South Africa was the first country to protect white sharks Carcharodon carcharias—an important decision taken despite limited data on population status, but guided by a precautionary approach in recognition of the species’ ecological and economic value. Unfortunately, several lines of evidence suggest an ongoing population reduction, including declines in sightings from aggregation sites in the last decade (especially of large mature individuals), low genetic diversity, and low effective population size. Simulation modelling indicated that current levels of white shark removals by South Africa’s lethal shark control program are alone unsustainable and sufficient to drive population decline. This has led to growing calls for further conservation actions. Nevertheless, a recent study has claimed that this population has remained stable since 1991 and likely redistributed eastward due to the predatory effects of orcas. On this basis, no additional conservation management action has yet been taken. Here, we synthesize several lines of historical and newly acquired information to argue that this white shark population is more likely in decline. While predator-prey dynamics are natural phenomena, anthropogenic threats (i.e. the lethal shark control program and demersal shark fishery) are subject to management. We recognize that management must balance public safety, community livelihoods, and conservation goals. However, consistent with the country’s history of applying a precautionary approach and its commitments to existing national and international frameworks, we urge the South African government to reduce anthropogenic sources of white shark mortality, to conserve this population and its attendant ecosystem services that South Africans depend upon.

Graphical AbstractThis study provides empirical evidence of a trophic cascade following the loss of white sharks (Carcharodon carcharias) from False Bay, South Africa. Arrow thickness represents the relative strength of top-down predation effects (thicker arrows indicate stronger effects, thinner arrows indicate weaker effects). Left Panel: Historically, white sharks occupied the apex of the food web, preying on Cape fur seals (Arctocephalus pusillus pusillus) and both competing with and feeding on sevengill sharks (Notorynchus cepedianus). Seals primarily preyed on schooling fishes, while sevengill sharks primarily preyed on benthic sharks. Right Panel: Following the decline and eventual disappearance of white sharks from False Bay, both seals and sevengill sharks have increased in relative abundance, coinciding with declines in small fish that seals feed on and smaller sharks that sevengills prey upon. Illustration by Kelly Quinn / Canvas of the Wild.

Bowlby et al. (2023) assessed spatio-temporal trends in South Africa’s white shark (Carcharodon carcharias) population using a range of different proxies of white shark occurrence. The authors concluded that, despite significant declines in white shark sightings in several historical aggregation sites, the population as a whole has remained relatively stable throughout South Africa since its protection in 1991. The study also suggests a population redistribution eastward, likely driven by natural predator–prey dynamics (i.e., predation and related risk from orcas, Orcinus orca). Here, we highlight several issues with the methods and the inferences made in that study and argue that the data, as currently analysed and interpreted, cannot support population stability, or redistribution, of South Africa’s white sharks. We also point out that the onset of the decline of white sharks at historical aggregation sites began before the documented appearance of specialist shark-eating orcas (the main alleged cause of the decline put forward in Bowlby et al. 2023). Our concern is that unsupported claims of population stability could jeopardize conservation actions urgently needed for white sharks, if the declines documented at their historical aggregations are representative of the population trend. Below we summarize our arguments.

The spotted gully shark Triakis megalopterus (Triakidae) is a mesopredatory species endemic to southern Africa. It is currently listed as Least Concern on the IUCN Red List in accordance with an estimated increase in population size, general release by recreational linefishers and incidental catches in the commercial linefisheries. Previous research suggests this species to be resident, and as such it is likely to receive protection in coastal marine protected areas (MPAs). However, its ecology and movement behaviour remain poorly studied. This study employed acoustic telemetry to provide information on the species' movements along the coast of the Western Cape Province, South Africa. We used network analyses to investigate movement randomness, associations between individuals, sexual segregation, and the effectiveness of MPAs. Our findings reveal nonrandom movements as well as patterns of co-occurrence between individuals. Spatial network analysis suggested sexual segregation, because areas of high use (Walker Bay and De Hoop) differed between males and females. Co-occurrences were observed exclusively in Walker Bay, chiefly between males, with no co-occurrence found between females. The tagged spotted gully sharks were not detected extensively within existing MPA boundaries, though there was no significant difference between their movements inside and outside protected areas for both sexes.

The coastal waters of South Africa are habitat to a diverse composition of sharks that are vulnerable to exploitation, many of which are endemic and/or classified by the International Union for Conservation of Nature (IUCN) Red List as Threatened or Data Deficient. Accordingly, this region has been identified as a global research and conservation priority for elasmobranchs. The De Hoop Marine Protected Area (MPA), in the Western Cape Province of South Africa, provides 288 km 2 of no-take protection within its boundaries. However, the region experiences heavy commercial fishing, with two vessels actively operating as dedicated shark longliners (as of 2022). When crossing MPA boundaries, sharks are susceptible to capture by these vessels. Utilizing passive acoustic telemetry, the present study evaluated the movements of a threatened juvenile shark species, the smooth hammerhead ( Sphyrna zygaena ), both inside and adjacent to the De Hoop MPA, and along the greater coastline. Movement data from 20 tagged sharks were used to explore the effects of spatial, environmental, and management variables on their residency and movement patterns. Results indicate a high reliance of sharks on unprotected waters immediately adjacent to the MPA’s eastern boundary, an area of high biological productivity due to its proximity to the mouth of an estuary. Although some tagged sharks did move regionally along the South African coastline, individuals spent 95% of their days detected just outside the eastern boundary of the MPA, rendering them vulnerable to commercial shark longlining occurring there. These findings have conservation implications for smooth hammerhead sharks in South Africa and present an opportunity to revisit management practices that may optimize spatial protection for an important life stage of this threatened species.

The International Union for Conservation of Nature (IUCN) estimates that over a third of all chondrichthyan species (sharks, rays and chimaeras) are threatened with extinction, primarily by overfishing (as target or bycatch species). Owing to the wide-ranging distributions of many chondrichthyans, they are often overlooked in marine protected area (MPA) design. South Africa is a biodiversity hotspot for chondrichthyan species diversity, and to improve the conservation status of these species in the country's continental exclusive economic zone (EEZ), we collaborated widely to collate existing occurrence data. Ensemble models were developed for 87 species' distributions, which informed a systematic conservation planning analysis for 64 threatened and endemic species. We assessed the current representation of these species in South Africa's MPA network and identified priority areas for protection, avoiding fishing pressure where possible. Results show that many MPAs are well placed to protect chondrichthyans, especially along the east coast (KwaZulu-Natal province). Unfortunately, permissive fishing regulations within many MPA zones reduces their effectiveness at protecting chondrichthyans. Improved regulations designed to protect chondrichthyans within all MPAs should be considered a high priority. Priority areas for increased spatial protection were identified along the west coast continental shelf, the Agulhas Bank off the south coast, and south coast embayments. We found that supplementing the current MPA network by an additional 5 % of the EEZ would be sufficient to protect >30 % of the range of all 64 species, provided there is adequate enforcement. As South Africa prepares to expand its MPA estate to meet international targets, these findings can ensure that chondrichthyans are well represented.

Predators can impact prey via predation or risk effects, which can initiate trophic cascades. Given widespread population declines of apex predators, understanding and predicting the associated ecological consequences is a priority. When predation risk is relatively unpredictable or uncontrollable by prey, the loss of predators is hypothesized to release prey from stress; however, there are few tests of this hypothesis in the wild. A well-studied predator–prey system between white sharks (Carcharodon carcharias) and Cape fur seals (Arctocephalus pusillus pusillus) in False Bay, South Africa, has previously demonstrated elevated faecal glucocorticoid metabolite concentrations (fGCMs) in seals exposed to high levels of predation risk from white sharks. A recent decline and disappearance of white sharks from the system has coincided with a pronounced decrease in seal fGCM concentrations. Seals have concurrently been rafting further from shore and over deeper water, a behaviour that would have previously rendered them vulnerable to attack. These results show rapid physiological and behavioural responses by seals to release from predation stress. To our knowledge, this represents the first demonstration in the wild of physiological changes in prey from predator decline, and such responses are likely to increase given the scale and pace of apex predator declines globally.

Sharks are among the most threatened vertebrates on the planet. Marine protected areas (MPAs) have been widely established and promoted as a shark conservation tool. However, the geographic ranges of most imperiled shark species (endemic and threatened) fall outside the current global networks of MPAs, leaving the protective benefits of this tool questionable for the shark species of highest conservation concern. The Western Cape of South Africa is a hotspot for endemic and threatened shark species. Here, we examined the potential protective benefit of a no-take marine reserve (the De Hoop MPA) for imperiled shark species using baited remote underwater video stations (BRUVS). Eleven shark species were documented, with six of 11 species (55%) classified as threatened with extinction by the International Union for the Conservation of Nature. The composition of the shark assemblage was dominated by small to mid-sized species, including small endemics. Species-specific habitat preferences were identified, with all these habitats represented in the MPA. Frequency of occurrence and relative abundance of sharks on BRUVS were significantly higher inside the De Hoop MPA than outside. Both protected and commercially exploited sharks species exhibited higher relative abundance inside the MPA. Relative abundance also increased inside the MPA with increasing distance from the reserve boundaries. Our findings suggest that no-take MPAs can be an effective tool for protecting shark species of conservation concern, including threatened endemics, particularly if the MPA adequately incorporates their preferred habitats.

Ectosymbionts, such as bacteria and parasites, are found on the surface of organisms throughout the world's ecosystems. Hosts have evolved a variety of mechanisms across ecosystems to rid themselves of ectoparasites or other skin irritants including chafing behavior, whereby an organism curves their body to rub the convex portion of their body along a rough surface (Eibl-Eibesfeldt 1955; Wicklund 1969; Myrberg & Gruber 1974; Wyman & Walters-Wyman 1985; Mooring et al. 2004; Papastamatiou et al. 2007; Grossman et al. 2009; Ritter 2011; Berth et al. 2017).

Despite global declines of apex predatory sharks, evidence for ecosystem consequences remains limited and debated. This is likely a result of both the logistical difficulties of measuring such processes in marine systems and also due to shifting baselines, whereby the ecosystem changes have occurred prior to monitoring. Between 2000–2018, we conducted standardized monitoring of white shark ( Carcharodon carcharias ) abundance patterns (N = 6,333 shark sightings) and predatory activity (N = 8,076 attacks on seals) at Seal Island, a Cape fur seal ( Arctocephalus pusillus pusillus ) colony in False Bay, South Africa. Over the 18-year study, declines in white shark abundance and attack rates were documented between 2015–2018, with anomalous lows occurring in 2017 and 2018. This included prolonged periods of complete white shark absence from Seal Island. The disappearance of white sharks from Seal Island coincided with the unprecedented appearance of sevengill sharks ( Notorynchus cepedianus ; N = 120 sightings), an otherwise allopatric kelp-associated apex predator in False Bay. We also recorded a sevengill shark attacking a live seal in the absence of white sharks. These data provide empirical evidence for behavioral shifts in an allopatric marine predator following the decline and disappearance of white sharks from a foraging site. This study demonstrates the importance of historical data and long-term monitoring for disentangling ecological consequences of apex predator declines.

Understanding potential responses of aquatic animals to climate variability is important, given the wide-ranging implications of current and future climatic change scenarios. Here, we used long-term data from natural predator-prey interactions between white sharks Carcharodon carcharias and Cape fur seals Arctocephalus pusillus pusillus in False Bay, South Africa, paired with environmental monitoring to examine potential relationships between temperature variability and shark predation rates on seals. Based on generalized linear modelling of a dataset of 941 shark attacks on seals collected over 15 years (1999-2013) during the austral winter (May-September) season, we found water temperature was included as a significant predictor of daily and monthly variability in predation rates. However, the signal of temporal variability over the season emerged as a more predominant predictor. Moreover, inter-annual variability in predation rate appeared linked to other environmental factors (wind, water visibility, and the occurrence of El Nino and La Nina events) rather than water temperature. These data suggest that water temperatures on an intra-annual scale might contribute to predation patterns in white sharks either directly or indirectly (e.g. due to associated changes in prey availability), but do not implicate water temperature as a primary driver in this scenario, or at an interannual scale. It is possible that (1) the metabolic demand of white sharks may be modulated against temperature variability by their partially endothermic nature, and (2) the predation patterns of white sharks on seals are the result of a complex interplay between ambient physical conditions and broader oceanographic, biological, and ecological factors.

Predators can impact ecosystems through consumptive or risk effects on prey. Physiologically, risk effects can be mediated by energetic mechanisms or stress responses. The predation-stress hypothesis predicts that risk induces stress in prey, which can affect survival and reproduction. However, empirical support for this hypothesis is both mixed and limited, and the conditions that cause predation risk to induce stress responses in some cases, but not others, remain unclear. Unusually clear-cut variation in exposure of Cape fur seals (Arctocephalus pusillus pusillus) to predation risk from white sharks (Carcharodon carcharias) in the waters of Southwestern Africa provides an opportunity to test the predation-stress hypothesis in the wild. Here, we measured fecal glucocorticoid concentrations (fGCM) from Cape fur seals at six discrete islands colonies exposed to spatiotemporal variation in predation risk from white sharks over a period of three years. We found highly elevated fGCM concentrations in seals at colonies exposed to high levels of unpredictable and relatively uncontrollable risk of shark attack, but not at colonies where seals were either not exposed to shark predation or could proactively mitigate their risk through antipredatory behavior. Differences in measured fGCM levels were consistent with patterns of risk at the site and seasonal level, for both seal adults and juveniles. Seal fGCM levels were not correlated with colony population size, density, and geographic location. Investigation at a high risk site (False Bay) also revealed strong correlations between fGCM levels and temporal variation in shark attack rates, but not with shark relative abundance. Our results suggest that predation risk will induce a stress response when risk cannot be predicted and/or proactively mitigated by behavioral responses.

Predator-prey relationships can be influenced by environmental conditions, including changes in moon phase and associated lunar illumination. Two primary hypotheses have been proposed underlying the effects of moonlight on predator-prey interactions: the predation risk hypothesis and visual acuity hypothesis. However, few studies have tested these hypotheses during twilight hours or involved large mobile aquatic species. In the present study, we evaluated these hypotheses using data collected over 16 years on predator-prey interactions between white shark (Carcharodon carcharias) and Cape fur seals (Arctocephalus pusillus pusillus) at sunrise. Data from 1476 natural predation events demonstrated shark attack frequency and seal capture success was significantly higher at sunrise during periods of low (0–10 %) versus high (90–100 %) lunar illumination, which is consistent with the visual acuity hypothesis. We propose that during full moon periods, white sharks at night are at a visual and tactical advantage over seals which are silhouetted at the surface in the moonlight and thus easier to isolate in darkness, while sharks remain camouflaged hunting from below through deep water. However, at sunrise, we hypothesize this advantage shifts to seals as the added lunar illumination, combined with emerging sunlight, may decrease shark stealth and increase the ability of seals to detect and avoid sharks. These finding suggest that lunar effects on predator-prey dynamics can be context specific, likely moderated by visual acuity of predators and prey which may change according to the photoperiod.

The top-down effects of predators on ecosystem structure and dynamics have been studied increasingly. However, the nature and consequence of trophic interactions between upper-trophic-level predators have received considerably less attention. This is especially the case in marine systems due to the inherent challenges of studying highly mobile marine species. Here we describe the first documentation of asymmetrical intraguild predation by a pinniped predator on a mid-sized predatory shark. The report is based on direct observations in South African waters, in which free-swimming blue sharks Prionace glauca were captured and partially consumed by Cape fur seals Arctocephalus pusillus pusillus. These observations are important not just for understanding the interactions between these two species but more broadly for their implications in understanding the trophic ecology of pinnipeds, many populations of which have increased while numerous shark populations have declined.

Scavenging, a result of a temporary pulse of resources, occurs in virtually all ecosystems containing carnivores, and is an important energy transfer pathway that can impact ecosystem structure and function, and this ecological significance has largely been considered from a terrestrial standpoint; however, little is known about the role of scavenging in shaping the behavioral ecology of marine species, specifically apex predators. Here we present findings from multiple opportunistic observations of white sharks scavenging on whale carcasses in False Bay, South Africa. Observations of white sharks scavenging over successive days provided evidence of strategic and selective scavenging by this species. Moreover, extended daily observations permitted recordings of unique social, aggregative, and feeding behaviors. We further compare these data against observations of natural predation by sharks on seals in the study area. We discuss these data in relation to environmental conditions, shark social interactions, migration patterns, whale biology, and behaviorally-mediated trophic cascades. While the appearance of a whale carcass is largely a stochastic event, we propose that white shark scavenging on whales may represent an underestimated, yet significant component to the overall foraging ecology of this species, especially as individuals attain sexual maturity.

Effects of environmental factors on frequency and success rate of 2,546 natural predatory attacks by white sharks, Carcharodon carcharias, on Cape fur seals, Arctocephalus pusillus pusillus, were studied over an 8-year period at Seal Island, South Africa. Attacks occurred primarily during winter months (June–August). Attack frequency increased significantly during northerly winds, during high tides, and within 400 m of the island, but predatory success rate decreased with proximity to the island. Attacks occurred over a depth range of 5–31 m, with significantly more occurring at depths of 26–30 m. Attack frequency and success rate increased significantly at low light levels. These results are compared with published effects of environmental factors on white shark predation frequency at the Farallon Islands, California, and discussed in terms of the Predation Cycle. Suggestions for future work at this site are offered.

between 1997 and 2003, there were 2088 natural predations by white sharks (carcharodon carcharias) on cape fur seals (arctocephalus pusillus pusillus) and 121 strikes on towed seal-shaped decoys were documented from observation vessels at seal island, south africa. white sharks at seal island appear to selectively target lone, incoming young of the year cape fur seals at or near the surface. most attacks lasted <1 min and consisted of a single breach, with predatory success rate decreasing rapidly with increasing duration and number of subsequent breaches. a white shark predatory ethogram, composed of four phases and 20 behavioural units, is presented, including four varieties of initial strike and 11 subsequent behaviour units not previously defined in the literature. behaviour units scored from 210 predatory attacks revealed that, for both successful and unsuccessful attacks, polaris breach was the most commonly employed initial strike, while surface lunge was the most frequent second event, closely followed by lateral snap. examination of video footage, still images, and tooth impressions in decoys indicated that white sharks at seal island bite prey obliquely using their anterolateral teeth via a sudden lateral snap of the jaws and not perpendicularly with their anterior teeth, as previously supposed. analysis of white shark upper tooth morphology and spacing suggest the reversed intermediate teeth of white sharks occur at the strongest part of the jaw and produce the largest wound. white shark predatory success at seal island is greatest (55%) within one hour of sunrise and decreases rapidly with increasing ambient light; the sharks cease active predation on seals when success rate drops to ±40%; this is the first evidence of cessation of foraging at unproductive times by any predatory fish. at seal island, white shark predatory success is significantly lower at locations where frequency of predation is highest, suggesting that white sharks may launch suboptimal strikes in areas of greatest intraspecific competition; this is the first evidence of social influence on predation in any elasmobranch. idiosyncratic predatory behaviours and elevated success rates of known individual white sharks at seal island suggest some degree of trial-and-error learning. a hypothetical decision tree is proposed that models predatory behaviour of white sharks attacking cape fur seals at the surface.

This paper reports the first record of Carcharhinus galapagensisl/Ig in the Mozambique Channel from 54 individual sightings and describes their association with the oceanic atoll, Bassas da India. The geographic distribution of C. galapagensisl/Ig is updated and the importance of the atoll to this species as a nursery area within the Mozambique Channel is discussed.