Investigating the link between Nephrops norvegicus burrow density and sediment composition in Scottish waters

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Nephrops norvegicus is a burrowing decapod crustacean, found in the North Atlantic Ocean and Mediterranean Sea, at depths of between 10m – 1200m. It is currently the most valuable single species exploited by the commercial fishing industry in Scotland. It constructs and inhabits extensive burrow complexes in suitable muddy sediments, the composition of which is believed to limit the extent of burrow construction, and hence population size. Due to variable and sex specific emergence patterns of Nephrops, catch rates from traditional trawl surveys are not considered a good estimator of population size. Nephrops populations around Scotland are currently assessed using an underwater TV (UWTV) survey method to estimate burrow density, which is assumed to be a proxy for population density and, raised to total area of muddy sediments in the region of interest. Sediment samples are collected at the end of each UWTV deployment. This study explores the relationship between Nephrops burrow density and sediment composition in two areas off the coast of Scotland over the period 2002-2007, and attempts to answer the question of whether changes in population size have represented a colonisation of less favourable sediment types or have reflected an overall increase in burrow density.