To ensure a sustainable fishery, scientists are studying how red king crabs respond to a changing environment. In the last week of September, as the northern days were rapidly growing shorter, three NOAA Fisheries biologists dove to the bottom of Cozy Cove. On the east side of Kodiak Island and opening into the vast and frigid Gulf of Alaska, the cove is the site of an experiment that’s never been tried before.
The biologists, all three of them expert cold water divers, planted stakes in the gravelly bottom and ran lines between them, marking out a dozen 5-by-5-meter plots. After squaring the lines, they opened small jars and emptied the contents into the plots: a total of 5,000 juvenile red king crabs. The crabs were each about the size of a pencil eraser and had been hatched and raised at the Alutiq Pride Hatchery in Seward, Alaska. Scientists have spent the last seven years learning through trial and error how to collect fertilized eggs from wild female crabs and raise the resulting larvae to juvenile size. Now the research was entering phase two.
“It’s been a long time in development,” said Pete Cummiskey, one of the NOAA Fisheries biologists who dove that day. “But we’re finally starting field trials, and now we’ll see what happens.”
By releasing them in different densities in each plot, and then coming back to check on their progress weekly, Cummiskey and his colleagues hope to determine the release density that yields the highest rate of survival. The research is organized by the Alaska King Crab Research, Rehabilitation, and Biology program, a partnership of government and academic scientists and community and industry groups interested in the future of crab.
If all goes well, wild red king crab stocks in the Gulf of Alaska and blue king crab in the Bering Sea might someday be supplemented by hatchery-raised cousins. But whether or not that day comes, the research is already paying off.
“This is the first controlled experiment that looks at what happens to known quantities and densities of juvenile king crab over time,” Cummiskey said, “and the knowledge we gain will help us to sustainably manage the wild populations that are already out there.”
When Crab was King
As anyone who’s watched The Deadliest Catch on cable TV knows, crabs are big business in Alaska. Between the three major commercial crab species in that state-red king, blue king, and snow-fishermen landed more than 100 million pounds in 2012. That catch was worth more than $258 million at the dock. But big as those numbers are, they’re a small fraction of what fishermen were landing 35 years ago.
The red king crab harvest, for instance, has fallen more than 90 percent from its peak in 1980. There is far less red king crab out there than there used to be, and scientists suspect that the decline was caused in part by heavy fishing pressure during the peak years. In 1980, the Magnuson-Stevens Act, the law that governs the nation’s fisheries, was only four years old, and controls against overfishing were still in their infancy. But overfishing was soon brought under control, and the catch today is sustainable.
The other factor that reduced the crab stocks was something outside the ability of humans to control. Temperatures in the Pacific oscillate between relatively warm and cool phases about once every ten years. In the early 1980s, this Pacific Decadal Oscillation, as it’s known, entered a warm phase. Crabs, which prefer cooler temperatures, declined.
This isn’t all bad news. The warmer temperatures favored groundfish like pollock, which today is the largest catch in the nation by weight.
“We believe that there was an ecological shift,” said Bob Foy, who leads the team of scientists studying crab on Kodiak Island. “We went from a system dominated by crab and shrimp to one dominated by groundfish.” Those fish happen to prey on juvenile crab, and scientists believe that predation kept a lid on the crab population even after cooler temperatures returned.
NOAA Scientists Keep Close Tabs on Crabs
Fishing sustainably means leaving enough fish in the water-or in this case, crabs-for the population to replace through reproduction what we remove through fishing. To do that, you need to know how many are out there to begin with.
With crab, finding the right balance can be tricky. NOAA scientists survey crab populations every year, but because they often live in rocky habitat that’s difficult to sample with a net, estimates of their abundance have an extra measure of uncertainty.
To protect the reproductive potential of the stock, all crab fisheries in Alaska are male-only fisheries; the females are released, along with undersized crabs, as soon as the crab pots come up on deck. And depending on the crab stock, between thirty and 100 percent of boats have an independent fisheries observer on board to collect data and to verify that the regulations are followed. And catch limits are set conservatively to account for uncertainty in the population estimates.
Knowing the Numbers is Only Half the Battle
But scientists need to know more than just how many crabs are out there. “To manage these stocks, you have to do more than just count them,” said Foy. “That’ll tell me how many there were this year, but I need to know how many will be there next year.” To do that, scientists need to understand both the environment, and how the animals will respond to that environment.
That’s where the experiment of raising and releasing crab is paying off. “There’s not a whole lot of knowledge about survival of small crab in the wild,” Cummiskey said. “With these experimental releases, we’ll get a better idea of survival rates and the impact of predation.”
The Kodiak lab also researches the effect of ocean acidification on juvenile crabs. The oceans absorb about half of the carbon that humans pump into the atmosphere, and when that carbon is absorbed it reacts to form carbonic acid. The increased acidity makes ocean water more corrosive to animals with shells.
To study this effect, NOAA researchers have been raising juvenile red king crabs in the lab under conditions of acidity that are expected in fifty years. This research has shown that juvenile crabs, like many shell-bearing species, are especially vulnerable to acidification.
“That will be a huge issue as we go forward in terms of how we manage these stocks,” Foy said.
What Does the Future Hold?
Raising crabs to the juvenile stage in a hatchery might increase their survival because it gets them past the phase at which they’re most vulnerable to ocean acidification. Of course, it would be impossible to stock the entire Gulf of Alaska with hatchery-raised crabs, let alone bring them back to where they were in 1980.
But for individual communities such as Old Harbor, the village that abuts the experimental site in Cozy Cove, crab planting can have a big impact. The residents of Old Harbor fish for halibut and salmon. Decades ago they fished for red king crab, and if all goes well with the experiment, they might be fishing for them again.
Thirty-five years ago the Gulf of Alaska ecosystem shifted and crab stocks declined even as groundfish proliferated. But despite the drop in numbers, crab fishing is still sustainable. That’s because scientists keep a close eye on the population and study how environmental conditions effect their survival. Fishery managers then take that information and set catch limits at a level that does not deplete the stock. That feedback loop is the essence of science-based sustainable management.
The ocean environment is never stationary. In the 1980s, oscillating temperatures caused a profound ecological shift. In the coming decades, ocean acidification may threaten the health of crab stocks. But as scientists increase their understanding of how crabs interact with their environment, we will be better able to adapt to whatever changes come our way.
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