Ageing European lobsters (Homarus gammarus) using DNA methylation of evolutionarily conserved ribosomal DNA.

Crustaceans are notoriously difficult to age because of their indeterminate growth and the moulting of their exoskeleton throughout life. The poor knowledge of population age structure in crustaceans therefore hampers accurate assessment of population dynamics and consequently sustainable fisheries management. Quantification of DNA methylation of the evolutionarily conserved ribosomal DNA (rDNA) may allow for age prediction across diverse species. However, the rDNA epigenetic clock remains to be tested in crustaceans, despite its potential to inform both ecological and evolutionary understanding, as well as conservation and management practices. Here, patterns of rDNA methylation with age were measured across 5154 bp of rDNA corresponding to 355 quality-filtered loci in the economically important European lobster (Homarus gammarus). Across 0- to 51-month-old lobsters (n = 155), there was a significant linear relationship between age and percentage rDNA methylation in claw tissue at 60% of quality-filtered loci (n = 214). An Elastic Net regression model using 46 loci allowed for the accurate and precise age estimation of individuals (R 2 = 0.98; standard deviation = 1.6 months). Applying this ageing model to antennal DNA from wild lobsters of unknown age (n = 38) resulted in predicted ages that are concordant with estimates of minimum size at age in the wild (mean estimated age = 40.1 months; range 32.8-55.7 months). Overall, the rDNA epigenetic clock shows potential as a novel, nonlethal ageing technique for European lobsters. However, further validation is required across a wider range of known-age individuals and tissue types before the model can be used in fisheries management.

Filling the gap: Using fishers' knowledge to map the extent and intensity of fishing activity.

Knowledge of the extent and intensity of fishing activities is critical to inform management in relation to fishing impacts on marine conservation features. Such information can also provide insight into the potential socio-economic impacts of closures (or other restrictions) of fishing grounds that could occur through the future designation of Marine Conservation Zones (MCZs). We assessed the accuracy and validity of fishing effort data (spatial extent and relative effort) obtained from Fishers' Local Knowledge (LK) data compared to that derived from Vessel Monitoring System (VMS) data for a high-value shellfish fishery, the king scallop (Pecten maximus L.) dredge fishery in the English Channel. The spatial distribution of fishing effort from LK significantly correlated with VMS data and the correlation increased with increasing grid cell resolution. Using a larger grid cell size for data aggregation increases the estimation of the total area of seabed impacted by the fishery. In the absence of historical VMS data for vessels ≤15 m LOA (Length Overall), LK data for the inshore fleet provided important insights into the relative effort of the inshore (<6 NM from land) king scallop fishing fleet in the English Channel. The LK data provided a good representation of the spatial extent of inshore fishing activity, whereas representation of the offshore fishery was more precautionary in terms of defining total impact. Significantly, the data highlighted frequently fished areas of particular importance to the inshore fleet. In the absence of independent sources of geospatial information, the use of LK can inform the development of marine planning in relation to both sustainable fishing and conservation objectives, and has application in both developed and developing countries where VMS technology is not utilised in fisheries management.

Regional variation in bycatches associated with king scallop (Pecten maximus L.) dredge fisheries.

The biomass and composition of bycatch from king scallop dredge fisheries was assessed and compared between the English Channel, Cardigan Bay in Wales and around the Isle of Man. Bycatch composition varied significantly at localised, and broad, geographic scales. The mean proportion of scallop dredge bycatch biomass in the English Channel was 19% of total catch biomass. The proportion of bycatch was lower in Cardigan Bay (15%) but notably higher around the Isle of Man (53%). The proportion of individual bycatch species in dredge catches were low, therefore scallop dredging is unlikely to cause a substantial increase the population mortality of individual commercially fished species beyond that caused by the target fisheries for those species, or bycatches of other fisheries. The amount and mortality of organisms left on the seabed in the dredge path was not quantified in this study but should also be considered in management of the fishery. The discard rate of finfish and shellfish of commercial value from the king scallop dredge fishery in the English Channel was between 18 and 100%, with a higher rate of discarding occurring in the eastern English Channel compared to the west. The clear regional differences in bycatch composition and variation in the quantity of discards mean that an area by area approach to managing bycatch species is required in relation to the king scallop dredge fishery.

Nephrops fisheries in European waters.

This review focuses on the Norway lobster (Nephrops norvegicus) as a resource, describing how the fishery has developed from the 1960s to the present day to become one of the most economically important fisheries in Europe. In 2010, the total landings were 66,500 tonnes, of which UK fishers landed a significant part (58.1%). The Nephrops fishery is also important for countries such as Ireland (11.7% of the total) and Sweden (1.9%) where it is of regional importance. Some are also taken in the Mediterranean, where Italian, Spanish and Greek fishers together take approximately 7% of the total landing. More than 95% of Nephrops are taken using single- or multi-rig trawlers targeting Nephrops or in mixed species fisheries. In regions such as Western Scotland and the Swedish West Coast, creel fisheries account for up to a quarter of the total landings. Across the range, a small proportion (<5%) is taken using traps in a fishery characterised by larger sized animals that gain a higher price and have lower discard and by-catches of ground fish with low mortalities. The trawling sector, however, is reducing the by-catches of ground fish with the aid of technical measures, such as square-mesh panels and grids and national systems of incentives. Assessments for Nephrops are operated via the 34 functional units (FUs) regarded as stocks. Changes in management procedures have arisen as a result of the advisory input from underwater TV fishery-independent stock surveys. The total allowable catch does not follow FUs but is agreed upon per management area.