Blue Crab

Because of restrictions placed on the Bay's blue crab harvest in 2008, the 2011 dredge survey revealed a total of 460 million crabs in the Bay—the second highest recording since 1997. Photo by Carrie B. GrishamBecause of restrictions placed on the Bay's blue crab harvest in 2008, the 2012 dredge survey revealed a total of 764 million crabs in the Bay—nearly three times the number in 2007. Photo by Carrie B. Grisham

Back from the Brink

The fact that we can't control Mother Nature makes it even more imperative that we focus on the elements we can control, especially reducing pollution to the Bay and maintaining higher numbers of spawning age female crabs.

Also known as "beautiful swimmer," the blue crab is inextricably linked to the oyster. With the drastic decline of the Bay's oysters in the 1980s, watermen's attention quickly shifted to the blue crab and with it came a longer crabbing season. A decade or so and 665,000 crab pots later, the fishery neared collapse. Not only was the blue crab itself threatened, but so too were the oyster reefs and underwater grasses that provide it with food, shelter, and oxygen.

Results from the 2011-2012 winter dredge survey estimated 764 million blue crabs in the Chesapeake. That marked the first time since the early 90s that the crab remained at sustainable levels. But 2012-2013 survey numbers dropped to 300 million—a drastic loss even considering that the crab population has always been prone to fluctuations.

These most recent numbers serve as a reminder of just how fragile and complex the process of restoration can be and why continual vigilance is necessary if we are to bring back not only a sustainable crab fishery, but a sustainable Bay.

A "Perfect Storm"

The survey released in April 2013 showed mixed results for the blue crab population.

  • The total number of crabs and the total number of juvenile crabs dropped significantly.
  • The total number of spawning age females and males, though still low, was on the rise.

According to CBF Director of Fisheries Bill Goldsborough weather, habitat loss, abundant predators and low numbers of spawning-age females led to a "perfect storm" for the population. Record production of young crabs in 2011 was offset by unusually high populations of predators feeding on the small crabs in 2012—2012 saw a banner year for 1-year-old striped bass and an unusually high population of red drum—combined with the ongoing decline of underwater grasses, an essential habitat for blue crabs, made juveniles especially vulnerable.

To make matters worse, winds and tides that swept crab larvae into the Bay in large numbers in 2011 were not favorable in 2012. Combined with the low numbers of spawner females seen in last year's survey, the result was very poor "recruitment" of young crabs into the Bay in 2012.

In response, Maryland and Virginia have agreed to reduce this year's harvest of female crabs by an additional 10 percent, increasing the odds of good reproduction in 2013.

The fact that we can't control Mother Nature makes it even more imperative that we focus on the elements we can control, especially reducing pollution to the Bay and maintaining higher numbers of spawning age female crabs. Reducing the levels of nutrients reaching the Bay from farms and lawns and better managing stormwater runoff before it gets into rivers and streams, will help mitigate weather extremes, improve water quality, and contribute to the recovery of both blue crabs and Bay grasses.

"Virginia, Maryland, Pennsylvania, the other Bay states, and the District of Columbia all committed to reducing pollution from all sources as their part of their Clean Water Blueprint. The decline in both blue crabs and grasses this year underscores the need to implement the Blueprint as quickly as possible," emphasized CBF President Will Baker.

Creating a Sustainable Fishery

"The crab population is truncated, meaning we catch crabs so quickly, there are very few crabs bigger than legal size," Goldsborough said. "As a result, the fishery is very dependent on each year class that comes in.

And that creates instability, which is not a good thing for the crabs or the crabbers. We want more older crabs in the crab population so that we have ongoing high reproductive potential, which helps stabilize the population."

One way to build stability in the crab population is for Maryland and Virginia to continue the science-based approach to managing the fishery adopted in 2008. Although some watermen have called for relaxing restrictions, lifting the protections could lead to another collapse.

Blue crabs can live for up to about four years and can grow up to 10 inches across the shell from point to point. But until Virginia and Maryland imposed restrictions on catching crabs in 2008, two thirds or more of all crabs in the Bay were caught annually. This meant that most did not live much beyond one or two years or grow much larger than the legal catch-limit of five inches.

"The blue crab was really affected most by overexploitation by fishing," said Dr. Thomas Miller, Director of the Chesapeake Biological Lab. "A decade ago, they were experiencing 70 percent removal rates. And you can't take 70 percent of the trees and still have a forest. And if you take 70 percent of the crabs, you no longer have a healthy crab stock."

Since 2008, fisheries managers in Maryland and Virginia have been keeping total annual harvests below 46 percent of all crabs. Regulators have also now adopted a target of allowing no more than 25.5 percent of all females to be caught in any one year. If these limits continue, and the Bay states are successful in reducing pollution, the wide fluctuations in the blue crab populations should moderate. And this should allow the Chesapeake's scrappy fighters to continue their peculiar sideways march to restored health.

The Fight to Shrink "Dead Zones"

Another strategy to improve the long-term stability and health of the Chesapeake's crab populations is to cut significantly the nitrogen and phosphorus pollution into the Bay. Nitrogen and phosphorus stimulate explosive growth of algae. Algal blooms darken the water, blocking light and killing underwater grasses that crabs need for shelter. Algal blooms fed by polluted runoff quickly die and decay, sucking up oxygen and creating "dead zones." The dead zones force crabs to find oxygen in shallow waters where they are more easily caught.

"Dead zones" also kill the food that crabs eat, destroying or preventing the growth of 75,000 metric tons of clams and worms a year in the estuary, according to a scientific study in the journal Science. That is enough food to support half the commercial crab harvest.

In an effort to shrink the Bay's "dead zones," the U.S. Environmental Protection Agency issued pollution targets for the Chesapeake Bay in December 2010. These targets have come under attack by industry lobbying groups, however, and CBF is fighting to defend them in court and in Congress

At the center of this fight are blue crabs and the more than 6,000 watermen and other workers who depend on the crabs for their livelihoods.

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