Observing fish interactions with marine energy turbines using acoustic cameras

Abstract

Marine current energy converters such as tidal and riverine turbines have the potential to provide reliable, clean power. The risk of collision of fishes with marine energy turbines is not yet well understood, in part due to the challenges associated with observing fish at turbine sites. Turbidity and light availability can limit the effectiveness of optical sensors like video cameras, motivating the use of acoustic cameras for this task. However, challenges persist in collecting and interpreting data acquired from acoustic cameras. Given the limited number of turbine deployments to date, it is prudent to draw on the application of acoustic cameras to monitor fish in other scenarios. This article synthesizes their use for other fisheries applications to inform best practices and set realistic expectations for the results of acoustic camera monitoring at turbine sites. We discuss six key tasks performed with acoustic cameras: detecting objects, identifying objects as fish, counting fish, measuring fish, classifying fish taxonomically and analysing fish behavior. Specific challenges to monitoring fish at turbine sites are discussed. This article is intended to serve as a reference for researchers, regulators and marine energy developers on effective use of acoustic cameras to monitor fish at turbine sites. The studies detailed in this article provide evidence that, in some scenarios, acoustic cameras can be used to inform the risk of fish collision with marine energy turbines but doing so requires careful study design and data processing.

A Probabilistic Methodology for Determining Collision Risk of Marine Animals with Tidal Energy Turbines

“…If a marine animal were to enter the rotor swept area of a tidal turbine and collide with a blade, the consequences of such a collision could be a minor recoverable injury, immediate mortality, or a critical injury that results in permanent disability or death at a later time (i.e., latent mortality). There has never been an observation of a marine mammal struck by a turbine, and while there is video evidence of fish coming very close to a turbine [66], no harm has been observed. There are few studies that provide definitive information on what the consequences of a strike from a tidal turbine might be, although studies of equivalent forces on marine mammal tissue have shown that damage to skin, blubber, and muscle are likely recoverable from a typical tidal blade strike [39,119].…”

“…Underwater passive acoustic monitoring systems can be deployed to detect and locate vocalizing marine mammals, while a range of active acoustic instruments like single-beam or split-beam echosounders, multibeam acoustic cameras and multibeam imaging sonars and acoustic cameras can all be used to assess the location of marine animals. Underwater video is often very useful in identifying species but collects large amounts of data for analysis and may be prone to failure [66].…”

“…Their presence is commonly observed using passive acoustics for vocalizing cetaceans [54,55], active acoustics such as imaging sonars [56][57][58], underwater optical cameras (still or video) [59,60], and observations made from vessels, aircraft, or land [61]. Fish are commonly assessed as individuals or schools (depending on the species) using various active acoustic instruments like single beam or split beam echosounders [62][63][64], multibeam acoustic cameras [32,65,66] and multibeam imaging sonars [26,67], acoustic telemetry [41,42,68], and with underwater optical cameras [25,69]. Other marine animals such as sea turtles and diving sea birds may be assessed in conjunction with marine mammal surveys, or from other dedicated monitoring campaigns [70] using some of the approaches mentioned above.…”

“…While fish have been observed to avoid or evade an operational turbine, some have been observed to pass through the rotor swept area [25,110]. Flume studies and a small number of field studies show that fish that pass through a rotating turbine may become disoriented but do not appear to suffer harm [22,24,25,66]. The relative size of the turbine, the design and solidity of the rotor swept area, and the species present near an operational device, are all likely to affect the ability of marine animals to detect and avoid or evade the rotating blades.…”

The accuracy of length measurements made using imaging SONAR is inversely proportional to the beamwidth

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The remote measurement of underwater targets is an important task for a range of disciplines, such as subsea engineering and maintenance (Cotter & Staines, 2023;Rofallski et al, 2020), defence operations (Reed et al, 2003), archaeology (Green et al, 2002) and marine science studies (Harvey et al, 2001;Harvey & Shortis, 1995). One of the most effective methods for measuring targets underwater is using stereo-video cameras

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