Depredation

Commercially reared aquatic animals can be subject to significant predation by a variety of animals. These include birds, seals, crabs, flatworms and starfish. The economic impact of this depredation is difficult to quantify with precision. The US catfish industry, in association with the USDA Wildlife Control Service estimates that in Mississippi, Alabama and Louisiana cormorants consume $10-30 million worth of commercially raised channel catfish per year. Other birds known to predate on commercially raised aquatic animals include great blue herons, black-crowned night herons, kingfishers and white pelicans.

As aquaculture has prospered, so have various fish-eating birds. In some areas, according to natural resource managers, these birds have increased their numbers dramatically, far exceeding the normal carrying capacity of the area. The increased population of these birds has negatively impacted natural roosting areas and island habitats.

Both salmonid net pen culture and molluscan aquaculture operations have also been negatively impacted by depredation. Net pen salmonid aquaculture operations are subject to predation by seals (gray and harbor) and sea lions. The seals and sea lions cause net damage allowing fish to escape and they consume fish. Various burrowing shrimps invade oyster growing areas burrowing into the sand causing the oyster to sink and suffocate. Crabs consume large numbers of clam seed each year. Oysters are also subject to predation by starfish. The net loss and financial cost of these depredations have yet to be quantified but is significant.

Control of depredation is difficult and costly. Many trout farmers have completely covered their facilities with wire to prevent bird and other animals access. This method of deterrence can only be used where ice and snow are unlikely to damage the netting. More expansive production systems such as 10 to 20 acre catfish ponds or extensive shellfish beds are not suitable for covering and other methods to limit depredation must be developed. Some clam farms have been completely covered with mesh but this exacerbates fouling problems and is only partly effective. Clam farms on the US East Coast lose at least 30% or more of their planted seed due to predation. The various aquaculture species groups are working with the regulatory community to establish the best control methods possible. The NAA strongly supports this effort.