BIOLOGICAL POLLUTION - Marine Pollution: What Everyone Needs to Know - page 196

explosion. They travel long distances upstream into freshwa-
ter, feeding on native species. They also burrow into stream
and river banks leading to bank collapse. British zoologists
fear that this crab could both eat and out-compete vulner-
able freshwater species and that native crayfish (which are
already in decline) could be affected. Economic impacts in
Europe from fishery losses due to mitten crabs are estimated at
around 80 million Euros. Many animals prey on them, includ-
ing raccoons, river otters, wading birds, and fishes, but they
apparently do not eat enough of the crabs to slow down their
invasion.
Considered a delicacy in Asia, live mitten crabs have been
imported illegally into seafood stores in the United States.
They became established on the West Coast in the 1990s and
are considered a threat to native invertebrates, to the structure
of freshwater and estuarine communities, and to some com-
mercial fisheries. They may imperil California's endangered
salmon, due to their appetite for salmon eggs. They can walk
on land and enter new rivers to disperse far and wide. Another
problem in California is their impact on water diversion and
on fish salvage facilities. In the summer of 2006 they appeared
in Chesapeake Bay, and by 2007 were spotted in Delaware Bay
and the New York/New Jersey vicinity. New York and New
Jersey have issued alerts for crabbers to report any sightings.
Sightings along the East Coast have been sporadic without
any indication (so far) that a population is established and
growing.
The Asian Shore Crab, Hemigrapsus sanguineus , a small spe-
cies, was first observed by John McDermott in New Jersey
in 1988 after it probably arrived as larvae in ballast water. It
has extended its range to Maine and North Carolina, becom-
ing abundant in pebbly intertidal and shallow water habi-
tats. They reproduce readily in a wide range of conditions,
and are found in very high densities; in some areas they have
displaced green crabs, possibly because they prey on small
green crabs. H. sanguineus is now the dominant crab in rocky