Wind and shipping influences on sea currents around an inshore fish farm in a heavily contested Mediterranean embayment

Abstract

Marine aquaculture expansion will continue to be challenged by a lack of space in areas of the marine domain that can support aquaculture, due to competition from other maritime activities vying for the same spaces. This research attempts to characterise those natural and anthropogenic forces that influence and drive sea currents measured over a 16-month period around a nearshore fish farm located within a busy multiple-use bay in the central Mediterranean Sea. Evidence from a concomitant two-year-long meteorological dataset reveals the occurrence of variable winds that result in a dominant and perpetual forcing on near-surface current magnitude and direction. The correlation coefficient between wind and sea currents decreases with increasing depth and hourly time lag. Moreover, the observed water level variations were more related to meteorological forcing factors than to tidal influences recorded at the mouth of the bay. However, intermittently observed water current values could not be exclusively explained by atmospheric forcing variables when the relationship between in-situ measurements and sea current values predicted by the hydrodynamic-wave model (Marine Forecasting System) was analysed. Consequently, this lack of correlation spurred further analysis, which revealed that relevant water current disturbances, particularly in near-surface sea currents, corresponded to 131 different Automatic Identification System (AIS) records of vessels. These vessels included bunkering barges, pilot boats and dredging vessels operating and navigating within a 650 m radius from the fish farm and during a 10-min window. This study thus provides evidence for natural and anthropogenically-derived influences on local fish farm-scale hydrodynamics that have important implications for the effective and sustainable development of aquaculture within a marine spatial context, especially in congested, multi-use environments.