; and finally, the crab were just smaller than usual.
Researchers took data from the many possible hypotheses for the disappearance and they examined it alongside the data they have on the collapse. They examined possible mortality from a range of sources, including directed fishing from the snow crab industry as well as bitter crab syndrome — a fatal disease among crustaceans caused by parasites — and trawl bycatch.
“The take-home message is really that none of those other proposed mechanisms explains the collapse with the data we have,” Litzow said.
He said it’s tough to know what the collapse from increased ocean temperatures could mean for other species, but it’s safe to say we’ll probably see more marine heatwaves like this, and they’re likely to be bigger and more frequent, as the world continues warming.