Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

A novel method for determining post-release mortality, behavior, and recovery period using acceleration data loggers

Recent declines in global fish stocks have raised questions regarding the sustainability of both extractive and catch-and-release fishing activities, and prompted efforts to quantify the total impact of fishing pressure. While at-vessel mortality rates are relatively easy to obtain, accurately assessing post-release mortality and sub-lethal behavioral effects has proven difficult. Acceleration data loggers (ADLs) represent a useful tool in post-release studies, but have yet to be fully utilized. The goal of this paper is to demonstrate the utility of ADLs in identifying mortality events, and to provide an example of recovery period quantification methods using acceleration-based swimming metrics. To illustrate the application of this method, we use sample data from blacktip sharks (Carcharhinus limbatus) captured and released in the Florida recreational shark fishery. Mortality events were inferred from stationary depth traces and the eventual cessation of all tailbeat activity, while posture information confirmed that the tag was still attached to the animal. We also detail how ADL data from surviving individuals were used to calculate 58 metrics of fine-scale swimming behavior. Using nonlinear mixed modeling, we found 19 of these metrics displayed a significant logistic relationship with time post-release, indicative of a recovery period. Calculated recovery periods ranged from 5.1 to 19.5 h, with a mean of 10.54 ± 3.78 h. The low cost of ADLs and their capacity for multiple deployments allows for relatively large sample sizes at a fraction of the cost of satellite tag studies. ADLs provide definitive evidence of post-release mortality, and also allow for the quantification of sub-lethal effects which can be used to measure the impact of different gear types or handling methods, even in species for which mortality events are rare

Body temperature of the Atlantic bluefin tuna (Thunnun thynnus L.) in the Western Mediterranean

This study documents body temperature in the Atlantic bluefin tuna (Thunnus thynnus L.) in the Mediterranean Sea and temperature variability caused by the stress of capture. The investigation was carried out in the traditional trap (tonnara) of Isola Piana (Sardinia, W Mediterranean) where body temperature recordings were conducted on free-swimming bluefin confined in the system of nets known as “camere” or chambers. We tracked the body temperature of two bluefin tuna (214 and 191 cm CFL) using a commercial data logger (HOBO U12, Onset Computer Corporation), under two conditions: the pre-fishing phase, when specimens confined in the “camera di ponente” are undisturbed and the fishing phase when bluefin tuna are trapped in the “camera della morte” and undergo the stress of confinement and capture (mattanza). Body temperature increased by about 2°C during the “mattanza”, whereas no temperature variation was exhibited during the pre-fishing phase. The heat transfer coefficient (K), calculated for both bluefin tuna during the “mattanza”, revealed a rapid increase in heat transfer. Additional data on ambient temperature Ta, white muscle Tw (n = 65; 110–287 cm CFL) and red muscle temperature Tr, (n = 249; 107–287 cm CFL) were obtained from live fish during angling operations, and excess body temperature (Tx = Tr–Ta) was calculated. Mean red muscle temperature was 27.6 ± 1.48°C in an ambient temperature of 18.9 ± 0.84°C. The excess red muscle temperature Tx was 8.21–9.10°C, and the red muscle was 2.4 ± 1.78°C warmer than white muscle

Global collision-risk hotspots of marine traffic and the world’s largest fish, the whale shark

Marine traffic is increasing globally yet collisions with endangered megafauna such as whales, sea turtles, and planktivorous sharks go largely undetected or unreported. Collisions leading to mortality can have population-level consequences for endangered species. Hence, identifying simultaneous space use of megafauna and shipping throughout ranges may reveal as-yet-unknown spatial targets requiring conservation. However, global studies tracking megafauna and shipping occurrences are lacking. Here we combine satellite-tracked movements of the whale shark, Rhincodon typus, and vessel activity to show that 92% of sharks’ horizontal space use and nearly 50% of vertical space use overlap with persistent large vessel (>300 gross tons) traffic. Collision-risk estimates correlated with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. Hotspots of potential collision risk were evident in all major oceans, predominantly from overlap with cargo and tanker vessels, and were concentrated in gulf regions, where dense traffic co-occurred with seasonal shark movements. Nearly a third of whale shark hotspots overlapped with the highest collision-risk areas, with the last known locations of tracked sharks coinciding with busier shipping routes more often than expected. Depth-recording tags provided evidence for sinking, likely dead, whale sharks, suggesting substantial “cryptic” lethal ship strikes are possible, which could explain why whale shark population declines continue despite international protection and low fishing-induced mortality. Mitigation measures to reduce ship-strike risk should be considered to conserve this species and other ocean giants that are likely experiencing similar impacts from growing global vessel traffic

Global spatial risk assessment of sharks under the footprint of fisheries

Brucellosis is a highly contagious zoonosis affecting humans and a wide range of domesticated and wild animal species. An important element for effective disease containment is to improve knowledge, attitudes and practices (KAP) of afflicted communities. This study aimed to assess the KAP related to brucellosis at the human–animal interface in an endemic area of Egypt and to identify the risk factors for human infection. A matched case–control study was conducted at the central fever hospitals located in six governorates in northern Egypt. Face‐to‐face interviews with cases and controls were conducted using a structured questionnaire. In total, 40.7% of the participants owned farm animals in their households. The overall mean practice score regarding animal husbandry, processing and consumption of milk and dairy products were significantly lower among cases compared with controls (−12.7 ± 18.1 vs. 0.68 ± 14.2, respectively; p < .001). Perceived barriers for notification of animal infection/abortion were predominate among cases and positively correlated with participants’ education. The predictors of having brucellosis infection were consumption of unpasteurized milk or raw dairy products and practicing animal husbandry. Applying protective measures against infection significantly reduced its risk. A model predicting risk factors for brucellosis among those who own animal showed that frequent abortions per animal increased the chance for brucellosis infection among human cases by 50‐fold (95% CI: 8.8–276.9), whereas the use of protective measures in animal care reduced the odds (OR = 0.11 [95% CI: 0.03–0.45]). In conclusion, consumption of unprocessed dairy products was equally important as contact with infected/aborted animals as major risk factors for Brucella spp. infection among humans in Egypt. There is poor knowledge, negative attitudes and risky behaviours among villagers which can perpetuate the risk of brucellosis transmission at the human–animal interface. This supports the need for integrating health education into the national brucellosis control programme