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Bay Blog: winter dredge survey

Apr
13
2016

Adult female blue crab abundance rises 92 percent in 2016

The Chesapeake Bay’s adult female blue crab population has increased 92 percent since the population was surveyed last winter. While the current adult female blue crab abundance of 194 million is well above the overfishing threshold, it remains below the 215 million abundance target.

The Chesapeake Bay’s blue crab population is an indicator of Bay health.

Maryland and Virginia estimate the Bay’s blue crab population through an annual winter dredge survey. Over the course of three and a half months, scientists visit 1,500 sites around the Bay, using metal dredges to pull up crabs over-wintering in the mud.

Results of the 2016 winter dredge survey show the Bay’s total blue crab population has increased from 411 million to 553 million since last winter. Results also show the number of adult females has risen from 101 million to 194 million. The number of juvenile crabs has increased from 269 million to 271 million, which is just above the long-term average.

“The crab stock has been on a rollercoaster for most [of] the last decade,” said Virginia Marine Resources Commissioner John M.R. Bull in a media release. “We’ve seen a few great years of reproduction followed by awful years of abundance. Two years does not make a trend, and this news inspires both wary optimism and cautious management.”

In the short term, Maryland officials do predict a good crab season. “Due to a milder winter, favorable currents and tides, and wise Bay-wide management measures, the Maryland crab population continues to rebound and strengthen,” said Maryland Department of Natural Resources Fisheries Service Director Dave Blazer in a media release. “With an increase in abundance and steady recruitment, we fully anticipate a robust crab season this year.”

Maryland and Virginia estimate the Bay’s blue crab population through an annual winter dredge survey.

The Chesapeake Bay Program tracks the adult female blue crab population as an indicator of Bay health, and in the Chesapeake Bay Watershed Agreement committed to maintaining a sustainable blue crab population based on a target of 215 million adult females. The Chesapeake Bay Stock Assessment Committee (CBSAC), which includes scientists and representatives from states, academic institutions and the federal government, will use this data to make recommendations on sustaining the blue crab population in its 2016 Blue Crab Advisory Report, expected to be released this summer.

Learn more about the winter dredge survey in Maryland and Virginia.



Mar
17
2016

Photo Essay: The blue crab winter dredge survey completes its course

Senior Marine Scientist Mike Seebo of the Virginia Institute of Marine Science (VIMS) prepares water quality monitoring equipment aboard the R/V Bay Eagle, after departing Gloucester Point, Va., at sunrise on March 8, 2016. The annual blue crab winter dredge survey estimates populations of blue crab in the Chesapeake Bay.

From December to March, assessing the health of the Chesapeake Bay’s blue crab population means long stints on the water for scientists from the Virginia Institute of Marine Science (VIMS). Every year the blue crab winter dredge survey samples 1,500 randomly-chosen sites divided equally between Virginia and Maryland waters, in a partnership between VIMS and the Fisheries Service of the Maryland Department of Natural Resources (DNR). The data provides a bay-wide estimate of blue crab populations that helps agencies determine how many can be harvested without hampering the recovery of one of the Chesapeake Bay’s defining resources.

After a clear, calm sunrise in the second week of March, the VIMS team left their headquarters in Gloucester Point, Virginia, with 742 of 750 sites under their belt. Their boat, the R/V Bay Eagle, is their home during trips lasting up to four days at a time. With just eight sites left to sample using their six-foot-wide crab dredge, this would be a relatively short day—the last one of the season.

“That sort of puts a smile on our face,” said Mike Seebo, a VIMS marine scientist who has worked on the winter dredge survey since its second winter in 1990.

Marine Scientist Gabrielle Saluta, right, and Research Specialist Alison Smith pull blue crabs from the dredge near the mouth of the York River in Virginia.

The dredge relies on the blue crab’s winter behavior of burrowing into the mud and lying dormant when the temperature drops below 45 to 50 degrees Fahrenheit. When the crabs wake up in the coming months, the mature females will migrate to lower-salinity spawning grounds in the Bay’s tributaries, a journey of up to 150 miles for crabs reaching the northernmost habitats.

And many of the crabs will end up harvested, steamed and covered in Old Bay seasoning. For one of the region’s mainstays, the numbers coming from the survey teams will be highly awaited.

See how the process unfolds in our video from the Maryland half of the winter dredge survey.

Seebo records numbers of blue crab as well as bycatch, location and water quality data.

Marine Scientist Katie Knick pushes a crab dredge into position while the team hauls up a dredge sample.

Saluta, left, examines a peppermint shrimp held by Seebo. Dredge bycatch can include small fish, plants and invertebrates like hydroids, tunicates and clams.

Saluta, top, and Smith tie tags to blue crabs for an ongoing program that yields information on blue crab mortality, longevity and migrations. Anyone who catches a tagged crab can earn a $20 reward by calling in and then filling out a data sheet mailed to them.

Saluta returns tagged blue crabs to the lower stretch of the Chesapeake Bay.

From left, Smith, Saluta and Knick wait as a dredge is performed. At every site the six-foot-wide dredge travels at three knots for 60 seconds, and the team records GPS data to measures the distance traveled.

Sluggish from the cold, a male blue crab rests on the deck of the R/V Bay Eagle after being pulled from the mud of the Chesapeake Bay. The winter dredge survey operates as blue crabs remain dormant in the mud, before water temperatures rise.

Seebo collects a blue crab caught at a sample site.

From left, Knick makes a sandwich while taking a lunch break with Smith and Saluta aboard the R/V Bay Eagle. "One thing to look forward to is food—so we try to eat well," Seebo said.

Seebo hoses off the deck of the R/V Bay Eagle after the completion of sampling on the last day of the blue crab winter dredge survey. “It’s sort of bittersweet—as soon as [the weather] starts getting pleasant and nice we stop,” Seebo said.

Keith Mayer of VIMS unloads gear from the R/V Bay Eagle at the end of the last day of the blue crab winter dredge survey in Gloucester Point, Va., on March 8, 2016.

To view more photos, visit the Chesapeake Bay Program’s Flickr page

Photos and text by Will Parson

Video by Steve Droter

Will Parson's avatar
About Will Parson - Will is the Multimedia Specialist for the Chesapeake Bay Program. A native of Bakersfield, California, he acquired an interest in photojournalism while studying ecology and evolution at University of California, San Diego. He pursued stories about water and culture as a graduate student at Ohio University's School of Visual Communication, and as an intern at several newspapers in New England before landing in Maryland.



Apr
27
2015

Chesapeake Bay’s blue crab population shows modest rise

The Chesapeake Bay’s blue crab population has seen a modest rise, increasing 38 percent since the population was counted last winter. While an increase in blue crabs is an indicator of Bay health, the adult female crab population remains below its target, indicating the variability of the blue crab population and the complexities of managing the fishery.

Image courtesy jpellgen/Flickr

Maryland and Virginia measure the Bay’s blue crab population through an annual winter dredge survey. Over the course of three and a half months, scientists visit 1,500 sites around the Bay, using metal dredges to pull up crabs over-wintering in the mud.

Results of the 2015 winter dredge survey show the Bay’s total blue crab population has increased from 297 million to 411 million since last winter. Results also show the number of spawning-age females has risen from a depleted 69 million to 101 million. The number of juvenile crabs has jumped from 199 million to 269 million, which is just above the long-term average.

According to the Maryland Department of Natural Resources (DNR), the cold winter and resulting low water temperatures contributed to a “substantial mortality” among blue crabs, killing an estimated 19 percent of adults.

“We are pleased that crab numbers increased despite the harsh winter temperatures,” said DNR Secretary Mark Belton in a media release.

The Chesapeake Bay Program tracks the adult female blue crab population as an indicator of Bay health. The Chesapeake Bay Stock Assessment Committee (CBSAC), which includes scientists and representatives from the federal government, state governments and academic institutions, will use this data to make recommendations on sustaining the blue crab population in its 2015 Blue Crab Advisory Report, expected to be released this summer.

Learn more.



Jul
02
2014

Experts recommend ‘risk-averse’ approach to managing depleted blue crab stock

Fisheries experts have recommended a “risk-averse” approach to managing blue crabs in the Chesapeake Bay, following poor harvests and a dramatic decline in the abundance of adult female crabs.

Image courtesy bionicteaching/Flickr

In its annual evaluation of the Bay’s blue crab fishery, the Chesapeake Bay Stock Assessment Committee (CBSAC) urged the Maryland Department of Natural Resources (DNR), the Virginia Marine Resources Commission (VMRC) and the Potomac River Fisheries Commission (PRFC) to protect female and juvenile crabs in an effort to rebuild the overall population. The committee, which is made up of scientists, academics and government representatives and housed under the Chesapeake Bay Program’s Sustainable Fisheries Goal Implementation Team, also recommended establishing sanctuaries to protect females and improving data related to crab harvests and winter death rates.

According to the 2014 Chesapeake Bay Blue Crab Advisory Report, the start of the 2014 crabbing season saw 68.5 million adult female crabs in the Bay. This marks a 53 percent decline from last year’s abundance of adult females. This number is based on the results of the winter dredge survey, and is tracked by the Bay Program as an indicator of Bay health. It is below the 215 million target abundance and the 70 million threshold, indicating adult females are in a depleted state.

“The poor performance of the Bay’s 2013 blue crab fishery—the lowest reported harvest in the last 24 years—combined with the winter dredge survey results that indicate a depleted female population warrants management actions to conserve both females and juveniles,” said CBSAC Chair Joe Grist in a media release. “The cold winter and other environmental factors affected the crab population, and we expect that conservative regulations will help females and juveniles—the future of the blue crab population—rebound.”

Earlier this month, The Capital reported that Maryland, Virginia and the PRFC have promised to cut harvests of female crabs by 10 percent. Virginia announced its plans in June, while Maryland and the PRFC are expected to release their regulations soon.



May
07
2014

Chesapeake Bay’s blue crab abundance remains low

The blue crab population in the Chesapeake Bay has dropped, due to a range of factors that include weather patterns, coastal currents and natural predators.

According to scientists with the Maryland Department of Natural Resources (DNR), the long, cold winter and resulting low water temperatures killed an estimated 28 percent of adult crabs in state waters. This marks one of the worst “cold-kill” events since the state started tracking blue crab populations in 1990.

Both Maryland and Virginia measure the Bay’s blue crab population by conducting an annual winter dredge survey. Over the course of three and a half months, scientists visit 1,500 sites around the Bay, using metal dredges to pull up the crabs that are over-wintering in the mud.

Results of the most recent winter dredge survey show that the Bay’s total blue crab population fell from 300 million to 297 million between 2012 and 2013; the number of spawning-age females fell from 147 million to 69 million, passing the minimum threshold that managers adopted in 2011. The Chesapeake Bay Program tracks this latter number as an indicator of Bay health, and a decline could be a factor in determining blue crab management methods.

Indeed, Maryland, Virginia and the Potomac River Fisheries Commission (PRFC) have committed to collaborating on a two-pronged management approach to conserve adult female crabs: first, the groups will work to protect adult females that will be spawning this summer. Second, the groups will work to protect the current population of juvenile females through next spring, in order to build up the population of females that will spawn next year.

“Even though our 2008 conservation measures were designed to allow for naturally occurring fluctuations in crabs, these results are not what we had hoped to see,” said DNR Fisheries Director Tom O’Connell in a media release. “What is most important here is that the structure we put into place to cooperatively manage this fishery is strong, and that we continue to work with our partners and stakeholders to initiate a new stock assessment that could help evaluate our current management framework.”

The Chesapeake Bay Stock Assessment Committee (CBSAC) is expected to release their 2014 Blue Crab Advisory Report this summer.

Learn more.



Jun
26
2013

Chesapeake Bay’s blue crab stock considered sustainable in 2013

A report on the Chesapeake Bay’s blue crab population reveals a stock that is not overfished and within which overfishing is not occurring.

According to an annual evaluation from the Chesapeake Bay Stock Assessment Committee (CBSAC), the start of the 2013 crabbing season saw 147 million adult female crabs in the Bay, which marks a 54 percent increase from last year’s abundance of adult females. The Chesapeake Bay Program tracks this female-specific reference point as an indicator of Bay health. While this number is below CBSAC’s target, it is above the committee’s overfished threshold.

Image courtesy smaneal/Flickr

The 2013 Chesapeake Bay Blue Crab Advisory Report, presented by CBSAC at the June meeting of the Bay Program’s Sustainable Fisheries Goal Implementation Team, is based on the results of the winter dredge survey. This annual estimate of the blue crab population is considered the most comprehensive blue crab survey conducted in the Bay.

To maintain a sustainable blue crab fishery, CBSAC recommends taking a risk-averse management approach and making a 10 percent cut to the 2013 female blue crab harvest. The Maryland Department of Natural Resources (DNR), the Virginia Marine Resources Commission (VMRC) and the Potomac River Fisheries Commission (PRFC) have agreed to pursue the latter recommendation.

CBSAC also recommends better accounting of commercial and recreational harvests and continued efforts to monitor the inactive commercial crabbing licenses in the fishery, which could lead to significant increases in harvest if they were to come into sudden use.

Learn more about the 2013 Chesapeake Bay Blue Crab Advisory Report.



Apr
25
2013

From the Field: Winter dredge survey counts Chesapeake Bay crabs

When cold weather arrives, blue crabs up and down the Chesapeake Bay stop their scurrying. The summertime rush of food-hunting and mate-finding is over, and the crustaceans will spend the winter months buried in sand and sediment. It is at this moment that researchers in Maryland and Virginia must strike: to count the crabs while they are still.

Known as the winter dredge survey, this annual count of the Bay’s blue crab population is a critical part of blue crab management. Without an accurate estimate of blue crab abundance, fisheries managers cannot set harvest limits for the season ahead.

“The winter dredge survey is the most vital tool that we have in crab management,” said Chris Walstrum, a natural resources biologist with the Maryland Department of Natural Resources (DNR). “This is the best chance we have to assess the [blue crab] population, because the crabs are stationary.”

Walstrum and his team are responsible for counting crabs in Maryland waters; the Virginia Institute of Marine Science (VIMS) conducts the winter dredge survey in the Virginia portion of the Bay. Between the two agencies, a total of 1,500 Bay sites are visited over the course of three and a half months before the numbers are crunched and fisheries managers can make recommendations on how blue crab harvests should or shouldn’t change.

From the Field: Winter dredge survey counts Chesapeake Bay crabs from Chesapeake Bay Program on Vimeo.

On a warmer-than-normal January morning, Walstrum is aboard a boat in Broad Creek, a tributary of the Choptank River on Maryland’s Eastern Shore. The DNR vessel has been captained for more than a decade by Roger Morris, a fifth-generation waterman who used to dredge for crabs commercially and whose skills are invaluable to the success of the survey.

“Whether people like it or not, the winter dredge survey is the whole basis for our [blue crab harvest] limits,” Morris said. “That’s why I try to do the best I can do at it. It takes experience. You just can’t walk on a crab dredge boat and expect to catch crabs.”

At each survey site—six of them in this particular waterway—Morris will line up his boat and drop its so-called Virginia crab dredge into the water. The metal dredge is towed along the bottom for one minute before it is hoisted back on board, where the newly caught contents of its mesh liner are dumped out and sorted through. In each catch, there are brown leaves, oyster shells, little fish and, more often than not, a collection of blue crabs.

Each crab is weighed, measured and sexed before it is tossed back into the water. This provides an accurate picture of the blue crab population, as researchers track the number of young crabs that will form the backbone of the fishery next fall and the number of females that will produce the next generation of blue crab stock.

“The winter dredge survey provides us with a cornerstone piece of data from which to operate our [blue crab] management,” said Brenda Davis, chief of the DNR Blue Crab Program.

“It’s a long-running survey, and it’s been consistently accurate,” Davis said. “It gives us a good, static picture of the number of crabs in the Bay.”

Video produced by Steve Droter.

Catherine Krikstan's avatar
About Catherine Krikstan - Catherine Krikstan is a web writer at the Chesapeake Bay Program. She began writing about the watershed as a reporter in Annapolis, Md., where she covered algae blooms and climate change and interviewed hog farmers and watermen. She lives in Washington, D.C.



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