Diel patterns in the habitat utilisation of sandeels revealed using integrated acoustic surveys

Tracking the movements of sandeels in relation to their habitat will provide an improved understanding of sandeel ecology, including their interrelationships with predators and fishing activity. We examined spatial and temporal changes in the behaviour and distribution of the lesser sandeel Ammodytes marinus by integrating the acoustic ground discrimination system QTC VIEW with a Simrad EK500 fisheries scientific echosounder. QTC VIEW was used to identify acoustic changes in the properties of the seabed in the presence of buried sandeels, whilst the EK500 simultaneously recorded temporal changes in their distribution throughout the water column. Our results suggest that high densities of sandeels buried in sediment give a different acoustic signal to that of its surroundings. This integrated approach showed that sandeels had a diurnal activity pattern that was strongly, although not exclusively, associated with day length. Using this integrated survey method will enable large-scale cost-effective surveys of sandeel behaviour, distribution and abundance to be conducted. (C) 2004 Elsevier B.V. All rights reserved.