One of the most important biological questions facing the marine and hydrokinetic (MHK) energy industry is whether fish and marine mammals that encounter MHK devices are likely to be struck by moving components. For hydrokinetic1 (HK) devices, i.e., those that generate energy from flowing water, this concern is greatest for large organisms because their increased length increases the probability that they will be struck as they pass through the area of blade sweep and because their increased mass means that the force absorbed if struck is greater and potentially more damaging (Amaral et al. 2015). Key to answering this question is understanding whether aquatic organisms change their swimming behavior as they encounter a device in a way that decreases their likelihood of being struck and possibly injured by the device. Whether near-field or far-field behavior results in general avoidance of or attraction to HK devices is a significant factor in the possible risk of physical contact with rotating turbine blades (Cada and Bevelhimer 2011).
Although numerous hydrokinetic device designs are under development (see DOE 2009 for a description of the technologies and their potential environmental effects), the ultimate goal for most developers is to deploy multiple devices in a large array positioned in high-velocity (high-energy) zones of rivers or tidal channels. The diverse designs imply a diversity of environmental impacts (Čada et al. 2010), but a potential impact common to most is the risk of blades striking aquatic organisms. Only a limited number of studies have been conducted to examine the risk of blade strike from HK technologies to freshwater fish (Turnpenny et al. 1992; NAI 2009; Schweizer et al. 2011; EPRI 2011; Amaral et al. 2015; Castro-Santos and Haro 2015).
Recent federal licensing requirements (e.g., see projects by Verdant Power in New York, New York and Ocean Renewable Power Company in Eastport, Maine) have included evaluation of possible interactions by fish and marine mammals with devices and additional monitoring as pilot arrays are deployed. Until it is demonstrated that these devices provide little risk of injury to aquatic organisms, this concern will likely persist for all device types and aquatic environments. These concerns are officially addressed by regulators under several regulatory statutes. For example, Section 7(a)(2) of the Endangered Species Act (ESA) requires federal agencies to ensure that their actions are not likely to jeopardize the continued existence of federally listed threatened and endangered species, or result in the destruction or adverse modification of their designated critical habitat. The Marine Mammal Protection Act (MMPA) prohibits, with certain exceptions, the “take” (defined under the statute as actions that are or may be lethal, injurious, or harassing) of marine mammals in US waters and the high seas. Section 10(j) of the Federal Power Act requires the Federal Energy Regulatory Commission (FERC), when issuing a license, to include conditions based on recommendations by federal and state fish and wildlife agencies, submitted pursuant to the Fish and Wildlife Coordination Act, to “adequately and equitably protect, mitigate damages to, and enhance fish and wildlife (including related spawning grounds and habitat)” affected by the project.