DOUBLE-CRESTED CORMORANT PREDATION ON CATFISH AQUACULTURE

Brian S. Dorr*
 
*USDA, Wildlife Services, National Wildlife Research Center
Box 6099 Mississippi State, MS 39762
E-mail: brian.s.dorr@aphis.usda.gov
 

Commercial production of catfish (Ictalurus spp.) is one of the largest aquaculture industries in North America. Due to favorable geologic, climatic, and socioeconomic factors, much of this catfish production occurs in the southeastern United States and the southern end of the Mississippi flyway, a major migratory route for birds, including Double-crested Cormorants (Phalacrocorax auritus). Cormorant depredation at catfish farms has been extensively studied. Here I provide an overview of some of the research conducted by the National Wildlife Research Center (NWRC) and their collaborators to try and address issues associated with cormorant depredations on catfish aqculture.

The NWRC estimated that direct predation impacts due to cormorants in western Mississippi alone were estimated at US $6 to $12.0 million annually. While these estimates of regional impacts are important to the industry, individual farmers experience losses at the pond level. Trying to estimate impacts at the farm and pond level have proved challenging for a host of reasons.

Research at NWRC has shown an average of about 16 cormorants per day feeding on a 6-ha catfish pond in a single-batch production system over the winter (October-March) could cause a 22% decline in biomass at harvest and negative return to the producer. This reduction occurred even in the presence of buffer prey and accounting for compensatory growth of surviving catfish. Other research evaluated declines in catfish production based on simulated levels of cormorant predation on only stocker size fingerlings in a multibatch system. This research evaluated a scenario in which about 50% of the harvestable catfish had been removed and replaced with stocker size fingerlings. The sale price needed to break even increased with increasing predation on fingerlings up to a maximum of U.S. 14.3¢/kg, largely due to reductions in biomass at harvest due to cormorant predation (Figure 1).

The research conducted at NWRC and elsewhere has shed considerable light on issues associated with cormorant predation and aquaculture. This research has informed management and policy with regard to cormorant depredations. However, much has changed in the catfish aquaculture industry and with cormorant management in recent years and a better understanding of cormorant impacts to catfish aquaculture under current conditions is needed.