Individual variability in activity patterns in Atlantic halibut (Hippoglossus hippoglossus) revealed using pop-up...

Understanding fish behaviour and activity patterns is essential for interpreting their ecology and the processes that shape population dynamics, yet such information remains limited for wild fishes because observing individuals in situ is challenging. Recent technological advances make it possible to collect high-resolution movements and activity data over extended periods, opening the door to detailed descriptions of fine-scale behaviours and their temporal variability. We evaluated the coarse and fine-scale activity patterns of 25 Atlantic halibut (Hippoglossus hippoglossus) individuals throughout a complete seasonal cycle in the Gulf of St. Lawrence using acceleration data at a resolution of 5 s extracted from 25 pop-up satellite archival tags (PSAT). We sought to classify individuals into behavioural contingents within the population and to identify specific behaviours that could be identified with the fine resolution of the available data using dynamic factor analysis, visual representations and variance partitioning. Despite some common general patterns of activity during reproduction, the data were characterized by a high level of individual variability in the amount and patterns of activity, with each halibut exhibiting a unique activity profile across the year. Periodic daily behaviours (diurnal and nocturnal) were identified for several individuals but with no clear pattern in their recurrence over time within individuals or coherence between individuals. Overall, individual variability in activity dominated over the common patterns detected, with little evidence of distinct activity contingents among individuals. The high-frequency activity data available from PSATs in this study challenge the traditional view of halibut and flatfish in general, as passive bottom dwellers exhibiting simple, perhaps periodic behaviours, instead supporting growing evidence that fish exhibit substantial individual behavioural differences.