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.
1 day ago