Variability in behaviour of four fish species attracted to baited underwater cameras in the North Sea

Baited underwater camera (BUC) systems to estimate demersal fish abundance are becoming increasingly considered as an alternative to traditional survey methods, particularly in environments that contain sensitive habitats or protected species. Based on 27 replicate deployments of BUCs at 100 m depth in the northern North Sea, in rank order of abundance, hagfish (Myxine glutinosa), flatfish mainly dabs (Limanda limanda), whiting (Merlangius merlangus) and haddock (Melanogramus aeglefinus) were observed consistently at baits. Higher maximum numbers (N _max) occurred during daytime in all species with the most significant effect in flatfish, 18 in daytime and 5 at night-time. Bottom current had no significant effect on numbers of whiting, flatfish or haddock. The N _max of hagfish was strongly related to current speed in a non-linear way with an increase in numbers up to 10 cm s⁻¹ and then decrease in N _max at higher water speeds. Understanding and accounting for such species-specific influences is important in the design of long term monitoring surveys using baited cameras.