Causes and consequences of variation in the energy expenditure in grey seals (Halichoerus grypus)

Oxygen consumption of captive grey seals was measured over a period of 2.5 years at the captive facility of the Sea Mammal Research Unit at the University of St Andrews. The conditions under which in-water resting metabolic rate (RMR) was measured had a significant effect on the resulting estimates. RMR was highest when seals were at the surface breathing periodically. Surface apnoea and periodic submergence reduced RMR estimates by 25 and 35% respectively. There was significant seasonal variation in RMR's of adult females, with rates being highest in the spring and declining throughout the summer months. This variation was unrelated to changes in water temperature. Changes in mass explained some of this variation but this seasonality was still evident when rates were expressed mass-specifically. RMR of juvenile grey seals increased with age, as did lean body mass, although there was no relationship between age and total body mass. Diving metabolic rate (DMR) was measured while seals were voluntarily diving in a quasi- natural setting. Overall DMR was lower than RMR measured in the same animals. Mean DMR was 1.6 times predicted BMR. Average DMR decreased with dive duration and increased swimming activity during dives increased DMR. A model was developed that predicts DMR given information on the behaviour during the dive. This model was used to predict the at-sea metabolic rate of 5 wild grey seals from telemetry data. Overall, predicted at-sea metabolic rates were similar to DMR of the captive seals. Travelling dives had a higher energetic cost than foraging dives. Feeding during diving caused DMR to be increased 1.4-1.6 times pre-feeding levels. Metabolic rate data was incorporated into a population energy flux model. Energy requirements of different components of the population were estimated on a quarterly basis and all these were summed to produce an estimate of population annual energy requirements. Error in input parameters were used to calculate confidence limits in these estimates

Same space, different standards : a review of cumulative effects assessment practice for marine mammals

The lead author is a PhD student, whose stipend during the undertaking of this work was provided by a James Watt scholarship (Heriot-Watt University). Financial support enabling the open access publication of this research was provided by Natural England - the government’s adviser for the natural environment in England.Marine mammals are vulnerable to a variety of acute and chronic anthropogenic stressors, potentially experiencing these in isolation, successively and/or simultaneously. Formal assessment of the likely impact(s) of the cumulative effects of multiple stressors on a defined population is carried out through a Cumulative Effects Assessment (CEA), which is a mandatory component of the Environmental Impact Assessment (EIA) process in many countries. However, for marine mammals, the information required to feed into CEA, such as thresholds for disturbance, frequency of multiple (and simultaneous) exposures, interactions between stressors, and individual variation in response, is extremely limited, though our understanding is slowly improving. The gaps in knowledge make it challenging to effectively quantify and subsequently assess the risk of individual and population consequences of multiple disturbances in the form of a CEA. To assess the current state of practice for assessing cumulative effects on marine mammals within UK waters, 93 CEAs were reviewed across eleven maritime industries. An objective framework of thirteen evaluative criteria was used to score each assessment on a scale of 13-52 (weak - strong). Scores varied significantly by industry. On average, the aquaculture industry produced the lowest scoring CEAs, whilst the large offshore windfarm industry (≥ 20 turbines) scored highest, according to the scoring criteria used. There was a significant increase in scores over the sample period (2009-2019), though this was mostly attributed to five industries (cable, large and small offshore wind farms, tidal and wave energy). There was inconsistency in the language used to define and describe cumulative effects and a lack of routinely applied methodology. We use the findings presented here, along with a wider review of the literature, to provide recommendations and discussion points aimed at supporting the standardisation and improvement of CEA practice. Although this research focused on how marine mammals were considered within UK CEAs, recommendations made are broadly applicable to assessments conducted for other receptors, countries and/or environments. Adoption of these proposals would help to ensure a more consistent approach, and would aid decision-makers and practitioners in mitigating any potential impacts, to ensure conservation objectives of marine mammal populations are not compromised.Publisher PDFPeer reviewe

Animal displacement from marine energy development : Mechanisms and consequences

This work would not be possible without funding support from the U.S. Department of Energy, Energy Efficiency and Renewable Energy Water Power Technologies Office to Pacific Northwest National Laboratory (PNNL) under contract DE-AC05- 76RL01830 . We are grateful to all the international marine energy researchers and regulatory advisors who attended the online Expert Forum hosted by OES-Environmental on December 7th, 2022, and provided feedback and input on an earlier version of this work. We also thank Stephanie King (PNNL) for creating the original illustrations, as well as the anonymous reviewers for their constructive feedback.For marine wave and tidal energy to successfully contribute to global renewable energy goals and climate change mitigation, marine energy projects need to expand beyond small deployments to large-scale arrays. However, with large-scale projects come potential environmental effects not observed at the scales of single devices and small arrays. One of these effects is the risk of displacing marine animals from their preferred habitats or their migration routes, which may increase with the size of arrays and location. Many marine animals may be susceptible to some level of displacement once large marine energy arrays are increasingly integrated into the seascape, including large migratory animals, non-migratory pelagic animals with large home ranges, and benthic and demersal mobile organisms with more limited ranges, among many others. Yet, research around the mechanisms and effects of displacement have been hindered by the lack of clarity within the international marine energy community regarding the definition of displacement, how it occurs, its consequences, species of concern, and methods to investigate the outcomes. This review paper leveraged lessons learned from other industries, such as offshore development, to establish a definition of displacement in the marine energy context, explore which functional groups of marine animals may be affected and in what way, and identify pathways for investigating displacement through modeling and monitoring. In the marine energy context, we defined displacement as the outcome of one of three mechanisms (i.e., attraction, avoidance, and exclusion) triggered by an animal's response to one or more stressors acting as a disturbance, with various consequences at the individual through population levels. The knowledge gaps highlighted in this study will help the regulatory and scientific communities prepare for mitigating, observing, measuring, and characterizing displacement of various animals around marine energy arrays in order to prevent irreversible consequences.Peer reviewe

Resolving issues with environmental impact assessment of marine renewable energy installations

Growing concerns about climate change and energy security have fueled a rapid increase in the development of marine renewable energy installations (MREIs). The potential ecological consequences of increased use of these devices emphasizes the need for high quality environmental impact assessment (EIA). We demonstrate that these processes are hampered severely, primarily because ambiguities in the legislation and lack of clear implementation guidance are such that they do not ensure robust assessment of the significance of impacts and cumulative effects. We highlight why the regulatory framework leads to conceptual ambiguities and propose changes which, for the most part, do not require major adjustments to standard practice. We emphasize the importance of determining the degree of confidence in impacts to permit the likelihood as well as magnitude of impacts to be quantified and propose ways in which assessment of population-level impacts could be incorporated into the EIA process. Overall, however, we argue that, instead of trying to ascertain which particular developments are responsible for tipping an already heavily degraded marine environment into an undesirable state, emphasis should be placed on better strategic assessment.Publisher PDFPeer reviewe

Eat now, pay later? Evidence of deferred food-processing costs in diving seals

Seals may delay costly physiological processes (e.g. digestion) that are incompatible with the physiological adjustments to diving until after periods of active foraging. We present unusual profiles of metabolic rate (MR) in grey seals measured during long-term simulation of foraging trips (4–5 days) that provide evidence for this. We measured extremely high MRs (up to almost seven times the baseline levels) and high heart rates during extended surface intervals, where the seals were motionless at the surface. These occurred most often during the night and occurred frequently many hours after the end of feeding bouts. The duration and amount of oxygen consumed above baseline levels during these events was correlated with the amount of food eaten, confirming that these metabolic peaks were related to the processing of food eaten during foraging periods earlier in the day. We suggest that these periods of high MR represent a payback of costs deferred during foraging

Review of offshore wind farm impact monitoring and mitigation with regard to marine mammals

Monitoring and mitigation reports from 19 UK and 9 other European Union (EU) offshore wind farm (OWF) developments were reviewed, providing a synthesis of the evidence associated with the observed environmental impact on marine mammals. UK licensing conditions were largely concerned with mitigation measures reducing the risk of physical and auditory injury from pile driving. At the other EU sites, impact monitoring was conducted along with mitigation measures. Noise-mitigation measures were developed and tested in UK and German waters in German government-financed projects. We highlight some of the review’s findings and lessons learned with regard to noise impact on marine mammals.</p

How long does a dive last? Foraging decisions by breath-hold divers in a patchy environment: a test of a simple model

International audienceMany theoretical models have been proposed to explain and predict the behaviour of air-breathing divers exploiting a food resource underwater. Many field observations of the behaviour of divers do not fit with the prediction that to maximize energetic gain divers should dive close to their aerobic diving limits. In an attempt to explain this paradox, Thompson & Fedak (2001, Animal Behaviour, 61, 286e297) proposed a model of diving behaviour that takes into account patchily distributed prey patches of varying quality. We tested this model experimentally in a simulated foraging set-up. We measured the diving behaviour of grey seals, Halichoerus grypus, diving to patches of varying prey density and distance from the surface. Our results were equivocal with respect to the model predictions. Seals responded to prey density, leaving lowquality patches earlier. However, this pattern was still evident at long dive distances, contrary to the prediction that during deep dives seals should stay at a patch regardless of prey density. While seals maximized dive durations at high prey densities and long distances, they did not do so at short distances. The apparent quitting strategy of the seals always produced higher net rates of energy gain than would have been achieved if they had remained at the foraging site up to their aerobic dive limit on every dive. These results indicate that seals' diving behaviour, particularly bottom duration, may indicate the relative prey availability in their environment

First<i> in situ</i> passive acoustic monitoring for marine mammals during operation of a tidal turbine in Ramsey Sound, Wales

The development of marine renewables has raised concerns regarding impacts on wildlife, and environmental monitoring is often required. We examined 3 mo of continuous passive acoustic monitoring (PAM) data collected at the Tidal Energy Ltd. DeltaStream turbine deployment in Ramsey Sound, UK. We aimed to assess the performance of the PAM system at an operational turbine, describe the 3D movements and behaviours of small cetaceans in the vicinity of the turbine, and model changes in detection rates against temporal and environmental variables. The PAM system was designed to acoustically detect, classify and track porpoises and dolphins via their vocalisations within a ∼100 m radius of the turbine. In total, 247 small cetacean encounters were identified from click detections, which were also used to reconstruct the spatial movements of porpoises and dolphins, including close approaches to the turbine. Not all hydro - phones were functional, which limited the ability to localise porpoise clicks; the probability of detecting and localising a click decreased by 50% at a range of ∼20 m. Mechanical sounds on the turbine may have alerted cetaceans of its presence. In models examining acoustic detection patterns, the tidal state, time of day, low low-frequency noise levels and moon phase best explained the acoustic presence of porpoises. The limited duration of turbine operation yielded insufficient data to understand the effect of turbine rotation on animal presence and movement near the turbine. This is the first description of how small cetaceans behave and move around a tidal turbine, and we present recommendations regarding how PAM can be used to improve environmental monitoring at future tidal energy sites.</p

Empirical measures of harbor seal behavior and avoidance of an operational tidal turbine

There is global interest in marine renewable energy from underwater tidal turbines. Due to overlap in animal habitat with locations for tidal turbines, the potential for collisions has led to concern around strike risk. Using data from tagged harbor seals collected before construction and after operation of the SeaGen tidal turbine in Northern Ireland, this study quantifies risks of an operational turbine to harbor seals by taking into account turbine characteristics, tidal state, and seal behavior. We found 68% spatial avoidance (95% C.I., 37%, 83%) by harbor seals within 200 m of the turbine. When additionally accounting for variation in seal occupancy over depth and tidal flows, there is an overall reduction in collision risk from 1.29 to 0.125 seals per tidal cycle (90.3% reduction; (95% C.I., 83%, 98%)) compared to risk calculated under assumptions of uniform habitat use. This demonstrates the need to incorporate environmental conditions to properly assess strike risk

Empirical measures of harbor seal behavior and avoidance of an operational tidal turbine

There is global interest in marine renewable energy from underwater tidal turbines. Due to overlap in animal habitat with locations for tidal turbines, the potential for collisions has led to concern around strike risk. Using data from tagged harbor seals collected before construction and after operation of the SeaGen tidal turbine in Northern Ireland, this study quantifies risks of an operational turbine to harbor seals by taking into account turbine characteristics, tidal state, and seal behavior. We found 68% spatial avoidance (95% C.I., 37%, 83%) by harbor seals within 200 m of the turbine. When additionally accounting for variation in seal occupancy over depth and tidal flows, there is an overall reduction in collision risk from 1.29 to 0.125 seals per tidal cycle (90.3% reduction; (95% C.I., 83%, 98%)) compared to risk calculated under assumptions of uniform habitat use. This demonstrates the need to incorporate environmental conditions to properly assess strike risk