Food habits of wintering double-crested cormorants in the Mississippi Delta

Given its ubiquity, it is not surprising that agriculture, including finfish aquaculture, contributes to food webs worldwide and is used by numerous wildlife for foraging and meeting other needs. Double-crested Cormorants (Phalacrocorax auritus) impact United States commercial aquaculture and are considered the primary avian predator in catfish (Ictalurus spp.) aquaculture facilities in the Mississippi Delta. Recent changes in aquaculture practices, regulatory policies, and decreased overall hectares in production prompted this study that assessed cormorant consumption of catfish in relation to their night roosts through surveys and diet analysis. Cormorants were collected from night roosts from October through April 2016–2018 (n = 69 collections). On average, catfish constituted 33% of a cormorant's overall diet, which is less than reported in previous studies. There was no statistical difference between consumption of channel (I. punctatus) and hybrid catfish (I. punctatus x I. furcatus) based on biomass estimates, and the greatest consumption of catfish occurred in the months of February and March. The best fit model for predicting catfish consumption was the cubic polynomial function of the area of catfish aquaculture within a 30.6 km forage buffer of a night roost. Our findings will inform wildlife managers about relationships between cormorant night roost locations and consumption of catfish and aid decision making with respect to cormorant management. Despite cormorants having shifted consumption to naturally occurring fish species associated with changes to aquaculture, aquaculture remains an important part of regional food webs.