Sea lice, particularly Lepeophtheirus salmonis, pose significant ecological and economic challenges to salmon aquaculture. Dispersal occurs via planktonic larval stages which may spread widely, driven by interacting physical and biological processes. Direct observations are challenging, and biophysical particle tracking models are commonly used to estimate infestation pressure. Nevertheless, there is substantial uncertainty in model parameterization. We assessed ensemble approaches that aim to harness this uncertainty to improve predictions of farm-associated sea lice distributions. Using public data from salmon farms in Scotland (2021-2024) and 20 parameterizations, we compared three ensemble methods: a simple average, a model with spatially varying blending weights, and a machine learning model. Ensemble performance was assessed against that of the constituent parameterizations, all using adult-equivalent infestation pressure (rolling sum of copepodid pressure adjusted for on-fish demographics) to predict the reported mean adult female lice per fish. Cross-validation showed superiority of machine learning ensembles for dynamics on farms, though more direct data on larval concentrations would be required to predict larval infestation pressure. On average, the ensemble model with spatially varying weights outperformed all constituents, particularly for spatial patterns, and predicts ensemble infestation pressure as a latent variable. The simple average ensemble performed better than the median constituent. A resampling experiment confirmed the robustness of these results across constituents and ensemble sizes (3-15). Ensemble modelling is thus a promising pathway toward improving predictions of sea lice infestation pressure, with flexibility to tailor ensembles toward particular goals. Better predictions of sea lice dispersal enable better management of infestations, ultimately improving the welfare and production of farmed fish and reducing lice burdens for wild salmonids.

The movements of aquatic animals affect their exposure to threats and the efficacy of conservation measures, such as Marine Protected Areas (MPAs). However, many species' movements remain poorly understood and difficult to reconstruct from available datasets, hampering conservation efforts. This is especially the case for species that rarely surface, for which data are often limited to observations from acoustic telemetry (detections) and ancillary sensors, such as archival tags. Here, we pioneer the use of state-of-the-art particle algorithms to model animal movement, integrate datasets and assess MPA design, using a case study of the Critically Endangered flapper skate ( Dipturus intermedius ) in Scotland. Our algorithms led to 5-fold improvements in maps of space use and 30-fold improvements in residency estimates (lower mean error) compared to prevailing heuristic methods. By formally integrating tracking datasets, we were uniquely able to examine movements beyond receivers into fished zones, MPA-scale residency and specific habitats beyond protected areas that may warrant protection. This work showcases a probabilistically sound modelling framework that is sufficiently fast, flexible and accessible to meet the demands of modern animal-tracking datasets in acoustic telemetry systems. This represents a marked advance for analyses of animal movements and MPA efficacy worldwide. ### Competing Interest Statement The authors have declared no competing interest.

Deep-sea polymetallic nodule mining is in the exploration phase at present with some groups proposing a move towards extraction within years1. Management of this industry requires evidence of the long-term effects on deep-sea ecosystems2, but the ability of seafloor ecosystems to recover from impacts over decadal scales is poorly understood3. Here we show that, four decades after a test mining experiment that removed nodules, the biological impacts in many groups of organisms are persistent, although populations of several organisms, including sediment macrofauna, mobile deposit feeders and even large-sized sessile fauna, have begun to re-establish despite persistent physical changes at the seafloor. We also reveal that areas affected by plumes from this small-scale test have limited detectable residual sedimentation impacts with some biological assemblages similar in abundance compared to control areas after 44 years. Although some aspects of the modern collector design may cause reduced physical impact compared to this test mining experiment, our results show that mining impacts in the abyssal ocean will be persistent over at least decadal timeframes and communities will remain altered in directly disturbed areas, despite some recolonization. The long-term effects seen in our study provide critical data for effective management of mining activities, if they occur, including minimizing direct impacts and setting aside an effective network of protected areas4,5.

Animal movements affect their exposure to threats and the efficacy of conservation measures, such as marine protected areas (MPAs). However, many species' movements are difficult to reconstruct from available datasets, hampering conservation efforts. This is especially the case for aquatic species that rarely surface, for which data are often limited to observations from acoustic telemetry (detections) and ancillary sensors. Here, we pioneer the use of state-of-the-art particle algorithms to model movements, integrate datasets, and assess MPA design, leveraging a case study of a Critically Endangered elasmobranch. Our algorithms led to 5-fold improvements in space-use maps and 30-fold improvements in residency estimates compared to prevailing methods. By integrating tracking datasets, we were uniquely able to examine movements beyond acoustic receivers, MPA-scale residency, and specific habitats beyond protected areas that warrant protection. This work reveals a modeling framework that enhances the conservation value of acoustic telemetry, supporting analyses of MPA efficacy worldwide.

The biology of shipwrecks and hard substrata in the deep sea remains poorly explored. These complex habitats alter biodiversity on the deep seafloor and facilitate connecting populations over large distances. We analysed biological and environmental data collected at the RMS Titanic wreck site (3800 m) and a seamount ridge (2900 m) during the 2022 Titanic Expedition (15 June-25 July). The ridge is part of Seamount U, approximately 40 km southeast of the Titanic, and was explored for the first time on July 23, 2022. We analysed megafaunal occurrence across 920 images of the wreck site and 169 images of the ridge site, from digital video. The most common megafauna overall were Ophiuroidea, Munidopsis sp., Cushion-Encrusting Porifera, Geodia spp., and cold-water corals including Keratoisididae and Pennatuloidea. We describe the patterns in community composition across five benthic habitats, likely controlled by substrate type, local hydrodynamics, and food availability. The ridge yielded a higher number of observed megafauna and higher Shannon diversity (n = 73; H = 2.89) than the wreck (n = 21; H = 1.39). The communities associated with the ridge showed high dissimilarity to those at the wreck. We also explored the temporal variability of biofouling organisms on the Titanic using video from 1986 to 2022. We observed a net increase in Chrysogorgia sp. and Lepidisis sp. coral colonies over time with estimated average linear growth rates of up to 10 mm/yr and linear rusticle extensions of up to 14 mm/yr, raising questions about the wreck's ecological succession as it deteriorates.

Harmful algal blooms pose a significant threat to marine ecosystems, aquaculture industries, and human health. To mitigate these risks, agencies around the globe perform regular monitoring and operate early warning systems based on expected risk levels. However, bloom dynamics can be influenced by a large range of physical and biological factors, leading to high uncertainty in predictions of future blooms. Here, we explore the effectiveness of ensemble models for forecasting risk of algal blooms and associated toxins in Scotland, employing a diverse set of candidate models, including tree-based approaches, neural networks, and hierarchical Bayesian regression. These models predicted the probability that algal densities or biotoxin concentrations would exceed a threshold (either 'amber' status in the traffic light guidance system, or 'detection') in the next week using publicly available environmental products combined with regulatory monitoring data from dozens of locations in Scotland (2015-2022; Alexandrium spp., Dinophysis spp., Karenia mikimotoi, Pseudo-nitzschia spp. [+ delicatissima, serriata groups], domoic acid (DA), okadaic acid / dinophysistoxins / pectenotoxins (DSTs), paralytic shellfish toxins (PSTs)). The forecasted probabilities from the candidate models were used as inputs for a stacking ensemble model. Compared to individual candidate and null models, the ensemble models consistently improved forecasting performance across two years of withheld out-of-sample validation data, as assessed by five distinct performance metrics (ensemble skill scores among metrics and targets: mean = 0.499, middle 95 % = 0.214-0.900; skill score give improvement over the null model, with 1 indicating perfect performance). Performance varied by monitoring target, with best forecasts for DSTs (mean ensemble skill: 0.747) and poorest for K. mikimotoi (mean ensemble skill: 0.334). Autoregressive terms and regional spatiotemporal patterns emerged as the most informative predictors, with effects of environmental conditions contingent on the algal density or toxin concentration. Our results demonstrate the clear advantage of the ensemble approach. The operational implementation of these models provides probabilistic forecasts to enhance Scotland's monitoring program and early warning system. Ensemble modelling leverages the combined strengths of the wide array of modern techniques available, offering a promising path toward improved forecasts.

Catch-and-release angling is a popular recreational pastime and an essential component of many fish research programmes. Marked physiological disturbances have been documented in elasmobranchs in response to angling and handling, but skates and rays remain understudied. Here, we describe for the first time the physiological responses of the critically endangered flapper skate (Dipturus intermedius) to angling, handling and tagging in Scotland. Sixty-one skate were captured by angling as part of a tagging research programme. We assessed individual health, measured blood parameters at two time points (post-capture and prior to release) and recorded heart and respiratory rates during handling and the surgical insertion of acoustic tags. Injuries or infections were identified in 10% of individuals and attributed to prior angling in two cases. Skate generally experienced a mild metabolic acidosis characterized by decreases in blood pH and bicarbonate and increases in lactate and glucose. Respiratory acidosis characterized by limited increases in PCO2 was also observed. The degree of acidosis was greater with warmer sea temperatures and longer fight times, and worsened during the time that skate were handled on deck. Heart rates during handling were negatively associated with body size, positively associated with temperature and also linked to time on the line. Taken together, our results suggest that elevated fight times and temperatures increase the physiological stress experienced by rod and reel-caught flapper skate. Efforts to reduce fight times and minimize heat exposure (including shading, irrigation and reduced handling time) should be beneficial for skate.

Fish farming is the fastest growing food production sector worldwide and now accounts for most human fish consumption. Expansion of finfish aquaculture to exposed offshore marine environments is appealing where additional sheltered areas are unavailable. While more energetic environments may reduce waste accumulation and parasite exposure, effects on fish health and wellbeing are largely speculative. The multiple stressors faced by fish on offshore farms may interact synergistically and increase their cumulative impact. We used 20 months of health and welfare data from eight Atlantic salmon (Salmo salar) sea pen farms in Scotland along a wave exposure gradient to assess the effects of, and interactions between, environmental variables and management treatments on fish mortality and parasite loads. While farms showed high variability in mortality rate and sea lice infections, multi-level Bayesian modelling indicated that wave exposure primarily modulated effects of other variables. Higher exposure farms showed steeper increases in mortality with time and with extreme temperatures. Similarly, sea lice infections tended to increase with time, with higher exposure farms seeing steeper increases at higher Amoebic Gill Disease (AGD) scores and at high temperatures. The effect of AGD was greater at slow water speeds. Treatments against parasites were more frequent at low exposure farms, leading to uncertainty in their impact on welfare across farms. The support for interactive effects of wave exposure with other variables rather than strong direct effects suggests an accumulation of chronic and acute stressors. Expansion of aquaculture to more energetic offshore environments may have negative impacts on fish health in some circumstances, requiring adaptation of practices. In particular, the stronger increase in mortality over time may have implications for cycle length in different environments, and the more dramatic impacts of the warmest temperatures at high exposure farms call for consideration of the change in water temperature both inshore and offshore.

The mussel industry faces challenges such as low and inconsistent levels of larvae settlement and poor-quality spat, leading to variable production. However, mussel farming remains a vital sustainable and environmentally responsible method for producing protein, fostering ecological responsibility in the aquaculture sector. We investigate the population connectivity and larval dispersion of blue mussels ( Mytilus edulis ) in Scottish waters, as a case study, using a multidisciplinary approach that combined genetic data and particle modelling. This research allows us to develop a thorough understanding of blue mussel population dynamics in mid-latitude fjord regions, to infer gene-flow patterns, and to estimate population divergence. Our findings reveal a primary south-to-north particle transport direction and the presence of five genetic clusters. We discover a significant and continuous genetic material exchange among populations within the study area, with our biophysical model’s outcomes aligning with our genetic observations. Additionally, our model reveals a robust connection between the southwest coast and the rest of the west coast. This study will guide the preservation of mussel farming regions, ensuring sustainable populations that contribute to marine ecosystem health and resilience.

Massive swarms of the red crab Pleuroncodes planipes (Stimpson, 1860), a species of squat lobster, are a dominant functional component of the upwelling ecosystem in the eastern Pacific Ocean (Boyd, 1967; Smith et al., 1975). These swarms can wash ashore on the coast, creating mass depositions of crustacean carcasses, a striking phenomenon that has been long documented in Baja California and California (Aurioles-Gamboa et al., 1994; Boyd, 1967). However, little is known about the fate of crab swarms transported offshore by oceanic currents. In May 2015, using an autonomous deep-sea robot, we discovered an unexpectedly large fall of red crab carcasses (>1000 carcasses ha−1) at a depth of 4050 m on the abyssal Pacific seafloor (Figure 1), almost 1500 km from their spawning areas off the northwest American coast. Several questions arise from this unexpected finding that may help unveil additional close linkages in nutritional transport between processes at the sea surface and the remote abyssal seafloor. While carrying out an extensive visual survey of the abyssal seafloor in the Pacific, we were surprised by the high abundance of squat lobsters. These crustaceans can be encountered from the poles to the tropics and from intertidal rockpools to the greatest depths of the ocean. However, in the abyss, 4000 m deep, it would be very unusual for them to be the most abundant organism observed. On closer inspection, it became clear that our squat lobsters were all dead, often lying on their back with their abdomen extended, a very unnatural pose for a living squat lobster (Figure 1). Further research suggested we were dealing with a mass fall of P. planipes. Carcasses exhibited a surprisingly low state of decomposition, still brilliant red colored in all of the almost intact appendages, though fading in the abdomen. Relatively rapid sinking rates and the large numbers falling might have minimized the scavenging of carcasses during their descent through the water column, as occurs in other massive deep-sea food falls, like those in jellyfish or pyrosomes (Lebrato et al., 2012; Lebrato & Jones, 2009). In turn, the lack of many scavengers feeding on the carcasses suggested that the deposition was recent, or even ongoing. The densest carcass aggregations were found on an abyssal hilltop (mean density: 1053 carcasses ha−1) extending over an area of approximately 30 km2. Less dense aggregations (18–240 carcasses ha−1) were found in equivalently large seascapes surveyed nearby (a plain and a trough; Figure 2b). Carcass density was relatively variable at fine scales (i.e., a few meters), with patches containing up to three to four carcasses m−2 observed mostly in the hilltop area. This finding emphasizes the value of using observations from autonomous underwater vehicles (or other imaging platforms) to supplement and expand physical sample collection methods, for example, trawl, box, and multicore samples collected within the seabed locations imaged (during the same expedition; Jones et al., 2021) missed the carcass fall. The red crab P. planipes is the most abundant species in the micronekton community (size: 20–200 mm) along the southern part of the California Current (i.e., Appendix S1: Figure S2), one of the four major upwelling systems of the world (Robinson et al., 2004). P. planipes plays an important role in the cycling of carbon from primary production to higher up into the food chain (Longhurst et al., 1967). Being an important primary consumer and common prey of many marine vertebrates, red crabs are an energetically important link in the food web with a similar trophic role as anchovy and sardine (Robinson et al., 2004; Smith et al., 1975). The larvae, juveniles, and young adults of P. planipes are mostly planktonic. Red crabs start the benthopelagic stage of their life cycle, including diurnal migrations, toward the second year of life when their standard carapace length (SCL) is between 17 and 20 mm, until they reach 32–34 mm and become fully benthic (Boyd, 1967). We measured the SCL of a random subset of 800 carcasses identified in scaled seabed imagery. These ranged from 10.5 to 34.2 mm (median length: 21.2 mm; Appendix S1: Figure S1), suggesting all red crabs were planktonic subadults. Although benthic adult populations are typically found in subtropical continental margins and nearby seamounts at depths of 50–400 m, they have been sighted as far north as Oregon (Sanford et al., 2019) and as far south as Panama (Pineda et al., 2016). The other species in the genus, P. monodon, is very similar in both appearance and ecological role (Gutiérrez et al., 2008) but has a more southerly distribution, tending to occur off Chile, and has never been recorded at the latitude of our observations. Upwelling-induced phytoplankton blooms attract large aggregations of young adult planktonic red crabs in surface waters (Robinson et al., 2004). These swarms can at times find themselves in disadvantageous oceanographic situations. Crustacean swarms can be washed ashore (Appendix S1: Figure S3), or currents can transport them offshore (southwest) toward a point of no return within the California Current, where they become expatriates that no longer contribute to the maintenance of the species (Longhurst et al., 1967). The fate of the latter we document here. Our observation revealed a remarkably large aggregation of carcasses at abyssal depths and at a large distance (~1500 km) from their closest known spawning areas. Indeed, the original description of P. planipes was made from material collected over 1500 km offshore and 1000 km northwest from our site (Stimpson, 1860), and there is likely an oceanic pathway connecting the spawning areas to the locations of the mass falls. The California Current sweeps surface waters south along the American coast, swinging westward approximately at the latitude of southern Baja California (Boyd, 1967) to ultimately connect with the North Pacific Equatorial Current, flowing westward between 8° and 18° N across the Pacific basin (Kawabe & Fujio, 2010), right above our study area (Figure 2a). However, why so little decomposition was found in crab carcasses seems unclear. Self-propagating westward mesoscale eddies are a potentially significant regional mechanism for the material transport of upper seawater layers and its inhabitants thousands of kilometers offshore. These originate under strong winds, blowing through two main gaps in the Sierra Madre Mountains and over the Gulf of Papagayo and Tehuantepec, which are occasionally capable of amplifying abyssal currents in the northeast (NE) Pacific (Aleynik et al., 2017). Averaged over 24 years of satellite observations, the estimates of the radius of relatively stable anticyclonic (rotating clockwise) eddies are 92 km (range 60–110 km), and the average translation speed is 12.5 cm s−1 (range 3.4–18.1 cm s−1; Purkiani et al., 2020). Therefore, a year is a realistic minimal arrival timescale from the California and Baja California shelf to our site. But a year seems a rather long time for the transport to occur with such little decay, hence other processes might be involved. Because of the high carcass numbers observed in the abyssal area, we assessed the potential importance of such a large food fall to this typically low-food environment (e.g., Smith et al., 2008). We did so by estimating the carbon contribution of the food fall based on allometric relationships of the species (i.e., SCL to wet weight; Boyd, 1962) and wet weight to organic carbon conversion factors (Childress & Nygaard, 1974). Based on this analysis, each carcass would contain an average of 390 mg of Corg (± 239 mg SD) when fresh. Assuming that the decomposition in the water column appeared to be low and that at least 75% of the carbon was preserved during the abyssal descent, the carbon flux associated with the mass fall over the entire mapped hilltop area (where the fall was most severe) would be equivalent to 0.03 g Corg m−2. At fine scales, in areas with the highest carcass density, the mass fall could provide as much as 1.23 g Corg m−2, which is almost 1.5 times the expected yearly flux (i.e., 0.85 g Corg m−2 year−1) of particulate organic carbon from the surface in the study location (e.g., Henson et al., 2012; Appendix S1: Section S3), in a single deposition event. Although it is unclear how regular these crustacean mass falls are in time or the area they cover, our calculations show that even a single deposition might play a much more important role in the biological carbon pump than was previously known in the otherwise extremely oligotrophic abyssal areas. Abyssal ecosystems are known to be strongly modulated by the quantity and quality of detrital food material sinking from the surface ocean (Smith et al., 2008), which makes seabed communities highly sensitive to variations in this flux (Ruhl & Smith, 2004). It appears remarkable that the mean densities of benthic scavenging megafauna (animals >10 mm) found in our study area (i.e., mostly decapods, isopods, and amphipods: 404 ind ha−1; Simon-Lledó et al., 2019) were substantially larger than those typically reported farther away from the potential influence of the California Current, in more southerly locations within the Clarion Clipperton Zone (i.e., 140–170 ind ha−1, Amon et al., 2016; Simon-Lledó et al., 2020). This distinctive benthic community structure (already in place at the time of deposition) in the APEI-6 site suggests that red crab mass falls might be a periodic yet spatially restricted event in the NE Pacific abyss. But without more information, it is impossible to establish how often and how widespread these events are in this region or their precise role in deep-sea food webs. The discovery of this red crab mass fall and its potential oceanographical, trophic, and ecological implications suggests that the connection between abyssal and surface processes might be tighter than commonly perceived. As with P. planipes, other crustacean species also aggregate in large swarms. These include the “langostilla”, Munida gregaria, in the western South Pacific (Zeldis & Jillett, 1982), the portunid crab, Charybdis smithii, in the Arabian Sea (Christiansen & Boetius, 2000), or krill, Euphausia superba in the Southern Ocean (Atkinson et al., 2008) and Meganyctiphanes norvegica in the North Atlantic. The latter species are also known to provide food subsidies to deep seabed communities (Christiansen & Boetius, 2000; Hirai & Jones, 2012; Schmidt et al., 2011), and our observations suggest a globally relevant role of crustacean carcasses in deep-water benthic systems (Halfter et al., 2021). This may not just have ecological implications. Crustacean species like P. planipes are a known vector for microplastics (Choy et al., 2019), and mass depositions could facilitate the transport of contaminants from coastal environments to the deep sea. With such a wealth of open questions, dedicated research focusing on the tracking and monitoring of crustacean mass deposition events appears urgent to better understand the periodicity, magnitude, causes, and consequences of these processes in the deep sea. Erik Simon-Lledó, Brian J. Bett, and Daniel O. B. Jones collected the data and conceived the study. Erik Simon-Lledó and Noëlie M. A. Benoist processed and analyzed image data. Tammy Horton, Henk-Jan Hoving, and Dmitry Aleynik provided expert insight in data interpretation. Erik Simon-Lledó composed the manuscript with significant input from all coauthors. We would like to thank Stephanie Henson (National Oceanography Centre) for processing and providing particulate carbon flux data for the abyssal North Pacific region. We would also like to thank Kyra Schlining (Monterey Bay Aquarium Research Institute) and Steve Lonhart (National Oceanic and Atmospheric Administration Monterey Bay National Marine Sanctuary) for providing additional images of the species (see Appendix S1). This work was part of the UK Natural Environment Research Council funded Seabed Mining And Resilience To EXperimental impact (SMARTEX) project (Grant Reference NE/T003537/1). Henk-Jan Hoving is funded by the DFG (Deutsche Forschungsgemeinschaft) under Grant HO 5569/2-1 (Emmy Noether Junior Research Group). All authors declare no conflicts of interest. Survey data (Simon-Lledó et al., 2022) are available in Zenodo at https://doi.org/10.5281/zenodo.7042090. Appendix S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

In Scotland, bivalves are widely distributed. However, their larvae dispersion is still largely unknown and difficult to assess in situ . And, while Mytilus spp. dominate shellfish production, it is mostly dependent on natural spat recruitment from wild populations. Understanding the larval distribution pattern would safeguard natural resources while also ensuring sustainable farming practises. The feasibility of a model that simulates biophysical interactions between larval behaviour and ocean motions was investigated. We employed an unstructured tri-dimensional hydrodynamic model (finite volume coastal ocean model) to drive a particle tracking model, where prediction of larval movement and dispersal at defined locations might aid in population monitoring and spat recruitment. Our findings reveal a strong link between larval distribution and meteorological factors such as wind forces and currents velocity. The model, also, depicts a fast and considerable larval movement, resulting in a substantial mix of plankton and bivalve larvae, forming a large connection between the southern and northern regions of Scotland’s West coast. This enables us to forecast the breeding grounds of any area of interest, potentially charting connectivity between cultivated and wild populations. These results have significant implications for the dynamics of ecologically and economically important species, such as population growth and loss, harvesting and agricultural management in the context of climate change, and sustainable shellfish fisheries management. Furthermore, the observations on Scottish water flow suggest that tracking particles with similar behaviour to bivalve larvae, such as other pelagic larval stages of keystone species and potential pathogens such as sea lice, may have policy and farming implications, as well as disease control amid global warming issues.

Various field methods have been used globally in an attempt to understand and quantify plastic pollution. However, in regions, such as the west coast of Scotland, sparse populations, combined with complex coastlines of numerous islands, sea lochs and headlands, has resulted in limited field data. The Clyde Sea is the most populated and industrialised region on the west coast of Scotland and therefore a potential source of land-based plastic litter to the less populated coast to the north. This study first presents an analysis of Marine Conservation Society (MCS) citizen-science beach-clean data, from 1994 to 2019, revealing spatial patterns between beach-clean sites. Plastic litter was categorised into land, marine and unknown sources, with the most common items in these three categories being crisp packets, fishing rope and fragments, respectively. On the west coast of Scotland there is on average 380.3 ± 419.9 plastic items per 100 m of coast, with the site average number of items recovered ranging from 1–2,355 per 100 m of coast. To simulate marine plastic litter movement from the Clyde Sea to a defined northwest model sub-area, an unstructured-grid hydrodynamic model was coupled with a particle tracking model subject to currents, diffusion, and wind. Three coastal boundary conditions were used to compare transport paths with or without particle beach resuspension, and for the resuspending cases, with or without a distinction between coastal type (retentive beaches versus reflective rocky coasts). Of the total released particles, the percentage that beached within the model sub-area, after a 1-year model run, ranged between 45.7% and 88.3% depending on the coastal boundary condition. The Clyde Sea was found to be a potential source of beached land-based plastic litter to the north, as on average, 6.8% (range: 2.9%–11.7%) of particles exited the Clyde Sea, crossed a defined northern boundary, and beached on the northwest coast. Both hydrodynamic and particle tracking models were tested, and the varying boundary conditions were compared to investigate holistic methodologies to better understand plastic pollution.

Marine Protected Areas (MPAs) are widely used in marine management, but for mobile species understanding the spatio-temporal scale of management measures that is required to deliver conservation benefits depends on a detailed knowledge of species' movements that is often lacking. This is especially the case for species of skate (Rajidae) for which relatively few movement studies have been conducted. In Scotland, the Loch Sunart to the Sound of Jura MPA covering 741 km(2) has been designated for the conservation of the Critically Endangered flapper skate (Dipturus intermedius), but fine-scale movements within this area remain poorly understood. A passive acoustic telemetry study which coupled acoustic tagging of 42 individuals and a static array of 58 receivers was conducted from March 2016 to June 2017. Using acoustic detection time series, angler capture-recapture data and depth time series from archival tags, fine-scale movements of individuals were investigated. Overall, 33 of the 42 tagged individuals were detected. Residency, site fidelity and transiency were documented. Residency around receivers, lasting from 3 to more than 12 months, was documented in 16 acoustically detected individuals (48%) and all life-history categories, but was most noticeable among females. Acoustic detections were associated with depth, salinity and season, but there was no evidence that individuals formed close-knit groups in the areas in which they were detected. Taken together with historical occurrence records of flapper skate, the prevalence and scale of residency documented here suggest that the MPA is sufficiently large to benefit a notable percentage (38 [24-52]%) of skate found in the study area over monthly and seasonal timescales. This result strengthens the case for the use of MPAs to support the conservation of flapper skate and other skate species that display similar movement patterns in areas of high local abundance.

Offshore aquaculture has gained momentum in recent years, and the production of an increasing number of marine fish species is being relocated offshore. Initially, predictions of the advantages that offshore aquaculture would present over nearshore farming were made without enough science-based evidence. Now, with more scientific knowledge, this review revisits past predictions and expectations of offshore aquaculture. We analysed and explained the oceanographic features that define off-shore and nearshore sites. Using Atlantic salmon ( Salmo salar ) as a case study, we focussed on sea lice, amoebic gill disease, and the risk of harmful algal blooms, as well as the direct effects of the oceanography on the health and physiology of fish. The operational and licencing challenges and advantages of offshore aquaculture are also considered. The lack of space in increasingly saturated sheltered areas will push new farms out to offshore locations and, if appropriate steps are followed, offshore aqua-culture can be successful. Firstly, the physical capabilities of the farmed fish species and infrastructure must be fully understood. Secondly, the oceanography of potential sites must be carefully studied to confirm that they are compatible with the species-specific capabilities. And, thirdly, an economic plan considering the operational costs and licencing limitations of the site must be developed. This review will serve as a guide and a compilation of information for researchers and stakeholders.

Catch-and-release angling is widespread, but the impacts of this practice for captured individuals are understudied, especially among elasmobranchs. Studies on sub-lethal behavioural impacts are particularly sparse, despite their importance for the interpretation of biologging data and for assessments of species’ tolerance to capture. In this study, the behavioural responses of flapper skate ( Dipturus intermedius ) to catch-and-release angling were described for the first time, using archival observations (depth and temperature) for 21 tag deployment/retrieval events and five recreational angling events that occurred during tagged individuals’ time at liberty from charter vessels off the west coast of Scotland in 2016–17. During capture (8–50 minutes), the changes in depth and temperature experienced by individuals typically exceeded natural variability. Post-release, behavioural change was apparent from visual inspection, regression and functional data analysis of the time series. Immediately following release, movements into deeper water and short periods of low vertical activity (usually 1–2 hours in duration) were common. However, overall average vertical activity was typically around 38% higher in the 12 hours following release than in undisturbed activity. A small number of individuals (n = 3, 14%) exhibited irregular post-release behaviour in the form of rapid, transient re-ascents towards the surface following release. Collectively, the evidence for limited, short-term behavioural changes suggests that flapper skate behaviour is relatively resilient to catch-and-release angling from charter vessels, but irregular post-release behaviour in 14% of individuals is sufficiently notable to indicate that further research is required on the impacts of this practice. This study clearly demonstrates the value of biologging data and behavioural analyses for examining the impacts of disturbance and separating ‘disturbed’ and ‘undisturbed’ behaviours in studies of animal movement.

Developments in animal electronic tagging and tracking have transformed the field of movement ecology, but interest is also growing in the contributions of tagged animals to oceanography. Animal-borne sensors can address data gaps, improve ocean model skill and support model validation, but previous studies in this area have focused almost exclusively on satellite-telemetered seabirds and seals. Here, for the first time, we develop the use of benthic species as animal oceanographers by combining archival (depth and temperature) data from animal-borne tags, passive acoustic telemetry and citizen-science mark-recapture records from 2016–17 for the Critically Endangered flapper skate ( Dipturus intermedius ) in Scotland. By comparing temperature observations to predictions from the West Scotland Coastal Ocean Modelling System, we quantify model skill and empirically validate an independent model update. The results from bottom-temperature and temperature-depth profile validation (5,324 observations) fill a key data gap in Scotland. For predictions in 2016, we identified a consistent warm bias (mean = 0.53 °C) but a subsequent model update reduced bias by an estimated 109% and improved model skill. This study uniquely demonstrates the use of benthic animal-borne sensors and citizen-science data for ocean model validation, broadening the range of animal oceanographers in aquatic environments.

1. Management interventions to reduce human-wildlife conflict can have unintended consequences for non-target species. Acoustic deterrent devices (ADDs) are used globally by the aquaculture sector. However, the potential for these sound emissions to impact non-target species, such as cetaceans, has not yet been quantified at population relevant spatial scales. 2. To better understand the extent of potential impacts on cetaceans, such as harbour porpoises, we used acoustic modelling to investigate levels of ADD noise throughout the west coast of Scotland and across a Special Area of Conservation (SAC) for this species. 3. Using an energy-flux acoustic propagation model and data on aquaculture sites known to be using ADDs, we predicted the spatial extent of ADD noise on the Scottish west coast from 1 February 2017 to 31 January 2018. Noise maps were produced to determine the risk of auditory impairment for harbour porpoises under a range of scenarios which assumed single or multiple ADDs and simultaneous use across all sites. 4. The acoustic propagation model performed well when tested against field measurements up to 5 km, with 98% of sound exposure level (SEL) predictions within +/- 10% of the measurements. Predictions of SELs over a 24-hr period suggested extensive temporary hearing loss zones (median radius: similar to 28 km) for harbour porpoises around aquaculture sites. Assuming a single device at each site, 23% of the harbour porpoise SAC was predicted to be exposed to ADD noise sufficient to induce a temporary threshold shift, and under the worst-case scenario (multiple, continuously running devices per site with an aggregate duty cycle of 100%), levels exceeding permanent threshold shift could reach 0.9% of the SAC. 5. Policy implications. This study highlights the potential for 'collateral damage' from interventions such as acoustic deterrent devices (ADDs) which are intended to reduce human-wildlife conflicts with pinnipeds but may affect the long-term health and habitat use of non-target species. This is especially true for harbour porpoises which are protected under the EU and UK Habitats Regulations. The aquaculture industry, policymakers and regulators in countries where ADDs are used should consider these findings when attempting to mitigate pinniped depredation.

We present an on-line early warning system that is operational in Scottish coastal waters to minimize the risk to humans and aquaculture businesses in terms of the human health and economic impacts of harmful algal blooms (HABs) and their associated biotoxins. The system includes both map and time-series based visualization tools. A “traffic light” index approach is used to highlight locations at elevated HAB/biotoxin risk. High resolution mathematical modelling of cell advection, in combination with satellite remote sensing, provides early warning of HABs that advect from offshore waters to the coast. Expert interpretation of HAB, biotoxin and environmental data in light of recent and historical trends is used to provide, on a weekly basis, a forecast of the risk from HABs and their biotoxins to allow mitigation measures to be put in place by aquaculture businesses, should a HAB event be imminent.