Cracking a Tough Crab Season

While any Baltimorean will tell you there is plenty to do, see and enjoy around here, there is no disputing that perhaps the most iconic symbol of our region is the Chesapeake Bay blue crab, and locals and visitors alike look forward to the summer crab harvest as the perfect time to enjoy fresh, local Maryland crabs. In fact, some might argue that we look forward to it a little too much, with demand for crabs frequently outpacing supply from local waterways. According to the Maryland Department of Natural Resources, this year's local crab population is estimated at an all-time low of 227 million crabs, which represents a drop off of about 20% from last year's count of 282 million—and is just a fraction of the 1993 high count of 852 million, the largest population in the 33 years of recorded data.

Since crabs are not only a staple of Chesapeake Bay cuisine, but also a keystone species critical to the health and natural balance of the Bay itself, we've asked National Aquarium General Curator—and all-around Chesapeake expert—Jack Cover to walk us through the natural ebb and flow of local crab populations while sharing some pointers on how to indulge in our favorite local delicacy without putting future crab seasons at risk.

First of all, how do we know how many crabs there are in the Chesapeake Bay from one year to the next?

Local officials gain an understanding of the annual crab populations by analyzing data from an annual winter dredge survey during which hibernating crabs are dredged up, counted and returned to the water at various locations throughout the Bay. This survey includes counts of adult males, females and juvenile crabs. The daily limits of male and female crabs, legal size, and harvest season duration are determined by the Maryland Department of Natural Resources, which conducts the survey in Maryland waters, and the Virginia Institute of Marine Science which conducts the winter dredge survey in Virginia waters. At this point in time, regulators do not feel that blue crabs are being over-harvested.

What conditions create the difference between a strong crab harvest and the record lows we're seeing this year?

First, blue crab populations in the Chesapeake Bay have undergone boom and bust cycles over the years and there are multiple factors contributing the number of blue crabs in the Chesapeake Bay each year. Weather, as well as ocean and Bay currents, are certainly some of the factors that determine our annual blue crab numbers. Females, bearing egg masses, migrate to the mouth of the Bay early in the winter. There, their eggs hatch into minute larvae that drift out into the ocean where they develop and grow until, in a good year, currents, weather and wind carry developing larvae back into the Bay. In a bad year, these larvae do not return to the Chesapeake Bay and are mostly lost at sea.

Assuming they make their way back into the Chesapeake, the next thing blue crabs need are healthy habitats to continue to find food, grow and hide from predators. This is where the overall health of the Bay comes into play. Tidal salt marshes are critical nursery habitats for young blue crabs to find food and escape predation. In the past, tidal marsh habitat existed over the entire shoreline of the Bay, but much of this critical habitat has been lost to development. This frequently means that salt marsh habitat has been replaced by "hardened shorelines"—riprap stone or wooden or concrete bulkheads that are often used to prevent shoreline erosion.

How does the health of the Chesapeake Bay impact crab numbers?

Another crucial Chesapeake Bay habitat necessary to support blue crabs is underwater grass habitat known as submerged aquatic vegetation. The existence of this habitat is critical to the survival of both young and adult blue crabs. As invertebrates, blue crabs must shed their hard outer exoskeletons in order to grow. Females molt—or shed—their hard shells about 18 to 20 times over their lifecycle as they outgrow their hard shells; males molt 21 to 23 times, and young crabs molt most frequently. After they molt, they are then temporarily in "soft crab stage" which is a very vulnerable state. Soft crabs, without their tough outer shells, are easy prey for numerous predators, including people and other blue crabs. Soft blue crabs move to the safety of aquatic grass habitat to molt and hide until their new shell hardens.

In the Bay, submerged aquatic vegetation acreage was steadily increasing years ago but, in recent years, it has been in decline. This shallow-water vegetation needs relatively clear water to survive as sunlight must reach down to the bottom of the Bay to sustain these underwater meadows. Suspended sediments or algal blooms block sunlight, and a prolonged lack of sunlight means the aquatic vegetation eventually dies, leaving a barren bottom—and no place for a soft crab to hide. Polluted stormwater runoff from land, the one Chesapeake Bay pollutant that is still increasing, puts too much sediment into Bay waters after every storm event. This runoff includes excess nutrients that end up in the Bay, where they fuel algal blooms, an overgrowth of algae that initially blocks out sunlight at the surface of the water. When the algae eventually uses up the excess nutrients, it dies, sinking to the bottom where it fuels a bacterial bloom. The excess bacteria consumes dissolved oxygen, creating dead zones that kill fish and crabs. So, in this way, controlling human-generated pollutants and maintaining a healthy Bay is critical to sustaining a robust crab population, one that can be harvested sustainably.

It is also worth noting that invasive species, like the growing population of introduced blue catfish—a major blue crab predator—may also be contributing the lack of young crabs in the Chesapeake Bay.

So, the health of the Bay impacts crab populations. As Marylanders, is there a way to partake in our traditional crab cracking in a more responsible and sustainable way?

Let's first talk about the commercial harvest of crabs in the Bay. There is no doubt that the removal of large numbers of adult crabs from the Chesapeake for sale and human consumption is an obvious factor that effects the size of the Bay's blue crab population, but the practice is closely regulated. In Maryland, commercial and recreational crabbing regulations are determined by the Maryland Department of Natural Resources and Potomac River Fisheries Commission; in the Virginia side of the Bay, crabbing is regulated by the Virginia Marine Resources Commission. This year, the 2022 Maryland crabbing regulations were adjusted in regard to maximum daily catch for commercial and recreational crabbers, as well as a shortening of the crabbing season in an effort to keep the fishery sustainable and avoid over-harvesting. In the meantime, a large number of blue crabs sold in Maryland this season are coming from other states including Texas, Louisiana and North Carolina. If the winter dredge survey results mandate a reduction in the annual catch or even a moratorium on local crabs, it is the responsibility of the regulators to mandate such actions.

But, while officials do their jobs, there are also several personal actions crab lovers can take to help ensure that critical Bay habitats are protected and restored in support of robust crab populations for more sustainable future harvests. Make changes around your home and community—and in your dining habits—that protect the Bay and its crab population.

• Eliminate the use of fertilizers and herbicides on your lawn. These chemicals wash off your lawn during storm events and eventually end up in the Bay, fueling algal blooms that negatively affect critical crab habitats including submerged aquatic vegetation.
• Plant a tree or a rain garden to capture and filter stormwater runoff before it enters the Bay. Planting a tree is the most cost-effective way to improve water quality in the Chesapeake Bay watershed.
• Participate in a National Aquarium conservation or habitat restoration event to help us protect and preserve critical habitat for blue crabs.
• Support organizations working to restore the Bay and implement the Chesapeake Bay Clean Water Blueprint.
• If you are an oyster lover, visit restaurants that recycle oyster shell and participate in the Oyster Recovery Partnership (ORP). If shucking oysters at home, take your shells to an ORP collection site. Oyster reef habitat is another critical Bay habitat utilized by blue crabs looking for food and shelter from predators.
• When eating out, order blue catfish when it's on the menu. Reducing the number of this and other invasive species allows blue crab populations to flourish. When visiting the Aquarium, you can order some blue catfish at our on-site eateries.
• Use your vote to elect candidates that support Bay restoration efforts at local, state and federal levels, and then hold those elected officials accountable.