Va. Scientist Thinks He Knows What’s Killing Off Blue Crabs

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(Photo credit: PAUL J. RICHARDS/AFP/Getty Images)

(Photo credit: PAUL J. RICHARDS/AFP/Getty Images)

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LANHAM, Md. (WNEW) — An annual dredge of the Chesapeake Bay says the number of harvestable blue crabs decreased significantly between 2013 and 2014 — to levels that haven’t been seen since before strict conservation restrictions went into effect more than five years ago.

In fact, it’s one of the Bay’s smallest harvestable crab populations in a quarter of a century.

Some have pointed the finger at the harsh winter the Mid-Atlantic experienced. While that may have been a factor, it’s not the only one, according to Virginia Institute of Marine Sciences disease ecologist Jeff Shields.

After researching the issue with the help of a National Science Foundation (NSF) grant, Shields believes a major contributing factor to the population decline of Chesapeake blue crabs and other marine creatures may be a single-celled parasite called Hematodinium.

Hematodinium was first reported along the East Coast in the 1970s and found in the Chesapeake’s blue crabs in the 1990s, according to a National Science Foundation report.

“Infection is almost always fatal for the crabs,” Shields says.

He and other scientists recently found out more about the parasite’s life cycle, which may prove to be a breakthrough for the livelihood of the Chesapeake’s crabs.

Shield’s research says Hematodinium usually infects young crabs, which means they may be dying before they can even make their way from spawning grounds along the coast to tributaries, where they become large enough to catch.

Unfortunately, the Bay has several factors that may facilitate epidemics like Hematodinium, Shields says, such as minimal immigration and emigration, restricted water exchange with the open ocean and stressful environmental conditions like overfishing.

Shields is now working to better understand how Hematodinium is transmitted. In the case of blue crabs, he believes infection is linked with their molting cycles.

“We hope to develop ‘best practices’ for managing, in particular, the Chesapeake’s wild blue crabs,” he says.

According to him, “there’s a perception among resource managers and fishers that diseases aren’t important to the fishing industry, or that little can be done to manage them.”

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