It was crab harvest time in downtown Baltimore. With each dip of the net, dozens of crabs were being pulled from the water. A couple of hundred yards away in Baltimore Harbor, it would have been a remarkable catch. But these crabs were being fished out of big blue tanks, each seething with anywhere from 1,500 to 7,000 small crabs.
Rather than coming out of the Bay, these crabs were headed to the Chesapeake. For the past three years, biologists at the University of Maryland Biotechnology Institute’s Center of Marine Biotechnology have raised tens of thousands of crabs in their basement hatchery, then turned them over to other scientists who placed the nickel-size crustaceans in small coves to see what happened.
What has happened, for the most part, is exactly what would have happened with “wild” crabs. Most were eaten. But enough survived, and grew large enough fast enough, to offer encouragement that the hatchery may eventually help to boost a Chesapeake crab population that is near a record low.
It’s a huge leap forward since researchers were asked at a legislative budget hearing five years ago whether they could do anything for the state’s pressured crab population. The question was handed to COMB Director Yonathan “Yoni” Zohar, who stood up and said, “I think we can do it, given the resources.”
It was a bold statement. Rearing fish in hatcheries is nothing new: Millions of striped bass, shad, trout—even carp—have been reared and released into the Bay or its watershed over the decades. But crabs are another matter. Previous efforts around the Bay had not been promising. “The dogma was that you cannot do it for the blue crab,” Zohar said.
Blue crabs have eight distinct larval stages, each of which can require its own diet. Unlike oysters and many small fish, which feed on algae, blue crabs eat higher on the food chain. So biologists had to create an “algae kitchen” to raise various types of algae that are fed to small animals called rotifers, which in turn are fed to crabs. Different “cocktails” of algae have to be fed to rotifers to support various blue crab life stages.
When they transform into tiny clawed post-larvae, called megalopes, the crabs themselves become part of the buffet. “That is the big issue,” said Odi Zmora, who manages the COMB hatchery. “Any time they molt, they are going to be hunted by their siblings because they are soft.”
Biologists learned that they could reduce cannibalism by giving the crabs a lot of other things to eat. They also incorporated black plastic mesh into the tanks to simulate grasses and other cover that the crabs would find in the wild. They also separated the crabs by size, grouping similar-size ones together.
Overall, about a quarter of the organisms survive from tiny larval specs, just after hatching, to small crabs ready to go into the Bay—something that takes about two months.
But they still had it considerably easier than their wild cousins, who are released near the mouth of the Bay where they hatch, only to be washed into the coastal ocean as larvae, where they float—and are eaten—for months while waiting to be washed back into the Chesapeake as tiny crabs, largely at the whim of nature. They then run a gantlet of predators as they search for grass beds and other cover.
Over the past three years, more than 100,000 crabs have gone from the hatchery into the wild. That’s barely a drop in a Baywide crab population that still runs in the hundreds of millions. But there is serious talk of ramping up production to rear millions of young crabs to enhance the Bay’s breeding population, which is near record low levels.
Such potential has generated support from a wide range of partners, from Phillips Foods, a major Maryland seafood company, to the Maryland Waterman’s Association, which has raised money and volunteered labor to help the hatchery. In recent years, the National Oceanic and Atmospheric Administration’s Chesapeake Bay Office has been the largest supporter.
“We are by no means developing the magic bullet here,” Zohar cautioned. “Protecting and restoring the blue crab population in the Chesapekae requires multiple tools and approaches. This may be an additional important tool.”
On a cloudy August afternoon, workers from the Smithsonian Environmental Research Center took coolers filled with 5,000 small, hatchery-reared blue crabs and boated them across Maryland’s Rhode River to Boat House Creek. There, in a small cove, they began tossing handfuls of crabs into the water.
The cove had been picked because while it had few crabs of its own, it had a lot of shallow water, woody debris where young crabs can hide, and food such as small clams. “We don’t want to release crabs where there are insufficient resources,” noted Eric Johnson, a post-doctoral fellow at SERC working on the crab project.
Before being tossed overboard, each crab had been injected with a tiny microwire tag, about 1 millimeter in length, which can be detected by a magnetic wand. They were also injected with different colored pigments. Over time, those markers will allow biologists to track the crabs and determine how they fare.
If a large stocking program were to take place, scientists would need to know how many crabs they can stock in an area—place too many crabs, and they begin to eat each other and lure other predators as well.
Scientists want to understand what habitats make the best release sites, and what time of year produces the best survival. “If you can show different survival in different habitats, that could go a long way in determining how successful you might be,” Johnson said.
Studies at SERC and by scientists at the Virginia Institute of Marine Science suggest that anywhere from 5–25 percent of the crabs that are released ultimately survive to maturity and migrate out of the coves to head down the Bay. These numbers are similar to those of wild crabs studied in nearby coves. And, significantly, scientists have seen no major behavioral differences between wild and hatchery-reared crabs.
“For the most part, hatchery crabs do equally well as wild crabs,” said Anson “Tuck” Hines, director and senior scientist at SERC. “No better, no worse. And on average, we have been able to double the populations of crabs in these small coves.”
The studies are also helping to determine the optimal size for released crabs to improve survival. To figure out what’s eating crabs, scientist tether them by a string to a stake and track what happens to particular individuals. If the crabs are 20 mm or more, their odds of surviving for a while are good. But survival for smaller crabs, “is on the order of a day,” said Rochelle Seitz, a VIMS researcher. “They get munched pretty quickly.”
One option to improve survival takes advantage of the hatchery’s ability to produce young crabs any time of the year. By getting females to spawn in the winter, while their wild counterparts are hibernating in the mud, young crabs can be reared and released in the spring, when there is little competition from other crabs. Enjoying the warm temperatures of the Bay, those crabs can reach maturity in four months, meaning that hatchery-reared crabs can potentially join the spawning stock the same year they are hatched. “We phase-shift the entire life cycle so that the baby crabs have the best chance to make it to the spawning grounds,” Zohar said.
Another hurdle is safeguarding the crabs once they mature and leave the coves to encounter intense fishing pressure. The goal of any stocking program is to boost the population by increasing the number of spawning females—not create a “put and take” fishery.
To make that happen, Rom Lipcius, a VIMS scientist working on the project, envisions a network of sanctuaries to protect crabs in shallow nurseries that would be stocked with hatchery-reared crabs. Those sanctuaries would be connected to an existing sanctuary near the mouth of the Bay with narrow migration corridors — in effect giving female crabs a free pass to the spawning grounds.
“That’s a critical part of the equation,” Lipcius said. “Otherwise, if we release the crabs anywhere, they just become part of the wild fishable stock and I don’t think that will get us anywhere.”
Sanctuaries, especially in shallow areas, have been controversial because they disproportionately affect local watermen. Lipcius said the hatchery creates an opportunity to make sanctuaries more acceptable: It opens the possibility of stocking crabs in a nearby, fishable area to offset the impact of making another area off-limits. “I think that makes it more palatable to the crabbers. It is not just taking away from them,” Lipcius said.
Still, the task of enhancing the stock would be daunting. Millions—and likely tens of millions—of crabs would be needed, possibly requiring a hatchery other than COMB’s. Also needed would be a network of nurseries where the small crabs could be grown to at least 20 mm in size; nursery space in COMB’s basement is severely limited.
The first step in that direction came this year, as part of the Maryland Department of Natural Resources’ old hatchery at Piney Point was transformed into a crab nursery where COMB researchers, with help from student interns and workers from Phillips Food, are tending the crustaceans.
Ultimately, numerous underutilized coves with suitable resources would need to be identified all around the Bay so they could be stocked. “It’s a difficult proposition,” Seitz said, “but we are extremely hopeful that it will be feasible.” She said the hatchery could help to manage the fishery without putting all of the pressure on watermen. “We want to do something that is a different approach, that may have the same ultimate outcome.”
Many scientists wonder if the blue crab actually warrants such a huge effort. David Secor, a fisheries biologist with the University of Maryland Center for Environmental Science, is one of the most outspoken skeptics. Although he praises the information gained from the hatchery crabs—his own research has benefited from them—he believes it’s unlikely enough crabs would be produced to make a difference in the overall reproductive potential for the stock.
Individual wild crabs can each produce millions of eggs, he noted, so the wild population has far more productive capacity than any hatchery.
Further, to put out enough crabs to make a difference would require a huge investment—likely millions of dollars—to support all of the hatcheries and nursery grow-out facilities needed to rear crabs and stock them. “There are so many better ways that I could see expending those kinds of resources,” Secor said. “There are so many more pressing problems in the Bay. To say that we are developing seed production centers to help crabs—it’s just a very inefficient way to do that.”
A hatchery, he said, is “a very indirect way of dealing with a problem.” Bay crab populations may be suffering from a variety of issues, he said. Those include overharvesting, a loss of habitat from development and pollution, and a climate cycle which, for several years, may have reduced the production of young crabs. But, “the hatchery doesn’t take care of any of these problems,” he said. “All it does is allow them to continue.”
Many scientists have suggested that, by adjusting fishing pressure, the blue crab population would not only recover, but could be managed in a way that would ultimately produce more—and larger—crabs, which are more valuable to fishermen. But the bi-state panel that was trying to coordinate Baywide fishery management to accomplish those goals was disbanded for lack of $100,000 in funding.
“The hatchery thing has become a major diversion from real issues that we need to deal with that will have better benefits to fishermen, such as regulating the fishery, and doing things about habitat that could have multispecies benefits,” Secor said.
“I am very optimistic about crabs,” he added. “I think if we could relax the fishing pressure a little bit and be patient for when climate conditions again favor the reproduction of blue crabs, they will be back and we won’t have to spend a lot of money to amend the population.”
Steve Minkkinen, who formerly oversaw the Maryland Department of Natural Resources hatchery program and now heads the U.S. Fish and Wildlife Service’s Maryland Fisheries Resource Office, said that hatchery programs that take place while there are active fisheries often end up supplementing the stock—not rebuilding the population.
“Normally, you have really drastic fishery restrictions while you are doing restoration efforts,” he said. “Can they restore the fishery with hatcheries? I don’t know the answer to that, but they are going to have to produce very large numbers of organisms.”
Minkkinen, though, acknowledges that the ingenuity of the COMB researchers has yielded surprising successes. “I thought cannibalism would be a little bit harder to overcome, but they actually have had some pretty good success on those young crabs in putting substrates in there to keep them from eating each other.”
Even if the hatchery never becomes a major player for enhancing the blue crab stock, it has already led to major insights about the blue crab. Despite its importance as a Bay fishery, much about the crab’s life history was unknown. Serious policy debates in past years have focused on such basic issues as how long crabs live—a question no one could answer with certainty.
Work with hatchery crabs has helped Secor and his colleagues to develop new techniques to determine the age of wild crabs by measuring the amounts of a certain chemical in eyestalks that increases with age. Before, the age of crabs was determined based on size, which was highly inaccurate because individual crabs can grow at widely different rates. Being able to determine the age structure is important for managing the stock—and determining whether management efforts are working.
Before the hatchery work, it was widely accepted that in the Chesapeake, females would typically produce just one egg-filled “sponge” in her lifetime. “We’ve proved that wrong,” Zohar said. “We’ve had up to five successive sponges here in the lab, which I think is very indicative of what a female blue crab can do in the wild.” And successive sponges have sometimes had increased numbers of eggs.
Important findings are on the horizon. To track crabs after they are released, COMB researchers have documented the entire mitochondrial DNA sequence for blue crabs. Because the DNA sequence varies from crab to crab, it is possible to identify the DNA in a mother crab and track that unique genetic “mark” in her offspring, allowing biologists to better follow the fate of hatchery-reared crabs, and to determine if hatchery-reared crabs are contributing to the overall population.
Further, biologists have generally considered the Bay’s crabs to be a single, homogenous population because larvae are released into the mouth of the Bay and mixed off shore, before the small crabs are randomly returned to the Chesapeake. The genetics work will allow biologists to determine whether there are slight differences among crabs in different areas of the Chesapeake. For instance, watermen often report that crabs in one river are larger than those in another.
Scientists are learning about how hormones affect crab behavior. If the hormones that regulate molting could be controlled, the crabs might be made to molt in unison—and therefore not pose a threat to each other. “When they are soft, they are not cannibalistic. They are subject to cannibalism. If they are all soft at the same time,” Zohar said, “I think this will completely eliminate it.”
That also may open the door to aquaculture. If crabs molting in sync could be raised to adults, they could help supply the soft shell market—and eliminate the growing “peeler” fishery. The peeler harvest catches smaller crabs, starting at 3.5 inches, reducing crabs available for other sectors of the blue crab fishery
“We don’t think that we will ever be able to raise blue crab hard shells and compete with the Bay on an economic basis,” said Allen Place, a blue crab geneticist at COMB. “But if we can actually figure out how to regulate molting and produce soft shells, the market is very, very large.”
It’s possible that the next big catch in Baltimore might be Chesapeake soft crabs that have never touched Bay water before finding their way on plates throughout the region—and beyond.