Bird Barrier Decreases Pond Plundering by
Cormorants By Jim
June 16, 2003
Twine serves as the basis for a low-tech solution to a growing
problem for aquaculture in the Mississippi River Delta.
Double-crested cormorants, commonly called water turkeys, are
migratory birds that winter in the Delta region. They feed on channel catfish
fingerlings in farm ponds, typically from September to mid-April, and sometimes
longer. The Agricultural Research
Service wants to help reduce cormorant damage by dispersing their
populations away from areas of high catfish production.
Andy Radomski, a wildlife biologist at the ARS
Harry K. Dupree Stuttgart National
Aquaculture Research Center in Arkansas, developed a barrier by stringing
twine at 30-meter intervals (about 100 feet) across ponds. He estimates a
three-person crew can manually complete a 15-acre pond in about three hours.
The material cost ranges from $20 to $80 per 15-acre pond. The twine must be
tied to posts so that it remains at least three feet above the water in the
middle of the pond. If the string is too close to the water, the birds are more
likely to still land.
Only 2.3 birds an hour on average were counted on ponds where
the technique was tested, compared with 10.6 birds on control ponds.
The technique initially decreases the number of cormorants
landing on a pond, and then additional cormorants are less likely to land
because they seek safety in numbers.
Aquaculturalists claim cormorant depredation as their biggest
wildlife problem. Besides eating fingerlings, the birds also injure catfish,
disturb their feeding patterns and potentially carry diseases. Although their
populations were once threatened, cormorant numbers in the Delta have steadily
risen, nearly tripling during the past decade alone. They fly from nearby roost
trees, land on ponds and periodically dive for young catfish. Each bird can
consume 1-1.5 pounds of catfish a day.
The technique is easy to use and maintain, nonlethal, and
cost-efficient, though it would not deter all fish-eating birds, according to
ARS is the U.S. Department of
Agriculture's chief scientific research agency.