(AP) -- A study finds that South Carolina's blue crabs are moving farther upstream as the marsh estuaries they prefer become increasingly salty.
The Post and Courier of Charleston reports Monday that the crabs' migration is another sign of a troubled coastal marsh.
Since 1998, the annual commercial blue crab catch has dropped from more than 7 million pounds to 4 million pounds.
Clemson University biological science professor Michael Childress is trying to determine why.
Sampling by the state Department of Natural Resources has found that salinity in commercial crabbing waters has risen since 1998.
Childress finds that crab that remain in the saltier water are more prone to get a lethal virus.
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