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.
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.
Every day, non-native plants, pests and diseases are introduced to the United States from around the world. These invaders have the power to out-compete native species, causing damaging effects to ecosystems and local economies. April is National Invasive Plant, Pest and Disease Awareness Month and the Chesapeake Bay is no stranger to these obtrusive critters.
The Bay is a vacation destination, shipping hub and home to more than 17 million people, a combination that puts it at high risk for invasive species introduction. Typically, non-native species travel to new areas by hitching rides on trade ships, travelers’ luggage and recreational vehicles. Although not all invasive species are a threat, it is important to know which ones can and have caused widespread damage. Use the list below to identify 10 invasive species in the Bay watershed.
Image courtesy rbairdpccam/Flickr
10. Blue Catfish. The blue catfish is a large, smooth-skinned fish with a bluish gray body and whisker-like barbells around its mouth. It is native to the Mississippi, Missouri, and Ohio river basins but was introduced to the James, Rappahannock, and York rivers during the late 20th century. Blue catfish are considered invasive because of their active reproduction rates and large appetite for native fish and shellfish species. The fish feeds mainly on shad, menhaden, blue crab and river herring and has few natural predators that can prevent it from out-competing native species. Blue catfish can grow up to 100 pounds, live up to 20 years and are thought to make up 75 percent of the fish biomass in some portions of the Bay.
9. Mute Swans. The mute swan is a large, aggressive bird that is native to northern and central Eurasia. It was introduced to North America in the mid-1800’s to add ambiance to parks and ponds, but individuals quickly escaped, set up nesting territories and the population spread. A single mute swan can consume up to 20 pounds of submerged aquatic vegetation daily, threatening important native aquatic plants. Mute swans are one of the most aggressive waterfowl species in the world, especially when nesting or brooding. They have been known to chase off, injure and even kill native waterfowl species.
Image courtesy of Chrisdetmer/Flickr
8. Zebra Mussels. The zebra mussel is a tiny bivalve with zebra-like stripes and a triangular shell. It lives in freshwater lakes, rivers and reservoirs in parts of the Bay watershed. It was introduced to the Great Lakes region in the 1980s, most likely via ballast water from a European ship, and quickly spread throughout the United States. Once introduced to a waterway, the zebra mussel attaches itself to hard surfaces and can produce millions of offspring annually. Zebra mussels compete with native bivalves, fish and invertebrates for plankton and are responsible for the drastic decline of native clam, mussel and oyster populations in some areas.
Image courtesy of Bernd Loos/Flickr
7. Nutria. The nutria is a large, brown, semi-aquatic rodent that looks like a beaver and lives in marshes and wetlands on the Delmarva Peninsula and other parts of the Bay watershed. Native to South America, the nutria was introduced in Maryland to Blackwater National Wildlife Refuge in 1943 for fur farming. Escaped animals soon began to reproduce, bearing up to three litters of four offspring each year, spreading rapidly. In Maryland, nutria is the greatest threat to salt marsh habitat because it eats sediment-holding plants and causes significant erosion.
6. Phragmites. Phragmites is a perennial plant with feathery plumes at the top of tall, stiff stalks. It grows in wetlands, along roadsides and along shorelines throughout the Bay watershed. Although its origin is unclear, it is widely distributed across Europe, Asia, Africa, North America and Australia. It was introduced to North America inadvertently in the 19th century from the ballasts of Eurasian trade ships. Phragmites crowd out native plants by creating tall, dense stands in wetland habitats.
Image courtesy of Lisa Roukis/Flickr
5. Purple Loosestrife. Purple loosestrife is a perennial plant with spikes of bright purple flowers that bloom in mid-to late summer. Native to Europe and Asia, the plant was both accidentally and intentionally introduced in the 18th and 19th centuries. Ship ballasts unintentionally carried the tiny seeds to North America while others planted it for its aesthetic value and healing properties. The plant is considered an invasive because it quickly establishes itself in wetlands, crowding out native plant species and producing up to 2 million seeds per year with no known natural predators.
Image courtesy of U.S. Department of Agriculture/Flickr
4. Emerald Ash Borer. The emerald ash borer is a green, shiny beetle that lives on ash trees in certain parts of Virginia, Maryland and Pennsylvania. Native to Asia, the emerald ash borer was discovered outside of Detroit in 2002 and made its way to the Bay watershed in 2003 when a Michigan nursery shipped ash trees to Maryland. Adult beetles cause little damage to ash trees but larvae feed on the inner bark, disrupting the dispersion of water and nutrients throughout the tree.
Image courtesy of Smithsonian Environmental Research Center/Flickr
3. Chinese Mitten Crab. The Chinese mitten crab is a light brown crustacean with a distinctive pair of hairy, white-tipped claws. Native to East Asia and a member of LaFondation’s top 100 worst invasive alien species list, it has recently been found in small numbers in the Bay. In abundance it not only competes with native species for resources and threatens populations through predation but also damages fishing industries by feeding on fish in nets and damaging nets and other equipment. It is also known to erode soft sediment banks, dykes and costal protection systems through excessive burrowing.
2. Veined Rapa Whelk. The rapa whelk is a large, predatory marine snail that inhabits the lower Bay. It is native to the Sea of Japan and the Bohai, Yellow and East China seas in Asia. It was first discovered in the Bay in 1998 by a trawl survey group from the Virginia Institute of Marine Science (VIMS) and is believed to have been transported in larval form through ballast water from trade ships. It poses a threat to the Bay because it preys on native bivalves like clams, oysters and mussels, which are vital to the region’s economy and ecosystem. It feeds by wrapping itself around the hinge of its prey’s shell, then feeding between the openings.
Image courtesy of Sergey Yeliseev/Flickr
1. European Gypsy Moth. The European gypsy moth is one of the most destructive pests that has ever been introduced to North America. Moth larvae gorge themselves on the foliage of shrubs and trees, leaving the plants bare and susceptible to disease and damage from other pests. The gypsy moth was accidentally introduced to the United States in Medford, Mass., in 1869, by a professor conducting silk research. It has been established in parts of eastern North America for more than a century.
For the past decade, the Alliance for the Chesapeake Bay has led Project Clean Stream--a vast network of organized annual trash cleanups along the Bay's many tributaries--to help clean up the Bay and connect residents to their local waterways.
During this year's unified day of service on Saturday, April 6, a group of 13 volunteers gathered near the small town of Marydel on Maryland's Eastern Shore, where resident Carol Sparks (not pictured) had reported an illegal dump site along a drainage ditch running adjacent to her property.
According to Sparks, residents from two nearby trailer parks often travel along the foot path adjacent to the ditch, and some have been dumping trash here for years. "I've called everybody and it seemed like nobody wanted to do anything about it. I finally contacted Debbie Rowe, the mayor of Marydel, and she's the one who organized this group, bless her heart."
"I got a call from the property owner that the ditch was in disrepair," said Rowe (below left, with volunteer Wilbur Levengood, Jr.), who had recently learned about Project Clean Stream through the Choptank Tributary Team, a volunteer watershed group from Easton, Md. "To be honest, I didn't know this was back here."
Jennifer Dindinger chairs the Choptank Trib Team, which was searching for neglected sites in neighboring Caroline County where they could make a bigger impact during this year's Project Clean Stream effort. "You don't see trash floating down the Choptank River, but there are places like this that, although it might not end up in the main stem of the Bay, negatively impact life along the tributaries to the river."
Despite the strong odor and armed with garden rakes and stainless steel dip nets, Project Clean Stream volunteers spent their Saturday morning combing through layers of algae in the stagnant drainage ditch. "It's just a nice thing to do on a sunny day," said William Ryall, a fellow Choptank Trib Team volunteer and wetland restoration engineer from Easton, Md. "All of these ditches are connected to the Bay, so it's really important to get this stuff out of here."
"We need everyone to understand how important the drainage is to the Eastern Shore of Maryland, and what it will do health-wise and for the environment if we do it correctly," said Wilbur Levengood, Jr., president of the Caroline County Commissioners. "We don't need to bring huge machines in here and disturb a lot of earth to achieve the drainage, we just need to keep it clean."
According to Levengood, the many drainage ditches in Caroline County are an environmental compromise critical to this landscape. "Without these ditches, ponds and wetlands like the one next door to here would otherwise require chemical pesticides to control the mosquito population. Cleaning up the trash will lower the water level in this ditch by a few inches and get the water moving again."
While most of the trash collected from the Marydel site was of the household variety--36 bags total, including diapers, beverage containers and rotting food--a tell-tale oil slick is evidence of even more hazardous materials lying beneath the surface.
According to Levengood, non-salvageable appliances like television sets and mattresses, as well as toxic materials like motor oil and other automotive fluids that cost money to discard, are often thrown into the drainage ditches along Caroline County roads.
"It's not just necessarily that it looks bad. It's an all-around health hazard, and if we don't keep the water going it's just going to get stagnant and cause mosquitoes and more problems," said Mayor Rowe, who recruited local youth to help with the cleanup. "Now that we know it's here, we can all help as a community to help keep it clean and it'll be safe for everybody."
"My mom is friends with Ms. Debbie [Rowe], so she asked if I could come help with cleaning up trash from the ditch," said Gary Colby of Marydel (top), who in turn recruited his friend Daniel Santangelo. "I just wanted to help out Marydel," Santangelo said.
According to Rowe, part of the dumping problem stems from the challenge of cross-cultural communication. More than half of Marydel's population are Hispanic or Latino immigrants, but today's effort to reach the town's young people seems to be paying off.
"I just offered to help my buddies out," said Carlos Martinez (left), who moved to Marydel last year from Mexico City and volunteered with friends Omar Fuentes (center) and Jordy Cordova (right). "I know it's not young people littering because I know my friends."
"I think we just need to recycle more," said Cordova. Fuentes agrees. Like Mayor Rowe, he says "I never even noticed the trash in the ditch, and I've lived here for 10 years."
During a well-deserved break from the cleanup, Mayor Rowe and the other volunteers discussed the idea of posting bilingual signs to explain the ditch's importance in controlling the mosquito population, and to warn of health risks associated with litter and water pollution. Omar Fuentes and Jordy Cordova agree that signs in Spanish might help curb the littering problem, and promised to talk to their neighbors about the ditch. For first-time cleanup volunteer Wilbur Levengood, Jr., this point made the purpose of the day's effort overwhelmingly clear: "This project puts all aspects of people together working for the better, and we just need more of that."
The blue crab population in the Chesapeake Bay has dropped, but a substantial boost in the number of spawning-age females has offered officials a piece of good news in spite of this disappointing decline.
According to the results of the annual winter dredge survey, which measures the blue crab population in Maryland and Virginia, the number of spawning-age females in the Bay has risen 52 percent. The Chesapeake Bay Program tracks this number as an indicator of Bay health, and an increase is a sign that management methods to conserve adult female crabs are working. But an overall decline in the Bay’s blue crabs—from 765 million in 2012 to 300 million in 2013—could lead to the tightening of commercial harvest restrictions.
Image courtesy Benjamin Wilson/Flickr
Scientists have attributed the decline in blue crabs not to overfishing, but to high mortality rates among juveniles. While last year’s winter dredge survey measured an unprecedented number of juvenile crabs in the Bay, last summer and fall saw an alarming loss of blue crab habitat and a large influx of red drum, which often feed on young crabs. Young blue crabs are also known to feed on each other when population densities are high.
“It is important to keep these results in perspective,” said Jack Travelstead, commissioner of the Virginia Marine Resources Commission (VMRC), in a news release. “Five years ago this fishery was declared a federal disaster. That is no longer the case: overfishing is no longer occurring, a good fisheries management framework is in place, the stock is healthy and spawning-age females are doing well. If not for the disappointingly small reproductive year class we would have much to celebrate.”
In an effort to make up for this shift in blue crab abundance, Maryland, Virginia and the Potomac River Fisheries Commission (PRFC) are pursuing strategies to establish a 10 percent cut in the commercial harvest of female blue crabs. Both Maryland and the PRFC will consider adjusting or enacting daily bushel limits, which have been put in place in Virginia. Maryland and Virginia will also consider shortening their crab seasons, and it seems likely that Virginia’s winter dredge fishery will remain closed.
The Chesapeake Bay Stock Assessment Committee (CBSAC) will draft their 2013 Blue Crab Advisory Report over the next few weeks.
Read more about the 2013 winter dredge survey results.