Wave energy converters (WECs) and tidal energy converters (TECs) are only beginning to be deployed along the U.S. West Coast and in Hawai‘i, and a better understanding of their ecological effects on fish, particularly on special-status fish (e.g., threatened and endangered) is needed to facilitate project design and environmental permitting. The structures of WECs and TECs placed on to the seabed, such as anchors and foundations, may function as artificial reefs that attract reef-associated fishes, while the midwater and surface structures, such as mooring lines, buoys, and wave or tidal power devices, may function as fish aggregating devices (FADs), forming the nuclei for groups of fishes. Little is known about the potential for WECs and TECs to function as artificial reefs and FADs in coastal waters of the U.S. West Coast and Hawai‘i. We evaluated these potential ecological interactions by reviewing relevant information about fish associations with surrogate structures, such as artificial reefs, natural reefs, kelps, floating debris, oil and gas platforms, marine debris, anchored FADs deployed to enhance fishing opportunities, net-cages used for mariculture, and piers and docks.
Based on our review, we postulate that the structures of WECs and TECs placed on or near the seabed in coastal waters of the U.S. West Coast and Hawai‘i likely will function as small-scale artificial reefs and attract potentially high densities of reef-associated fishes (including special-status rockfish species [Sebastes spp.] along the mainland), and that the midwater and surface structures of WECs placed in the tropical waters of Hawai‘i likely will function as de facto FADs with species assemblages varying by distance from shore and deployment depth. Along the U.S. West Coast, frequent associations with midwater and surface structures may be less likely: juvenile, semipelagic, kelp-associated rockfishes may occur at midwater and surface structures of WECs in coastal waters of southern California to Washington, and occasional, seasonal, or transitory associations of coastal pelagic fishes such as jack mackerel (Trachurus symmetricus) may also occur at WECs in these waters. Importantly, our review indicated that negative effects of WEC structures on special-status fish species, such as increased predation of juvenile salmonids or rockfishes, are not likely. In addition, WECs installed in coastal California, especially in southern California waters, have the potential to attract high densities of reef-associated fishes and may even contribute to rockfish productivity, if fish respond to the WECs similarly to oil and gas platforms, which have some of the highest secondary production per unit area of seafloor of any marine habitat studied globally (Claisse et al. 2014).
We encountered some information gaps, owing to the paucity or lack, in key locations, of comparable surrogate structures in which fish assemblages and ecological interactions were studied. TECs are most likely to be used in the Puget Sound area, but suitable surrogates are lacking there. However, in similarly cold-temperate waters of Europe and Maine, benthopelagic fish occurred around tidal turbines during lower tidal velocities, and this type of interaction may be expected by similar species at TECs in Puget Sound. To address information gaps in the near term, such as whether WECs would function as FADs in temperate waters, studies of navigation buoys using hydroacoustics are recommended.