Estimating Blue Crab Population Size in the Rhode River

Since 2001, the Smithsonian Environmental Research Center (SERC) has conducted experiments to assess the feasibility of blue crab stock enhancement in the Chesapeake Bay. We have tracked the survival and growth of thousands of hatchery-reared juvenile blue crabs released into small coves in the upper and lower Chesapeake Bay. At this scale, we are able to estimate the level of enhancement (hatchery contribution in relation to the wild population). However, to assess the extent of stock enhancement at a larger scale, such as the Rhode River subestuary, we need an accurate estimate of the wild blue crab population size. Thus, the goal of this tagging project is to estimate the size of the legal-sized blue crab population in the Rhode River.

Based on our tests of juvenile survival in combination with an accurate estimate measure of wild crab abundance, we can then calculate the numbers of juveniles needed to increase the blue crab population to within a subestuary like the Rhode River.

 

One way we can estimate population size is with a mark-recapture (tagging) study.  If we tag and release a known number of individuals from a population, based on the number of tagged and untagged individuals captured afterwards, we can estimate the total population size.

 

Not every recaptured tag is reported, which can bias certain analyses of mark-recapture data. Therefore to estimate the reporting rate of tagged blue crabs a subset of crab tags are marked with a high reward ($100 high reward, $5 standard reward). Assuming a 100% reporting rate of high reward tags the overall reporting rate can be estimated.

If you have recaptured tagged blue crabs please click here.