wild fish spatial structure in response to presence of fish farms

Abstract

acoustic surveys were carried out in three regions of the aegean sea where fish farming zones have been established in order to study the mesoscale effect of fish farms on the spatial structure of wild fish communities. in each area two sites were sampled during may and september. one site was close to the fish-farming zone while the other (reference site), was located in a place with similar topography at a mean distance of 20 nautical miles from the fish-farming zone. geostatistical techniques (omnidirectional and exhaustive variograms) were used to analyse and visualize the spatial structure of the wild fish assemblage in each site. the spatial structure of wild fish aggregations at all three fish farming zones showed consistently a pronounced directionality during both sampling periods, indicating that the wild fish patch was oriented towards a specific direction. this was not observed in the respective reference areas. the observed directionality suggested a response at a mesoscale level of the wild fish biota to the presence of the fish farms in the adjacent coastal area.