Wrasse fishery on the Swedish west coast: towards ecosystem based management

Aims: Corkwing, goldsinny and ballan wrasse (Symphodus melops, Ctenolabrus rupestris and Labrus bergylta) are fished on the Swedish west coast for use as cleaner-fish in Norwegian salmon farms. Current information on the biology and population structure of these species is not sufficient to support sustainable management. Here, we aim to provide knowledge and recommendations to support ecosystem-based management for wrasse fisheries in Sweden.Methods: We compared fished and non-fished areas to test if current fishery levels have led to stock depletion. In addition, we sampled the mobile epifauna and fouling organisms on habitat-building brown algae in fished and non-fished areas. To gain insight on the role of wrasse in the algal belt trophic chain, we analyzed the gut contents of goldsinny and corkwing using metabarcoding. Finally, we analyzed the trophic interactions of wrasse and potential prey in a mesocosm study.Results and conclusions: We could not detect any signs of stock depletion or altered size structure in fished areas compared to the protected control area. Gut analyses confirmed both goldsinny and corkwing as non-specialized, omnivorous opportunists and revealed, with 189 prey taxa detected, a broader spectrum of prey than previously known. Common prey items included mesoherbivores such as small gastropods and crustaceans, but also insects and algae.Mesocosm experiments confirmed the role of wrasses as efficient predators on fauna associated with the algal belt, and suggest that decimating wrasse populations may result in cascading effects on lower trophic levels such as epiphytes on habitat building brown algae. We conclude that there are no visible signs of stock depletion at the current removal level of wrasses by the fishery. However, this emerging fishery should be closely monitored for potential cascading effects on the algal belt ecosystem, and our study could provide a baseline for future monitoring.