WHAT'S BEHIND THIS YEAR'S BOOM in Chesapeake Bay blue crabs? Good management? Good weather? Or good luck?

The question sounds simple, but the answer may not be. Not if you look for an answer among the various scientists who study blue crabs for a living. Some of them, the crab biologists, focus on the in-Bay travels and travails of this colorful, two-clawed crustacean. Others, the oceanographers, track the offshore exodus of blue crab larvae — the tiny offspring who will grow into the next generation of Bay crabs — but only if they work their way off the ocean and back into the estuary.

So what's behind the comeback? Martin O'Malley's answer: good management. He's not a biologist — he's the current governor of Maryland — but he has a lot of biologists backing his answer. This April, Governor O'Malley stood on the back deck of a local crab house on the Severn River and announced that there were 764 million crabs in the Chesapeake Bay this year, a huge increase from five years earlier.

Posing behind him was an array of officials, most of them men, most of them dressed in shirts and ties, all there to represent state agencies, environmental organizations, and the Maryland Watermen's Association. Standing in front of the governor was an array of reporters, some of them in jeans, none in ties or jackets. As he delivered a short, triumphal speech, the newspaper people scribbled in notebooks, the television people worked their big cameras.

Crab numbers matter in Maryland. Several thousand watermen catch them for profit, working from their traditional deadrise workboats, and many other natives catch them for fun, leaning off local docks with dip nets or wading out into creeks and rivers. "The crab represents for many people some of the best moments they share with family," said O'Malley from the deck at Mike's Crab House. "You pull one of these beautiful creatures up out of the dark waters, and they are shining there in all their color — the red and the blue and the greenish hues. It's a moment every child remembers, and it's a moment that every parent remembers."

Total Abundance of Blue Crabs in Chesapeake Bay

The annual winter dredge survey has been estimating blue crab populations since 1990. This year's survey counted 764 million crabs, the highest number on record since 1993 when the survey estimate reached 852 million. The graph shows clear evidence that populations can rise and fall dramatically from year to year. It also highlights the 10-year slump (1998-2007) that led scientists and managers to argue that current fishing levels were unsustainable. New restrictions on the harvesting of female crabs were enforced in 2009, and crab populations began to recover. Graph Source: Maryland Department of Natural Resources.

By the next day, most people in the state who read a paper, watch television news, or listen to the radio knew about this year's blue crab number, and they knew it was a good number. How good a number? There are more crabs out there now than any year since 1993, said the governor. After a long losing streak, the Bay looked like a big winner in a blue crab lottery that seems to spit out up years and down years in a random sequence.

The governor's good news number came from the annual winter dredge survey that biologists from Maryland and Virginia have been running since 1990. Working with watermen, scientists spend weeks motoring around the Bay to 1,500 randomly selected spots where they dig crabs out of the mud, count them, measure them, weigh them, record their sex, and estimate their ages. They work from November through early March. It's the best time to count crabs because they all stay in place, buried in the mud, waiting for warmer water. After crunching the numbers, the biologists come up with an annual crab estimate, a kind of Baywide census of blue crabs. It's a number that goes up and down.

In 2007, when the crab number sank to the lowest point of a low decade, the survey results drove home a gospel that scientists and managers had been preaching for years. "Our female crabs were being overfished," O'Malley told the press, echoing the consensus of many crab biologists,"and our fishery was at risk of complete collapse."

The answer to the crisis was a new management policy, a cutback on the harvest of female crabs. In 2008, Maryland, Virginia, and the Potomac River Fisheries Commission agreed to reduce the harvest of female crabs by 34 percent. Their options included limiting the number of fishermen, the number of pots and traps, the number of hours in a fishing day, and/or the number of months in a fishing season. In Maryland, the major change was shortening the fall crabbing season. And in Virginia, the big change was outlawing the winter crab dredge season.

It was a policy change based on the hard-won findings of crab biologists who've documented the life cycle of the species in impressive detail. In the fall, female crabs start south after mating, headed for their spawning grounds in the high salinity waters near the mouth of the Bay. During this mass migration down-Bay, females have to run a gauntlet of crab pots, trotlines, bank traps, channel pounds, and grass scrapes, especially in Maryland where watermen are hoping to catch females before they reach Virginia waters. During past winters, Virginia watermen were allowed to dredge the bottom of the Bay and dig up many of the hibernating females that made it out of Maryland. The net result of this fall and winter crabbing: many female crabs never got a chance to spawn.

Maryland-Style Crabbing

Crab potting

Trotlining

When Marylanders go crabbing for fun or a family feast, most of them use some chicken necks on a line to bait the crabs and a dip net to catch them. The more ambitious, however, can try some of the tools the pros use. more . .

Bank trapping

The management solution — a cutback on catching females — sounds like simple biology, one scientist called it "the kindergarten solution." But it's a solution that took some courage and some complicated politics. The two states that share the Chesapeake also share a long history of disagreeing with each other about how to manage the blue crabs that travel back and forth across that invisible, watery state boundary that bisects the Bay. And the sharpest disagreements center on the harvest of female crabs.

As early as 1917, for example, Maryland banned the harvesting of sponge crabs, females carrying packets of fertilized eggs, but Virginia refused to go along with the idea. It took a series of poor harvests and a rising sense of crisis before Virginia finally banned sponge crab fishing in 1926. When harvests rose soon after, especially in Maryland waters, Virginia backtracked, re-opening its sponge crab season in 1932. Crab harvests were soon cut in half in Maryland, and that state responded by extending its fall crabbing season through November. That allowed Maryland watermen to catch more south-moving females before they could reach Virginia waters.

This bi-state game of regulatory volley and response would be played and replayed numerous times over the decades. The two states eventually negotiated a 1935 deal with Virginia promising to reduce its harvest of sponge crabs and Maryland, in a quid pro quo, agreeing to once again shorten its fall crabbing season. The deal sounded a lot like the 2008 bi-state agreement, but it would not last. In later years Virginia would expand its harvest of sponge crabs, and in a tit-for-tat, Maryland would lengthen its fall fishing season. Both states on occasion would try their own conservation efforts. Virginia established a crab sanctuary near the mouth of the Bay, and Maryland several times shortened its fall fishing season.

If it lasts, the bi-state deal of 2008, with its cutback on the fishing of females, could be a final reversal of that history of interstate wrangling. If so, it's a hard-won reversal engineered in part by the Bi-State Blue Crab Advisory Committee (BBCAC), a multi-year effort to get groups from both states to talk with each other about crab science and management. Organized and managed by the Chesapeake Bay Commission, BBCAC set up workshops and conferences that brought together legislators, scientists, watermen, seafood processors, and resource managers to review crab science, debate the management options, and struggle towards consensus. BBCAC ceased operations in 2003 after it was defunded by the Virginia legislature, but its technical workgroup kept going.

Despite its demise, BBCAC left an important science legacy. The committee kept crab biologists working together long enough to hammer out an action plan that set threshold and target levels that resource managers could use in maintaining a sustainable fishery. A threshold spells out the reality that crab populations can crash if they are fished below a certain minimum level. And a target establishes a population level that managers should aim for to keep populations in safe territory.

With the 2008 cutback on harvesting females, both states finally seem to be moving towards bi-state management based on ecology more than economics. "Both states took a lot of economic losses for doing that," says Tom Miller, director of the Chesapeake Biological Laboratory at the University of Maryland Center for Environmental Science (UMCES). "I think Maryland and Virginia," he says, "have a lot to be proud of in the way they've approached their crab fishery."

Sounds like good management is the best answer then, the true cause behind the current blue crab recovery. Following the 2008 cutback, female crab numbers went up at the end of the first year, while male numbers did not. Good evidence says Miller "that the conservation effort on females actually increased female abundance. " In the second year after the cutback, the number of new, young crabs went up. More good evidence, according to Miller, that crab populations were responding to the new policy.

Unless those populations were responding to something else, a suggestion that comes from Tuck Hines, a blue crab biologist with the Smithsonian Environmental Research Center. According to his analysis, the count of adult crabs actually dropped in 2011, the third year after the cutback on female harvests, and then dropped again in 2012 to the lowest-ever count of females on record. Watermen, he says, may still be finding ways to get around the new regulation and keep fishing out a lot of females.

And some force besides females may be pumping up the high crab number that Governor O'Malley announced back in April. Swelling the 2012 crab census was the highest number of juvenile crabs ever recorded in the annual survey. Why were juveniles increasing while spawning females were decreasing? "Perhaps offshore storms brought more (crab) larvae into the Bay," wrote Hines in a recent blog. Good weather, rather than good management, may be behind the blue crab recovery.

Good and bad weather conditions can play a big role in causing all those ups and downs of blue crab abundance. When female crabs spawn near the mouth of the Bay, each female releases millions of tiny, barely visible larvae, up to eight million larvae according to some estimates. These first-stage larvae, looking like extraterrestrial fleas rather than tiny crabs, tend to rise up into the Bay's seaward-flowing surface waters and ride the flow right out of the estuary into offshore coastal waters. Whether these fleas ever get back into the Bay to become crabs depends in large part on weather-driven forces like winds and currents. If a good number return, the Bay's blue crab population will jump two years later. If hardly any return, it will plummet.

With all the right weather and wind and current forces kicking in, only a small percentage of larvae make it back into the estuary during a high-return year. According to one model, that influx can drop by 90 percent during a low-return year.

Here's the attraction of weather-based scenarios: they help explain why crab populations have jumped and plummeted numerous times in the past.

And here's the problem with weather-based scenarios: they are not much help in predicting how many crabs are coming next year or the year after — at least not yet. Winds and currents are complicated topics, a domain ruled not by biologists who describe the life cycles of crabs but by oceanographers who describe the physics of offshore air and water masses that push blue crab larvae around.

What are the big forces that drive the winds and currents that, in turn, can bring the blue crabs into Chesapeake Bay? In recent years, oceanographers have looked at river flows and freshwater plumes and phases of the moon, and now they are moving farther afield trying to examine larger-scale climate forces. Forces like the Bermuda-Azores High, for example, can create winds that drive larvae toward or away from the Chesapeake. The North Atlantic Oscillation (NAO) can, in turn, create favorable or unfavorable Bermuda-Azores Highs. And the Atlantic Multidecadal Oscillation (AMO) creates a warming or cooling of ocean waters that lasts for decades. It can also play a role in creating all those pressure systems and wind events and current patterns that eventually push tiny, flea-like crab larvae towards the Chesapeake Bay in large numbers — or scatter them far out on the waters of the continental shelf.

The good-weather scenario is becoming the big-weather scenario. "We are just kind of opening our eyes to large-scale weather patterns and what that means for coastal circulation on weekly to monthly scales," says Elizabeth North, a fisheries oceanographer with the UMCES Horn Point Laboratory, who has led ocean-going cruises designed to track blue crab larvae. "It is exciting to think that what's going on over Iceland has anything to do with blue crabs here on our tables," she says.

So back to the big question: what's behind this year's great blue crab number? Good management or good weather? A cutback on the harvest of female crabs? Or some big-weather patterns that blew a lot of crab larvae back home?

Probably both, says Tom Miller. "We could have had females go up, and if the oceanic conditions hadn't been right, we may not have seen the recruits go up," he says. "An increase in females is important, but it is not guaranteeing you great recruitment."

The right weather conditions, on the other hand, almost guarantee great recruitment. In past decades, after all, those weather forces have lined up to churn out great, unexpected blue crab abundances — often during eras of heavy fall fishing in Maryland and annual winter dredging in Virginia.

You see the dilemma faced by fisheries managers and scientists: they can make the smart move, say increasing the number of females, and still get no results. Or they can do nothing and perhaps get great results.

It's a sobering thought. "We can manage for female abundance," says Miller. "But we can't manage for oceanographic conditions."

And where does good luck come in? This time the Chesapeake Bay blue crab lottery seems to have spit out a big crab number, 764 million crabs for 2012, just when good management and good weather were both in play.