With over 12,000 water hectares in catfish (Ictalurus sp.) aquaculture production, and annual production greater than $112 million, the Black Belt region of eastern Mississippi and western Alabama is one of the largest regions of catfish aquaculture production in the U.S. Recent regional declines in farmed water acres highlight the importance of understanding challenges to production, such as fish losses, due to avian predators, especially double-crested cormorants (Nannopterum auritum: hereafter cormorant). While considerable research has documented and quantified losses due to cormorants in the Mississippi Delta, little has been done in the Black Belt. Therefore, the objectives of this study were to: 1) assess the distribution and relative abundance of cormorants on catfish farms in the Black Belt, 2) quantify the diet of these cormorants, and 3) evaluate the economic impacts of cormorant predation on catfish production.
During the 2023-2024 field season, we conducted surveys from a fixed-wing aircraft every 2-4 weeks between November-April to estimate the relative abundance of cormorants on a subset of 37 farms in the region. Following each survey, we collected cormorants with firearms for diet analyses from a subset of farms where cormorants were observed during the preceding survey. Collected birds were immediately gavaged with 60cc phosphate buffered saline to halt digestion, placed on ice, and then transported to a lab for necropsy. We then removed the esophagus and proventriculus from collected birds and catalogued prey items.
A total of 74 cormorants were collected during the first field season, with 29 consuming ≥1 catfish, and 33 consuming ≥1 shad (Dorosoma sp.). Of cormorants that consumed catfish, most were collected in April (n=12). The average weight of catfish consumed was 80.3 g.
We will use non-linear mixed models to assess spatial and temporal variability among diets. Occupancy and n-mixture models will be used to predict cormorant distribution and abundance, and we will combine this data with bioenergetics models to determine regional catfish consumption and develop enterprise budgets reflecting farm characteristics with and without depredation by cormorants. Results will be used to inform the timing and implementation of management.