Bird Barrier Decreases Pond Plundering by Cormorants

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 Radomski.

ARS is the U.S. Department of Agriculture's chief scientific research agency.