About 25 years ago, University of Oregon biology professor Alan Shanks, recently retired, started daily counts of the bean-sized baby Dungeness crabs washing toward shore in Coos Bay.
Over time, he found that the number of megalopae, or larval crabs, counted through the summer correlates with the crab catch four years later, when they’re large enough to eat.
But, Shanks told KLCC, factors such as marine heat waves, which began around 2014, can skew the data.
“If it's not a marine heat wave year, my predictions are remarkably good,” he said. “If there's a marine heat wave the first summer, then my predictions are way off. They’re very much lower than what actually happens.”
Shanks thinks warmer water allows the cold-blooded crabs to mature into less vulnerable sizes faster, but he said there isn’t enough data yet to test the theory.
He encountered another anomaly earlier in his research, when an astounding number of baby crabs showed up in his traps.
“Up through 2006, the most megalopae I caught was 100,000 in 6 months,” he said. “In 2007, we caught 2 million.”
Shanks said the result of that incredible count was not a bigger catch four years later, but a smaller one.
His theory? They were probably starving.
“There's not gonna be enough food for them,” he said, “and they're cannibals, and so they eat each other.”
Each time a crab molts, it becomes a vulnerable, soft-shelled animal, and they molt about a dozen times a summer. Shanks said this hypothesis is also unproven.
This year, his prediction for Oregon’s harvest is for 15,247,000 pounds of crab, which is a solid amount. But he says 2022 was a marine heat wave year, so the numbers will probably be higher.
The Oregon Department of Fish and Wildlife has announced the Dungeness crabbing season will open Dec. 16 from Cape Falcon to the California border.
