The False Mystery of the Blue Crabs

Let’s not create a great mystery about the Chesapeake's blue crabs where there is none.  Any false sense of scientific uncertainty about what happened to the beautiful swimmers could be used to undermine the very successful crabbing restrictions that Maryland and Virginia imposed two years ago, and that would be a tragedy.

An editorial this morning in the (Salisbury, Md) Daily Times claimed that the reason for the more than doubling of the Bay’s blue crab populations over the last two years is “debatable.”  The newspaper said it “isn't clear what factor is primarily driving the recovery” of the blue crabs, or what caused the nearly catastrophic two-thirds decline in crabs between 1990 and 2007.  Just two years ago, the state of the blue crabs was so grim -- with numbers near record lows -- that the U.S. Secretary of Commerce declared an economic disaster, making watermen eligible for emergency relief payments.

“Watermen say pollution is chiefly responsible,” for the decline of the crabs, according to the newspaper.  “Scientists point to overharvesting.” This phrasing suggests that such management questions are best resolved by "he said/she said" debates.  This makes no sense, especially when one of the parties in the debate has a personal interest in the outcome, and the other party has a professional obligation to be objective and impartial.

The science on blue crabs is clear.  While pollution over time has played a role in the slow erosion of the Bay’s carrying capacity for blue crabs and other life forms, the evidence is overwhelming that overharvesting (especially of female crabs in the southern Bay) was a major factor causing the steep decline in blue crabs over the last two decades.

Watermen harvested an astounding 79 percent of all crabs in the Bay in 1999, 71 percent in 2001, 70 percent in 2004 and 55 percent in 2007, according to a 2009 Chesapeake Bay Foundation report on blue crabs in the Bay. The annual take averaged 62 percent of all crabs between 1997 and 2007. 

Meanwhile, experts have concluded that, for the Bay’s blue crab populations to be sustainable, watermen should catch no more than 46 percent of the crabs in any given year. 

Not surprisingly, when Maryland and Virginia in 2008 took the prudent step of restricting the harvest of female crabs, to allow maximum reproduction, the populations of blues in the Bay came roaring back. A survey conducted this past winter found that – after years of decline – crab populations had multiplied to about 650 million, the highest numbers in more than a decade and more than double the  260 million crabs estimated in 2007.

The resurgence of crabs since the 2008 regulations cannot be explained by any sudden decline in water pollution in the Bay.  The most logical explanation, scientists say, is the restrictions on catching female crabs. Other factors, such as weather or ocean currents, could certainly be factors. But it would be silly to pretend that (for example) Virginia’s 2008 landmark ban on the wintertime dredging of hibernating females had no effect on crab populations.

After the crab population boom of 2008 and 2009, Maryland and Virginia this year slightly loosened up some restrictions on catching females.  For example, Maryland this year will be allowing the catching of females for the week between Sept. 26 and Oct. 4.  This minor alteration should not pose a problem for the continued recovery of the crabs.

What really matters is that the states keep in place the bushel limits and overall catch regulations, so that no more than 46 percent are harvested in any given year.  As long as Maryland and Virginia stand firm on this limit, and protect against overharvesting, the rebound of the blue crabs should continue. Of course, over the long term, controlling water pollution is also very important for the Bay, because clean water will increase the capacity of the Bay to feed and shelter not only more crabs, but all varieties of life.

There should be no mystery about this.

By Tom Pelton

Chesapeake Bay Foundation

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Comments

[Rick Edmund]

I have lived among the watermen of Smith Island now for ten years. I don't believe that the DNR can immediately manage the reproduction of blue crabs or any other species, as Tom Pelton apparently does. He makes no mention of the rebound of the rockfish and their effect on the crab population. Fishermen can catch a large rock which may have 100 small undigested crabs in it's belly. Rock like crabs. To think that the comeback of the Rock has no effect on the decline in crabs is not realistic. In the last ten years watermen's catch has been reduced by about 50% according to the goals set by the DNR. Also there are fewer and fewer watermen on the Bay due to younger men not wanting to invest in the risky business of uncertain crabs and restrictions. Let's give the watermen some credit rather than blame.
Rick Edmund Smith Island

[John Koontz]

Looking at the Sun article on line the photo of the crab pickers showed about 1/2 the crabs were sponge crabs. If we take the yooung before they are born it has to create decline in population. So now once crabs show a little come back watermnan want to go back to free for all on the Bay.

[Ken Smith]

Did the restrictions placed on the Bay crabber also cause the huge increase in crabs in Delaware and North Carolina. People give the Lord some credit.

[thor]

All available data points to watermen as the primary predator on blue crabs, not rockfish. The rockfish arguement presented is identical to arguments used to eliminate predators from wolves, who prey on deer and elk, to seals who prey on fish. Such arguments are made not with the intent of any preservation, but simply to let human predators take an even higher percentage of the prey. What's your solution, waterman? A reduction fishery to wipe out the rockfish? If rockfish were taking as many crabs as you, there would be no crabs left at all. Give you "credit" for what? It is quite obvious that watermen can and will take every crab they can lure into a pot, at any time you are able to fish. Last I heard there were so many crabs you were angry about the price you were getting. The delaware uptick in crab numbers was weather related.

[Peter Legg]

Very well written editorial, Tom. The real question is why did it take until 2008 for Virginia to enact their "landmark" ban on wintertime dredging of female crabs? It's been common knowledge for years that this was the primary cause of the decline of the blue crab in Chesapeake Bay. It's really one of those "duh" moments in Chesapeake Bay restoration. Maybe now they could clamp down on menhaden overharvesting by Omega!

[Tom Pelton]

Yes, you are right -- menhaden are also being overfished and have been for years. Some kind of action on this front is certainly warranted.