The movement of five wrasse species (Labridae) on the Norwegian west coast.

During the 1980`s it was discovered that fishes from the wrasse family (Labridae) along the Norwegian coast could be utilized as cleaner fish for controlling sea-lice infestations in commercial fish farming. Since this discovery, the demand for wild-caught wrasse has generated a large and profitable fishery. And subsequently, knowledge regarding the biology and ecology of temperate wrasses is needed to manage a sustainable fishery. In this thesis, I analyzed movements of the five wrasse species using mark-recapture data collected over five periods in 2017 and 2018 on three islands outside Huftarøy in Austevoll municipality in western Norway. A total of 8454 wrasses were tagged, and 839 were recaptured. The five species of wrasse found at the study location; Corkwing (Crenilabrus melops), goldsinny (Ctenolabrus rupestris), ballan wrasse (Labrus bergylta), rock cook (Centrolabrus exoletus) and cuckoo wrasse (Labrus mixtus). Horizontal movement made by individuals from these species was obtained by calculating the distance between observations. Life-history traits and environmental factors were then used in order to explain movement patterns. In this thesis, I found that the five species of wrasse moved locally with little horizontal movement. This was reinforced by the lack of observations of movement between the three islands. Corkwing wrasse was found to have moved longer distances with larger body size, and the island and habitat where captured had an effect on the distance traveled. Goldsinny wrasse was found to move shorter distances than corkwing, and the island where captured influenced horizontal movement. Factors influencing the recapture probability was found to mirror factors influencing movement, and the time of year influenced the probability of being recaptured. Local island populations of territorial fishes such as the wrasses in this study are particularly vulnerable to overexploitation and would likely struggle to recover. The movement patterns observed for corkwing make this species especially susceptible to sex-selective harvesting, which can have a negative impact on population productivity. The way fishes move is directly linked with the probability of being harvested. In order to protect small local populations of temperate wrasses, further research on wrasse movement should be carried out with different techniques such as acoustic or radio telemetry in order to get a more detailed understanding of the movement patterns of the five species of wrasse found along the Norwegian coast.