ANNAPOLIS – The latest tool for tracking the migration of female blue crabs is a hot-pink fashion accessory – an eraser-sized backpack with a microchip inside that captures a flood of information for scientists to study.
Scientists call the stylish ladies “robo-crabs,” and reward watermen who catch them with $25, or $20 and a commemorative baseball cap, for returning the pink backpack.
They hope the data will solve enduring mysteries about how pregnant females, called “sooks,” make their way from brackish upper regions of the bay where they mate, to the mouth of the bay where they give birth. And they hope that information eventually will help ensure the long-term viability of the Chesapeake’s most celebrated, but diminishing, crab fishery.
Results from the study will be used to advise Maryland and Virginia agencies that regulate crabbing. Due to declining populations, both states agreed in 2001 to a 15 percent harvest reduction by next year.
“There’s really heavy fishing pressure on these ladies,” said Tom Wolcott, a marine biologist from North Carolina State University who is conducting the study for the National Oceanic and Atmospheric Administration.
NOAA reports that the bay’s crab harvest in 2002 was the lowest since 1981, and the three-year average harvest of 51 million pounds during the years 2000 to 2002 is well below the bay’s long-term average of 73 million pounds.
Wolcott plunked around 200 backpack-strapped, pregnant crabs into the bay’s northern waters this week. He’d prefer not to hear from them again until they’ve reached the mouth. That way he’ll get back the maximum amount of data.
The microchip “wakes up” every six minutes when the crab is submerged; it then checks temperature to make sure the crab is active. If so, the chip records changes in time, temperature, depth and salinity from the previous reading.
If the crab is caught – and that’s part of the experiment – the pink backpack grabs the crabber’s attention and displays instructions for its return.
The first batch of robo-crabs was released last fall and so far Wolcott has received 25 chips back.
When he receives a chip, he plugs it into his computer and marvels at the “gorgeous graphs” it produces.
These graphs may yield clues to the riddle of how and when pregnant females migrate to their spawning grounds.
Conventional wisdom holds that they migrate either during the summer after spring mating or the following spring after late-summer mating.
This operating theory led Virginia two years ago to close its central corridor to crabbing from June to mid-September to protect the females, which develop a “sponge” containing millions of eggs as they travel south.
But Wolcott found evidence of fall migration among the batch of robo-crabs he released last year – a finding that may mean crabbing regulations need reconsideration to protect fall migration.
But not everyone is enthusiastic about the prospect of more regulation.
“Seems like every time we help out on surveys they put us out of business,” said J. Robert Coleman, a waterman from Rock Hall who has caught several of Wolcott’s robo crabs since last year.
He said he had no problem spotting the robo-crabs and was willing to participate in the study, but added that watermen should be kept better informed of scientists’ activities.