Tuesday, December 30, 2008

Crabs - Dying from Pollution and Overharvest

The Chesapeake Bay Foundation just released a report today describing the dire situation for blue crabs (Callinectes sapidus) in the Bay. The problem is two-fold:

1) Pollution from the land has damaged the Bay, so it produces fewer crabs. The picture below shows crabs forced to crawl out of the water to flee an oxygen-depleted "dead zone".


2) Large numbers of crabs are still being harvested; more than the damaged ecosystem can replenish.

Some of the "executive summary" of the report is pasted below. If you have adobe acrobat you can read the full version here. There's a picture of my postdoc advisor, Dr. Anson Hines, on page 7.


Bad Water and the Decline of Blue Crabs in the Chesapeake Bay


Blue crabs are not only the most economically important fishery in the Chesapeake Bay. They are also a powerful icon of the whole mid-Atlantic region— a symbol of our cultural roots in the Chesapeake. And they are an essential strand in the web of life that forms the nation’s largest estuary. For all these reasons, it is a matter of grave concern that the blue crab population has fallen to near record lows. Scientists say there are two causes of the problem: pollution and overfishing, especially of female blue crabs. (Overfishing means catching crabs faster than they can reproduce.) Here are some key facts:

° Less Crab Food- Low-oxygen “dead zones” on the bottom kill the food that crabs eat, wiping out or preventing the growth of 75,000 metric tons of clams and worms a year. That is enough food to support about half the commercial crab harvest, more than 60 million blue crabs annually.
° Less Crab Habitat- Sediment from runoff and algal blooms caused by nitrogen and phosphorus pollution are darkening the Bay’s waters, killing the underwater grasses that young crabs need as shelter from predators. More than half of the Bay’s eelgrass has died since the early 1970s.
° Overfishing- Because a diminished Bay can support fewer crabs, overfishing has become an even more urgent problem. Watermen have caught an average of 62 percent of the Bay’s blue crabs each year over the last decade—well more than the 46 percent that scientists say is sustainable.
° Regulation- If the Bay were cleaner and crabs more plentiful, watermen could continue to catch the same number of crabs they are harvesting today without exceeding the 46 percent threshold. Then, additional government regulation of watermen—and relief for them—might not be necessary.



PeconicPuffin said...

They need to regulate sooner rather than later. I love a good crab cake, but maybe we need to close the fishery (the crabery?) for a few years so it can rebuild while environmental challenges are addressed, and THEN reopen it.

-Michael (former Baltimore resident and lover of da blue crab!)

James Douglass said...

Michael- That's not a bad idea. There was a moratorium on striped bass fishing a decade or so ago when their population was really low. It was unpopular at first, but it worked wonders for the population, and the fishery has been booming ever since they reopened it under stricter regulation. Oysters are another important Chesapeake Bay species that would really benefit from a moratorium.

Ian Berger said...

I worry a lot about the environment, especially when we as a culture allow problems, like pollution, to get so bad. I admire your environmental angle, because these things are important, and you have the expertise to speak knowledgeably about it. Please post more on these issues.

Me, I'm just a tree-hugger who likes to windsurf, but I think I'll start presenting these issues on my blog too. I know some windsurfers get turned off by this. I've seen some pretty nasty comments on the iWindsurf forum against “environmentalists”. They bothered me for a while, especially when we engage in a sport which requires a healthy environment. Thirty years ago, you could not windsurf or do anything in the Hudson River because it was so polluted. Now there are beaches. We Hudson windsurfers owe a debt to the environmentalists.

Sorry about the rant. Please keep up what you're doing. It's really important.

James Douglass said...

Ian- Thanks for the kudos! I will definitely continue to post on environmental issues as they come to mind. I know not everyone in the windsurfing community is convinced that environmental protection is a priority, but I see that as all the more reason to be outspoken about it. :)

Andy said...

I'll admit to saying some pretty ridiculous stuff concerning environmentalists lately. Shocking stuff, actually. But I think its important to note: I was angry with the sue-hungry lawyer environmentalists who lived hundreds of miles away from the lands their actions were affecting.

I was certainly not blaspheming the actual biologists and environmental scientists working in the field. They get all the respect in the world from me.

All "environmentalists" are not the same, nor are all environmental causes worth supporting simply because they are deemed "environmental."

Hudson River toxic sludge cleanup? Hell yeah! Reducing pollution in the Chesapeake Bay (or any waterway, for that matter)? Hell yeah! Limiting ALL public beach access because an endangered bird is nesting 100 meters away? Gimme a break!

But anyway, please keep up the good work, and keep us informed!

PeconicPuffin said...

Ian...the anti-environmentalist comments in iWIndsurf's forum are principally from two or three boneheads who think "live and let live" means "shit and let shit."

Andy...I hear you about closing down land because there's a birds nest somewhere, but I don't look at environmental issues overall as causes that one can be for or against. The thought that the planet and "nature" can take everything we've done is a 20th century relic. Lots of species of whales, cheetahs, orangutans etc are essentially toast already...their total populations are too low to provide enough genetic diversity. And that's not going to stop.

I'm a pessimist these days. I recently watched a 300 pound woman buy her 200 pound daughter (who looked to be about 14 years old)a party size bag of cheetos to munch on. Nobody arrested the mother.