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▲ Aquaculture ponds where the red swamp
crayfish was once cultured
▀
Watersheds with feral stream populations of
red swamp crayfish now established
The invaders have been found in most Maryland
streams and have established significant populations
in the areas in red.
in ponds located on the Patuxent Wildlife Refuge near Laurel
in 1963. The intention of this introduction was to provide a
food source for waterfowl and wading birds during their annual
migration. Refuge biologists dropped what amounted to
“a handful” of crayfish into the ponds. Following the introduction,
the crayfish were largely forgotten.
The next introduction of the red swamp crayfish did not
occur until 18 years later, when a group of farmers became
interested in the idea of culturing crayfish for profit. Most
Maryland residents would be surprised to learn that a commercial
crayfish industry, albeit small, exists within the state.
Unlike most aquaculture, commercial culturing of crayfish
requires little more than a farm pond, a little patience, and
a few chicken-wire traps. In fact, add a few pounds of live
crayfish, throw in some food every now and then, and in a
year’s time, a relatively small farm pond can produce a profitable
harvest. That is exactly what attracted several farmers to
the idea of crayfish culturing.
It all began in 1981, when a small group of farmers on
the Delmarva Peninsula pooled their resources, and sent one
brave soul to Louisiana with a refrigerated truck, with “$5,000
in cash and a shotgun on his lap” to protect his bounty.
The cash bought seed stock from a Louisiana crayfish
farmer. Once back in Maryland, the crayfish were spread
among three ponds near Salisbury as part of the Worcester
County Crawfish Trial of 1981. This trial was conducted to
determine whether or not crayfish aquaculture was possible
in Maryland’s climate. The crayfish survived their first Maryland
winter, and grew quickly throughout the year. The results
of the trial were promising and indicated that crayfish
aquaculture was not only feasible, but also profitable.
In 1983, the Mid-Atlantic Crawfish Association was established.
Armed with 250 members (at its peak) and the
catchy slogan, “The tail is the best, you can suck the rest,” this
association promoted crayfish aquaculture throughout the
region. Thereafter,
the original
Louisiana crayfish were
used to stock farm ponds and drainage ditches throughout the
Delmarva and southern Maryland, many undocumented.
Unlike many finfish, crayfish are nearly impossible to
contain in a pond. After a heavy rainstorm, it is quite common
to find them walking about. They are also adept at colonizing
new areas. Thus, the culture of crayfish, like the red swamp
crayfish, often results in the establishment of feral populations
in nearby waterways. This has occurred throughout the
world and Maryland is no exception.
In 2006, the MDNR Maryland Biological Stream Survey
conducted surveys of streams and rivers throughout the
state’s Coastal Plain, including areas near known aquaculture
ponds. During these surveys, biologists discovered feral red
swamp crayfish in 14 watersheds. They were discovered adjacent
to every known location where this species was once
cultured in ponds, including portions of the Patuxent River
near the site where they were first introduced in 1963.
So, why is it a concern?
North American crayfish, the most diverse in the world,
are considered the second most imperiled group of animals
on the continent, behind only freshwater mussels. The most
pervasive threat is the introduction of non-native species.
Crayfish tend to be fierce competitors and physically fight
one another for prime feeding and shelter habitats in streams,
rivers, and lakes. These conflicts usually end in the death of
the smaller, less competitive crayfish.
Introductions of large, non-native species usually occur to
the detriment of smaller, and therefore less competitive, native
crayfish species. Non-native crayfish introductions have
caused declines and outright loss of crayfish throughout the
world. Maryland, home to nine native species, has already
experienced this phenomenon. The virile crayfish, another