Radio Script
2000

 

The transmitter being glued to this golden king crab in Southeast Alaska will help researchers follow the crab as it explores the sea floor. UAF/SFOS photo

 
Deep Crabs
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INTRO: If you want to know where crabs go, you pretty much have to follow them around. As Doug Schneider reports in this week's Arctic Science Journeys Radio, that's just what scientists in Southeast Alaska are doing.

STORY: The beeping you hear is coming from a golden king crab, some 1,200 feet beneath the ocean surface in Southeast Alaska. The king crab itself isn't making the sound. Rather, it's coming from a special transmitter that researchers have glued to the crab's shell. Dr. Tom Shirley is a marine scientist at the University of Alaska Fairbanks.

Here is a brief video clip of a tagged crab walking on the ocean floor. UAF/SFOS photo

SHIRLEY: "The tags are sonic tags; each one has a unique code, something like 2-5-1. So you'd listen for two, then five beeps, then a space and then one beep. So you'd know exactly which crab you're working with. They also have a unique frequency, so between frequency and code we can identify the crab."

The crabs were caught by a local fisherman contracted to help with the project. Shirley, along with more than two dozen graduate students from the university, put the transmitters onto 26 golden king crabs. It's all for science, says graduate student Zac Hoyt.

HOYT: "Golden king crab inhabit really, really deep water in Southeast Alaska. There's not a lot known about them because of where they live. So we've placed these sonic tags on the crab and we're trying to track them with the submarine over eight or nine days to see if they would move up and down in the water column. We put them at different depths than which we caught them at. We're trying to see if they inhabited certain types of areas, if they liked silty sediment bottoms over rocky bottoms or if they preferred certain depths. We wanted to see what habitat they used and use that information to manage the fishery a little bit better because there's not much known about these critters."

The Delta, a two-person research submersible, gets ready to go looking for crab in the waters of Southeast Alaska. UAF/SFOS photo

The scientists used a two-man submarine equipped with cameras, lights and an underwater microphone to home in on and follow the beeping signal coming from the crabs. Tom Shirley.

SHIRLEY: "The crabs are found far below the depth range of the sub, which is 1,200 feet. We're working right up against that depth range now. The submarine right now is close to about 1,000 feet. So, fairly deep depths."

One of the things scientists want to know is just how far golden king crab roam on the sea floor.

SHIRLEY: "We're finding out some things about them. One of the crabs we relocated today had moved 300 meters in about a day and a half. So, they're fairly active."

This time of year, golden king crabs are in the midst of their annual mating cycle. Crabs are on the move, looking for companionship among the rocks and boulders that litter the sea floor. In just a week's time, researchers have spotted 25 mating pairs of golden king crabs. Shirley says such information should be useful to fishery managers.

SHIRLEY: "We'll know where the different sexes and sizes of crabs are located in terms of depth and habitat. If you're trying to target a fishery on a particular size class, say adults and males only, well then you can perhaps open fishing only in certain areas that meet those criteria. You can have more selectivity in your management."

Shirley's funding—for things like the research vessel and the mini-submarine—comes from the university's National Undersea Research Center. Although they only have funding for research this summer, graduate student Zac Hoyt hopes to keep track of the crabs over the next couple of years.

HOYT: "I'm going to try and make this into my thesis work. We're going to try and go back several different times of the year and try to track them from the surface to see if they are moving long distances, if they're staying in more confined areas."

Two years is just about how long the sonic tags—which cost $260 apiece—are expected to last, since they'll fall off when the crab molts out of its old shell and begins to grow a new one.

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.

Cruise plan (PDF) for the golden king crab habitat study.

For more information about golden king crab, visit these web sites:

King Crab Species Profile

Alaska Sea Grant publications on king crab and other shellfish species

Thanks to the following individuals for help preparing this script:

Dr. Tom Shirley and Zac Hoyt
University of Alaska Fairbanks
School of Fisheries and Ocean Sciences
Juneau Center, Fisheries Division
Juneau, AK 99801
Phone: 907-465-6449

Email: fftcs@uaf.edu