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INTRO: Fishing for crabs is one of Alaska's best paying jobs. It's also one of the hardest. Fishermen work in cold, unforgiving seas, lowering large steel cages, called pots, to the bottom of the sea floor. Baited with fresh fish or squid, the pots are a virtual magnet for crabs. To find the pots later, fishermen attach a floating buoy to the pots. But as Doug Schneider reports in this week's Arctic Science Journeys Radio, sometimes the buoys break free, leaving the pots lost to the fisherman. But that doesn't mean the pots stop catching crabs.
STORY: Scientists call them ghost pots. No one really knows how many of the large round and square crab potsthat weigh anywhere from 300 to 700 pounds apieceare lost each year in waters off Alaska. But Dr. Brad Stevens, a crab biologist with the National Marine Fisheries Service, found nearly 200 of them at the bottom of Chiniak Bay, literally a stone's throw away from the bustling fishing community of Kodiak, on Alaska's Kodiak Island.
STEVENS: "There's lots of crab pots and the density of the crab pots in Chiniak Bay worked out to one crab pot every 50 feet. When you figure that a crab fisherman typically would lay pots about 10 per mile, at one-tenth mile intervals, or every 500 feet. So between the two crab pots that he's laid there are probably ten lost crab pots."
Stevens found the pots with a camera attached to a remotely operated vehicle, called an ROV. The problem, says Stevens, is that even though fishermen have long since forgotten about them, these pots continue to catch crabs for years, perhaps even decades.
STEVENS: "They continue to fish, that's a fact. Let's say a pot that a fisherman puts out is run over by another boat and it cuts off the buoy, and it's still got bait in it. Those pots will continue to fish as long as the bait lasts. And the bait might last a week. They will continue to catch crabs at a pretty high rate. Once the crabs get in there, about half can get out over time. And the other half do not. And those end up dying in the pot, and as they do they become bait for other animals."
In 1996, Stevens obtained a grant from the U.S. Army Corps of Engineers, and he retrieved 150 of these ghost pots from Chiniak Bay. In a study published in the May issue of the journal Fisheries Bulletin, Stevens reports he found crabs in virtually every pot.
STEVENS: "One of them had 120 Tanner crabs in it. That was the highest number we found. And that was probably a pot that had been lost within a month. As the pots were older, they had fewer crabs. The oldest pots we found had an average of 1.5 crabs per pot. So if you go out and find any derelict pot and pull it up, you can expect to find a crab in it. Or maybe two."
Stevens says his discovery was just a snapshot in the afterlife of a crab pot. It's anybody's guess how many other crabs become trapped and die. By law, crab pots are supposed to have a special panel made from biodegradable twine that allows crab to escape if the pot is lost. But of the crab pots Stevens recovered, at least one-third of them lacked the required escape panel.
Stevens' study focused only on one small bay. He says it's anyone's guess how many crab pots lie at the bottom of the Alaska's Bering Sea and Gulf of Alaska, since fishermen aren't required to report lost pots.
STEVENS: "Looking at Chiniak Bay, if we look at the densities there, and apply those to the Bering Sea, we come up with an estimate more like 1.5 million lost pots."
That many lost pots could be killing as many as ten million crabs each year, according to Stevens' back-of-the-envelope calculations. By just about anyone's measure, that's a lot of crabs. Still, when it comes to setting catch limits for the commercial fishing industry, biologists don't factor in what's caught by these ghost pots.
STEVENS: "It doesn't even enter into the catch quotas because there's really no way to deal with it."
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
For more information about Tanner crabs, visit these Web pages:
Tanner Crabs (ADF&G Wildlife Notebook Series)
Check out these books on crabs!
Thanks to the following individual for help preparing this script:
Dr. Brad Stevens
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
Alaska Sea Grant Homepage
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