Impact of harvesting cleaner fish for salmonid aquaculture assessed from replicated coastal marine protected areas

ABSTRACT

Wrasse (Labridae) fisheries have increased markedly in Norway since 2010. Wrasse are being used as cleaner fish in salmonid aquaculture to control sea-lice infestations. However, fundamental knowledge on the demography and abundance of the targeted wrasse populations in Norwegian waters is lacking, and the consequences of harvesting at the current intensity have not been assessed. Here, we compared catch per unit effort (CPUE), size, age and sex ratio of goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) between marine protected areas (MPAs) and control areas open for fishing at four localities on the Skagerrak coast in Southern Norway. The CPUE of goldsinny larger than the minimum size limit was 33–65% higher within MPAs, while for corkwing three of four MPAs had higher CPUE with the relative difference between MPAs and control areas ranging from −16% to 92%. Moreover, corkwing, but not goldsinny, was significantly older and larger within MPAs than in control areas. Sex ratios did not differ between MPAs and control areas for either species. Our study suggests that despite its short history, the wrasse fisheries have considerable impacts on the target populations and, further, that small MPAs hold promise as a management tool for maintaining natural population sizes and size structure. Goldsinny, being a smaller-sized species, also seems to benefit from the traditional minimum size limit management tool, which applies outside MPAs.

RESPONSIBLE EDITOR:

• Sanja Matic-Skoko

KEYWORDS:

• Marine protected areas
• aquaculture–environment interactions
• wrasse
• fisheries management
• fishing impacts
• Skagerrak

Acknowledgements

The research was conducted at the Institute of Marine Research Flødevigen, Nye Flødevigveien 20, 4817 His, Norway. We would like to thank Benjamin Hanssen for assistance during fieldwork and otolith analyses and the fisherman in Flødevigen for providing catch data.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Norges Forskningsråd under grant 201917 (project PROMAR); the University of Agder through funding from the Norwegian Ministry of Education and Research and the Öresund-Kattegat-Skagerrak Interreg program (project: MarGen).