Mother nature may have lent a helping hand to government regulations in causing a rebound in the Chesapeake Bay’s blue crabs over the last two years. But it was not the only hand, as new conservation policies gave the beautiful swimmers a primary boost, crab researchers and regulators say.
Weather conditions favorable to the survival of blue crab larvae appear to have assisted in the more than doubling of Bay blue crab populations that was also driven by restrictions on catching female crabs imposed by Maryland and Virginia in 2008, according to scientists with the Smithsonian Environmental Research Center.
However, the Chesapeake Bay’s neighboring states to the North and South along the Atlantic have no evidence that they experienced as large a jump (if any) in crab populations as Maryland and Virginia. North Carolina and Delaware have not imposed new crabbing restrictions in the last two years. And the lack of similar crab population increases in North Carolina and Delaware suggests that the Chesapeake Bay’s blue crab boom was not solely due to good weather, as some critics of the Bay’s crabbing restrictions have claimed.
The implication is that Maryland and Virginia’s protections for female crabs are, in fact, valuable for the Chesapeake’s ecology and economy -– and should be kept in place.
“First we clearly benefitted from regulations, and then we benefited from a combination of regulations and mother nature,” said Lynn Fegley, assistant director of the Fisheries Service at the Maryland Department of Natural Resources.
After decades of decline, the Chesapeake Bay’s estimated blue crab population hit a near record low of 260 million in 2007. And then, after Maryland and Virginia imposed tight new restrictions on catching female crabs, the Bay’s crab population jumped to 650 million –- the most in more than a decade -- in a survey conducted this past winter.
Within three or four months of the regulations going into effect in the fall of 2008, a dredge survey of crab populations in the Bay during that winter suggested an immediate increase in the number of adult female crabs. That quick rise must have been the direct result on the restrictions on catching female crabs, Fegley said. Then, the next winter, in 2010, the survey found both more adults and more juveniles, Fegley said. It is possible that more of the juveniles produced by the females survived this second year because of favorable weather conditions, Fegley said.
The theory that both regulation and good weather played roles in the Chesapeake’s crab multiplication is supported by Tuck Hines, a blue crab expert and director of the Smithsonian Environmental Research Center, and Eric Johnson, a crab researcher at the Smithsonian.
Hines noted that the increase in young blue crabs in the Bay this year happened at the same time as increases in numbers of young fish -– spot and perhaps also menhaden –- whose survival (like that of blue crab larvae) is dependent on weather conditions along the Atlantic‘s continental shelf. A shift in the global El Nino weather pattern could have assisted all three species, he wrote in an e-mail to Bay Daily.
“I think that the major increase in blue crabs resulted from a combination of (survival of more crab larvae) due to the shift to southern fronts from El Nino, and from the increasingly effective conservation of female crabs in the spawning stock -– especially due to the elimination of the Virginia winter dredge fishery,” Hines said.
In other words, protecting mother crabs was helpful. But the ocean's currents and winds might also have helped the crab larvae find their way back into the Chesapeake Bay, where they could find shelter in eelgrass and grow.
"I think we're all on the same page," wrote Rom Lipcius of the Virginia Institute of Marine Science in an email to colleagues on the subject. Regulations helped boost the spawning stock of the blue crabs, and the survival of larvae "was helped to some (unknown) degree...by favorable environmental conditions."
Tom Miller, a blue crab expert at the University of Maryland Center for Environmental Science, said that two years of crab population estimates are not nearly enough to reach a firm conclusion about the effectiveness of the 2008 regulations imposed by Maryland and Virginia.
Miller said in an email that there is a “strong possibility” that the regulations caused the Bay’s crab quick population jump. But he added: “It might have been, as with striped bass, that management regulations were coincident with environmental factors” that encouraged survival of young crabs, Miller said.
In Delaware, the estimated blue crab populations in Delaware Bay grew in 2009, to 114 million crabs, compared to 66 million in 2008, according to the Delaware Division of Fish and Wildlife. But even these 2009 figures were below the estimates for 2007 (187 million crabs), 2006 (169 million), and 2005 (115 million). An estimate for 2010 is not yet available, Wong said.
“We did not see the same doubling in abundance the last two years that the Chesapeake Bay experienced,” said Richard Wong, a biologist who studies blue crab populations in Delaware Bay for the Delaware Division of Fish and Wildlife. “I would say that the conservation of spawning females the last couple of years (in Maryland and Virginia) could be a logical explanation for why that stock has been increasing. But we’ll learn a lot more in the next two or three years.”
It is possible (although far from certain) that the 2009 crab increase in Delaware Bay was the result of the rise in the nearby Chesapeake Bay, said Eric Johnson of the Smithsonian Environmental Research Center. "The Chesapeake Bay blur crab population is much larger than that in Delaware Bay, and Delaware is a likely destination for many crabs spawned by (Chesapeake) Bay females," Johnson speculated in an email.
Less likely to be influenced by the Chesapeake Bay's crab increases is North Carolina, Johnson said.
The Tarheel state, like Delaware, has imposed no new crab regulations in recent years. And in North Carolina, there have been no clear trends upward or downward since 2008 in the number of crabs, said Lynn Henry, a biologist with the North Carolina Division of Marine Fisheries. In fact, the abundance of young crabs fell from 2008 to 2009, and harvests of crabs also dropped slightly over this time period.
Over the last decade, crab harvests in what has been North Carolina’s biggest crabbing area –- Pamlico Sound –- have fallen sharply, from more than 40 million pounds a year in 1998 to less than 10 million pounds in 2009, according to state figures.
Anecdotally, Henry said, watermen this summer are saying that they are finding good harvests of crabs in Pamlico Sound, and are finding a "tremendous amount of small crabs" in another important crabbing area, Albemarle Sound.
But figures for 2010 are not yet available from North Carolina. And Henry said he would not even try to predict whether crab populations and harvests this year will be up or down.
"Crabs are a highly variable species," said Fegley of Maryland's Department of Natural Resources. "They are like dandelions. They live fast and die young. And we have to account for that natural variability in our management."
By Tom Pelton
Chesapeake Bay Foundation
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