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Funding: Scottish Government (GrantNumber(s): MMSS/002/15), Natural Environment Research Council (GrantNumber(s): NE/R015007/1). 1. Uptake of tidal turbine technology to generate renewable energy has been partly limited by poor understanding of ecological impacts, including the potential for collisions between cetaceans and rotating turbine blades. To address this concern, it is necessary to identify whether cetaceans behaviourally respond to operating turbines. 2. A turbine in Scotland was instrumented with hydrophones to detect cetacean vocalizations. A generalized additive model was used to investigate temporal variability in harbour porpoise presence close to the turbine. As there were incidentally periods when the turbine was not operating, it was possible to determine the effect of blade rotation, whilst accounting for the potentially confounding effect of tidal flow. 3. Harbour porpoise presence varied intra-annually, diurnally and with tidal state. Peak presence occurred during winter (September–February), at night and at high flow speeds on the flood tide. 4. Porpoises exhibited significant avoidance of the tidal turbine when it was operating; avoidance increased with flow speed, whereby mean porpoise presence was reduced by up to 78% (95% CIs, 51%, 91%) on the flood tide and up to 64% (95% CI, 3%, 91%) on the ebb tide. 5. The temporal variability in encounter rate in the present study highlights that collision risk assessments assuming static densities probably fail to capture the temporal variability of collision risk. Future studies should conduct long-term baseline monitoring to derive encounter rates at larger spatio-temporal scales and as a reference from which to measure change in habitat use. It is also critical that the generality of the avoidance rates presented here is assessed for other sites, turbine types, array sizes and cetacean species. As the tidal industry expands, it will be important to reconcile the benefits of avoidance responses from a collision risk perspective with potential chronic effects of displacement from, or barriers between, important habitats. Publisher PDF

Funding: Data collection was funded as part of the Department of Energy and Climate Change’s (now Department of Business, Energy and Industrial Strategy) Offshore Energy Strategic Environmental Assessment programme, with additional resources from National Capability funding from the Natural Environment Research Council to the Sea Mammal Research Unit (Grant No. SMRU1001). Sound propagation modelling and subsequent analyses were funded by RaceBank Wind Farm Ltd. KFW was funded by University of St Andrews and the Department of Business, Energy and Industrial Strategy, as part of a PhD studentship. Understanding the potential effects of pile driving sounds on marine wildlife is essential for regulating offshore wind developments. Here, tracking data from 24 harbour seals were used to quantify effects and investigate sensitivity to the methods used to predict these. The Aquarius pile driving model was used to model source characteristics and acoustic propagation loss (16 Hz–20 kHz). Predicted cumulative sound exposure levels (SELcums) experienced by each seal were compared to different auditory weighting functions and damage thresholds to estimate temporary (TTS) and permanent (PTS) threshold shift occurrence. Each approach produced markedly different results; however, the most recent criteria established by Southall et al. [(2019) Aquat. Mamm. 45, 125–232] suggests that TTS occurrence was low (17% of seals). Predictions of seal density during pile driving made by Russell et al. [(2016) J. Appl. Ecol. 53, 1642–1652] were compared to distance from the wind farm and predicted single-strike sound exposure levels (SELss) by multiple approaches. Predicted seal density significantly decreased within 25 km or above SELss (averaged across depths and pile installations) of 145 dB re 1 μPa²·s. However, there was substantial variation in SELss with depth and installation, and thus in the predicted relationship with seal density. These results highlight uncertainty in estimated effects, which should be considered in future assessments. Publisher PDF

D.C., J.M., P.T. and S.W. acknowledge the financial support of the Tidal Stream Industry Energiser project (TIGER), which is co-financed by the European Regional Development Fund through the Interreg France (Channel) England Programme. A.A. acknowledges the support of NERC through the Industrial Innovation fellowship grant no. NE/R013209/2. D.G., B.S., T.S., D.W., R.W. and B.W. acknowledge EPSRC for supporting part of this work through EP/S000747/1. G.H. and C.S. acknowledge support by the Scottish government-funded Marine Mammal Scientific Support Programme MMSS/002 with additional resources from the Natural Environment Research Council grant nos. NE/R014639/1 and NE/R015007/1. M.L. acknowledges the support of the Smart Efficient Energy Centre (SEEC) at Bangor University, part-funded by the European Regional Development Fund (ERDF), administered by the Welsh Government, and the EPSRC METRIC fellowship grant no. (EP/R034664/1). L.M. acknowledges the financial support of an EPSRC PhD studentship award, grant no. EP/R513052/1(18-22). J.McN. acknowledges the financial support of R.Willden’s EPSRC Advanced Fellowship grant no. EP/R007322/1. S.N. acknowledges the support of SEEC (Smart Efficient Energy Centre) at Bangor University, part-funded by the European Regional Development Fund (ERDF), administered by the Welsh Government. This review provides a critical, multi-faceted assessment of the practical contribution tidal stream energy can make to the UK and British Channel Islands future energy mix. Evidence is presented that broadly supports the latest national-scale practical resource estimate, of 34 TWh/year, equivalent to 11% of the UK’s current annual electricity demand. The size of the practical resource depends in part on the economic competitiveness of projects. In the UK, 124 MW of prospective tidal stream capacity is currently eligible to bid for subsidy support (MeyGen 1C, 80 MW; PTEC, 30 MW; and Morlais, 14 MW). It is estimated that the installation of this 124 MW would serve to drive down the levelized cost of energy (LCoE), through learning, from its current level of around 240 £/MWh to below 150 £/MWh, based on a mid-range technology learning rate of 17%. Doing so would make tidal stream cost competitive with technologies such as combined cycle gas turbines, biomass and anaerobic digestion. Installing this 124 MW by 2031 would put tidal stream on a trajectory to install the estimated 11.5 GW needed to generate 34 TWh/year by 2050. The cyclic, predictable nature of tidal stream power shows potential to provide additional, whole-system cost benefits. These include reductions in balancing expenditure that are not considered in conventional LCoE estimates. The practical resource is also dependent on environmental constraints. To date, no collisions between animals and turbines have been detected, and only small changes in habitat have been measured. The impacts of large arrays on stratification and predator–prey interaction are projected to be an order of magnitude less than those from climate change, highlighting opportunities for risk retirement. Ongoing field measurements will be important as arrays scale up, given the uncertainty in some environmental and ecological impact models. Based on the findings presented in this review, we recommend that an updated national-scale practical resource study is undertaken that implements high-fidelity, site-specific modelling, with improved model validation from the wide range of field measurements that are now available from the major sites. Quantifying the sensitivity of the practical resource to constraints will be important to establish opportunities for constraint retirement. Quantification of whole-system benefits is necessary to fully understand the value of tidal stream in the energy system. Publisher PDF

Funding: The work was funded under the Scottish Government Demonstration Strategy (Project no. USA/010/14)and as part of the Department of Energy and Climate Change’s Offshore Energy Strategic Environmental Assessment programme, with additional resources from the Natural Environment Research Council (grant numbers: NE/R014639/1 and SMRU1001). 1. Many marine industries may pose acute risks to marine wildlife. For example, tidal turbines have the potential to injure or kill marine mammals through collisions with turbine blades. However, the quantification of collision risk is currently limited by a lack of suitable technologies to collect long‐term data on marine mammal behaviour around tidal turbines. 2. Sonar provides a potential means of tracking marine mammals around tidal turbines. However, its effectiveness for long‐term data collection is hindered by the large data volumes and the need for manual validation of detections. Therefore, the aim here was to develop and test automated classification algorithms for marine mammals in sonar data. 3. Data on the movements of harbour seals were collected in a tidally energetic environment using a high‐frequency multibeam sonar on a custom designed seabed‐mounted platform. The study area was monitored by observers to provide visual validation of seals and other targets detected by the sonar. 4. Sixty‐five confirmed seals and 96 other targets were detected by the sonar. Movement and shape parameters associated with each target were extracted and used to develop a series of classification algorithms. Kernel support vector machines were used to classify targets (seal vs. nonseal) and cross‐validation analyses were carried out to quantify classifier efficiency. 5. The best‐fit kernel support vector machine correctly classified all the confirmed seals but misclassified a small percentage of non‐seal targets (~8%) as seals. Shape and non‐spectral movement parameters were considered to be the most important in achieving successful classification. 6. Results indicate that sonar is an effective method for detecting and tracking seals in tidal environments, and the automated classification approach developed here provides a key tool that could be applied to collecting long‐term behavioural data around anthropogenic activities such as tidal turbines. Postprint

The work was funded by the Scottish Government Demonstration Strategy (Project no. USA/010/14) and by the UK's Natural Environment Research Council and Department of the Environment Food and Rural Affairs (RESPONSE project, NE/J004251/1). This work was also supported by National Capability funding from the Natural Environment Research Council to the Sea Mammal Research Unit (grant no. SMRU1001). 1. Understanding how marine predators utilize habitats requires that we consider their behaviour in three dimensions. Recent research has shown that marine mammals often make use of tidally energetic locations for foraging, yet data are generally limited to observations of animals at the water surface. Such areas are also of interest to the renewable energy industry for the deployment of tidal-stream energy turbines; this has led to concerns about potential impacts on marine mammals. 2. Methods for measuring animal movements underwater are limited; however, active sonar can image marine mammals and could potentially measure 3D movements in tidally energetic locations. Here, a dual 720 kHz sonar system was developed to investigate the 3D movements of harbour seals (Phoca vitulina) in a tidally-energetic channel. 3. Estimated mean depth (distance from the surface) of seals was 12.0 m (95% CIs = 11.6–12.4), and the majority of time was spent at the surface and at approximately 10–12 m distance from the surface. When expressed as distances from the sea bed, mean distance was 18.5 m (95% CIs = 18.0–18.9), and the majority of time was spent at 14 m from the sea bed. 4. Seal movements were generally in the same direction as the tidal flow with mean horizontal speeds of between 0.51 and 3.13 m s−1 (95% CIs = 1.24–1.54 m s−1). Mean vertical velocities (where negative and positive values represent a descent and ascent respectively) for each seal track ranged between −1.76 and +0.88 m s−1 (95% CIs: −0.23 to +0.03 m s−1). 5. These results provide a basis for understanding how seals utilize a dynamic tidal environment and suggest that harbour seal behaviour can be markedly different to less tidally energetic habitats. The results also have important implications for the prediction of risk associated with interactions between diving seals and tidal turbines in these dynamic habitats. Postprint

This research was funded through a research grant from the Scottish Government as part of the Marine Mammal Scientific Support Program MMSS/002/15. A wide range of anthropogenic structures exist in the marine environment with the extent of these set to increase as the global offshore renewable energy industry grows. Many of these pose acute risks to marine wildlife; for example, tidal energy generators have the potential to injure or kill seals and small cetaceans through collisions with moving turbine parts. Information on fine scale behaviour of animals close to operational turbines is required to understand the likely impact of these new technologies. There are inherent challenges associated with measuring the underwater movements of marine animals which have, so far, limited data collection. Here, we describe the development and application of a system for monitoring the three-dimensional movements of cetaceans in the immediate vicinity of a subsea structure. The system comprises twelve hydrophones and software for the detection and localisation of vocal marine mammals. We present data demonstrating the systems practical performance during a deployment on an operational tidal turbine between October 2017 and October 2019. Three-dimensional locations of cetaceans were derived from the passive acoustic data using time of arrival differences on each hydrophone. Localisation accuracy was assessed with an artificial sound source at known locations and a refined method of error estimation is presented. Calibration trials show that the system can accurately localise sounds to 2m accuracy within 20m of the turbine but that localisations become highly inaccurate at distances greater than 35m. The system is currently being used to provide data on rates of encounters between cetaceans and the turbine and to provide high resolution tracking data for animals close to the turbine. These data can be used to inform stakeholders and regulators on the likely impact of tidal turbines on cetaceans. Publisher PDF

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.

High-resolution distribution maps can help inform conservation measures for protected species; including where any impacts of proposed commercial developments overlap the range of focal species. Around Orkney, northern Scotland, UK, the harbour seal (Phoca vitulina) population has decreased by 78% over 20 years. Concern for the declining harbour seal population has led to constraints being placed on tidal energy generation developments. For this study area, telemetry data from 54 animals tagged between 2003 and 2015 were used to produce density estimation maps. Predictive habitat models using GAM-GEEs provided robust predictions in areas where telemetry data were absent, and were combined with density estimation maps, and then scaled to population levels using August terrestrial counts between 2008 and 2015, to produce harbour seal usage maps with confidence intervals around Orkney and the North coast of Scotland. The selected habitat model showed that distance from haul out, proportion of sand in seabed sediment, and annual mean power were important predictors of space use. Fine-scale usage maps can be used in consenting and licensing of anthropogenic developments to determine local abundance. When quantifying commercial impacts through changes to species distributions, usage maps can be spatially explicitly linked to individual-based models to inform predicted movement and behaviour.

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.

The annual moult in harbour seals (Phoca vitulina L.) follows a few weeks after the end of lactation and is characterised by a progressive loss and regrowth of hair which is apparent over a 4–6 week period. It is thought that during the moult harbour seals increase the time spent ashore as an adaptation to avoid additional energy costs associated with blood flow to the skin surface. The aim of this study was to determine the extent to which harbour seals regulated their surface temperature in order to maximise hair regrowth during the moult. The surface temperatures of two female harbour seals were recorded in captivity from late pregnancy to completion of the moult using infrared thermography. In this study, animals hauled out (exited the water onto land) more frequently during lactation and throughout the moult. Compared to the premoult period the temperature difference between body surface and air temperature ( d T ¯ ) showed a ∼10 °C elevation at the peak of the moult. Also, during the moult d T ¯ reached a higher maximum at a faster rate over a two hour haul-out period. Heat loss was estimated to increase during the moult and was equivalent to an approximate doubling of resting metabolic rate. It was therefore evident that harbour seals minimise the energetic cost of the moult by hauling out so that they can maintain optimal high skin surface temperature for hair growth. Human disturbance at haul-out sites that causes animals to enter the water during the moult may have consequences for harbour seals for two reasons. Firstly, reduced time spent ashore in optimal conditions for hair regeneration may prolong the duration of the moult and secondly, repeatedly forcing animals into the water when their skin temperature is high will incur an energetic cost.

The efficacy of seal rehabilitation is examined in a postrelease study of dive ability in harbor seal pups (Phoca vitulina) in the Wash, United Kingdom. Six rehabilitated seals were fitted with Sea Mammal Research Unit (SMRU) Argos Satellite Relay Data Logger tags and their individual dive behavior was monitored for an average of 122 d. The upper 90 percentile edge of dive behavior (dive duration [DD90] and percentage of time at-sea spent in a dive [PD90]), in 7 d bins, was used as a proxy for physiological dive ability. The results are compared with data from five wild adult harbor seals. There was no statistically significant difference between (1) the mean track duration of rehabilitated seals (126.20 ± 27.48 [SD] d) and adult seals (150.2 ± 24.62 d) (P= 0.108), indicating no evidence that short-term survival was less in the rehabilitated group; (2) the mean mass-scaled DD90 of rehabilitated seals (3.95 ± 0.37 min) and adult seals (4.09 ± 0.55 min) (P= 0.632); and (3) the mean PD90 of rehabilitated seals (81.62 ± 1.21%) and adult seals (81.48 ± 3.93%) (P= 0.943). These three results all suggest the success of the rehabilitation program in terms of short-term survival and dive ability.

Infrared thermography was used to monitor the healing process at flipper tag sites in gray seal (Halichoerus grypus) pups. We tested the hypothesis that tagging would result in a rise in surface temperature associated with tag site healing processes compared with adjacent untagged areas of the flipper. Prior to tagging thermal images were recorded of the dorsal side of hind flippers of pups tagged in early lactation (n= 20) and at weaning (n= 19) on the Isle of May, Scotland (56°11′N, 02°33′W) from October to December 2008. Pups tagged in early lactation were sampled again at late lactation, at weaning and then every 3 d for an average of 29 d post-tagging while pups tagged at weaning were sampled every 3 d for an average of 17 d post-tagging. Tag sites were also scored for signs of infection or swelling at each sampling. Results showed that (1) small temperature increases associated with wound healing processes around the tag site returned to pre-tagging levels before animals leave the island and (2) there was little evidence of tagging-related infections or tag loss irrespective of age at tagging.

*Sea Mammal Research Unit, University of St AndrewsyCentre National de la Recherche Scientifique, Institut Pluridisciplinaire Hubert Curien, Departement Ecologie,Physiologie et Ethologie (DEPE)(Received 1 March 2006; initial acceptance 25 April 2006;final acceptance 26 June 2006; published online 10 July 2007; MS. number: 8866R)Many theoretical models have been proposed to explain and predict the behaviour of air-breathing diversexploiting a food resource underwater. Many field observations of the behaviour of divers do not fit withthe prediction that to maximize energetic gain divers should dive close to their aerobic diving limits. In anattempt to explain this paradox, Thompson & Fedak (2001, Animal Behaviour, 61, 286e297) proposeda 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 ofgrey seals, Halichoerus grypus, diving to patches of varying prey density and distance from the surface. Ourresults were equivocal with respect to the model predictions. Seals responded to prey density, leaving low-quality patches earlier. However, this pattern was still evident at long dive distances, contrary to theprediction that during deep dives seals should stay at a patch regardless of prey density. While seals max-imized dive durations at high prey densities and long distances, they did not do so at short distances. Theapparent quitting strategy of the seals always produced higher net rates of energy gain than would havebeen achieved if they had remained at the foraging site up to their aerobic dive limit on every dive. Theseresults indicate that seals’ diving behaviour, particularly bottom duration, may indicate the relative preyavailability in their environment.

Previous research has highlighted the importance of minimising hydrodynamic drag from biologging instruments fitted to marine mammals. However, there is a need to investigate other possible impacts of instruments on animals. The aim of this study was to examine the effect of deploying instruments on the surface temperature distribution of grey seals (Halichoerus grypus). Infrared (IR) thermography was used to record the surface temperature of two juveniles that had been fitted with heart rate recorders and mounting straps for the attachment of a time depth recorder. When animals were fully wet and inactive, the surface temperature pattern was unaffected by instruments. However, as animals dried out regions of high temperature were recorded around the edges of attachment sites compared to surrounding fur. This appeared to be due to heat leakage around the sides of instruments and mounting straps that provided an additional layer of insulation. There were no obvious changes in the surface temperature distribution around instruments associated with duration of deployment. This work shows that attachment of relatively small biologging instruments will produce localised effects on heat transfer in air but will not significantly change the total heat exchange of grey seals on land or at sea. IR thermography was also shown to be a useful method of detecting surface temperature patterns associated with epidural anaesthesia and blubber biopsy.

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.

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.

Many animals rely on stored energy through periods of high energy demand or low energy availability or both. A variety of mechanisms may be employed to attain and conserve energy for such periods. Wild grey seals demonstrate seasonal patterns of energy storage and foraging behaviour that appear to maximize the allocation of energy to reproduction--a period characterized by both high energy demand and low food availability. We examined seasonal patterns in resting rates of oxygen consumption as a proxy for metabolic rate (RMR) and body composition in female grey seals (four adults and six juveniles), testing the hypothesis that adults would show seasonal changes in RMR related to the reproductive cycle but that juveniles would not. There was significant seasonal variation in rates of resting oxygen consumption of adult females, with rates being highest in the spring and declining through the summer months into autumn. This variation was not related to changes in water temperature. Adults increased in total body mass and in fat content during the same spring to autumn period that RMR declined. RMR of juveniles showed no clear seasonal patterns, but did increase with increasing mass. These data support the hypothesis that seasonal variation in RMR in female grey seals is related to the high costs of breeding.

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 PDF

Currently, there is great uncertainty surrounding the environmental impacts of tidal turbines on marine mammals; one major concern derives from the potential for physical injury through direct contact with the moving structures of turbines. Collecting data to quantify these risks is challenging and methods for measuring movements underwater and interactions with turbines are limited. However, potential tools include a small number of cutting-edge technologies that are being used increasingly for research and monitoring; these include animal-borne telemetry, and active and passive acoustic tracking. Recent developments in these technologies are described along with their means of application in measuring fine-scale movements and avoidance or evasion responses by marine mammals around turbines. From a risk-characterization perspective, each technique can provide information to inform risk assessments or help parametrize collision risk models; however, each has its associated benefits and drawbacks and it is clear that, in isolation, none of them can provide all the data needed to address the problem. The three approaches appear highly complementary, with the strengths of one complementing the weaknesses in others; the solution to characterizing the risks posed by tidal turbines is likely to be a combination of such techniques.

SUMMARYThe energetic cost of diving in marine mammals is a difficult value to derive given the problems of assessing metabolic rate for an animal at sea. Nevertheless, it is fundamental to our understanding of the foraging strategies of air-breathers exploiting underwater food sources. We measured the metabolic rates of eight captive grey seals, voluntarily diving in a quasi-natural setting. Oxygen consumption during post-dive surface periods was measured using open-flow respirometry, and dive behaviour of the seals was recorded using time depth recorders (TDRs). Mean diving metabolic rate (DMR)for both adults and juveniles was 1.7 times the predicted standard metabolic rate of terrestrial animals of equal size. For all animals, DMR was lower than the rate of metabolism measured whilst they were resting at the water's surface. On a dive-by-dive basis, DMR decreased with dive duration but increased with mean swim speed. Regressing the maximum 5% of DMRs against dive duration resulted in a significant negative relationship that was not significantly different from the relationship between the calculated maximum rate of aerobic metabolism and dive duration, suggesting that these seals were diving within, and up to, their aerobic limits. We developed a model that allows the prediction of DMR from information on dive behaviour of the type routinely collected in telemetry studies of wild seals. The model accurately predicts DMR using behavioural data from periods of diving with known metabolism data. This model can be used to predict the at-sea metabolic rate of wild grey seals, an important input into ecosystem models.