Resumen de Interactions between fish farming, wild fish populations, local fisheries and society: a case study in Catalonia, Spain
Kathrin Bacher
The overarching goal of this doctoral thesis was to advance the understanding of the interactions between marine fish farming, wild fish populations, the local small-scale fishery and the society. This thesis was designed as a multi-disciplinary study and is divided into three different sections: ecology (chapter 1 and 2), fisheries (chapter 3) and social science (chapter 4). In the ecological part we examined the spatial and temporal extent of the attraction effect of wild fish at an Atlantic bluefin tuna and a Gilthead seabream farm. At both farms wild fish aggregated closely to the cage structure, revealing an abrupt decline of fish abundance rather than a gradient. The intensity of the cage effect varied according to farm, season and depth. At the seabream farm, the cage effect persisted year round, whereas at the tuna farm, the effect was restricted to summer and spring. The variability of wild fish aggregations within the Gilthead seabream farm was analyzed because it can be a distorting factor in estimating the farm attraction effect. Our findings showed that at the surface, fish abundance was significantly higher during feeding compared with non-feeding periods. Moreover, the distance from the feeding vessel significantly influenced fish aggregations in the water column. At the bottom, substrate type was the dominant factor explaining aggregation variability. The effect of fish farming on the small-scale fishery was evaluated in order to determine whether farms act as protection zones or as traps for wild fish populations. The findings revealed a relevant amount of commercial and recreational fishing effort in farm vicinity. However, the results showed no benefit or difference of fishing in close proximity to the farm compared to areas away from the farm (in terms of yield, income, and catch composition). Yet, farm-aggregated fish are vulnerable to hidden fishing practices inside the farm. The analysis of the perception of marine fish farming in Catalonia was performed with five key stakeholder-groups (NGOs, local fishermen, fish farming industry, scientists and regional administration). Four perceptions were identified; two represented divergent views and two intermediate positions. Environmental impacts were not perceived as a high risk by the majority of the participants. The major weaknesses were attributed to economic (e.g. price competition with other producer countries) and social issues (e.g. lack of credible information about farmed products). Overall, this thesis provides new information about the complex dynamics of wild fish aggregations at marine fish farms and investigates how this attraction effect influences the local small-scale fishery. Moreover, an understanding of the different perceptions on marine fish farming can help to secure a social, economic and environmental sustainable activity.
