Blue crabs are undeniably strange. They don’t scuttle, they swim. They are denizens of both the shallows and the deep. They are well-known cannibals, they can regenerate lost limbs, and the many stages of their life cycle have given rise to a Chesapeake vernacular all its own—doublers, peelers, paper shells, buckram crabs.
Yet for all that blue crabs are one of the most loved and studied creatures in the Bay, they remain in many ways an enigma. One mystery is of particular concern to scientists and managers now—why isn’t the population doing better?
How Are Blue Crabs Doing?
Every year since 1990, Virginia and Maryland have partnered on an annual survey to estimate the abundance of crabs living in the Bay and its tributaries. The survey samples approximately 1,500 sites during the winter months, dredging crabs from the bottom where they bury in the mud and sand to wait out the cold weather.
Two years ago, the survey estimated that just 227 million crabs were in the Bay—the lowest level in the 32 years since it began. More worrisome was a decline in the number of adult female crabs, known as the ‘spawning stock’. Managers track the number of females closely because they produce the next generation of crabs.
“The female spawning stock provides resilience for the population,” says Rom Lipcius, a professor at the Virginia Institute of Marine Science (VIMS) of William & Mary, where he leads the lab that conducts the annual dredge survey in Virginia. “If it declines in one year, as long as you maintain a reasonable spawning stock, they can produce offspring the following year and the population can rebound.”
There are some positive signs. The population is not considered overfished, and the spawning stock is above the threshold (a warning level set to trigger protective action). Usually, that should mean many more young crabs. However, the population overall declined this year, though it is above the record low level in 2022. The number of female crabs also decreased from 2023 and it remains below the ideal target fisheries managers would like to see. Moreover, the number of young crabs surviving each year, known as the population’s ‘recruitment,’ has remained stubbornly low.
“The bad sign is that, for three years in a row, we’ve had very low recruitment according to the winter dredge survey,” Lipcius says. “Despite having a reasonable spawning stock, we’re not seeing the response in terms of recruitment.”
No one is quite sure why. Crab populations are notoriously fickle, falling one year and rising the next. Environmental conditions, like storms, or changes in the number of predators that like to eat blue crabs, including fish like red drum and blue catfish, can cause wide variability in any given year. There could also be something bigger going on related to climate change, or conditions in the offshore waters of the continental shelf—where blue crab larvae spend the first month of their life.
To answer some of those questions, the Chesapeake Bay Stock Assessment Committee, part of the Chesapeake Bay Program, kicked off a benchmark stock assessment for blue crabs this summer. The findings are scheduled for release in March 2026.
“We are looking forward to the results of the stock assessment,” says Chris Moore, CBF’s Virginia Executive Director and a fisheries expert. “We hope it will identify the key ecosystem factors that are influencing blue crab recruitment and survival, so that they can be mitigated and we can secure a healthy blue crab population.”
How a Changing Habitat Impacts Blue Crabs
In the meantime, there are many forces at play in the Bay right now that may also be influencing crabs—for both good and bad. One is the availability of habitat.
“Habitat is probably not the cause of the recent decline, but habitat is changing,” says Rochelle Seitz, a professor at VIMS who leads the Community Ecology Lab.
Blue crabs spend approximately the first month of their life in the ocean as larvae before reentering the Bay and moving up into nursery areas, often within the lower reaches of tributary rivers. The young crabs are primarily looking for places where they can hide from predators and find food.
Underwater seagrass beds check both boxes. Historically, the dominant seagrass in the Chesapeake Bay was eelgrass, especially in the lower Bay. Its relatively thick blades provide good cover for crabs as well as small prey that live among the roots and leaves. However, eelgrass in the Bay is at the very southern edge of its range, and it is highly sensitive to the rising water temperatures and heat waves caused by climate change.
“If there are any hot summers or prolonged periods of warm weather in summer, it’s detrimental to eelgrass,” Seitz says. “So that has negative ramifications for crabs because then they have to look for other habitats.”
Luckily, crabs seem to be adapting. Widgeon grass is another seagrass found in the Bay that is now taking the place of eelgrass in some areas. Students in Lipcius’ lab also published a recent study showing that young crabs are using stands of a non-native red algae, called Gracilaria, for habitat. Gracilaria has the added benefit of requiring less light than eelgrass and widgeon grass, meaning it can survive in muddier waters.
There was additional good news this summer. Underwater grasses in the Bay saw an overall increase in acreage over the past year, according to the annual grasses survey, though they remain far short of restoration goals.
Eat and Be Eaten
Salt marshes, too, are important. However, this habitat is at risk as shoreline development replaces natural marsh with hardened barriers, like vertical sea walls or riprap. Seitz has done research looking at how these structures influence the species crabs depend on for food, including clams and worms that live in shallow waters.
“Crabs themselves decrease when you get shoreline development,” she says. “For every 10 percent increase in shoreline hardening, you get a four percent decrease in crabs. So, it is really tractable to note that as we’re developing the shoreline, we are decreasing the number of crabs in that area.”
Overall, though, there seems to be enough food for crabs, which will feed on a wide variety of prey, says Seitz.
What might be more of a problem are the predators that feed on crabs. These are also changing. For example, a study by VIMS researchers in 2021 estimated that invasive blue catfish in a small section of the lower James River ate approximately 2.3 million blue crabs annually. The implications were especially dire for young blue crabs. The study noted that, while young blue crabs will typically bury into sediment or hide themselves in the crevices of oyster reefs to avoid detection, blue catfish can still find them thanks to highly sensitive chemical and electrical receptors that help them hunt.
Managing Blue Crabs Cautiously
Humans are also an important predator. In general, crab populations have been doing much better following the implementation of new management measures in 2008, says Moore. Those measures, which focused on protecting female crabs, helped turn around a long decline in the crab population that occurred in the early 1990s and culminated in the declaration of a fishery disaster in 2008.
Nonetheless, the recent surveys are again raising red flags, especially with so many unknowns about what is driving the sluggish rebound in young crabs.
In addition, the Virginia Marine Resources Commission (VMRC) narrowly voted in June to remove a 15-year ban on a winter dredge crab harvest, despite overwhelming public opposition and against the recommendation of its own staff. However, in a significant reversal, VMRC in September killed the possibility of reopening the winter harvest for the upcoming 2024/2025 season by approving a public comment period that will only consider keeping the fishery closed, along with possible extensions in the crab pot season. The harvest consists overwhelmingly of female crabs overwintering near the mouth of the Bay.
“It’s exactly the wrong time,” says Moore.
“Given the lackluster results of this year’s survey, the states need to proceed with caution when considering any regulatory changes for the upcoming seasons and avoid changes that would increase harvest, especially on females. Adding the winter dredge harvest while the assessment of the blue crab population is ongoing is really ill-advised. This decision imperils not only the vulnerable blue crab, but also the sustainability of harvests throughout the year and other species that depend on blue crabs for food.”
Instead, he says states need to consider more actions to help blue crabs.
That includes efforts to reduce pollution that causes low-oxygen dead zones in the deep-water channels crabs use to migrate, and like underwater grasses and marshes in shallow water areas could also help.
Living shorelines, for example, could help reduce the impact from shoreline development. These types of shorelines are also used to protect properties from erosion, but they do so with natural features like oyster shells and marsh plantings that have the dual benefit of providing habitat for fish, crabs, and other wildlife, says Seitz.
“The more marsh we can get into the Bay, the better it would be,” she says. The same is true of oyster reefs. In addition to local projects, the Chesapeake Bay restoration partnership, which brings together Bay states and the federal government, is nearing completion of a major goal to restore oyster habitat in 10 tidal rivers in Maryland and Virginia by 2025. Oyster reefs provide great foraging grounds for blue crabs, and they could help guard against the loss of other food sources as the climate changes, says Lipcius.
At the end of the day, blue crabs are one of the most resilient species in the Bay.
“In the Bay of the future, I think blue crabs will be one of the survivors,” he says. “I am pretty optimistic about the future as long as we can regulate the fishery well enough to maintain the spawning stock and the resilience of the population.”
