- Offshore renewable energy development (ORED) could induce local ecological changes, negatively affecting species of conservation interest. If well planned and coordinated, on the other hand, ORED could be beneficial to the marine environment in the region of device deployment in several respects.
Because of the current scale and pace of offshore renewable energy development, interest is growing in the opportunities offered by the changes in fishing patterns that could result. Trawling, one of the most severe threats to the marine environment, particularly to fish and benthic invertebrate assemblages, will be prohibited or limited inside wind and wave farms. Areas of several square kilometres may therefore, in some important respects, resemble Marine Protected Areas; for areas that were previously trawled this exclusion could lead to average increases in biomass of motile organisms. Primary data from wind and wave farms are still scarce, but results to date from surveys targeting fish assemblages within offshore wind farms in Denmark, the Netherlands, and Sweden basically indicate either increased abundance of some fish species (e.g., sand eels (Ammodytidae), cod (Gadus morhua), whiting (Merlangius merlangus), sole (Solea solea)) or no effect compared to conditions before construction of the wind farm. Effects are likely to be most prominent for species that had been heavily exploited in the area prior to the wind or wave farm establishment. It is believed that a relatively large area of exclusion is required to enhance biodiversity and generate spill-over effects.
Construction and deployment of artificial reefs (AR) in coastal waters is practiced worldwide to manage fisheries, mitigate damage to the environment, protect (i.e., from trawling) and facilitate the rehabilitation of certain habitats (e.g., spawning sites) or water bodies, or to increase the recreational value of an area (e.g., by providing opportunities for recreational diving and fishing). Unless animals are deterred by potential disturbances, such as noise, maintenance work, and electromagnetic fields from turbines, it is reasonable to expect offshore wind energy structures, and also foundations of some types of wave energy devices, to function as artificial reef modules and enhance local abundance of marine organisms, including commercially important fish and crustaceans. However, taxon- and age-specific responses of fishes to ARs vary greatly with AR design and position as well as by region and latitude. It can therefore be difficult to predict the structure of fish and crustacean assemblages associated with the submerged parts of wind and wave energy devices, as well as the radius of influence. Nevertheless, relatively recent studies targeting the potential for wind turbines and wave energy foundations to aggregate fish and motile invertebrates in Sweden, the Netherlands, Belgium, and Denmark suggest that densities of a number of fish and decapod species increase with proximity to these structures.
Another category of artificial habitat is a Fish Aggregation Device (FAD), a floating structure deliberately placed on the surface or suspended in the water column to attract fish and enhance fishing efficiency. FADs are widely used in Asia and the western Indian Ocean. It has been suggested that floating offshore energy devices may function as FADs for pelagic fish, which could provide additional opportunities for fisheries management.
Both ARs and FADs can have negative environmental and social effects if not properly planned and/or used. If ARs only aggregate fish from surrounding areas and do not contribute to added production, enhanced fishing efficiency in the AR area may aggravate overfishing if the new circumstances are not managed with caution. Similarly, increasing catchability, the main purpose of an FAD, may exacerbate the problem of overfishing on commercial species that are already at risk. ARs can also give rise to conflicts over user rights among fisher groups, and between recreational divers and fishers.
Further, densities of benthic prey items have been shown to decrease with proximity to ARs due to predation by fish residing on the structures. FADs have been suggested as potential “ecological traps,” meaning that their presence could lure fish into remaining near the structures under non-optimal local feeding conditions, affecting physical condition and growth. Artificial structures may also provide habitats suitable for establishment of non-indigenous species; deployment of clusters of artificial structures may facilitate the establishment of new taxa in the recipient region by providing “beach heads” and stepping-stones. Non-indigenous sessile invertebrates have already been recorded at wind farms in the North Sea and the Baltic Sea.
A range of design and location factors may influence the fish community structure on artificial reefs, such as height, size, inclination, protuberance, surface structure, void space and number of interior hollows, shade effects, distance between modules, isolation, and composition of the surrounding seabed. Research is underway to evaluate species-specific habitat preferences in the design of offshore energy foundations to optimize biomass of desired species, or alternatively, minimize artificial reef effects where desired. For example, in an experiment with wave energy foundations on the west coast of Sweden the potential for enhancing the abundance of associated fish and crustaceans through low-cost manipulations of the structural complexity of foundations was examined. Additional experiments will provide further guidance on the influence of different designs of foundations on commercially important fish and shellfish.
This presentation will focus on the potential influence of offshore wind and wave farms on fish and commercially important crustaceans. The uncertainties with regard to positive and negative effects of on benthic and pelagic assemblages and specific species will also be discussed. The presentation will draw on results from a number of field studies and experiments conducted in offshore wind and wave farms, as well as on secondary literature on the influence of differently designed artificial habitats on benthic fauna.
- Wilhelmsson, D. 2012. Effects of Altered Habitats and Fishing Practices in Wind and Wave Farms. In: Boehlert, G., C. Braby, A. S. Bull, M. E. Helix, S. Henkel, P. Klarin, and D. Schroeder, eds. 2013. Oregon Marine Renewable Energy Environmental Science Conference Proceedings. U.S. Department of the Interior, Bureau of Ocean Energy Management, Cooperative Agreement with Oregon State University M12AC00012. OCS Report BOEM 2013-0113. 149 pp.