The diet of deep-water sharks Martin, Ulrich; Mallefet, Jérôme
Deep-sea research. Part I, Oceanographic research papers,
February 2023, 2023-02-00, Volume:
192
Journal Article
Peer reviewed
548 shark species were considered in this paper. They were classified in function of their depth of occurrence: 218 deep, 114 transitory and 210 shallow. The diets of the 332 deep and transitory ...species are reviewed. 10 prey categories are recognized here: Chondrichthyes, Teleosts, Cephalopods, Crustaceans, Marine mammals, Annelids, Ctenophores, Egg of Chondrichthyes, Siphonophores, and Bivalves. There is a complete lack of data for 210 species, and 59 have only a limited amount of information available. In general, teleosts, crustaceans, and cephalopods were the main prey found in deep-water sharks. However, some species have a specialized diet. A simple index of dietary knowledge has been developed to highlight the current state of knowledge on the subject, further illustrating the lack of information. The proportion of empty and regurgitated stomachs varies significantly between species and studies. Most data on deep and transitory sharks come from stomach content analysis. Stable isotope analysis provides additional insight into their trophic ecology. Fatty acid profiling and DNA metabarcoding can also add important information, but their use is currently limited with deep-water sharks. The most important conclusion from this synthesis is the lack or scarcity of information for most deep and transitory species.
Graphical abstract (COLOR): Representation of the main prey taxa of four different families. A: Squalidae, B: Centrophoridae, C: Etmopteridae, D: Hexanchidae. The size of the prey taxa indicates its relative importance thourough the different studies reviewed. Display omitted
•We reviewed the diet of deep-water and transitory shark species.•The species are classified in function of depth: 218 deep-water, 114 transitory, and 210 shallow.•In general, teleosts, crustaceans, and cephalopods were the main prey found in deep-water sharks.•A diet knowledge index is proposed, with most species lacking data on the diet with a score of 0.•Stable isotope analysis is more and more used, but fatty acid profiling and DNA metabarcoding are also interesting.
Top carnivores have suffered widespread global declines, with well-documented effects on mesopredators and herbivores. We know less about how carnivores affect ecosystems through scavenging. ...Tasmania’s top carnivore, the Tasmanian devil (Sarcophilus harrisii), has suffered severe disease-induced population declines, providing a natural experiment on the role of scavenging in structuring communities. Using remote cameras and experimentally placed carcasses, we show that mesopredators consume more carrion in areas where devils have declined. Carcass consumption by the two native mesopredators was best predicted by competition for carrion, whereas consumption by the invasive mesopredator, the feral cat (Felis catus), was better predicted by the landscape-level abundance of devils, suggesting a relaxed landscape of fear where devils are suppressed. Reduced discovery of carcasses by devils was balanced by the increased discovery by mesopredators. Nonetheless, carcasses persisted approximately 2.6-fold longer where devils have declined, highlighting their importance for rapid carrion removal. The major beneficiary of increased carrion availability was the forest raven (Corvus tasmanicus). Population trends of ravens increased 2.2-fold from 1998 to 2017, the period of devil decline, but this increase occurred Tasmania-wide, making the cause unclear. This case study provides a little-studied potential mechanism for mesopredator release, with broad relevance to the vast areas of the world that have suffered carnivore declines.
Abstract
Understanding the trophic interactions and the position of species within a foodweb is crucial if we want to understand the dynamics of marine communities and the impact individual ...components of the community have on trophic network compartments. Recent studies have indicated sharks and rays are important elements within foodwebs. In this study, we evaluated the ecological importance of sharks and rays in a subtropical ecosystem off the coast of southern Brazil by using topological analyses. We tested the hypotheses that some elasmobranchs can be considered key elements within the foodweb, and that large predators have topological importance (act as keystones), so that, when large predators are excluded, mesopredator elasmobranchs occupy higher topological positions. Our results indicate that Galeocerdo cuvier, Carcharhinus obscurus, Carcharias taurus, Sphyrna lewini and S. zygaena are species with large ecological function values and may exert a powerful influence over lower levels. These issues need to be considered by conservation and fishery management groups since it appears that ecosystem integrity may be compromised by reductions in the populations of large predators. Carcharhinus obscurus, S. zygaena and Zapteryx brevirostris were found to be the elasmobranchs with largest values of centrality, and can, therefore, be considered key elements in the topological structure.
Apex predators perform important functions that regulate ecosystems worldwide. However, little is known about how ecosystem regulation by predators is influenced by human activities. In particular, ...how important are top-down effects of predators relative to direct and indirect human-mediated bottom-up and top-down processes? Combining data on species' occurrence from camera traps and hunting records, we aimed to quantify the relative effects of top-down and bottom-up processes in shaping predator and prey distributions in a human-dominated landscape in Transylvania, Romania. By global standards this system is diverse, including apex predators (brown bear and wolf), mesopredators (red fox) and large herbivores (roe and red deer). Humans and free-ranging dogs represent additional predators in the system. Using structural equation modelling, we found that apex predators suppress lower trophic levels, especially herbivores. However, direct and indirect top-down effects of humans affected the ecosystem more strongly, influencing species at all trophic levels. Our study highlights the need to explicitly embed humans and their influences within trophic cascade theory. This will greatly expand our understanding of species interactions in human-modified landscapes, which compose the majority of the Earth's terrestrial surface.
Central/West Africa is one of the most biodiverse regions on earth and one of the largest producers of cacao, producing about 68.4 % of the world's chocolate. Here, cacao pests and diseases can cause ...losses of $761 million annually. However, no studies from Africa have quantified the role of flying vertebrates as pest suppressors in cacao plantations. We used an exclusion experiment to prevent access of bats and birds to cacao trees for 12 months and quantified how their absence affected arthropod communities, herbivory, and cacao crop yield. Overall, important pests such as mealybugs and other hemipterans were more abundant in exclosures (9 and 1.6 times increase, respectively), despite potential multitrophic interactions with simultaneously increasing predatory arthropods such as spiders and mantis. Under heavy shade (90 %), cacao trees with flying vertebrate exclosures had 3.9 times fewer flowers and 3.2 times fewer large pods than control trees, corresponding to estimated losses on average of $478 ha−1y−1. Under low tree-level shade cover (10 %) however, the opposite pattern was evident: exclosure trees had 5.2 times more flowers and 3.7 times more large pods than control trees, corresponding to estimated savings on average of $796 ha−1y−1. We demonstrate that the enormous potential of African flying vertebrates as pest suppressors in cacao plantations is dependent on local shade tree management and only economically relevant above 50 % of shade. Despite higher productivity at low shade levels, our findings encourage African policymakers and farmers to adopt more high shade cacao agroforestry systems to maximize pest suppression services provided by bats and birds.
Central/West Africa produces most of the Earth’s cacao.Bats and birds are important pest suppressors in Asian and American cacao farms.We present results from a 1 yearlong exclusion experiment conducted in Cameroon.Bats and birds suppressed the population of the Mealybug pest and other Hemipterans.Farmer’s savings due to pest suppression was dependent on tree-level shade cover.
Resumen Cuando los depredadores tope como el jaguar y el puma han desaparecido o disminuido su número, es común un aumento de las poblaciones de mesodepredadores, como el ocelote. Esto a su vez ...provoca una disminución poblacional de especies depredadoras de talla más pequeña, o una modificación de sus patrones de actividad, fenómeno conocido como “efecto pardalis”. No se ha documentado que tan común es este fenómeno ni sus variaciones. El objetivo de este estudio es caracterizar el efecto pardalis y su variación en un bosque mesófilo de montaña, un bosque de pino y una zona antropizada, así como el efecto de las actividades humanas sobre él en Oaxaca, sureste de México. Se estimó la abundancia y se caracterizaron los patrones de actividad de las especies de felinos por medio de fototrampeo. Se obtuvieron 270 registros fotográficos independientes de 5 especies de felinos. La densidad para todas las especies difirió significativamente entre tipos de cobertura vegetal. No se encontraron diferencias significativas entre temporadas ni entre tipos de cobertura vegetal para los depredadores tope y el ocelote, pero sí entre tipos de cobertura vegetal para los felinos de talla menor. El efecto pardalis solamente se observó en la zona antropizada.
Populations of many ground-nesting bird species have declined substantially due to several factors, and predation can be a leading contributor to these declines. As a method for reducing the nest ...predation on ground-nesting birds, we tested whether conditioned food aversion (CFA) can reduce red-legged partridge (Alectoris rufa) nest predation by red foxes (Vulpes vulpes). With a before-after control-impact design we deployed 1329 artificial nests in two different habitats in Central Spain using thiram as an aversive. Artificial nests were monitored by camera traps to identify the red fox individuals during the predation events. 26 foxes were GPS-tagged to monitor their spatial movements and feeding behavior. Partridge density and productivity were monitored to assess the thiram treatment effect on partridge population. Thiram treatment decreased artificial nest predation by foxes in both study sites by 26.8–50.1%, but this was compensated by an increased predation by other predators, possibly enhanced by the availability of our artificial nests. 78% of identified foxes that ingested thiram-treated eggs, stopped nest predation after treatment. Foxes maintained stable territories during the whole study period. Partridge productivity was 132–677% higher in thiram-treatment areas than in control areas, and partridge density after treatment increased more in thiram-treated areas (193–292%) than in control areas (1.8–99%). Our study shows that CFA reduced ground nest predation by foxes, and had a positive effect on the partridge population despite the compensatory predation. This method could be used as a non-lethal tool for conservation of endangered ground-nesting bird species.
•Predation can play an important role in ground-nesting bird population's trend.•Conditioned food aversion (CFA) is a promising tool to reduce nest predation.•We evaluated the potential of CFA to protect red-legged partridge nests.•Nests predation by red fox was reduced, productivity and partridge density increased.•CFA could improve the cost-effectiveness of predator management.
Disturbances such as fire reduce the structural complexity of terrestrial habitats, increasing the risk of predation for small prey species. The postfire effect of predation has especially ...deleterious effects in Australian habitats owing to the presence of invasive mammalian predators, the red fox (Vulpes vulpes) and feral cat (Felis catus), that rapidly exploit burned habitats. Here, we investigated whether the provision of artificial shelter could alleviate the risk of predation perceived by two species of small marsupial, the dunnarts Sminthopsis hirtipes and S. youngsoni, in open postfire habitat in the sandridge system of the Simpson Desert, central Australia. We installed artificial shelters constructed from wire mesh that allowed passage of the dunnarts but not of their predators at one site, and measured and compared the perceived risk of predation by the dunnarts there with those on a control site using optimal patch-use theory (giving-up densities, GUDs). GUDs were lower near artificial shelters than away from them, and near dune crests where dunnarts typically forage, suggesting that the shelters acted as corridors for dunnarts to move up to the crests from burrows in the swales. Foraging was lower near the crest in the control plot. Two-day foraging bouts were observed in dunnart activity, with recruitment to GUD stations occurring a day earlier in the augmented shelter plot. Despite these results, the effects of the shelters were localized and not evident at the landscape scale, with GUDs reduced also in proximity to sparse natural cover in the form of regenerating spinifex grass hummocks. Mapping dunnart habitat use using the landscape of fear (LOF) framework confirmed that animals perceived safety near shelter and risk away from it. We concluded that the LOF framework can usefully assess real-time behavioral responses of animals to management interventions in situations where demographic responses take longer to occur.
Human welfare is significantly linked to ecosystem services such as the suppression of pest insects by birds and bats. However, effects of biocontrol services on tropical cash crop yield are still ...largely unknown. For the first time, we manipulated the access of birds and bats in an exclosure experiment (day, night and full exclosures compared to open controls in Indonesian cacao agroforestry) and quantified the arthropod communities, the fruit development and the final yield over a long time period (15 months). We found that bat and bird exclusion increased insect herbivore abundance, despite the concurrent release of mesopredators such as ants and spiders, and negatively affected fruit development, with final crop yield decreasing by 31% across local (shade cover) and landscape (distance to primary forest) gradients. Our results highlight the tremendous economic impact of common insectivorous birds and bats, which need to become an essential part of sustainable landscape management.
Theory predicts that loss of gape-limited sharks should lead to increases in the abundance and biomass of smaller size classes of prey. We used stereo-baited remote underwater video stations ...(stereo-BRUVS) and stereo diver-operated video systems (stereo-DOVS) to characterise the shark and fish assemblages on 2 remote, atoll-like reef systems in northwestern Australia, the Rowley Shoals and the Scott Reefs. Whereas the Rowley Shoals is a marine protected area, sharks have been removed from the Scott Reefs for over 3 centuries. We found that sharks were significantly more diverse, more abundant, larger in size and greater in biomass in the marine reserve relative to the Scott Reefs. Consistent with a priori hypotheses, bony fishes displayed greater species diversity, abundance and biomass where sharks were common relative to the predator-depleted location. The size and trophic structure of bony fish assemblages also differed between locations. Our results provide large-scale evidence consistent with the hypothesis that reef-associated sharks are gape-limited trophic omnivores that impose top-down effects on medium sized (<50 cm), low- to mid-trophic level fishes. On stereo-BRUVS, for example, prey in the 0 to 29.99 cm size class had 203% more biomass at the predator-depleted reef relative to the location where sharks were abundant. As body size is an important determinant of ecological role and fitness in fishes, these findings suggest that the rapid and ongoing loss of sharks from reefs globally may have important implications for reef management and investigations into the effect of fishing on reef systems.
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