Commercial production of catfish (Ictalurus spp.) is the largest aquaculture industry in the nation, with most production occurring in Mississippi. Human-wildlife conflict in Mississippi is a contentious issue between producers and fish-eating birds through the consumption of cultured fish. Most notable of these birds is the Double-crested Cormorant (Nannopterum auritum; hereafter, cormorant), which can cost producers millions of dollars annually.
Our research focuses on answering various questions related to cormorant behavior relative to catfish aquaculture in Mississippi. We examined historic versus current cormorant activity, pond and fish size preference, cormorant use of catfish ponds versus natural water bodies, roosting behavior, and the influence of regulatory policy on cormorant use of catfish ponds. We used cormorant roosting data and pond survey data from multiple sources collected over the last 20 years to address these questions. Information gained from this research will help reduce cormorant impact on the aquaculture industry and offers insight into cormorant foraging ecology.
Aquaculture production in Mississippi peaked in the early 2000s, but cormorant density on aquaculture ponds has not changed since that time even though aquaculture area has declined by 70% (Figure 1). Similarly, roost counts today are approximately one third of those 20 years ago. We also found cormorants prefer ponds located farther away from trees and farm workshops, larger ponds, and ponds nearer the edge of pond clusters. Specific pond contents influenced cormorant preference, including fish species cultured, pond systems, and fish types. Cormorants favored aquaculture over natural water bodies later in the winter season coinciding with spring migration, indicating a switch toward catfish in preparation for their migration north. Likewise, cormorants showed increased use of roosts with more surrounding aquaculture later in the winter season. Lastly, we found cormorant use of aquaculture relative to natural water bodies was greatest when lethal control was suspended and least when it was allowed, suggesting lethal measures provided by regulatory policies were an effective means of altering cormorant distribution, thereby reducing damage at aquaculture facilities.