Protecting the 'Beautiful, Savory Swimmer'

Richard Forward's Blue Crab Research Crucial to Saving Habitats and to Setting Sustainable Catch Limits p.3

   “If it’s fairly calm, you can hear the pings from a couple of kilometers away. But if there’s commotion and the current’s flowing, you’re limited to a couple hundred meters. Any farther than that,” Forward says, “and you lose the trail.”

  Bad weather, high winds, rough surf and heavy boat traffic can turn the tracking into a “fairly frightening experience,” he says.

  With perseverance and a little luck, the team can follow the crabs until they swim out of the estuary, heading for hatching grounds in the open ocean beyond.

  Ocean waters provide a better area than estuaries for larval development, Forward says, because water temperatures and salinity levels are more constant there, and there are fewer predators small enough to consider the minuscule larvae a satisfying meal.

  Relatively free from these dangers, the newly hatched larvae migrate 30 to 50 miles farther offshore to warm waters near the Gulf Stream. They remain there for between four to seven weeks, growing larger and eventually molting into megalopae, their postlarval stage, before being carried back to the estuary inlets by winddriven currents.

  Guided by currents and chemical cues in the environment, the megalopae— which now measure about five millimeters, or just under one-fifth of an inch, in size—move through the estuary toward sea grass beds that serve as their nursery grounds.

  Here, Forward says, they remain through several more moltings until they are large enough to leave the safety of the beds and move throughout the estuary, maturing into jimmies (mature males), sooks (mature females) or she-crabs (immature females) in about two years.

   Using data gleaned from their studies, Forward’s team has worked with Richard Tankersley of the Florida Institute of Technology, Richard A. Luettich Jr. of the University of North Carolina at Chapel Hill’s Institute of Marine Sciences, and two of Luettich’s graduate students, Sarah Carr and Jim Hench, to develop a model that allows them to determine where females begin their migration, how long it will take, and where they will end up for their larval release. Armed with this knowledge, they can predict the probability that the larvae will be released in a favorable location, where currents and winds can transport them successfully offshore for development.

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