This story first appeared in the SERC quarterly Newsletter Summer 2006
Scaling Up the Blue Crab Enhancement Project
Over the last four years, it has become a summer tradition for members of the SERC staff to gather en masse at the wet lab and, in assembly-line fashion, manually inject thousands of 20mm (3/4-inch) baby blue crabs with brightly colored dye and a tiny micro-wire before their release into the wild. This year, the biggest year yet for the Crab Lab, may well signal a shift in technology and an end to tradition as the blue crab enhancement project ramps up in scale. The injected tags allow the researchers to identify hatchery-reared crabs as they follow the crab populations in their study coves along the western shores of the upper Chesapeake Bay.
By following their little charges after release, the researchers have learned important information about how and where to release hatchery crabs to improve their survival. So far, they've more than doubled the population of blue crabs in their test coves, and they've seen their crabs grow to maturity and mate in the wild. The next step will be to determine if the same patterns hold true in other regions of the Bay, and if it's logistically and economically feasible to conduct this kind of stock enhancement with numbers large enough to increase the breeding population and help the struggling blue crab population recover in the Chesapeake Bay.
In the four years between May of 2002 and fall of 2005, they released about 91,000 hatchery-reared juvenile blue crabs in batches of between 1,500 and 10,000 crabs. This year, they've already released more than half that many and expect to reach that number by the end of the season. The tagging activity around the wet lab during releases is frenetic to say the least. But now that they are hoping to ramp up to release between 30,000 and 50,000 crabs at a time, the manual tagging parties may be coming to an end.
"When hatchery production reaches this level, traditional tagging will be time prohibitive, and genetic tagging will be required to follow released cohorts through time," said researcher Eric Johnson.
The juvenile crabs come from wild-caught mated females which are held at the University of Maryland Center of Marine Biotechnology until they become egg-bearing and hatch their larvae. By tracing the genetic signature of the mother through mitochondrial DNA (which remains exactly the same from mother to offspring), researchers will be able to identify both their hatchery crabs and crabs descended from any females they release that enter the breeding population.
So now, instead of processing thousands of crabs before release, the researchers need only take a little blood, or one of the legs from the crabs they catch on follow-up visits and send it to the lab for identification. Following the crabs through their DNA could begin as early as next season.
For more information, or to reach the scientists involved in this project, please contact SERC science writer Kristen Minogue.