Effective ocean management and conservation of highly migratory species depends onresolving overlap between animal movements and distributions, and fishing effort.However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort.We conclude that pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions (the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real-time, dynamic management.Industrialised fishing is a major source of mortality for large marine animals (marine megafauna) 1-6 . Humans have hunted megafauna in the open ocean for at least 42,000 years 7 , but international fishing fleets targeting large, epipelagic fishes did not spread into the high seas (areas beyond national jurisdiction) until the 1950s 8 . Prior to this, the high seas constituted a spatial refuge largely free from exploitation as fishing pressure was concentrated on continental shelves 3,8 . Pelagic sharks are among the widest ranging vertebrates, with some species exhibiting annual ocean-basin-scale migrations 9 , long term trans-ocean movements 10 , and/or fine-scale site fidelity to preferred shelf and open ocean areas 5,9,11 . These behaviours could cause extensive spatial overlap with different fisheries from coastal areas to the deep ocean. On average, large pelagic sharks account for 52% of all identified shark catch worldwide in target fisheries or as bycatch 12 . Regional declines in abundance of pelagic sharks have been reported 13,14 , but it is unclear whether exposure to high fishing effort extends across ocean-wide population ranges and overlaps areas in the high seas where sharks are most abundant 5,13 .Conservation of pelagic sharkswhich currently have limited high seas management 12,15,16would benefit greatly from a clearer understanding of the spatial relationships between sharks' habitats and active fishing zones. However, obtaining unbiased estimates of shark and fisher distributions is complicated by the fact that most data on pelagic sharks come from catch records and other fishery-dependent sources 4,15,16 .Here, we provide the first global estimate of the extent of space use overlap of sharks with industrial fisheries. This is based on the analysis of the movements of pelagic sharks tagged with satellite transmitters in the Atlantic, Indian and Pacific oceans, together with fishing vessel movements m...

Understanding how aquatic species respond to extremes of DO and temperature is crucial for determining how they will be affected by climate change, which is predicted to increasingly expose them to levels beyond their optima. In this study we used novel animal-borne DO, temperature and depth sensors to determine the effect of extremes of DO and temperature on the vertical habitat use of Atlantic salmon Salmo salar in aquaculture cages. Salmon showed a preference for temperatures around 16.5 to 17.5 °C, however, selection of preferred temperatures was trumped by active avoidance of low DO (<35% saturation) at the bottom of the cage. In addition to low DO, salmon also avoided warm surface waters (>20.1 °C), which led to a considerable contraction in the available vertical habitat. Despite their avoidance behavior, fish spent a large amount of time in waters with suboptimal DO (<60% saturation). These results show that vertical habitat contraction could likely be a significant consequence of climate change if the reduction in DO outpaces the increase in hypoxia tolerance through local adaptation. They furthermore highlight that site-specific environmental conditions and stock-specific tolerance thresholds may need to be considered when determining stocking densities.

Protecting essential habitats through the implementation of area closures has been recognized as a useful management tool for rebuilding overfished populations and minimizing habitat degradation. School shark (Galeorhinus galeus) have suffered significant stock declines in Australia; however, recent stock assessments suggest the population may have stabilized and the protection of closed nursery areas has been identified as a key management strategy to rebuilding their numbers. Young-of-the-year (YOY) and juvenile G. galeus were acoustically tagged and monitored to determine ontogenetic differences in residency and seasonal use of an important protected nursery area (Shark Refuge Area or SRA) in southeastern Tasmania. Both YOY and juvenile G. galeus showed a distinct seasonal pattern of occurrence in the SRA with most departing the area during winter and only a small proportion of YOY (33%) and no juveniles returning the following spring, suggesting areas outside the SRA may also be important during these early life-history stages. While these behaviors confirm SRAs continue to function as essential habitat during G. galeus early life history, evidence of YOY and juveniles emigrating from these areas within their first 1–2 years and the fact that few YOY return suggest that these areas may only afford protection for a more limited amount of time than previously thought. Determining the importance of neighbouring coastal waters and maintaining the use of traditional fisheries management tools are therefore required to ensure effective conservation of G. galeus during early life history.

Southern bluefin tuna (SBT; Thunnus maccoyii) are a popular component of the recreational large pelagic game fishery in Australia. The fishery is managed using individual fisher catch limits. Fifty-nine pop-up archival transmitting (PAT) tags were attached to individual SBT to estimate postrelease survival (PRS) rates. Fish caught on lures configured with J-hooks (n = 44) and those caught on circle hooks (n = 8) had similar PRS rates and were combined to increase sample size, revealing a PRS estimate of 83.0% (95% CI: 75.9%–90.7%, n = 54). The PRS estimate of fish caught on lures with treble hooks was much lower, 60% (95% CI: 20%–100%, n = 5). By sampling blood from 233 fish, including 56 of the PAT-tagged individuals, we show that angling duration is related to an elevation of lactate, cortisol, and osmolarity in blood plasma, indicative of increased physiological stress. Physical damage related to hooking location, angling duration, biochemical indicators of physiological stress, and handling duration were not identified as significant factors leading to postrelease mortality. The results quantify a previously unaccounted source of mortality for SBT.

Changes to the global climate are driving alterations to boundary current-influenced marine ecosystems. The diet of a pelagic teleost, Arripis trutta, was examined in the East Australian Current (EAC)-dominated coastal waters of southeastern (SE) Australia. The diet of A. trutta was dominated by pelagic baitfish, primarily Australian sardine (Sardinops sagax) and scads (Trachurus spp.). Diet varied substantially with both latitude and season linked to variability in the distribution and abundance of key prey species. An ontogenetic diet shift occurred, with crustaceans and polychaetes making up a large proportion of the diet of small fish compared with the dominance of baitfish at larger sizes. The diet of A. trutta has undergone a dramatic shift from one dominated by krill (Nyctiphanes australis) historically to baitfish today. This change is consistent with a well-documented regime shift caused by the increasing intensity of the EAC on coastal SE Australian waters. Understanding the temporal dynamics of this ecosystem is crucial for management of coastal fisheries and also for understanding the impacts of climate change on boundary current-dominated marine ecosystems worldwide.