First observations on seamount habitat use of blackspot seabream (Pagellus bogaraveo) using acoustic telemetry

The application of the “ecosystem approach” to fisheries management demands knowledge of the patterns of habitat use of target species but in the case of seamounts, this information is still very limited or, for most species, simply unavailable. Novel approaches, such as the use of acoustic biotelemetry in deep sea environments can potentially elucidate the spatial behaviour of seamount associated fishes. We tested the use of passive acoustic telemetry to study the residency of sub-adult and adult blackspot seabream (Pagellus bogaraveo) at the Condor seamount, Azores, mid-north Atlantic. Twenty‐eight fish tagged with acoustic transmitters were monitored by two receivers moored at the summit of the seamount (ca. 200m depth) over two and a half years. Twenty‐two of these fish were detected by the receivers but only twelve fish (43%) were detected beyond the two initial days after release. This sub-group of fish was detected at the seamount summit for an average 25% of the days monitored and up to 829days, with a predicted 50% chance of detection at the seamount 278days after release. While at the summit, fish were typically site attached to one side of the seamount summit, particularly at night. Our data indicate that 1) there is high individual variability in the residency at the seamount, ranging from short interspersed visits to year-long residency and 2) the fine-scale movements of blackspot seabream at the Condor seamount could well be characterised by horizontal displacements smaller than previously thought and by frequent diel vertical migrations. This work demonstrates the great potential of acoustic telemetry as a tool to study the habitat use of seamount fishes and to provide information relevant for the spatial management and conservation of these species and habitats. Concurrently, it also highlights the problems and methodological challenges with post-release mortality, particularly in larger individuals, and appropriate receiver coverage, that need to be addressed in future studies.