Fish and fisheries research to inform ScotMER evidence gaps and future strategic research in the UK: review

Evidence Gap FF.08: Collision risk (tidal turbines)

Review of current knowledge

Tidal energy devices are located in energetic and tidally dynamic sites which are often important to protected species. There is concern, therefore, with regard to the potential for tidal devices such as rotors to represent and obstacle and collision risk to marine animals. Whilst concerns in respect to collision risk relate more obviously to marine mammals and diving birds, there are also concerns on fish, particularly on large fish of conservation importance such as Atlantic salmon and basking sharks (SNH 2016).

As observing animal behaviour around tidal devices is challenging, limited field data on the interactions between tidal turbines and fish is currently available. To date only few observations have shown fish in contact with turbines or other MRE infrastructure, resulting in no obvious damage to fish. As such collision or even close encounters between fish and turbines are considered to be rare (Copping et al 2020).

Matzner et al (2017) analysed video data collected around a marine renewable energy device deployed in the Kvichak River in Alaska, to test underwater video cameras as a fish monitoring technique. Only on one occasion was an actual contact confirmed, and this was an adult fish making contact with the camera, rather than the turbine itself. Bevelhimer et al (2017) used multibeam hydro-acoustics to monitor fish passage at a tidal turbine in the East River, New York. The study found the density of fish in the sampled area when the turbine was absent was roughly twice the density observed when the turbine was in place, suggesting large-scale avoidance behaviour. Viehman and Zydlewski (2015) used acoustic cameras to observe fish interaction with a commercial-scale turbine in Cobscook Bay, Maine. The study found that fish were less likely to enter the turbine when it was rotating than when it was not. In addition, the probability of fish entering the turbine was higher at night than during the day and this difference was greater for small fish than larger fish. Similarly, studies on fish behaviour around a vertical axis hydrokinetic rotor (Hammar et al 2013) found that fish reduced their movement through the area when the rotor was present. In addition, fish that passed the rotor avoided the near-field area, with larger fish particularly cautious of the rotor. Berry et al (2019) studied the response of juvenile Atlantic salmon and sea trout to a hydrokinetic turbine in an experimental set up. No direct collisions were observed in the study and it was found that sea trout were less likely to pass the turbine than salmon. In addition, both species preferentially passed around the turbine rather than passing through the turbine.

In order to help inform and improve encounter probability and collision risk models, to better understand potential interactions between fish and tidal devices, further information on the behaviour of fish around devices needs to be collected. Recently (or yet to be) developed echosounder and camera data processing algorithms and suitable software and process to automate data analysis are expected to facilitate progress in this context (Fraser et al 2017, Viehman et al 2020, Sparling et al 2020, Hutchison et al 2020c).

It should be noted that to date the majority of research has been focused on the effects on individual fish and individual turbines. Future studies should examine the impacts of MRE arrays, as these may have implications substantially different from those of single devices (Sparling et al 2020). For example, arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity (Hammer et al 2013).

In addition, as the industry develops there is a need to consider potential community-level effects. The distribution of fish is likely to drive the foraging behaviour of larger predators and will likely influence risks to other species (Fraser et al 2018, Williamson et al 2019, Whitton et al 2020).

Next steps in research

The literature review presented above indicates that only few observations have shown fish in contact with turbines, and collisions or even close encounters are considered to be rare. However, only limited monitoring and field data have been collected to date. Furthermore, the majority of existing studies have been focused on the effects of individual devices rather than on the impact from arrays and little attention has been given to potential community level effects. With this in mind, the following steps are recommended to address current knowledge gaps:

• Monitoring and collection of field data and improvement of existing data analysis tools (i.e. processing algorithms and software and tools to automate data analysis).
• Development of fish collision risk models which incorporates relevant behavioural information as information becomes available.
• Strategic research to investigate the impact of MRE arrays both at population and community level.