This is an edited and abridged version of a Bay Journal article by Timothy B. Wheeler, “Scientists dredge for lowdown on Chesapeake Bay blue crabs,” published Feb. 27 on BayJournal.com.
Every winter, teams of scientists from Maryland and Virginia brave the cold waters of the Chesapeake Bay to sample the depths with steel-toothed dredges. The annual winter dredge survey has been conducted for over three decades and is considered the most reliable way to predict the number of blue crabs that will be available to catch and eat in the coming year.
The crabs settle on the bottom when the water temperature drops below 50 degrees Fahrenheit and stay dormant until the water warms again. The data collected from the survey has helped regulators manage commercial and recreational crabbing to prevent overfishing.
This year’s survey results are even more anxiously awaited than usual because last year’s survey found the crab population at its lowest abundance in more than 30 years. While the number of females old enough to reproduce was down, it was still above the minimum level deemed necessary to sustain the population. But the number of little juvenile crabs, the critical link between previous and future generations, was the second lowest ever, only slightly better than the record low in 2021.
The survey is messy and repetitive, but each crab discovered amid the detritus is measured, its sex determined, and its particulars recorded for later analysis. The results of this winter’s survey likely won’t be known until May, after the field sampling is finished and the numbers are crunched. The outcome could ease—or deepen—worries about the stability of the fishery.
“The wintertime gives us that chance to really get a quick snapshot on year-to-year changes up or down in the population,” said Michael Seebo, a senior marine scientist at VIMS, who’s been involved with the survey almost since its beginning. “I’ve put a lot of pride and time into making it consistent, and the people I work with are good people. And I think that the information that comes out of it is valuable to the [fishery] managers.”
Fishery managers in both states responded to the sub-par 2022 survey results by tightening harvest rules through the second half of the season that had already begun. Despite the added catch restrictions, the 2022 commercial harvest didn’t take that big of a hit. The preliminary figures from the Maryland Department of Natural Resources show that Maryland’s watermen landed about 22.7 million pounds of crab last year, with all but about 1 million pounds coming from Chesapeake waters. That’s on par with Maryland’s 2021 harvest from Bay waters. Virginia’s watermen landed about 15.3 million pounds of crabs in 2022, which is 8% below the 16.6 million pounds harvested in 2021.
Whatever the outcome of this winter’s survey, Virginia’s fishery managers must ensure that more spawning females can reproduce before being caught. That might mean limiting the spring catch rather than an overall harvest reduction. While the survey’s estimate of juvenile crabs is based on more limited data than other population segments, scientists and managers note there’s only been one year where its results failed to track with the harvest.
Last year’s results were concerning enough that scientists and fishery managers in Maryland and Virginia agreed it was time to perform another comprehensive stock assessment of the Bay’s crab population. The last one was in 2011. This one will revisit all the assumptions about crabs that went into the earlier assessment and incorporate the results of other surveys besides the winter dredge. Experts also plan to analyze the data using one or more mathematical models that might be more sensitive to the stages of crab maturation or variable conditions in different parts of the Bay or in different seasons.
They also plan to evaluate whether environmental conditions may have changed, including predation by other fish. Striped bass and red drum are known to feed on juvenile crabs. But nonnative blue catfish, which have proliferated throughout the Bay since being introduced in Virginia years ago, is a newer and potentially bigger threat. A 2021 VIMS study estimated they were consuming a couple of million little crabs yearly in one stretch of the lower James River.