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Vandeperre F.,University of The Azores | Vandeperre F.,LARSyS Associated Laboratory | Aires-da-Silva A.,Inter American Tropical Tuna Commission | Fontes J.,University of The Azores | And 7 more authors.
PLoS ONE | Year: 2014

Spatial structuring and segregation by sex and size is considered to be an intrinsic attribute of shark populations. These spatial patterns remain poorly understood, particularly for oceanic species such as blue shark (Prionace glauca), despite its importance for the management and conservation of this highly migratory species. This study presents the results of a long-term electronic tagging experiment to investigate the migratory patterns of blue shark, to elucidate how these patterns change across its life history and to assess the existence of a nursery area in the central North Atlantic. Blue sharks belonging to different life stages (n = 34) were tracked for periods up to 952 days during which they moved extensively (up to an estimated 28.139 km), occupying large parts of the oceanic basin. Notwithstanding a large individual variability, there were pronounced differences in movements and space use across the species' life history. The study provides strong evidence for the existence of a discrete central North Atlantic nursery, where juveniles can reside for up to at least 2 years. In contrast with previously described nurseries of coastal and semi-pelagic sharks, this oceanic nursery is comparatively vast and open suggesting that shelter from predators is not its main function. Subsequently, male and female blue sharks spatially segregate. Females engage in seasonal latitudinal migrations until approaching maturity, when they undergo an ontogenic habitat shift towards tropical latitudes. In contrast, juvenile males generally expanded their range southward and apparently displayed a higher degree of behavioural polymorphism. These results provide important insights into the spatial ecology of pelagic sharks, with implications for the sustainable management of this heavily exploited shark, especially in the central North Atlantic where the presence of a nursery and the seasonal overlap and alternation of different life stages coincides with a high fishing mortality. © 2014 Vandeperre et al.

Afonso P.,University of The Azores | Afonso P.,LARSyS Associated Laboratory | Graca G.,University of The Azores | Graca G.,LARSyS Associated Laboratory | And 4 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2012

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. 200. m 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 829. days, with a predicted 50% chance of detection at the seamount 278. days 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. © 2012 Elsevier B.V.

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