On-line behavioural monitoring systems are nowadays a common tool in ecotoxicological research. Although applied successfully to freshwater species, they are rarely used in the marine field. Here we present first results about the Marine On-line Biomonitor System (MOBS), a new automatic system for recording behavioural responses of marine and freshwater species. Low power electrical signals are modulated by the behavioural activities of the organisms and then monitored, processed and analysed in real-time. We applied this system to two marine fish species, seabream (Sparus aurata) and turbot (Scophthalmus maximus), and studied their behavioural responses at an acute hypoxic test condition (2 mg O2 l(-1)). The tests were performed for 15 min in small test chambers with isolated fish as well as in large aquaria with groups of six fish. In both cases, MOBS recorded significant alterations in their behaviour: isolated juvenile seabream increased their ventilation frequency (VF) in average by 20%, and grouped fish decreased their swimming activities by 40%. In contrast, isolated juvenile turbot responded to hypoxia with a 36% lower VF. The consequences for data interpretation based on tests for individual fish or groups of fish are discussed.

A B S T R A C TThis paper describes an interferometric synthetic aperture sonar system based on an unmanned surface vehicle customized for shallow water environments. Synthetic aperture sonar enables imagery of high resolution that is independent of range by using the displacement of the sonar platform to create a large virtual array. If two geometrically displaced images are obtained, the construction of threedimensional topographic maps is possible through the use of interferometric techniques. The use of an unmanned surface vehicle presents several advantages that alleviate some problems related to the formation of synthetic aperture images, which are mainly related to the fact that a precise navigation system can be used for the boat control and sonar imagery motion compensation. Also, a small unmanned surface vehicle is advantageous in terms of cost of operation, maintenance and ease of deployment. Mapping of shallow water areas is an important task for many commercial and scientific applications like river navigability, infrastructure maintenance and natural resource monitoring. These tasks can be done efficiently with this system. Sample data obtained during test trials illustrate how synthetic aperture can be used to generate underwater imagery and bathymetric data. A B S T R A C TThis paper describes an interferometric synthetic aperture sonar system based on an unmanned surface vehicle customized for shallow water environments. Synthetic aperture sonar enables imagery of high resolution that is independent of range by using the displacement of the sonar platform to create a large virtual array. If two geometrically displaced images are obtained, the construction of threedimensional topographic maps is possible through the use of interferometric techniques. The use of an unmanned surface vehicle presents several advantages that alleviate some problems related to the formation of synthetic aperture images, which are mainly related to the fact that a precise navigation system can be used for the boat control and sonar imagery motion compensation. Also, a small unmanned surface vehicle is advantageous in terms of cost of operation, maintenance and ease of deployment. Mapping of shallow water areas is an important task for many commercial and scientific applications like river navigability, infrastructure maintenance and natural resource monitoring. These tasks can be done efficiently with this system. Sample data obtained during test trials illustrate how synthetic aperture can be used to generate underwater imagery and bathymetric data.

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