Harbour porpoises exhibit localized evasion of a tidal turbine

Funding: Scottish Government (Grant Number(s): Marine Mammal Scientific Support Program MMSS/002/); Natural Environment Research Council (Grant Number(s): NE/R014639/1, NE/R015007/1).1. Tidal energy generators have the potential to injure or kill marine animals, including small cetaceans, through collisions with moving turbine parts. Information on the fine scale behaviour of animals close to operational turbines is required to inform regulators of the likely impact of these new technologies. 2. Harbour porpoise movements were monitored in three dimensions around a tidal turbine for 451 days between October 2017 and April 2019 with a 12-channel hydrophone array. 3. Echolocation clicks from 344 porpoise events were localized close to the turbine. The data show that porpoises effectively avoid the turbine rotors, with only a single animal clearly passing through the rotor swept area while the rotors were stationary, and none passing through while rotating. 4. The results indicate that the risk of collisions between the tidal turbine and porpoises is low; this has important implications for the potential effects and the sustainable development of the tidal energy industry.Publisher PDFPeer reviewe

Hydroacoustic Analysis of the Effects of a Tidal Power Turbine on Fishes

Tidal currents help shape coastal marine environments and are essential in life cycles of many fish species. Areas with strong tidal currents are also targeted by humans for energy extraction via tidal energy turbines. The effects of these devices on fishes are difficult to predict because fish behavior within fast tidal currents is largely unstudied. Based at a tidal energy site in Cobscook Bay, Maine, this work sought to describe fish reactions to a tidal energy device, to understand the natural presence of fish at the site, and to provide guidance for future monitoring of tidal energy device effects in these difficult environments. A bottom-mounted echosounder was used to monitor the behavior of fish 7-18 m away from a stationary MHK device for several weeks. Fish moved with the current, but those approaching the device showed signs of avoiding it by adjusting their direction. The same echosounder was used to collect a two-year record of hourly fish passage rate at the depth of the turbine, after it had been removed. Fish passage rate, and therefore potential encounter rate with the turbine, changed dramatically over time with the dominant environmental patterns (tidal, daily, lunar, and seasonal cycles). By timing surveys of fish abundance at tidal energy sites with these cycles (e.g., carrying out 24-hr surveys at the same lunar stage throughout the year), the quality of results can be improved. Using this approach at tidal energy sites could therefore increase our ability to detect device effects without requiring expensive continuous sampling over a long time. Monitoring costs may be further reduced by using single beam echosounders, rather than the typical split beam systems, as statistical methods (deconvolution) were found to make certain single beam data comparable to that from the split beam. Depending on monitoring goals, the use of single beam echosounders could substantially reduce costs while supplying sufficient information on device effects for use in management decisions. Results from Cobscook Bay are likely to be useful at other tidal energy sites, but study designs and results need to be considered in the context of fish species and life stages present

Hydrokinetic Turbine Effects on Fish Swimming Behaviour

Hydrokinetic turbines, targeting the kinetic energy of fast-flowing currents, are under development with some turbines already deployed at ocean sites around the world. It remains virtually unknown as to how these technologies affect fish, and rotor collisions have been postulated as a major concern. In this study the effects of a vertical axis hydrokinetic rotor with rotational speeds up to 70 rpm were tested on the swimming patterns of naturally occurring fish in a subtropical tidal channel. Fish movements were recorded with and without the rotor in place. Results showed that no fish collided with the rotor and only a few specimens passed through rotor blades. Overall, fish reduced their movements through the area when the rotor was present. This deterrent effect on fish increased with current speed. Fish that passed the rotor avoided the near-field, about 0.3 m from the rotor for benthic reef fish. Large predatory fish were particularly cautious of the rotor and never moved closer than 1.7 m in current speeds above 0.6 ms-1. The effects of the rotor differed among taxa and feeding guilds and it is suggested that fish boldness and body shape influenced responses. In conclusion, the tested hydrokinetic turbine rotor proved non-hazardous to fish during the investigated conditions. However, the results indicate that arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity if migration routes are exploited. Arrays of the investigated turbine type and comparable systems should therefore be designed with gaps of several metres width to allow large fish to pass through. In combination with further research the insights from this study can be used for guiding the design of hydrokinetic turbine arrays where needed, so preventing ecological impacts

Effects of propulsion system operation on military aircraft survivability

The recent advances in infrared (IR) weapon technology have dramatically altered the rules of air combat, leading to a consistent departure from “traditional” energy-maneuverability philosophy in aircraft design, prioritizing stealth and sophisticated armament instead. In this modern aerial warfare environment, it is obvious that new techniques need to be applied to properly assess aircraft survivability and produce successful designs for aircraft propulsion systems. The present study focuses on the development of such a methodology, which contrary to related work in the field includes considerations for both aircraft IR signature and missile/aircraft kinematic performance. An aircraft IR signature model is constructed using a collection of methods for area and temperature estimation and exhaust plume modeling; the latter is combined with missile-vs-aircraft and aircraft-vs-aircraft simulations to quantify aircraft survivability in the form of missile and aircraft lethal zones. The proposed methodology is applied to a study on propulsion system effects on aircraft survivability, in which a comparison between different engine configurations is performed: In the scenarios examined, IR signature at cruise conditions and maximum-power thrust performance are identified as key parameters for aircraft combat performance

Construction of Barrier in a Fishing Game With Point Capture

This paper addresses a particular pursuit-evasion game, called as “fishing game” where a faster evader attempts to pass the gap between two pursuers. We are concerned with the conditions under which the evader or pursuers can win the game. This is a game of kind in which an essential aspect, barrier, separates the state space into disjoint parts associated with each player's winning region. We present a method of explicit policy to construct the barrier. This method divides the fishing game into two subgames related to the included angle and the relative distances between the evader and the pursuers, respectively, and then analyzes the possibility of capture or escape for each subgame to ascertain the analytical forms of the barrier. Furthermore, we fuse the games of kind and degree by solving the optimal control strategies in the minimum time for each player when the initial state lies in their winning regions. Along with the optimal strategies, the trajectories of the players are delineated and the upper bounds of their winning times are also derived

Visual Adaptations and Behavioural Strategies to Detect and Catch Small Targets

Predatory behaviours are ideal for studying the limits of performance and control within animals. Predation naturally creates a competition between the sensors and physiology of predator and prey. Aerial predation demonstrates the greatest feats of physical performance, demanding the highest speeds and accelerations whilst both predator and prey are free to pitch, yaw, and roll. These high speeds and degrees of rotational freedom make control a complex problem. However, from the perspective of the researcher attempting to decipher the control laws that underpin predator guidance, the question is made more soluble by the predator’s fixation on its target. The goal of the pursuer is clear, to contact the target, and thus their systems are focused on the optimization of that action. This is as opposed to more mundane activities, where conflicting interests compete for the attention and behavioural response of the animal. In order to study the necessary trade-offs that underpin aerial predation, this thesis will focus on the hunting behaviour of two fly species. The first is a robber fly, Holcocephala fusca, on which the majority of the first two chapters focus. Secondarily, work with the killer fly Coenosia attenuata will be included in the latter two chapters as a direct contrast to results from Holcocephala. Both are miniature dipteran predators, but not closely related. The structure of this thesis is broken into six chapters, summarised in the following list: 1. Thecompoundeyeofinsectsgenerallyhasmuchpoorerresolutionthanthatofcameratype eyes. Poor resolution is exacerbated in smaller insects that cannot commit the resources required for eyes with large lenses that facilitate high spatial resolution. Holcocephala has developed a small number of facets into a forward-facing acute zone where the spatial acuity is reduced to ~0.28°, rivalling the very best resolution of any compound eye. The only compound eyes with a comparable spatial resolution belong to dragonflies, in excess of an order of magnitude larger than Holcocephala. 2. Numerous potential targets may be airborne within the visual range of a predator. Not all of these may be suitable. Chasing unsuitable targets may waste energy or result in direct harm should they turn out to be larger than the predator can overcome. It is thus a strong imperative for a predator to filter the targets it takes after. Targets silhouetted against the sky display a paucity of cues that a predator could use to determine their size. Holcocephala displays acute size selectivity towards smaller targets. This selectivity goes beyond heuristic rules and size/speed ratios. Instead, Holcocephala appears able to determine absolute size and distance of targets. 3. Both Holcocephala and Coenosia intercept targets, heading for where the target is going to be in the future rather than its current location. Both species plot trajectories in keeping with the guidance law of proportional navigation, an algorithm derived for modern guided missiles. There are key differences evident in the internal physiological constants applied to the control system between the species. These differences are likely linked to the specific environmental conditions and visual physiologies of the flies, especially the range at which targets are attacked. 4. Stemming from the use of the proportional navigational framework, this chapter dives into the intricacies of gain and the weighting of the navigational constant, and the geometric factors that underpin the control effort and eventual success of the control system. 5. “Falcon-diving” can be found in killer flies dropping from their enclosure ceiling, in which they miss targets after diving towards them. Through proportional navigation, it can be demonstrated that the navigational system combined with excessive speed results in acceleration demands the body cannot match. 6. Holcocephala is capable of evading static obstacle whilst intercepting targets. Application of proportional navigation and a secondary obstacle-evasive controller can demonstrate where the fly is combining multiple inputs to guide its heading.This work was funded by the United States Airforce Office of Scientific Research