Patterns of long-term climate variability and predation rates by a marine apex predator, the white shark Carcharodon carcharias

1. Apex predators are often assumed to be dietary generalists and, by feeding on prey from multiple basal nutrient sources, serve to couple discrete food webs. But there is increasing evidence that individual level dietary specialization may be common in many species, and this has not been investigated for many marine apex predators. 2. Because of their position at or near the top of many marine food webs, and the possibility that they can affect populations of their prey and induce trophic cascades, it is important to understand patterns of dietary specialization in shark populations. 3. Stable isotope values from body tissues with different turnover rates were used to quantify patterns of individual specialization in two species of 'generalist' sharks (bull sharks, Carcharhinus leucas, and tiger sharks, Galeocerdo cuvier). 4. Despite wide population-level isotopic niche breadths in both species, isotopic values of individual tiger sharks varied across tissues with different turnover rates. The population niche breadth was explained mostly by variation within individuals suggesting tiger sharks are true generalists. In contrast, isotope values of individual bull sharks were stable through time and their wide population level niche breadth was explained by variation among specialist individuals. 5. Relative resource abundance and spatial variation in food-predation risk tradeoffs may explain the differences in patterns of specialization between shark species. 6. The differences in individual dietary specialization between tiger sharks and bull sharks results in different functional roles in coupling or compartmentalizing distinct food webs. 7. Individual specialization may be an important feature of trophic dynamics of highly mobile marine top predators and should be explicitly considered in studies of marine food webs and the ecological role of top predators.

Marine predators are vital to the healthy functioning of coastal ecosystems, but to understand their roles, it is necessary to elucidate their movement ecology, particularly in relation to one another. A decade's worth of acoustic telemetry data (2011-2020) from Algoa Bay, South Africa, was investigated to determine how two mesopredatory species (teleosts: dusky kob Argyrosomus japonicus, n = 11, and leervis Lichia amia, n = 16) and two top predatory species (sharks: ragged-tooth sharks Carcharias taurus, n = 45, and white sharks Carcharodon carcharias, n = 31) used and shared this bay ecosystem. Multi-annual seasonal fidelity to the bay was exhibited by all species, but differences in residency were observed among species. Similarly, species used space in the bay differently-the teleosts moved less and had movements restricted to the central and western inshore regions of the bay. Conversely, the sharks roamed more, but detections were concentrated in the western part of the bay for C. taurus and in the eastern part of the bay for C. carcharias. Social network analysis showed that species segregated in space and time on a fine scale. However, there was some interaction observed between C. taurus, L. amia, and A. japonicus, but to varying degrees. This is likely because of strong habitat preferences exhibited by each species and predator-prey relationships between these predatory guilds. Results highlight that the sheltered marine Algoa Bay is a resource-rich environment, supporting multiple predators with different hunting strategies albeit similar prey preferences. Finally, these species are likely afforded some protection by the current Greater Addo Elephant National Park Marine Protected Area in the bay but are vulnerable to fishing pressure when they leave this ecosystem.

Climate variability has distinct spatial patterns with the strongest signal of sea surface temperature (SST) variance residing in the tropical Pacific. This interannual climate phenomenon, the El Niño-Southern Oscillation (ENSO), impacts weather patterns across the globe via atmospheric teleconnections. Pronounced SST variability, albeit of smaller amplitude, also exists in the other tropical basins as well as in the extratropical regions. To improve our physical understanding of internal climate variability across the global oceans, we here make the case for a conceptual model hierarchy that captures the essence of observed SST variability from subseasonal to decadal timescales. The building blocks consist of the classic stochastic climate model formulated by Klaus Hasselmann, a deterministic low-order model for ENSO variability, and the effect of the seasonal cycle on both of these models. This model hierarchy allows us to trace the impacts of seasonal processes on the statistics of observed and simulated climate variability. One of the important outcomes of ENSO’s interaction with the seasonal cycle is the generation of a frequency cascade leading to deterministic climate variability on a wide range of timescales, including the near-annual ENSO Combination Mode. Using the aforementioned building blocks, we arrive at a succinct conceptual model that delineates ENSO’s ubiquitous climate impacts and allows us to revisit ENSO’s observed statistical relationships with other coherent spatio-temporal patterns of climate variability—so called empirical modes of variability. We demonstrate the importance of correctly accounting for different seasonal phasing in the linear growth/damping rates of different climate phenomena, as well as the seasonal phasing of ENSO teleconnections and of atmospheric noise forcings. We discuss how previously some of ENSO’s relationships with other modes of variability have been misinterpreted due to non-intuitive seasonal cycle effects on both power spectra and lead/lag correlations. Furthermore, it is evident that ENSO’s impacts on climate variability outside the tropical Pacific are oftentimes larger than previously recognized and that accurately accounting for them has important implications. For instance, it has been shown that improved seasonal prediction skill can be achieved in the Indian Ocean by fully accounting for ENSO’s seasonally modulated and temporally integrated remote impacts. These results move us to refocus our attention to the tropical Pacific for understanding global patterns of climate variability and their predictability.

Recent advances in our understanding of the spatial behavior of white sharks have been based on only 3 geographical areas: the waters off Australia, southern Africa, and the northeast Pacific Ocean. Here we report results from the first study in New Zealand waters using satellite tags to study sharks. We attached pop-up archival tags to 4 white sharks Carcharodon carcharias at the Chatham Islands, New Zealand, during April 2005. One tag released prematurely, but 3 others showed long-distance northward movements of 1000 to 3000 km across the open ocean, with 2 sharks moving to the tropical islands of New Caledonia and Vanuatu. Our results are similar to recent find- ings elsewhere of fast oceanic travel and well oriented navigation. Circumstantial information sug- gests that some of these movements could be part of a regular foraging migration where white sharks visit humpback whale wintering grounds to feed on carcasses and prey on newborn calves. Before embarking on large-scale movements, all sharks remained over the continental shelf near the Chatham Islands for 2.6 to 5.0 mo, rarely swimming deeper than 100 m. In contrast, during oceanic large-scale movements, they spent most of their time in the top 1 m of water, showing periodic dives to depths over 900 m. The diving behavior in combination with the large-scale movements from tem- perate to tropical waters results in the sharks experiencing a very wide range of water temperatures.

Even though the risk of a negative encounter with a large and potentially dangerous shark species (e.g. white sharks—Carcharodon carcharias) is exceedingly rare, some localities implement indiscriminate shark culls to minimize this risk. Due to the negative ecological impact that these lethal shark control measures can have, the present study aimed to test a novel and eco‐friendly shark barrier system, known as the Shark Exclusion Barrier. The Shark Exclusion Barrier is a shark deterrent technology that is composed of a combination of interconnected and telescoping vertical barrier elements (i.e. the visual stimulus) and electromagnetic stimuli (e.g. electromagnets and Barium Ferrite (BaFe12O19) permanent magnets). Using this system, two separate C. carcharias swim pattern manipulation studies were conducted over the course of two research seasons. In the first season (i.e. 2021), 9, 1‐h trials were conducted where 9–13 different C. carcharias interacted with the barrier. In the second season (i.e. 2023), 35, 2‐h trials were conducted where 6–10 C. carcharias interacted with the barrier. Throughout experimentation, C. carcharias exhibited a significantly greater entrance frequency (p < 0.05) and a significantly reduced pass around frequency (p < 0.05) towards the control region when compared to the Shark Exclusion Barrier region. Furthermore, the barrier exhibited the ability to maintain its structural integrity during swells of ≥2.13 m, breaking waves of ≥1.52 m and a current of ≥1.12 m/s. Due to the promising results, this technology warrants further investigation to determine if it is a plausible alternative to lethal culling measures.

A general northward shift in marine species distributions has been observed in the western North Atlantic Ocean, which may have significant ecological consequences. Large coastal sharks can have wide migratory distributions but show fidelity to specific nursery habitats. Here we show evidence for nursery range expansion into Pamlico Sound, North Carolina by a marine apex predator, the Bull Shark (Carcharhinus leucas). Previous assessments have shown little to no use of estuarine North Carolina waters as nursery habitat by Bull Sharks from 1965–2011. Juvenile sharks were rarely captured in a fishery-independent gillnet survey conducted by the North Carolina Division of Marine Fisheries (NCDMF) from 2003–2011, but were present every year from 2011–2016. Juvenile Bull Shark presence in the Sound was strongly related to early summer temperatures and late summer salinities, which have increased in the estuary over the 13 survey years, and further evidence for increasing water temperatures in Pamlico Sound was found in a 45-year data set for the NCDMF estuarine trawl survey. These results suggest that increasing water temperature and salinity have allowed Bull Sharks to expand their nursery habitat. This shift will have unknown, but potentially strong, impacts on both the local ecosystem and interactions with humans.

The rapid pace of environmental change in the Anthropocene necessitates the development of a new suite of tools for measuring ecosystem dynamics. Sentinel species can provide insight into ecosystem function, identify hidden risks to human health, and predict future change. As sentinels, marine apex (top) predators offer a unique perspective into ocean processes, given that they can move across ocean basins and amplify trophic information across multiple spatiotemporal scales. Because use of the terms “ecosystem sentinel” and “climate sentinel” has proliferated in the scientific literature, there is a need to identify the properties that make marine predators effective sentinels. We provide a clear definition of the term “sentinel”, review the attributes of species identified as sentinels, and describe how a suite of such sentinels could strengthen our understanding and management of marine ecosystems. We contend that the use of marine predators as ecosystem sentinels will enable rapid response and adaptation to ecosystem variability and change.

Holocene climate variability in Europe: Evidence from δ 18O, textural and extension-rate variations in three speleothems

The magnitude and timing of spring snowmelt floods reflects seasonal snow accumulation and spring temperature patterns. Consequently, interannual variations in regions such as the intermountain West, with snowmelt annual maximum floods, may be related to low‐frequency variations in winter/spring large‐scale climate variability. Changes in the seasonality of basin precipitation and temperature consequent to slow changes in the baseline climate state (e.g., owing to natural climate variations and/or potential global warming trends) may have significant impacts on such floods. A case study of the Blacksmith Fork River in northern Utah that explores such a hypothesis is presented here. Trends and associations in the magnitude and timing of annual maximum floods are documented, their impact on time‐varying estimates of the 100 year flood is assessed, and relationships with known large‐scale, quasi‐oscillatory patterns of climate variability are explored. Evidence for structured low‐frequency variation in flood timing and magnitude and its relation to winter/spring precipitation and temperature and to tropical (El Niño– Southern Oscillation) and extratropical (Pacific Decadal Oscillation) Pacific climate precursors is presented. Mechanisms for these ocean‐atmosphere teleconnections to basin precipitation, temperature, and flood potential are discussed.

The order Lamniformes contains charismatic species such as the white shark Carcharodon carcharias and extinct megatooth shark Otodus megalodon, and is of particular interest given their influence on marine ecosystems, and because some members exhibit regional endothermy. However, there remains significant debate surrounding the prevalence and evolutionary origin of regional endothermy in the order, and therefore the development of phenomena such as gigantism and filter-feeding in sharks generally. Here we show a basal lamniform shark, the smalltooth sand tiger shark Odontaspis ferox, has centralized skeletal red muscle and a thick compact-walled ventricle; anatomical features generally consistent with regionally endothermy. This result, together with the recent discovery of probable red muscle endothermy in filter feeding basking sharks Cetorhinus maximus, suggests that this thermophysiology is more prevalent in the Lamniformes than previously thought, which in turn has implications for understanding the evolution of regional endothermy, gigantism, and extinction risk of warm-bodied shark species both past and present.

The Acoustic Tracking Array Platform (ATAP) is a marine science programme that monitors the movements and migrations of inshore marine animals along the South African coastline. Acoustically tagged animals are monitored by an expanded network of approximately 100 automated data-logging acoustic receivers moored at strategic node sites, from Cape Point in the west to the South Africa–Mozambique border in the east. During five years since its inception, in 2011, the ATAP has achieved outstanding progress in terms of the numbers of animals and the variety of species tagged. To date, the ATAP has yielded over 2.6 million detections from more than 700 acoustically tagged animals, representing 27 different species from 20 families, including the African penguin Spheniscus demersus, fishery-at-risk species (e.g. dusky kob Argyrosomus japonicus) and iconic elasmobranchs (e.g. white shark Carcharodon carcharias). Following a period of considerable equipment loss in 2014, refinement of the receiver network was required and the deeper receivers at each site were decommissioned without influencing the integrity of the nationwide array. The platform, managed by the South African Institute for Aquatic Biodiversity, ultimately represents a low-cost method of collecting long-term data that currently benefits approximately 25 researchers from 14 organisations. Case studies are presented to expose the opportunities provided by the ATAP, which will undoubtedly yield new discoveries and provide a greater understanding of the movement patterns and migrations of a wide variety of inshore marine and estuary-associated species.

Examination of the uterus of a dead female white shark (Carcharodon carcharias), which contained the earliest known white shark embryos, revealed that the uterine wall produces lipid-rich secretion (histotroph or "uterine milk") for embryonic nutrition. Uterine tissue was processed for light and electron microscopy, and immunohistochemical techniques to identify its secretory mechanism. Our results indicate that the white shark uterus secretes lipids via holocrine secretion. This type of secretion is characterized by the release of large lipid droplets accumulated in the epithelial cells into the uterine lumen through cell disintegration. The secretory epithelium of the uterus is stratified, and new surface epithelial cells are continuously supplied from deeper epithelial layers to replace the dead secretory cells at the surface. This vertical replacement possibly facilitates the active renewal of the surface epithelium, which is necessary for maintaining holocrine secretory mechanisms. These secretory mechanisms are different from those of myliobatiform stingrays, another elasmobranch taxon that exhibits lipid histotrophy. This may reflect the different origins of lipid histotrophy between these taxa.

1. There has been considerable debate over the past decade with respect to wildlife provisioning, especially resultant behavioural changes that may impact the ecological function of an apex predator. The controversy is exemplified by the shark diving industry, where major criticisms based on inference, anecdote and opinion stem from concerns of potential behaviourally mediated ecosystem effects because of ecotourism provisioning (aka‘chumming’ or feeding). 2. There is a general lack of empirical evidence to refute or support associated claims. The few studies that have investigated the behavioural impacts of shark provisioning ecotourism have generated conflicting conclusions, where the confidence in such results may suffer from a narrow spatial and temporal focus given the highly mobile nature of these predators. There is need for studies that examine the potential behavioural consequences of provisioning over ecologically relevant spatial and temporal scales. 3. To advance this debate, we conducted the first satellite telemetry study and movement analysis to explicitly examine the long-range migrations and habitat utilization of tiger sharks (Galeocerdo cuvier) originating in the Bahamas and Florida, two areas that differ significantly with regards to the presence/absence of provisioning ecotourism. 4. Satellite telemetry data rejected the behaviourally mediated effects of provisioning ecotourism at large spatial and temporal scales. In contrast, to the restricted activity space and movement that were hypothesized, geolocation data evidenced previously unknown long-distance migrations and habitat use for both tiger shark populations closely associated with areas of high biological productivity in the Gulf Stream and subtropical western Atlantic Ocean. We speculate that these areas are likely critically important for G. cuvier feeding forays and parturition. 5. We concluded that, in the light of potential conservation and public awareness benefits of ecotourism provisioning, this practice should not be dismissed out of hand by managers. Given the pressing need for improved understanding of the functional ecology of apex predators relative to human disturbance, empirical studies of different species sensitivities to disturbance should be used to guide best-practice ecotourism policies that maximize conservation goals.

This study assesses the trend and patterns of climate variability on the Hadejia-Nguru Wetland. The major sources of the climatic data were collected from Nguru Meteorological station and Ministry of Agriculture in Nguru, Yobe State. The climatic data include Maximum and Minimum temperature and rainfall for the period of 42 years (1970-2011) was collected. Time series analysis using linear trend model was used to analyze the data. The climatic results revealed changes in the climatic parameters especially in rainfall and maximum and minimum temperatures. It revealed that there was a little per unit increase in the mean annual maximum temperature which increased by 2.40⁰C when the time is at origin (initial time), and the mean of mean annual maximum temperature was 34.3⁰C. It also shows the per unit increase in the mean minimum temperature which increased by 4.33⁰C when the time is at origin (initial time), the mean annual minimum temperature was 19.4⁰C. Furthermore, it indicated that the per unit increase in years of the mean annual rainfall increased by 1.00mm, when the time is at origin, the mean of mean of annual rainfall was 32.8mm. As a result of decline in rainfall with continued increase in population, there has been more pressure exerted on the wetland resources. The implication of the climatic variation had greatly impacted on the environmental conditions of the region. This study therefore recommends the Management of the Hadejia Jama’are Komadugu Yobe Basin Trust Fund to put in place empowerment strategies for mitigating the current pressure exerted on the wetlands for sustainable livelihood.

Killer whales (Orcinus orca (Linnaeus, 1758); KWs) are apex marine predators. In Antarctica, they have diverse trophic interactions and belong to five known ecotypes that have substantial differences in morphology, ecology, and acoustic repertoire. Around the Antarctic Peninsula, two distinct sympatric forms of Type B KWs are the most common. Both ecotypes have similar pigmentation patterns, but the larger form has been observed to feed mainly on seals (B1), and a smaller form feed on Pygoscelis penguins (B2). The waters of the West Antarctic Peninsula are experiencing marine ecosystem transformations caused by climate change at one of the fastest rates on Earth. Little is known about the austral winter distribution and ecology of KWs in this changing environment. The purpose of the present study was to reveal the winter distribution and ecology patterns of KWs in the waters of the Wilhelm Archipelago. Boat-based visual and photo-identification observations were performed. The boat cruises were conducted within 14 nautical miles of the Ukrainian Akademik Vernadsky Research Station, Galindez Island. In 2019, 10 surveys of a total of 194 nm were conducted: 4 trips in June and 6 in July. In 2021, 37 surveys of a total of 605 nm were conducted: 12 trips in June, 14 in July, and 11 in August. Surveys were performed when the ice conditions were suitable. During both winters, we managed to record only three groups of KWs. A group of 7 KWs was encountered on 27 June 2019 near Hovgaard and Pleneau islands. The group consisted of adults of both sexes and juvenile individuals. In the same area, on 13 July 2021, another group of KWs was observed, consisting of at least 5 individuals (up to 7). This group included 1 adult male, 2 adult females, a calf, and a juvenile of unknown sex. A comparison of the photos showed different individuals in the two groups. According to the external morphology patterns, it was determined that both groups belong to Type B, most likely of a smaller form (B1). Large gatherings of Pygoscelis penguins were observed in this area during the winter in both years. On 22 July 2021, a group of KWs consisting of 2 adult males was observed in the Penola Strait. Detailed observations of their joint feeding on a crabeater seal (Lobodon carcinophaga Hombron & Jacquinot, 1842) were collected. According to external morphology patterns and behaviour, they belong to a large form of Type B ecotype (B2). As Antarctic krill (Euphausia superba Dana, 1850) move inshore during winter, the Pygoscelis penguins and crabeater seals likely took advantage of ice-free areas to feed on it, and their gatherings could attract KWs of both Type B ecotypes. Future work should include collecting photogrammetry data, skin biopsy samples, feeding behaviour observations, and acoustic recordings to clearly differentiate between KW ecotypes and better understand their winter distribution and ecological patterns in this rapidly changing marine ecosystem.