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ABSTRACT The brown crab is an important fishery resource in northern Europe. Understanding factors that affect fecundity in this species is complicated by the fact that ovigerous females enter traps [...]

The present study investigated the genetic efficiency of enhancing populations of wild scallops using hatchery-produced seed scallops. Scallops from the Isle of Man (IOM), Irish Sea, and from a scallop hatchery were genotyped using 15 microsatellite markers. Hatchery scallops had equivalent heterozygosity to wild scallops, but rare alleles were likely to be lost in hatchery scallops as represented by lower allelic richness. The effective number of breeders ([N.sub.b]) of the hatchery scallops was estimated at 32.4 (95% CI: 24.4-44.9). The confidence intervals for the estimates of [N.sub.b] for the IOM included infinity. When [N.sub.b] becomes large the genetic signal is weak compared with the sampling noise; therefore, while we can be confident that the [N.sub.b] of IOM scallops is larger than that of the hatchery, the precise difference is uncertain. Simulations showed it is possible, in some scenarios, that stock enhancement with hatchery seed can lead to an increase in the wild population's effective size; however, in the majority of scenarios a decrease in the effective size of the wild population is more likely. A precautionary approach to stock enhancement with hatchery seed is advised. La presente etude se penche sur l'efficacite genetique de la mise en valeur de populations de petoncles sauvages a l'aide de petoncles reproducteurs produits en ecloserie. Des petoncles de l'ile de Man (IOM), dans la mer d'Irlande, et d'une ecloserie de petoncles ont ete genotypes sur la base de 15 marqueurs microsatellites. Si les petoncles d'ecloserie presentaient une heterozygotie equivalente a celle des petoncles sauvages, la plus faible richesse allelique des petoncles d'ecloserie temoignait vraisemblablement de la disparition d'alleles rares. Le nombre effectif de geniteurs ([N.sub.b]) parmi les petoncles d'ecloserie a ete estime a 32,4 % (IC a 95 %: 24,4-44,9). Les intervalles de confiance pour les estimations du [N.sub.b] pour l'IOM comprenaient l'infinite; quand [N.sub.b] est grand, le signal genetique est faible par rapport au bruit d'echantillonnage de sorte que, s'il est permis de conclure que le [N.sub.b] des petoncles de l'IOM est plus eleve que celui des petoncles d'ecloserie, la difference exacte ne peut etre etablie avec certitude. Des simulations ont demontre qu'il est possible, dans certains scenarios, que la mise en valeur des stocks avec des petoncles producteurs provenant d'ecloserie puisse mener a une augmentation de la taille effective de la population sauvage. Cela dit, dans la majorite des scenarios, une diminution de la taille effective de la population sauvage est plus probable. Une approche prudente est donc a privilegier en ce qui concerne la mise en valeur des stocks a l'aide de petoncles reproducteurs issus d'ecloserie. [Traduit par la Redaction], Introduction Global scallop (Pectinid) capture production has risen from 500 000 tonnes in the 1980s to 840 000 tonnes in 2010 (FAO 2012), and these scallop fisheries are highly valuable. [...]

Brown crab contributes to small-scale fisheries in the Isle of Man and landings (495 t) were worth in excess of £0.5 million in 2012. The present study sought to fill evidence gaps needed to improve the scientific understanding of this fishery. Observer data were collected to examine the spatial and temporal variations in the size distribution and sex ratio of crabs around the Isle of Man. This study also aimed to evaluate the catch characteristics of brown crab using logbook data (2007–2012), observer data (2012–2013) and questionnaire survey data (2013). The sex ratio is highly variable in different areas across seasons and was perhaps indicative of migration patterns in relation to mating. This change was most notable with a strong increase in the proportion of females to the south and west of the Isle of Man in the autumn months. The depth and pot volume were important factors that influenced the catch per unit effort (CPUE). Future survey designs would need to ensure adequate spatial coverage of the east and west coast of the Isle of Man together with a seasonal sampling regime that captures the spatial change in the distribution and abundance of male and female crabs. [ABSTRACT FROM AUTHOR]

Baited trap or pot fisheries are considered to have relatively few wider ecosystem effects on the marine environment, particularly when compared with towed mobile fishing gear. However, this assumption is rarely tested in the field. This study aimed to determine the composition of non-target species that occur in crustacean pots and to assess spatial and temporal differences in catches in the waters around the Isle of Man, Irish Sea. The data were collected using fishery independent surveys and a questionnaire study. Based on fishery independent surveys, a total of five taxonomic groups and 43 species occurred as by-catch. The dominant by-catch species was velvet crab Necora puber. The by-catch per unit effort (BPUE) for all of the non-target species was low particularly in comparison to towed bottom gear fisheries around the Isle of Man. BPUE of species composition varied considerably between different locations around the Isle of Man. The results of both the fishery independent and questionnaire data suggested that the by-catch rates varied with season with peak BPUE occurring in spring which then declined into autumn and winter. By-catch composition did not decrease significantly with an increasing target species catch. Overall, by-catch was low relative to target species catch which may be partially attributable to the use of escape panels in pot fisheries in the Isle of Man. [ABSTRACT FROM AUTHOR]

Understanding the distribution of fishing activity is fundamental to quantifying its impact on the seabed. Vessel monitoring system (VMS) data provides a means to understand the footprint (extent and intensity) of fishing activity. Automatic Identification System (AIS) data could offer a higher resolution alternative to VMS data, but differences in coverage and interpretation need to be better understood. VMS and AIS data were compared for individual scallop fishing vessels. There were substantial gaps in the AIS data coverage; AIS data only captured 26% of the time spent fishing compared to VMS data. The amount of missing data varied substantially between vessels (45-99% of each individuals' AIS data were missing). A cubic Hermite spline interpolation of VMS data provided the greatest similarity between VMS and AIS data. But the scale at which the data were analysed (size of the grid cells) had the greatest influence on estimates of fishing footprints. The present gaps in coverage of AIS may make it inappropriate for absolute estimates of fishing activity. VMS already provides a means of collecting more complete fishing position data, shielded from public view. Hence, there is an incentive to increase the VMS poll frequency to calculate more accurate fishing footprints. [ABSTRACT FROM AUTHOR]

Monitoring and assessment of the status and distribution of marine seabed habitats is needed to support existing and emerging environmental policy commitments. Traditional monitoring of habitats and associated species using grabs and trawls is costly and labour intensive and might usefully be complemented by cheaper and more readily automated methods that can be used at higher frequencies and/or on larger spatial scales., We develop and apply two methods to measure seabed habitat complexity and demonstrate how they can be used to describe impacts (e.g. fishing gear impacts) and monitor recovery. The first method relies on the analysis of deviations in a laser line projected on the seabed. The second method is based on the pixel value distribution in seabed photographs. We use both methods to quantify the complexity created by different substrates and habitat-forming species and to establish links between habitat complexity and faunal diversity (richness) and abundance., The habitat complexity index calculated with the laser line method provided a reliable index of complexity across a range of habitat types, showing a monotonic increase with coarseness of the substratum and the abundance of sessile epifauna. Pixel value distributions in the photographs did not reflect the increase in complexity due to sessile epifauna but only reflected substratum differences., Results suggested that the laser line method would be suitable for monitoring the effect of disturbance on habitats ranging from gravelly sands to rock, and their subsequent recovery. The photographic method would be better suited to assessing complexity and heterogeneity of the substratum. Both methods complement conventional biological sampling and can be used at higher frequencies and/or on larger spatial scales per unit cost., The laser line method has considerable potential to support demands for frequent monitoring of seabed habitats and human impacts at a range of spatial scales. It is less costly and labour intensive than existing approaches and can be deployed from vessels of many sizes. [ABSTRACT FROM AUTHOR]