Blue crabs, a tasty delicacy of Lowcountry living, are on the move, seeking less salty water farther inland.
That's the early finding of a study of blue crabs that partially explains the recent drop in crab harvests.
Crabs are migrating partly because the brackish marsh estuaries they prefer have become saltier in the past decade, the study suggests. The prime habitat for juvenile blue crabs is now as much as 11 miles farther upstream than it was a decade ago, according to the study, done by Michael Childress, a Clemson University assistant biological science professor.
Childress' study seeks to explain why the annual commercial blue crab catch since 1998 has dropped from more than 7 million pounds to 4 million pounds. The nosedive had commercial and recreational crabbers squabbling and led to state limits on licenses for commercial crabbers.
The decline was blamed largely on too many people eating too many crabs, but studies found other problems -- viruses, bacteria, pollution and a five-year drought that accelerated an inward creep of saltwater. The decline ended when rainfall recovered, but the crab numbers didn't return to their previous levels, remaining at about 4 million per year.
Salinity in commercial crabbing waters has risen from 24 to 30 parts per million, also since 1998, according to the state Department of Natural Resources. That's forced more crabbers to compete in narrower waterways farther inland.
"We have no choice but to crowd in," said James Island crabber Fred Dockery, who works the Stono and Kiawah rivers.
Along with crabs, DNR biologists are beginning to see shrimp and horseshoe crabs farther upstream.
Meanwhile, other testing has shown that stormwater pollution is worsening water quality in upstream feeder creeks, leaving them less able to support marine life.
South Carolina has an estimated 400,000 acres of coastal marshes, considered the nursery for much of the sea life and seafood of the region.