Sex imbalance holding back Bay crabs' rebound?

It's a great time to be a jimmy in the Chesapeake Bay - if you're a blue crab looking for a good time.  There are nearly three times as many female crabs as there are males now, thanks to catch limits imposed by Maryland and Virginia to protect more "sooks" from harvest.

Those catch limits, which included banning winter crabbing in Virginia and shortening the season in Maryland, are widely credited with fueling a dramatic rebound in the population of the iconic crustacean, which only four years ago was believed to be dangerously close to crashing because of overharvesting.

But what's good for the jimmies may not be so great after all for rebuilding the population, suggests Anson C. "Tuck" Hines, a veteran crab scientist and director of the Smithsonian Environmental Research Center. There's some evidence that female crabs in the Bay aren't getting enough sperm to fertilize all their eggs, he said Tuesday during a seminar at his center in Edgewater.  And that may be keeping the stock from recovering as rapidly or as much as it could.

Female crabs only mate once, Hines explained, and they store up the sperm they receive from that single coupling to fertilize the several batches of eggs that they can produce in their lifetime.  Male crabs, by comparison, can mate with multiple females, but need 10 or more days after each coupling to completely replenish their sperm supply.

Hines said the sperm reservoirs of female crabs checked several years ago in the lower Bay were only about one-quarter full, a lot lower than the reserves found in female crabs outside the Chesapeake which are not as heavily harvested.

Sperm levels in bay crabs also vary during the year, he noted, with females that have mated in summer  holding only half as much sperm as those that mated in the fall.  Hines pointed out that the seasonal dip happens at a time when recreational and commercial crabbers alike are focusing on catching males for eating steamed whole in backyard cookouts and restaurants. That's prompted concern that the jimmies may be overworked or spread too thin in mating.

With a grant from the National Oceanic and Atmospheric Administration, Hines and colleagues plan to investigate the variations in sperm levels and whether some adjustment in harvest regulations might be warranted to re-balance the sex ratio among males and females. 

His research is among five fisheries studies receiving $425,000 in NOAA grants this year, said Peyton Robertson, head of the agency's Chesapeake Bay office. Other studies are looking at the bay's menhaden, striped bass and soft-shell clams, and one is examining the impact of introducing blue catfish in the bay watershed.  Officials hope the research will aid fisheries managers in setting policies and regulations for maintaining a healthy bay ecosystem.

Copyright © 2018, The Baltimore Sun, a Baltimore Sun Media Group publication | Place an Ad