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Using Molecular Markers to Manage Alaska’s Declining Red King Crab Fisheries

Courtesy of Dr. Stewart Grant (ADF&G & UAA)

If you aren’t a connoisseur of king crab meat–a crustacean-lover’s delight–you are missing out. Tell me that you are at least acquainted with the perils of king crabbing, which are chronicled in Discovery Channel’s documentary series, Deadliest Catch. The show hardly sensationalizes one of the most dangerous vocations in the world.  Over three hundred crab fishing fatalities per 100,000 fishermen per year were tabulated for the commercial fishing industry in the early 90′s.

The number of crab fishing-related fatalities is probably of little consolation to red king crabs, considering the numbers of their conspecifics that have been harvested for seafood aficionados around the world.  Several of the regional populations of red king crabs in the Bering Sea and North Pacific are on the decline. None-the-less, the delicacy, served in white table cloth restaurants in Japan, the US and Europe, shows no sign of waning. But can we sustain the crab harvest at this rate?

Obviously the large harvests of red king crab greatly affect their abundances. But other hidden factors are also important, especially in the North Pacific where populations must contend with decadal shifts in climate. These changes affect the survivals of red king crab larvae and juveniles, as well as the ability of adults to reproduce.

One factor that keeps populations depressed is the suit of predators, including fish and seastars, that prevent populations from expanding. Another less obvious factor is genetic diversity. Without high stores of genetic variation, crab populations cannot adapt to environmental changes. Climate warming will also add to the challenges facing red king crab populations in the future.

Alaska Department of Fish & Game’s fisheries research biologist, Dr. Stewart Grant, and a colleague of mine on faculty at the University of Alaska Anchorage recently set out to examine the genetic structure of red king crab populations  in the North Pacific and Bering Sea.  The study, to be published in the journal Evolutionary Applications, provides new details of the genetic structure red king crabs in Alaskan waters–information that will help fisheries managers ensure sustainable harvests of one of the most popular sea food delicacies in the world.

Red king crab is one of the largest crabs in the stone crab family  and is the most abundant of the king crabs.  The species’ current range extends across the North Pacific from the Sea of Japan to northern British Columbia and into Alaska’s Bering and Chukchi seas. Genetic markers were used to understand how connected these populations were with one another.

Stewart and his team, using DNA-based molecular markers, were not only able to delineate the population structure of Alaskan red king crabs for harvest managers, but they were able to provide insights into the history of red king crabs during the ice ages several thousands of years ago.  Red king crab populations are subdivided into three regional groups that appear to reflect isolations during glacial maxima, when glaciers covered coastal areas around the rim of the North Pacific.

The researchers used mitochondrial DNA as one of the population markers and found high levels of diversity in western North Pacific populations, but unusually low levels of diversities in eastern populations.  Just as the mitochondrial ‘Eve’ for humans is in Africa, the mitochondrial Eve for red king crab is in the waters of the Northwestern Pacific off Russian and Japan.

The very low diversity in Southeast Alaska probably indicates these populations have periodically gone extinct, perhaps during glacial maxima, and have been recolonized by red king crabs from Russian waters. These low levels of diversity also sound a note of caution for harvest management, because populations in Southeastern Alaska may not have enough genetic diversity to easily adapt to changing environmental conditions.

Courtesy of Dr. Stewart Grant (ADF&G & UAA)

Even though regional groups of populations differ genetically from one another, they are all very delicious. The next time you crack open the crab legs on your plate, think of how man and nature have worked to bring this delicacy to you. The North Pacific Ocean has provided opportunities for bountiful harvests, albeit under harsh conditions. Both Alaska state and Federal biologists are pursuing the research to ensure this bountiful harvest for generations to come.

Comments

  1. Don Johnson
    Alaska
    June 8, 2013, 5:04 am

    1980 – 2010 excess commercial harvest has resulted in a lack of extra salmon escaping, spawning, dying and rotting in our freshwater. The resulting lack of water nutrients resulted in our crab populations not being able to recover after excess commercial crab harvest 1980. The lack of crab resulted in a lack of >17 mm crab larval. Our juvenal king salmon and herring feed exclusively on >17 mm crab larva and 98% of them are gone. The result is that our juvenal king salmon are currently starving to death because we commercially scooped up most of our returning salmon and sold them around the world, thus killing our crab, thus killing our herring, thus killing our king salmon.

  2. kim barber
    February 5, 2012, 2:31 pm

    I wonder if HAARP has anything to do with the declining numbers?