Global-Scale Environmental Niche and Habitat of Blue Shark (Prionace glauca) by Size and Sex: A Pivotal Step to Improving Stock Management

Abstract

Blue shark (Prionace glauca) is amongst the most abundant shark species in international trade, however this highly migratory species has little effective management and the need for spatio-temporal strategies increases, possibly involving the most vulnerable stage or sex classes. We combined 265,595 blue shark observations (capture or satellite tag) with environmental data to present the first global-scale analysis of species’ habitat preferences for five size and sex classes (small juveniles, large juvenile males and females, adult males and females). We leveraged the understanding of blue shark biotic environmental associations to develop two indicators of foraging location: productivity fronts in mesotrophic areas and mesopelagic micronekton in oligotrophic environments. Temperature (at surface and mixed layer depth plus 100 m) and sea surface height anomaly were used to exclude unsuitable abiotic environments. To capture the horizontal and vertical extent of thermal habitat for the blue shark, we defined the temperature niche relative to both sea surface temperature (SST) and the temperature 100 m below the mixed layer depth (Tmld+100). We show that the lifetime foraging niche incorporates highly diverse biotic and abiotic conditions: the blue shark tends to shift from mesotrophic and temperate surface waters during juvenile stages to more oligotrophic and warm surface waters for adults. However, low productivity limits all classes of blue shark habitat in the tropical western North Atlantic, and both low productivity and warm temperatures limit habitat in most of the equatorial Indian Ocean (except for the adult males) and tropical eastern Pacific. Large females tend to have greater habitat overlap with small juveniles than large males, more defined by temperature than productivity preferences. In particular, large juvenile females tend to extend their range into higher latitudes than large males, likely due to greater tolerance to relatively cold waters. Large juvenile and adult females also seem to avoid areas with intermediate SST (~21.7-24.0°C), resulting in separation from large males mostly in the tropical and temperate latitudes in the cold and warm seasons, respectively. The habitat requirements of sensitive size- and sex-specific stages to blue shark population dynamics are essential in management to improve conservation of this near-threatened species.

Global hotspots of shark interactions with industrial longline fisheries

“…For example, catch risk hotspots identified off the coast of Southwest Africa occur in a known potential blue shark nursery habitat off the coast of Namibia where a high catch density of immature sharks have been recorded by onboard observers (Coelho et al, 2018). Fishery-independent studies of juvenile blue sharks have also identified foraging habitats in the same area (Druon et al, 2022). Shortfin mako sharks (Endangered) share this risk hotspot with blue sharks in Southwest Africa (ICCAT jurisdiction), confirmed by onboard observer reports from Spanish longliners in the region (Dinkel and Sańchez-Lizaso, 2020).…”

Stepping up to genome scan allows stock differentiation in the worldwide distributed blue shark Prionace glauca

“…Shifts in blue shark reproductive seasons between the two hemispheres might have contributed to maintain that scission. In fact, while reproduction occurs in the summer (July, August) in the Northern Hemisphere (Fujinami et al, 2017), it is reported as more likely from December to July in the southwestern equatorial Atlantic Ocean (Coelho et al, 2017), and from October to December in the Indian Ocean (Druon et al, 2022).…”

Building use‐inspired species distribution models: Using multiple data types to examine and improve model performance

“…This species is also the target of a number of research efforts using electronic tags to study behavior and ecology across multiple ecosystems (e.g., Braun et al, 2019; Vandeperre et al, 2014). The relative abundance and widespread distribution of blue sharks results in a diverse set of occurrence data available for species distribution modeling (Druon et al, 2022), thus enabling the evaluation of the data types and the associated model development process.…”