Monday, July 16, 2012

Scientists Sex Crabs

There are new concerns over the Chesapeake Bay crab population. Environmentalists worry that regulations to protect female crabs are causing a sperm shortage from the males.  Tim Williams looks at the new numbers and what they mean for your next crab feast.

In the dating world of crabs, it may take two but the current number of males to females is skewed.  “Male to female sex ratio has actually increased. That is, there are fewer females than males,” said Anson “Tuck” Hines, Smithsonian Environmental Research Center.
Traditionally, in Maryland and Virginia, male crabs, "Jimmies" are preferred over female crabs "Jennies" by people for the traditional crab feast, and command a higher price.  However, the females are caught in huge numbers for the picked crab trade.

One problem with evaluating the sex ratio of crabs is that crabs seem to have sexual preferences in the region of the Bay they utilize.  Male crabs favor lower salinity regions of the upper Bay and tributaries, where as females are found in higher abundance in the main Bay, and lower, more saline areas of the tributaries.  This is exacerbated by the trend toward sex selective fishing.
Results of the latest independent survey census or dredge survey done this winter show the number of female crabs has decreased in abundance for the second straight year while juvenile crabs have increased. The result is confusing fishery managers. “The ultimate goal of having more baby crabs is to have more adult crabs that are back into the fishery,” Hines said.

The new findings are a complete turnaround from recent results. In January, there were three females to every male. We are now closer to the ideal number of eight males to every female.
We have concerns because the crabs are closer to the ideal sex ratio than we can account for?  Are we looking a gift horse in the mouth, or what?
Since regulations in Maryland, Virginia and the Potomac River currently prohibit overfishing of females, the questions over where the females have gone and the timing of their cycles still remain.
Could it be that the number of female crabs being taken is being under reported? Naw; watermen would never cheat on quotas or other regulations...
“There’s a very narrow window in their life cycle in which they mate and receive all the sperm that they’re gonna need and use for their lifetime. If there’s not a male fully charged and ready to go at that point, it doesn’t happen as effectively,” Hines said.
A female crab's sex life is short, if not sweet.  Upon attaining full size, female crabs undergo "terminal molt", one which leaves them with adult characteristics, and fertile.  They can only be fertilized by males for a short period before their carapace fully hardens.  Meanwhile, the males continue to grow (and be harvested).
Still, the overall blue crab numbers are good which, in a nutshell, means enough of both sexes to go around.

The latest crab assessment suggests that studying the ratio should be a research priority to understand potential problems with the population in the future.
Years ago, I helped with a long term crab monitoring project here in the main Bay in the region off "Location" X.  Still lots of stories to tell from that.  Do have any idea how hard a big Jimmy can pinch a finger tip?  It still throbs when I think about it.

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