The rapid increase in offshore wind energy worldwide has raised concern about its potential risks to marine biodiversity due to habitat alteration, disturbance from noise and electromagnetic fields. This study presents results of surveillance studies performed at the Lillgrund wind farm in Sweden to investigate the integrated effects of these factors on the abundance and distribution patterns of benthic fish communities. The studies revealed no large-scale effects on fish diversity and abundance after establishment of the wind farm when compared to the development in 2 reference areas. Changes in some species and in community composition were observed over time but occurred in parallel in at least one reference area, indicating that fish communities in the wind farm area were mainly driven by the same environmental factors as those in surrounding areas. However, changes at smaller spatial scales were evident. Increased densities of all studied piscivores (cod, eel, shorthorn sculpin), as well as the reef-associated goldsinny wrasse, were observed close to the foundations in the first years of operation. The increase was probably attributed mainly to local changes in distribution rather than to immigration or increased local productivity. Simultaneously, weak or no aggregation of black goby, eelpout and shore crab, all potentially reef-associated but also prey species of the studied piscivores, was observed, which may indicate enhanced top-down control near the foundations.

The conflicts between grey seals and the cod fisheries in the Swedish Baltic Sea have increased steadily during the past 10 years. In this study we investigated damage to catches caused by seals in the inshore gillnet fishery for cod in the central Baltic Sea. Damage by seals includes both visible catch losses such as fish remains found and hidden losses where fish are removed entirely without leaving any visible fish remains in the net.An observer joined two professional fishermen in two locations, recording the fishing effort and catches on their daily fishing trips for a period of three months each year in 2005 and 2006. To estimate the hidden losses, marked fish were manually entangled in the nets before resetting. When hauling the nets, the number of marked fish either damaged or lost was used to calculate the "hidden" losses.A total of 324 fleets of nets were set and on 169 of these settings, damaged fish were found in the nets when hauled. 59 previously set fleets were selected for experimental trials in which fish were marked and replaced in the nets in order to estimate the extent of the hidden losses, and 39 of these set fleets were found to have been visited by seals. The mean hidden losses were calculated to be 44.2% of the marked fish (95% C.I 33.9-54.5) after allowing for fish lost due to handling of the nets. On average 4.1 fish were lost for each fish found damaged (max. 25.6 and min. 1.6) in 2005 and in 2006 the ratio was 2.7 (max. 11.3 and min. 1.4). Extrapolating these numbers to the actual catches landed in the fishery observed, the hidden losses would correspond to 36% of the total potential catches or 67% of the landed catches in 2005, and to 15% of the total potential catches or 19% of the landed catches in 2006.The results from the present study show that the damage caused by grey seals such as in hidden as well as visible catch losses are significant and that this needs to be taken into account when estimating the total impact of seal predation on fisheries.

Establishment of artificial reefs and no-take areas are management measures available for restoring deteriorated marine ecosystems, compensating for habitat loss and strengthening harvested populations. Following the establishment of no-take artificial reefs in western Sweden to compensate for hard bottoms lost to a shipping lane, we detected rapid positive effects on crustaceans and demersal fish compared to fished reference areas. The relative abundance and size structure of European lobster (Homarus gammarus) increased strongly in the no-take area indicating more than doubled and tripled egg production in 5 and 10 years, respectively. For benthic fish and crustacean communities, the abundances of gadoids and wrasses increased and the abundances of small decapod crustaceans decreased in the no-take area, likely indicating cascading effects of increased predation. The study demonstrates that relatively small no-take areas, enhanced by artificial reefs, can rapidly invigorate populations of lobster and fish that in turn may re-initiate local top-down control.