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Using data from mark recovery and electronic tag studies, we investigate the exchange of cod between three adjacent cod management areas; the Irish Sea (ICES Division VIIa), Scottish waters (ICES Division IVa) and in the western English Channel and Celtic Sea (ICES Divisions VIIe-k). We evaluate 2209 archived and current mark recovery data (1960’s – to 2010) to assess the seasonal changes in distribution of cod within ICES Divisions VIa, VIIa and VIIe-g. In addition, we report on the results of a collaborative electronic data storage tagging (DST) programme of cod in the Irish and Celtic Sea, spanning the years 1999 to 2010. During this time, 710 DSTs have been deployed on cod between 43cm and 110cm, and 107 of the tags have been returned yielding over 11000 days of data. We use a tidal geolocation model to determine the daily locations of each cod to reconstruct in detail the migrations of cod tagged with DSTs. The results describe fundamental features of cod spatial ecology in the Irish and Celtic Sea, such as the seasonality of migration and habitat occupation and the potential impact upon sub-stock structure.

Studies on the effects of offshore wind farm construction on marine life have so far focussed onbehavioural reactions in porpoises and seals. The effects on fish have only very recently come intothe focus of scientists, regulators and stakeholders. Pile-driving noise during construction is ofparticular concern as the very high sound pressure levels could potentially prevent fish from reachingbreeding or spawning sites, finding food, and acoustically locating mates. This could result in longtermeffects on reproduction and population parameters. Further, avoidance reactions might result indisplacement away from potential fishing grounds and lead to reduced catches. However, reactionthresholds and therefore the impacts of pile-driving on the behaviour of fish are completely unknown.We played back pile-driving noise to cod and sole held in two large (40 m) net pens located in a quietBay in West Scotland. Movements of the fish were analysed using a novel acoustic tracking system.Received sound pressure level and particle motion were measured during the experiments.There was a significant movement response to the pile-driving stimulus in both species at relativelylow received sound pressure levels (sole: 144 – 156 dB re 1μPa Peak; cod: 140 – 161 dB re 1 μPaPeak, particle motion between 6.51x10-3 and 8.62x10-4 m/s2 peak). Sole showed a significantincrease in swimming speed during the playback period compared to before and after playback. Codexhibited a similar reaction, yet results were not significant. Cod showed a significant freezingresponse at onset and cessation of playback. There were indications of directional movements awayfrom the sound source in both species. The results further showed a high variability in behaviouralreactions across individuals and a decrease of response with multiple exposures.This study is the first to document behavioural response of marine fish due to playbacks of pile-drivingsounds. The results indicate that a range of received sound pressure and particle motion levels willtrigger behavioural responses in sole and cod. The results further imply a relatively large zone ofbehavioural response to pile-driving sounds in marine fish. Yet, the exact nature and extent of thebehavioural response needs to be investigated further. Some of our results point toward habituationto the sound.The results of the study have important implications for regulatory advice and the implementation ofmitigation measures in the construction of offshore wind farms in the UK and elsewhere. First, theconcerns raised about the potential effects of pile-driving noise on fish were well founded. Thissuggests to both regulators and developers that the costs imposed by some mitigation measures thathave so far been applied following the precautionary principle go some of the way to addressing areal problem. We also suggest that our behavioural thresholds are considered in assessments ofimpacts of offshore wind farms in the UK and elsewhere. Mitigation measures should be furtherdiscussed developed and, if meaningful, applied especially if these could lead to a reduction ofacoustic energy that is emitted into the water column.Further studies should investigate the response at critical times (e.g. mating and spawning) and theeffects of pile-driving on communication behaviour. It will also be necessary to further investigatehabituation to the sound to effectively manage effects of pile-driving sound on marine fish.

Estimating the demographic parameters of contemporary populations is essential to the success of elasmobranch conservation programmes, and to understanding their recent evolutionary history. For benthic elasmobranchs such as skates, traditional fisheries-independent approaches are often unsuitable as the data may be subject to various sources of bias, whilst low recapture rates can render mark-recapture programmes ineffectual. Close-kin mark-recapture (CKMR), a novel demographic modelling approach based on the genetic identification of close relatives within a sample, represents a promising alternative approach as it does not require physical recaptures. We evaluated the suitability of CKMR as a demographic modelling tool for the critically endangered blue skate (Dipturus batis) in the Celtic Sea using samples collected during fisheries-dependent trammel-net surveys that ran from 2011 to 2017. We identified three full-sibling and 16 half-sibling pairs among 662 skates, which were genotyped across 6291 genome-wide single nucleotide polymorphisms, 15 of which were cross-cohort half-sibling pairs that were included in a CKMR model. Despite limitations owing to a lack of validated life-history trait parameters for the species, we produced the first estimates of adult breeding abundance, population growth rate, and annual adult survival rate for D. batis in the Celtic Sea. The results were compared to estimates of genetic diversity, effective population size (N e), and to catch per unit effort estimates from the trammel-net survey. Although each method was characterized by wide uncertainty bounds, together they suggested a stable population size across the time-series. Recommendations for the implementation of CKMR as a conservation tool for data-limited elasmobranchs are discussed. In addition, the spatio-temporal distribution of the 19 sibling pairs revealed a pattern of site fidelity in D. batis, and supported field observations suggesting an area of critical habitat that could qualify for protection might occur near the Isles of Scilly.