The realised distribution of species in disturbed environments depends upon the degree to which their optimum habitat has been altered by impacts arising from human pressures. We investigated how ...pressures such as fishing activity, changes in prey availability and habitat quality affect the distribution of Common Scoter (CS) in the north Irish Sea. CS distribution data were obtained from aerial surveys in the winter of 2018–2019. We developed two generalised additive models using covariate information on depth, seabed shear stress, VMS activity of fishing vessels, AIS data of passenger and cargo vessels, portion of fine sand in the benthos, abundance of deep-burrowing bivalves and abundance of surficial bivalves. There was no clear evidence that the fishery, through either disturbance effects nor direct prey competition caused by extraction of razor clams, affected the distribution of CS in the area. However, indirect effects of the fishery, mediated through impacts on abundance and perhaps recruitment of bivalves on CS, could not be ruled out. The absence of a disturbance effect may be due to the small size of vessels in this fleet and their slow fishing speeds. The abundance of surficial bivalves, depth, the portion of fine sand and shear stress at the seabed in the sediments influenced CS distribution. This indicates that the distribution of CS in the area is driven by foraging conditions rather than the presence of fishing vessels.
•The distribution of common scoter is related to the ease of foraging and the presence of prey.•There is no indication that the razor clam fishing fleet is affecting common scoter distribution.•There is no indication that the razor clam fishing fleet is causing disturbance to common scoter.•There was no direct prey competition between the razor clam fishing fleet and common scoter.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hydraulic dredging for bivalves, such as cockles (Cerastoderma edule), has the potential to cause significant impacts on marine intertidal benthos. Although this fishing activity is common in ...northern European Natura 2000 sites such impacts may be incompatible with conservation objectives for designated habitats and species within these sites. In 2009–2010 a spatially nested control-impact study was undertaken before (t0), 8–9 days after (t1) and 4 months (t2) following dredging and extraction of 108 tonnes of cockles from a standing stock of 2158 tonnes in Dundalk Bay. This study failed to detect significant effects on benthic sediments, or the overall community structure. However, a fishing effect on the target species C. edule in one sampling area and a short lived effect on the bivalve Angulus tenuis were identified. Significant spatial and temporal variability in abundance of species and taxonomic groups, unrelated to fishing effects, was observed. Previous studies on the effects of fisheries on marine intertidal benthos have reported variable results, related to study design and objectives and the physical characteristics of the study site. Site specific studies, relative to the intensity and frequency of proposed fishing activity, may be required to adequately inform managers whether such activities are compatible with specific conservation objectives for Natura 2000 sites.
Abstract
This study assesses the seabed pressure of towed fishing gears and models the physical impact (area and depth of seabed penetration) from trip-based information of vessel size, gear type, ...and catch. Traditionally fishing pressures are calculated top-down by making use of large-scale statistics such as logbook data. Here, we take a different approach starting from the gear itself (design and dimensions) to estimate the physical interactions with the seabed at the level of the individual fishing operation. We defined 14 distinct towed gear groups in European waters (eight otter trawl groups, three beam trawl groups, two demersal seine groups, and one dredge group), for which we established gear “footprints”. The footprint of a gear is defined as the relative contribution from individual larger gear components, such as trawl doors, sweeps, and groundgear, to the total area and severity of the gear's impact. An industry-based survey covering 13 countries provided the basis for estimating the relative impact-area contributions from individual gear components, whereas sediment penetration was estimated based on a literature review. For each gear group, a vessel size–gear size relationship was estimated to enable the prediction of gear footprint area and sediment penetration from vessel size. Application of these relationships with average vessel sizes and towing speeds provided hourly swept-area estimates by métier. Scottish seining has the largest overall gear footprint of ∼1.6 km 2 h −1 of which 0.08 km 2 has an impact at the subsurface level (sediment penetration ≥ 2 cm). Beam trawling for flatfish ranks low when comparing overall footprint size/hour but ranks substantially higher when comparing only impact at the subsurface level (0.19 km 2 h −1 ). These results have substantial implications for the definition, estimation, and monitoring of fishing pressure indicators, which are discussed in the context of an ecosystem approach to fisheries management.
Bycatch of protected species in static net fisheries is a global conservation concern and is currently considered the dominant anthropogenic threat facing many marine mammal species. Effective ...bycatch mitigation remains challenging, contingent on an understanding of the underlying mechanisms that cause individuals to become entangled.
We combined data collected by scientific observers and fishers to identify predictors of seal bycatch in static net fisheries along the west, southwest and south coasts of Ireland. We first analysed the broad regional and seasonal trends in seal bycatch before identifying environmental variables that could explain these patterns.
Based on negative binomial generalized linear mixed effects models, seal bycatch significantly varied with season and decreased with greater distance to major seal colonies and in clearer, less turbid water.
Synthesis and applications. Our results suggest that distance to major seal colonies was a significant driver of spatial variation in seal bycatch, and water turbidity a major driver of seasonal trends. These findings will enable us to identify future bycatch risk and target mitigation measures effectively. This is the first study to identify the effect of water turbidity on bycatch of a protected marine species. Increasing net visibility in turbid waters may provide a novel approach to mitigating against protected species bycatch in static net fisheries.
Our results suggest that distance to major seal colonies was a significant driver of spatial variation in seal bycatch, and water turbidity a major driver of seasonal trends. These findings will enable us to identify future bycatch risk and target mitigation measures effectively. This is the first study to identify the effect of water turbidity on bycatch of a protected marine species. Increasing net visibility in turbid waters may provide a novel approach to mitigating against protected species bycatch in static net fisheries.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract Seagrasses are considered to be globally important for carbon sequestration and they provide a range of ecosystem services. However, they are also known to be vulnerable to various ...anthropogenic activities, not least bottom contacting fishing gears such as dredging and potting. We set out to test the effects of dredge fishing, in early spring and potting in late summer, in a historically fished but considered “pristine” seagrass meadow on the west coast of Ireland. We found that despite dredging and potting pressures, growth of seagrasses was driven by seasonal changes in light and temperature and that neither fishing activity had any effect on rhizome weight or shoot or blade densities during the growing season. We hypothesize that it is possible for fishing to co‐occur with seagrass if fishing activities are restricted to winter or early spring, before the main seagrass growing season, and/or if particular types of gear, such as the traditional gears described here are used. High levels of dredging and potting had positive increases in the count of both sessile and mobile epifauna suggesting that for mobile species at least, they may take advantage of post‐fishing scavenging opportunities.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ensuring a balance of conservation and human activities within the marine environment requires complex decisions on how to achieve conservation objectives whilst considering the likely economic and ...social costs and benefits of such decisions. We assessed the risk of adverse effects from abrasion caused by bottom fishing, as a case study, to demonstrate an integrated spatial management methodology. Risk was quantified in the Galway Bay, Ireland region using a 1 km grid, as the ratio between mortality and recovery of benthic infauna exposed to abrasion effects estimated from fishing data. Risk was considered high if annual mortality exceeded recovery. A Bayesian network model, incorporating ecological and economic data, compared three management scenarios: i) business as usual (BAU), ii) exclusion of fishing vessels over 18 m within 6 nautical miles (68% of study area) (Length) and iii) a network of marine protected areas (MPAs) closed to all fishing vessels (11% of study area) (MPA). The BAU scenario indicated that risk was high for 85.6% of the study area. The length scenario resulted in a 14.6% reduction in high risk cells, affecting €0.9 M of landings, €0.7 M of indirect output and 19 full time equivalent (FTE) employees. The MPA scenario resulted in a 1.7% reduction of high risk cells. This scenario affected €0.17M in landings, €0.13M in indirect outputs and 3 FTE employees. We present a method which provides a quantitative, spatial, risk and economic impact assessment of the effects of human activities and pressures on the marine environment that assesses potential costs and benefits of management options to mitigate against these pressures. Future development of a mortality-recovery ratio for defined time periods would enable application across multiple habitats, human activities and pressures.
•An ecological and economic impact assessment of trawling on benthic habitats.•Bayesian network analysis of management scenarios demonstrate use for planners.•A Large vessel closure had ecological benefits but high economic consequences.•An MPA network had limited ecological and economic benefits.•Future work to assess other human activities such as aquaculture is on-going.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk ...of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.
Abstract
Assessing size at maturity for European lobster Homarus gammarus across the North East Atlantic remains a fundamental knowledge gap for this commercially valuable fishery. This study for the ...first time collates existing data on physiological maturity of female European lobster H. gammarus across the North East Atlantic, including new data from Scotland, Wales, and the Isle of Man. Physiological estimates of size at maturity were undertaken using 1309 lobsters from 11 locations using a standardized methodology. Carapace length (CL) at which 50% of the sampled population had reached physiological maturity (CL50) varied between populations, ranging from 82 to 92.5 mm. CL50 estimates reported here are broadly similar for historic population samples in England, but estimates for Irish samples were lower than previous results. The development of a H. gammarus specific staging guide and methodology in this study enables the future comparison of potential fluctuations in female size at maturity.
The velvet swimming crab Necora puber has been fished in Ireland since the early 1980s and contributes significant income to smaller fishing vessels. From 2016 onwards, reduced landings have been ...reported. We undertook a full pathological investigation of crabs from fishing grounds at 3 sites on the west (Galway), southwest (Castletownbere) and east (Howth) coasts of Ireland. Histopathology, transmission electron microscopy and molecular taxonomic and phylogenetic analyses showed high prevalence and infection level of Paramarteilia canceri, previously only reported from the edible crab Cancer pagurus. This study provides the first molecular data for P. canceri, and shows its phylogenetic position in the order Paramyxida (Rhizaria). Other parasites and symbionts detected in the crabs were also noted, including widespread but low co-infection with Hematodinium sp. and a microsporidian consistent with the Ameson and Nadelspora genera. This is the first histological record of Hematodinium sp. in velvet crabs from Ireland. Four N. puber individuals across 2 sites were co-infected by P. canceri and Hematodinium sp. At one site, 3 velvet crabs infected with P. canceri were co-infected with the first microsporidian recorded from this host; the microsporidian 18S sequence was almost identical to Ameson pulvis, known to infect European shore crabs Carcinus maenas. The study provides a comprehensive phylogenetic analysis of this and all other available Ameson and Nadelspora 18S sequences. Together, these findings provide a baseline for further investigations of N. puber populations along the coast of Ireland.
The combined effects of temperature and salinity on the survival and development of larval and juvenile Palaemon serratus from the west coast of Ireland were investigated. Survival over time was ...measured at thirty combinations of temperature and salinity ranging from 10–19°C and 9–34‰ in a fully factorial design. Salinity had a stronger influence than temperature on survival at all larval stages except stage V. For juveniles the main effect changed from temperature between 100 and 200 degree days to salinity between 200 and 600 degree days and temperature between 600 and 800 degree days. Estimates of time taken to 50% mortality showed that juveniles tolerated lower salinities for longer periods and exhibited optimal salinity values which were 3‰ lower than larvae, at temperatures between 10 and 15°C. Larval stage durations were found to be influenced by temperature but not salinity. Comparison with published data suggests that populations of P. serratus have adapted to local conditions of temperature and salinity. The results presented here have practical implications for fisheries assessment and management, as the incorporation of environmental effects into stock–recruitment models can improve their predictive capacity.
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