Interactions between wild fauna and farmed tuna in Maltese coastal waters

Abstract

Atlantic bluefin tuna (Thunnus thynnus) ranching is a major aquaculture activity in Malta, yet interactions between tuna farms and wild fauna remain poorly documented. This study addresses this gap by identifying which wild fauna aggregate around farm sites, the drivers of these aggregations, and the resulting ecological and operational implications. Nineteen semi-structured interviews were conducted with tuna farm personnel and environmental monitors across four ranching sites, providing multi-year observations on species presence, behavior, and interaction patterns. In total, 41 wild fauna species and 143 observations were recorded. Aggregation was primarily driven by uneaten baitfish, habitat provisioning from cage structures, and proximity to migratory routes. Findings indicate that tuna farms act as fish aggregating devices (FADs) that alter local trophic dynamics. Consumption of uneaten baitfish can reduce organic loading and improve the condition of aggregated fauna, offering localized ecological benefits. However, reliance on baitfish also perpetuates pressure on wild forage fish stocks, and predictable food subsidies may create ecological traps, behavioral dependency, and changes to natural movement patterns. This study provides the first baseline assessment of these interactions in Malta and highlights the need for long-term monitoring and adaptive management to balance aquaculture productivity with ecosystem sustainability.