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Abstract

Arguments for the need to conserve aquatic predator (AP) populations often focus on the ecological and socioeconomic roles they play. Here, we summarize the diverse ecosystem functions and services connected to APs, including regulating food webs, cycling nutrients, engineering habitats, transmitting diseases/parasites, mediating ecological invasions, affecting climate, supporting fisheries, generating tourism, and providing bioinspiration. In some cases, human-driven declines and increases in AP populations have altered these ecosystem functions and services. We present a social ecological framework for supporting adaptive management decisions involving APs in response to social and environmental change. We also identify outstanding questions to guide future research on the ecological functions and ecosystem services of APs in a changing world.

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... Marine ecosystems provide a multitude of goods and services for humans, including food, climate control, and cultural services such as tourism and recreation (Millennium Ecosystem Assessment, 2005;Hammerschlag et al., 2019;Tavares et al., 2019;Villéger et al., 2017). Among these cultural services, aesthetic values are instrumental, as they contribute to inspiration, cultural identity, spiritual connection, and opportunities for tourism and recreation. ...
... Aesthetic value plays a crucial role in shaping public perception and appreciation of natural environments, ultimately influencing conservation efforts. In marine ecosystems, these aesthetical aspects benefit human health and well-being by providing opportunities for outdoor activities and the enjoyment of unique scenic beauties (Hammerschlag et al., 2019;Spalding et al., 2017). Activities associated with reef ecosystems, for example, contribute significantly to economies, generating over US$144 million per year in high-income countries (Brander and Beukering, 2013). ...
... This is the case of the Blacktip Shark (Carcharhinus limbatus), a threatened predator that has a key role in prey control and nutrient transport (Heithaus et al., 2008), and of Greenback Parrotfish (Scarus trispinosus), an endemic Brazilian reef fish (Bonaldo, 2014;Francini-Filho and Moura, 2008). The loss of these species might not only harm reef functioning from altering nutrient transport and food web control (Heithaus et al., 2008;Tavares et al., 2019;Waechter et al., 2022), but also compromise the aesthetic value of reefs, a cultural ecosystem service that is essential to human well-being (Elliff and Kikuchi, 2017;Hammerschlag et al., 2019;Tavares et al., 2019). ...
Article
The marine wildlife and seascape components of reef environments are part of peoples' senses and perceptions of nature and and ecosystem services. While people worldwide perceive and value reef components differently, such aesthetics evaluations often overlook marginal reefs, limiting our comprehensive understanding of their cultural significance. We interviewed 320 different users (e.g., recreational divers, researchers, recreational and commercial fishers, and beach tourists) using an online questionnaire with embedded pictures of 82 fish species and 65 seascapes. To assess people's perception about reefs, we related the aesthetic value (i.e., the preference rate) of each picture to body size, body shape and colour for bony and cartilaginous fish, and to the presence of predators, fish schools, benthic organisms, reef patches and area for the underwater and out-of-the-water seascape. We then created an index composed by site-level species aesthetic values, species relative abundances, under and out-of-water aesthetics and measuredthe overall aesthetic value of nine reef sites along the Brazilian province. The different users attributed similar aesthetic values to fish species, under and out-of-the-water components, yet preferences differed among them. Divers preferred large parrotfishes, while tourists preferred coloured fish. The most valued fish traits were the body shape of manta rays and colorful bony species. Out-of-the-water seascapes with emerging reef patches had the highest aesthetic values. When combining the different aesthetic value components in the index, we found that marginal biogenic reefs in Northeastern Brazil had the highest aesthetic value among the evaluated sites. These reefs hold immense value for national tourism, significantly contributing to the revenue of these states. Also, they harbour threatened species, which possess both high aesthetic value and great ecological importance. Therefore, incorporating aesthetic value in conservation initiatives has the potential to improve our ability to maintain and develop cultural reef services.
... In food webs affected by overharvesting or climate change, predator populations often persist but with fewer old, large individuals and diminished stability and functions within food webs (4,14,39). The loss of the largest, oldest individuals and their trophic roles can result in herbivore or mesopredator release (106,107) and disrupted ecosystem processes (94). For example, reduced animal size and age structure may reduce food web stability (14) and affect nutrient cycling (108) from local to regional scales (94,109). ...
... The loss of the largest, oldest individuals and their trophic roles can result in herbivore or mesopredator release (106,107) and disrupted ecosystem processes (94). For example, reduced animal size and age structure may reduce food web stability (14) and affect nutrient cycling (108) from local to regional scales (94,109). ...
Article
Earth’s old animals are in decline. Despite this, emerging research is revealing the vital contributions of older individuals to cultural transmission, population dynamics, and ecosystem processes and services. Often the largest and most experienced, old individuals are most valued by humans and make important contributions to reproduction, information acquisition and cultural transmission, trophic dynamics, and resistance and resilience to natural and anthropogenic disturbance. These observations contrast with the senescence-focused paradigm of old age that has dominated the literature for over a century yet are consistent with findings from behavioral ecology and life-history theory. Here, we review why the global loss of old individuals can be particularly detrimental to long-lived animals with indeterminate growth, increasing reproductive output with age, and those dependent on migration, sociality and cultural transmission for survival. Longevity conservation is needed to protect the important ecological roles an ecosystem services provided by old animals.
... Elasmobranchs often play key ecological roles as apex-or mesopredators in the majority of these systems, including exerting controls on trophic structures and facilitating nutrient cycling and transport within and between habitats (Hammerschlag et al., 2019). For example, large predatory sharks regulate the abundance of prey populations, which acts to stabilize trophic interactions across complex marine food webs (Hammerschlag et al., 2019;Heithaus et al., 2008). ...
... Elasmobranchs often play key ecological roles as apex-or mesopredators in the majority of these systems, including exerting controls on trophic structures and facilitating nutrient cycling and transport within and between habitats (Hammerschlag et al., 2019). For example, large predatory sharks regulate the abundance of prey populations, which acts to stabilize trophic interactions across complex marine food webs (Hammerschlag et al., 2019;Heithaus et al., 2008). ...
Article
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Levels of dissolved oxygen in open ocean and coastal waters are decreasing (ocean deoxygenation), with poorly understood effects on marine megafauna. All of the more than 1000 species of elasmobranchs (sharks, skates, and rays) are obligate water breathers, with a variety of life‐history strategies and oxygen requirements. This review demonstrates that although many elasmobranchs typically avoid hypoxic water, they also appear capable of withstanding mild to moderate hypoxia with changes in activity, ventilatory responses, alterations to circulatory and hematological parameters, and morphological alterations to gill structures. However, such strategies may be insufficient to withstand severe, progressive, or prolonged hypoxia or anoxia where anaerobic metabolic pathways may be used for limited periods. As water temperatures increase with climate warming, ectothermic elasmobranchs will exhibit elevated metabolic rates and are likely to be less able to tolerate the effects of even mild hypoxia associated with deoxygenation. As a result, sustained hypoxic conditions in warmer coastal or surface‐pelagic waters are likely to lead to shifts in elasmobranch distributions. Mass mortalities of elasmobranchs linked directly to deoxygenation have only rarely been observed but are likely underreported. One key concern is how reductions in habitat volume as a result of expanding hypoxia resulting from deoxygenation will influence interactions between elasmobranchs and industrial fisheries. Catch per unit of effort of threatened pelagic sharks by longline fisheries, for instance, has been shown to be higher above oxygen minimum zones compared to adjacent, normoxic regions, and attributed to vertical habitat compression of sharks overlapping with increased fishing effort. How a compound stressor such as marine heatwaves alters vulnerability to deoxygenation remains an open question. With over a third of elasmobranch species listed as endangered, a priority for conservation and management now lies in understanding and mitigating ocean deoxygenation effects in addition to population declines already occurring from overfishing.
... Among these mosquito predators, the aquatic insects play an important role in the dynamics of aquatic ecosystem functioning and stabilisation (Hammerschlag et al. 2019;Mohammed and Saber 2020;Buxton et al. 2022). They are excellent witnesses of the quality of the habitats where they develop, and indicate changes in natural and anthropogenic resources (Feio and Dolédec 2012;Tupinambás et al. 2014). ...
... In aquatic ecosystems, natural enemies are an effective force for predation and regulation of the aquatic population (Hammerschlag et al. 2019;Zuharah and Lester 2019). However, aquatic culiciphagous predators form a diverse group of insects that includes Odonata, Coleoptera, and Hemiptera. ...
Article
Mosquitoes are insects of medical interest. They contribute to the transmission and spread of many viral and parasitic diseases. Various methods have been used to control mosquitoes such as conventional insecticides, which are widely used throughout the world and have a negative impact on the environment and targeted species. Predatory insects are significant for the biocontrol of various pests, including the important potential against the larval instars of mosquitoes. In this study, we tested the efficacy of five species Piona uncata Koenike, 1888; Notonecta glauca Linnaeus, 1758; Corixa punctata Illiger, 1807, Ilyocoris cimicoide Linnaeus, 1758; and Sympetrum striolatum Charpentier, 1840 against the fourth instars larvae of Culex pipiens Linnaeus, 1758, according to two exposure phases (Light phase, Twilight phase). The predation assays show a significant effect of tested species against mosquito larvae with the following decreasing order of efficacy: S. striolatum> N. gluca> P. uncata> I. cimicoides> C. pinctata. The early larval instars are the most favourable trophic choice of the five predatory species. On the other hand, we noticed a difference in the predation rate for each species during the two experimental periods. The light phase exhibits the highest predatory efficacy than the twilight phase.
... Predators are important drivers of ecosystem functioning within (Antiqueira et al., 2018;Atwood et al., 2014) and across ecosystems (Knight et al., 2005;Romero & Srivastava, 2010), affecting processes such as primary productivity, decomposition and nutrient cycling (Antiqueira et al., 2018;Breviglieri & Romero, 2017;Hammerschlag et al., 2019). Predator impacts on ecosystems can be direct, via the input of nutrients from excretion and the carcasses of their prey, and favour producers that use these nutrients as resources (Hammerschlag et al., 2019;Ngai & Srivastava, 2006;Vanni, 2002). ...
... Predators are important drivers of ecosystem functioning within (Antiqueira et al., 2018;Atwood et al., 2014) and across ecosystems (Knight et al., 2005;Romero & Srivastava, 2010), affecting processes such as primary productivity, decomposition and nutrient cycling (Antiqueira et al., 2018;Breviglieri & Romero, 2017;Hammerschlag et al., 2019). Predator impacts on ecosystems can be direct, via the input of nutrients from excretion and the carcasses of their prey, and favour producers that use these nutrients as resources (Hammerschlag et al., 2019;Ngai & Srivastava, 2006;Vanni, 2002). ...
Article
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Species in one ecosystem can indirectly affect multiple biodiversity components and ecosystem functions of adjacent ecosystems. The magnitude of these cross‐ecosystem effects depends on the attributes of the organisms involved in the interactions, including traits of the predator, prey and basal resource. However, it is unclear how predators with cross‐ecosystem habitat interact with predators with single‐ecosystem habitat to affect their shared ecosystem. Also, unknown is how such complex top‐down effects may be mediated by the anti‐predatory traits of prey and quality of the basal resource. We used the aquatic invertebrate food webs in tank bromeliads as a model system to investigate these questions. We manipulated the presence of a strictly aquatic predator (damselfly larvae) and a predator with both terrestrial and aquatic habitats (spider), and examined effects on survival of prey (detritivores grouped by anti‐predator defence), detrital decomposition (of two plant species differing in litter quality), nitrogen flux and host plant growth. To evaluate the direct and indirect effects each predator type on multiple detritivore groups and ultimately on multiple ecosystem processes, we used piecewise structural equation models. For each response variable, we isolated the contribution of different detritivore groups to overall effects by comparing alternate model formulations. Alone, damselfly larvae and spiders each directly decreased survival of detritivores and caused multiple indirect negative effects on detritus decomposition, nutrient cycling and host plant growth. However, when predators co‐occurred, the spider caused a negative non‐consumptive effect on the damselfly larva, diminishing the net direct and indirect top‐down effects on the aquatic detritivore community and ecosystem functioning. Both detritivore traits and detritus quality modulated the strength and mechanism of these trophic cascades. Predator interference was mediated by undefended or partially defended detritivores as detritivores with anti‐predatory defences evaded consumption by damselfly larvae but not spiders. Predators and detritivores affected ecosystem decomposition and nutrient cycling only in the presence of high‐quality detritus, as the low‐quality detritus was consumed more by microbes than invertebrates. The complex responses of this system to predators from both recipient and adjacent ecosystems highlight the critical role of maintaining biodiversity components across multiple ecosystems.
... Regarding predator-prey interactions in insects, Holling (1961) evaluated the parameters that may interfere with the behavior of predators, such as the prey and predator density, environment, and prey and predator characteristics. Therefore, the proper functioning of the main parameters mentioned above ensures the conservation of organisms with a predation strategy (Holling 1961) and, consequently, the good functioning of the ecosystem (Hammerschlag et al. 2019). ...
... The Anthropocene era has contributed to the disappearance of many insect species, making the global decline of entomofauna alarming (Hammerschlag et al. 2019). In aquatic ecosystems, among the anthropic actions responsible for the decline of insects, agricultural activities practiced in large monocultures stand out (Sluijs 2020). ...
Article
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Predation presents specific behavioral characteristics for each species, and the interaction between prey and predator influences the structuring of the food web. Concerning insects, predation can be affected in different ways, such as exposure to chemical stressors, e.g., pesticides. Therefore, analyses were carried out of the effects of exposure to insecticide fipronil and the herbicide 2,4-D on predation, parameters of food selectivity, and the swimming behavior of two neotropical predatory aquatic insects of the families Belostomatidae (giant water bugs) and larvae of Libellulidae (dragonfly). These predatory insects were exposed for 24 h to a commercial formulation of the chlorophenoxy herbicide, 2,4-D at nominal concentrations of 200, 300, 700, and 1400 μg L⁻¹, and to a commercial formulation of the phenylpyrazole insecticide, fipronil at nominal concentrations of 10, 70, 140, and 250 µg L⁻¹. In a control treatment, the insects were placed in clean, unspiked water. At the end of the exposure, the maximum swimming speed of the predators was evaluated. Afterward, the predators were placed in clean water in a shared environment for 24 h with several prey species, including the cladoceran Ceriodaphnia silvestrii, larvae of the insect Chironomus sancticaroli, the amphipod Hyalella meinerti, the ostracod Strandesia trispinosa, and the oligochaete Allonais inaequalis for 24 h. After this period, the consumed prey was counted. The results reveal that predators from both families changed prey consumption compared with organisms from the control treatment, marked by a decrease after exposure to fipronil and an increase in consumption caused by 2,4-D. In addition, there were changes in the food preferences of both predators, especially when exposed to the insecticide. Exposure to fipronil decreased the swimming speed of Belostomatidae individuals, possibly due to its neurotoxic effect. Exposure to the insecticide and the herbicide altered prey intake by predators, which could negatively influence the complex prey–predator relationship and the functioning of aquatic ecosystems in contaminated areas.
... A range of theoretical, observational, and experimental approaches have highlighted the importance of predator-prey interactions to ecosystem functioning [7]. Predators drive ecosystem processes by directly killing their prey, as reduced prey densities reshape trophic interactions, nutrient cycling, ecosystem engineering, and disease transmission, for example [8,9]. Predators also influence ecosystems nonlethally through the predation risk they pose [8]. ...
... Trends in Ecology & Evolution, Month 2023, Vol. xx, No. xx9 . ...
Article
Predator-prey ecology and the study of animal cognition and culture have emerged as independent disciplines. Research combining these disciplines suggests that both animal cognition and culture can shape the outcomes of predator-prey interactions and their influence on ecosystems. We review the growing body of work that weaves animal cognition or culture into predator-prey ecology, and argue that both cognition and culture are significant but poorly understood mechanisms mediating how predators structure ecosystems. We present a framework exploring how previous experiences with the predation process creates feedback loops that alter the predation sequence. Cognitive and cultural predator-prey ecology offers ecologists new lenses through which to understand species interactions, their ecological consequences, and novel methods to conserve wildlife in a changing world.
... Additionally, quantitative estimation and continuous monitoring must be prioritized because defining population status and size is fundamental in identifying the current problems, evaluating conservation strategies, and recommending better solutions. (Warden et al., 2017;Hammerschlag et al., 2019). The assessment of sea turtle population dynamics is conducted using both active and opportunistic methods. ...
... Fish biomass is often used as a proxy for estimating energy flow, which can be loosely termed as ecosystem functioning or productivity of a reef (Mora et al., 2011;Morais et al., 2020). Large-bodied fishes, such as sharks, barracuda, trevally, tunas, and groupers, play a critical role in reef ecosystem productivity (Kulbicki et al., 2015) and represent a significant energy store as piscivorous species at a high trophic level (Hammerschlag et al., 2019;Hussey et al., 2013). Top-level predatory reef fishes associate with high coral cover and structural complexity (Sartori et al., 2021), and their absence releases lower trophic taxonomic groups, thereby disrupting fish community trophic structure (Heithaus et al., 2008;Hixon, 2015;Robinson et al., 2019). ...
Article
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Predatory and large‐bodied coral reef fishes have fundamental roles in the functioning and biodiversity of coral reef ecosystems, but their populations are declining, largely due to overexploitation in fisheries. These fishes include sharks, groupers, Humphead wrasse (Cheilinus undulatus), and Green Humphead parrotfish (Bolbometopon muricatum). In the western Indian Ocean, this situation is exacerbated by limited population data on these fishes, including from conventional visual census methods, which limit the surface area surveyed. We developed a rapid timed scuba swim survey approach for application over large areas for estimation of the abundance of large‐bodied reef fishes and assessment of the effectiveness of marine protected areas (MPAs) in maintaining these species’ populations. Using this method, we sampled 7 regions in the western central Indian Ocean and Gulf of Aden, including 2 remote reference locations where fishing is prohibited. Eight families were selected for the surveys from across 3 categories: pelagic, demersal, and large‐bodied single species. Sharks (Carcharhinidae) were absent in 5 of the 7 regions, observed only in Mozambique and the Chagos Archipelago. Tunas (Scombridae) and barracudas (Sphyraenidae) were rarely observed (none in Madagascar, Djibouti, and Iles Glorieuses). The Giant grouper (Epinephelus lanceolatus) was absent in all regions, Humphead wrasse was absent in Comoros and Iles Glorieuses, and Green Humphead parrotfish was observed at only one site in Tanzania. The MPAs were not effective in protecting these single large‐bodied species or the 4 pelagic families, except for sharks in the highly protected reference locations. However, MPAs with medium levels of protection were effective in maintaining the abundance of some demersal families, notably large‐bodied groupers. Our results support the hypothesis of local extirpation of these large‐bodied fishes on many coral reefs in the western Indian Ocean.
... However, CEE are threatened by human activities, notably overfishing, aquaculture, tourism, and pollution (Halpern et al., 2008). Anthropogenic pressure on CEE often, if not systematically, decreases biodiversity (animal and plant), alters ecosystem functions and ecological state (Hammerschlag et al., 2019), leading to a possible loss of some ecosystem services. ...
... Platypus are phylogenetically unique, comprising one-third of the world's monotreme biodiversity. It is also an apex predator in many Australian waterways, making its conservation substantially important (Winemiller, Humphries, and Pusey 2015;Hammerschlag et al. 2019). ...
Article
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Freshwater waterways, and species that depend on them, are threatened by urbanisation and the consequences of the urban stream syndrome. In south‐east Queensland, Australia, little is known about the impacts of the urban stream syndrome on the platypus (Ornithorhynchus anatinus), meaning that populations cannot be adequately managed by conservation practitioners. The aim of this study was to determine how habitat and environmental variables, related to the urban stream syndrome, influenced platypus distribution across this region. We used environmental DNA sampling over a 5‐year period (2016–2020) to determine how platypus occurrence (presence or absence) was affected by habitat and the environment. Five scenarios based on key characteristics of the urban stream syndrome were modelled using binomial generalised linear models. The highest‐ranked model of platypus occurrence included positive effects of topographic wetness index and coarse organic matter. These findings reflect important waterway connectivity and food resources for platypus, highlighting relationships between platypus, their environment and their tolerance to urban stream threats. For example, platypuses are unlikely to occur in streams where water availability is reduced, and movement will be limited in shallow, dry streams. Therefore, waterway management should focus on water availability and connectivity, especially during drought. Our study can be used to guide management plans for the persistence of platypus and other freshwater species.
... Predation stands as a fundamental biological process that plays critical roles in maintaining the equilibrium and stability of marine ecosystems, namely in controlling marine organisms' abundance and distribution, promoting biodiversity and enhancing ecosystem functioning (Hammerschlag et al., 2019). However, in invaded ecosystems, the introduction of nonindigenous marine species (NIS) can disrupt this delicate balance by altering food web dynamics, which can lead to NIS out performing or outcompeting native species . ...
Thesis
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This dissertation investigates marine biological invasions, focusing on the trophic interactions between non-indigenous species (NIS) and native predators/foragers. Conducted in situ across various locations of the Portuguese coastline, the research provides insights into the impacts of NIS and their interactions with native predators. The studies examine marinas and their adjacent areas, identified as key gateways for NIS introduction and crucial battlegrounds for preventing NIS establishment, by evaluating predation effects on both NIS invertebrates and NIS macroalgae. Utilizing innovative methodologies, the research explores the influence of predation on NIS abundance through predation-exclusion and predation-observation experiments. A novel tool, the Remote Video Foraging System (RVFS), is introduced to identify potential defenders — predators capable of resisting NIS establishment. Predation exclusion experiments indicate that predation increased the relative abundance of NIS, particularly Watersipora subatra, in estuarine marinas in mainland Portugal, suggesting a facilitation effect. Conversely, in Madeira Island, the RVFS revealed that native species, specifically Sparisoma cretense, consumed NIS, indicating biotic resistance. Additionally, Canthigaster capistrata in Madeira showed a preference for NIS over native species, with ascidians being the most favored among the NIS, while local fish communities demonstrated reluctance to consume the invasive macroalga Asparagopsis taxiformis, highlighting its potential threat to biodiversity. A discernible trend emerged across experiments, revealing site-specific and species-specific predation effects on NIS abundance. In conclusion, this dissertation significantly advances understanding of NIS invasion dynamics and the complex interactions between NIS and native predators/foragers, particularly in terms of trophic relationships. The developed methodology offers predictive insights into local biotic resistance against NIS, with potential applications across geographical areas and marine NIS communities. These findings inform management strategies and conservation efforts in the global combat against NIS, ultimately safeguarding coastal ecosystems and their native species.
... These biogeographic patterns are determined in part by the overall habitat, i.e., the sum of the specific resources that are needed by organisms (Thomas, 1979), and constrained by specific habitat qualities such as temperature, salinity, light, oxygen, substrate, and prey and predator presence (see e.g., Jac et al., 2022). Sharks have a key role as secondary and tertiary consumers that move matter and energy across great distances within the ocean (Hammerschlag et al., 2019). However, the movement dynamics of sharks are often elusive and challenging to investigate, which has led to the increased use of electronic tagging to provide this information. ...
Article
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The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised attachment method for externally attached pop‐up satellite archival tags that was successful in long‐term deployments on pregnant females. Twenty‐one spurdogs were tagged in two fjord systems in western Norway for an average of 243 days and provided new details about their behaviour, demonstrating affinity for coastal habitat based on the pop‐up locations and recovery positions of the tags (84% within 40 km from tagging location), and depth–temperature profiles. It is likely that parturition therefore occurs in these coastal waters, making them important to the life cycle of this species. The realized depth niche of tagged individuals suggested that surveys may miss sharks if they do not cover the full water column because the sharks used large parts of the water column and spent much time in shallower waters, albeit with seasonal variations (deeper and shallower in winter and summer, respectively). Adoption of this tagging method and combination with movement data from acoustic transmitters will help to better resolve the behaviour of this species as it transitions from a species at risk to a managed fishery. Such studies will provide a more comprehensive understanding of the species' habitat requirements that will empower better informed protections against a return to the red list of threatened species.
... Understanding HMS movement patterns in response to changing oceanographic conditions and adapting their protective measures appropriately are research priorities (Hazen et al., 2013;Queiroz et al., 2019). In addition to the direct conservation benefits of HMS populations, adequate management of marine species remains ecologically beneficial to the ecosystems they inhabit and economically imperative for fisheries and ecotourism (Hammerschlag et al., 2019). ...
Article
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Dynamic ocean management (DOM) is a critical approach for protecting highly migratory species amid environmental variability and change. We conducted an adapted systematic review to assess how animal movement and environmental data are used in DOM applications, identifying key data traits, barriers, and research priorities. Animal tag data inform initial assessments of species distributions, development of habitat models, near real‐time model inputs, and iterative model evaluation for dynamic management. In documented examples, effective translation of scientific insights into dynamic management products has resulted from early communication between researchers and stakeholders, integration of environmental and fisheries‐dependent data into advanced habitat modeling approaches, and reformatting of outputs for interdisciplinary needs. However, challenges persist around data gaps, science‐policy translation, and technical capacity limitations. Our findings highlight the importance of intentional, collaborative data collection, translation, and sharing to enable dynamic, climate‐resilient management of migratory species. We demonstrate DOM's adaptability and provide guidance for researchers and practitioners to contribute and use impactful data that informs responsive management decision‐making.
... Indeed, we already know that hooks equipped with different types of magnets (neodymium, iron, boron or barium-ferrite) have the property to catch fewer elasmobranchs compared to control fishing hooks (O'Connell et al. 2011). The presence of these higher trophic level species enables them to play their important role in trophic cascades and ecosystem functioning (Natsukawa and Sergio 2022;Hammerschlag et al. 2019). In a global context where mankind's impact on ecosystems is increasingly marked, maintaining such functional diversity along highly anthropized coasts is essential to face up to present and future threats in terms of overexploitation, habitat degradation and global warming. ...
Article
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Aim The Mediterranean Sea is one of the most anthropized seas in the world but also a marine biodiversity hotspot with many fish species under threat. The main goal of the study is to test whether on the heavily fished and anthropized Mediterranean coast, the less impacted Corsica and Balearic Islands, can be considered as refugia for threatened and elasmobranch fishes independently of protection by marine reserves. Location The French Mediterranean coast and three north‐western Mediterranean islands: Corsica and also Mallorca and Minorca from the Balearic archipelago. Methods We performed 187 fish surveys using environmental DNA metabarcoding on three islands and 109 along the continental coast. Of the 78 surveys on islands 22 correspond to no‐take marine reserves and of the 109 continental surveys 26 were carried out within reserves. After eDNA filtration, extraction, amplification, and sequencing we estimated the number of fish species but also the number commercial, threatened and elasmobranch fish species on each sample. We then performed an ANOVA by permutation to test the effect of insularity and protection on these four biodiversity metrics. We also modelled these four biodiversity metrics as a function of protection and human pressure but also environmental, habitat and sampling conditions. We also built species accumulation curves to obtain asymptotes representing the potential regional pools for each species category on both island and continental coasts. Results We obtained a total of 175,982,610 reads over the 187 eDNA samples that were assigned to 153 fish species including 17 elasmobranch species among which 7 were only detected on islands. We observed a higher total fish richness on continental than island surveys regardless of protection but a higher threatened and elasmobranch fish richness on the island than on continental surveys. We obtained a significant, negative and predominant human gravity impact on the diversity of elasmobranch species. The modelled asymptote reached 148 teleostean fish species on islands and 196 on the continental coastline with a very similar rate of diversity increase with sampling effort but the shape of the species accumulation curves differed markedly for elasmobranchs with a stronger increase in diversity with sampling effort on islands. Main Conclusions Our findings highlight that Mediterranean islands can be refugia for sharks and rays but also threatened fishes in this overexploited region. Our results also suggest that reducing or banning trawling activities may play a key role for conserving vulnerable fishes, beyond the benefits of no‐take marine reserves, which appear limited on these large home‐range species.
... For SEMS subgroups, most of the included studies were for elasmobranchs (40%), followed by sea turtles (31%), cetaceans (21%) and seabirds (21%) (Supplementary Table 2). We found that measures generally reduced the bycatch of seabirds ( The examined measures, however, did cultural value to humans and their low population growth rates [12][13][14] . For fishermen, the interactions with SEMS may be undesirable because of the induced losses, including loss of bait and captured fish, damage to fishing gear and extra time to handle the bycatch 7 . ...
Article
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Reducing fisheries bycatches of vulnerable species is critical to marine biodiversity conservation and sustainable fisheries development. Although various preventive technical measures have been implemented, their overall effects are poorly understood. Here, we used a meta-analysis approach to quantify the effects of 42 technical measures on the target catch and the bycatch of seabirds, elasmobranchs, marine mammals and sea turtles. We showed that these measures generally reduced the bycatch while having no statistically significant effect on the target catch. Sensory-based measures generally outperformed physical-based ones in reducing the bycatch. Mitigation measures that worked well for several fishing gears or taxa, although useful, were very rare. Most of the adoptions by regional fisheries management organizations (59%) were supported by our findings, although many others are yet to be robustly evaluated. Our study encourages the innovation and adoption of technical measures and provides crucial insights for policy-making and further research in sustainable bycatch management.
... Though large predators are rare in nature, anthropogenic impacts can cause changes in their distribution and abundance that result in significant and relatively sudden direct and indirect effects on ecosystem functioning and food web structure (Hammerschlag et al., 2019;Ripple et al., 2014;Rooney et al., 2006). While many populations of various large apex predator fish species are in decline (He et al., 2019), stocks of the European catfish Silurus glanis (hereafter, catfish) are increasing. ...
Article
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The European catfish (Silurus glanis) is a large apex predator native to Eastern Europe. Increasing populations within and outside the species’ native range in recent years, and its popularity with recreational anglers are fueling discussions about appropriate management. To understand the motivations of anglers and their views on different management strategies, an internet survey was conducted in southern Germany. The results showed that catfish anglers differ in several aspects from those targeting other species. For specialists, catfish fishing is a central part of life, and they invest significant time and money to catch trophy sized fish. Most catfish anglers think that their targeted species has no negative effect on the local fish community and practice catch and release, despite this practice being illegal in Germany. Large catfish are often released under the misapprehension that they are inedible. The findings of this study suggest that new fishery management approaches are needed in order to mitigate the impact of European catfish in southern Germany. A co-production approach actively incorporating anglers’ perspectives will be essential in implementing education and incentives for catfish consumption alongside other aspects of fisheries management.
... Bangley et al., 2018;Goldner et al., 2022). Sharks and other ectotherms that currently undergo obligatory winter migrations in subtropical latitudes may forego these long-distance movements in the future due to warming temperatures, which will affect their ecological roles (Hammerschlag et al., 2019;Tanaka et al., 2021), economic values (Braun et al., 2023;Rogers et al., 2019) and conservation statuses (Birkmanis et al., 2020). However, our results indicate other extrinsic factors will play a role and lead to more complex outcomes. ...
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Seasonal variability in environmental conditions is a strong determinant of animal migrations, but warming temperatures associated with climate change are anticipated to alter this phenomenon with unknown consequences. We used a 40‐year fishery‐independent survey to assess how a changing climate has altered the migration timing, duration and first‐year survival of juvenile bull sharks (Carcharhinus leucas). From 1982 to 2021, estuaries in the western Gulf of Mexico (Texas) experienced a mean increase of 1.55°C in autumn water temperatures, and delays in autumn cold fronts by ca. 0.5 days per year. Bull shark migrations in more northern estuaries concomitantly changed, with departures 25–36 days later in 2021 than in 1982. Later, migrations resulted in reduced overwintering durations by up to 81 days, and the relative abundance of post‐overwintering age 0–1 sharks increased by >50% during the 40‐year study period. Yet, reductions in prey availability were the most influential factor delaying migrations. Juvenile sharks remained in natal estuaries longer when prey were less abundant. Long‐term declines in prey reportedly occurred due to reduced spawning success associated with climate change based on published reports. Consequently, warming waters likely enabled and indirectly caused the observed changes in shark migratory behaviour. As water temperatures continue to rise, bull sharks in the north‐western Gulf of Mexico could forgo their winter migrations in the next 50–100 years based on current trends and physiological limits, thereby altering their ecological roles in estuarine ecosystems and recruitment into the adult population. It is unclear if estuarine food webs will be able to support changing residency patterns as climate change affects the spawning success of forage species. We expect these trends are not unique to the western Gulf of Mexico or bull sharks, and migratory patterns of predators in subtropical latitudes are similarly changing at a global scale.
... These species are often assumed to be highly threatened, and data paucity hampers any further effort to draw rigorous conclusions about their population dynamics (Thompson, 2013) and conservation status. This is particularly true for marine top predators, such as sharks, which face strong declines due to a constantly increasing anthropogenic impact (McCauley et al., 2016;O'Hara et al., 2021), with large-scale ecosystem consequences not yet completely understood (Hammerschlag et al., 2019;Steneck, 2012). To address these information gaps, field surveys are often planned to gather additional abundance indices. ...
Article
Conserving oceanic apex predators, such as sharks, is of utmost importance. However, scant abundance and distribution data often challenge understanding the population status of many threatened species. Occurrence records are often scarce and opportunistic, and fieldwork aimed to retrieve additional data is expensive and prone to failure. Integrating various data sources becomes crucial to developing species distribution models for informed sampling and conservation purposes. The white shark, for example, is a rare but persistent inhabitant of the Mediterranean Sea. Here, it is considered Critically Endangered by the IUCN, while population abundance, distribution patterns, and habitat use are still poorly known. This study uses available occurrence records from 1985 to 2021 from diverse sources to construct a spatial log-Gaussian Cox process, with data-source specific detection functions and thinning, and accounting for physical barriers. This model estimates white shark presence intensity alongside uncertainty through a Bayesian approach with Integrated Nested Laplace Approximation (INLA) and the inlabru R package. For the first time, we projected species occurrence hot spots and landscapes of relative abundance (continuous measure of animal density in space) throughout the Mediterranean Sea. This approach can be used with other rare species for which presence-only data from different sources are available.
... Predators typically have a broad diet and respond to prey availability, diversity, and abundance through a multi-species functional re-sponse (Koen-Alonso & Yodzis 2005, Smith & Smith 2020. Foraging has wide-ranging impacts on the ecosystem, including direct, indirect, and non-consumptive effects on nutrient cycling and predator and prey abundance, distribution, and demography (Estes et al. 2016, Hammerschlag et al. 2019, Sinclair et al. 2019. For example, leeward waters of islands with pinniped and/or bird colonies are enriched and more productive, and the open ocean is fertilized by whales redistributing iron, phosphorus, nitrogen, and other micronutrients through the release of fecal material (Wing et al. 2014, Devred et al. 2021. ...
Article
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Predation shapes ecosystems, and quantifying the impacts of predation on the distribution and abundance of prey requires substantial effort at appropriate spatial and temporal scales for diet estimation of predators. Here, we present diet estimates of a marine predator (harbour seal Phoca vitulina richards i ) from scat collections (n = 3420) sampled at multiple haulout sites (n = 64) in the Strait of Georgia and other coastal regions around Vancouver Island, British Columbia, Canada, between 2015 and 2019. DNA metabarcoding and hard part analysis were used to identify the proportion and sizes of prey species consumed, respectively. We found that harbour seals consumed 62 primary prey species. Diversity in the diet was highly affected by the number of samples collected and varied at small spatial scales (haulout sites) as well as among broad bioregions. Three to 5 species dominated the diet depending on location, season, and year, including Pacific hake Merluccius productus , Pacific herring Clupea pallasii , and walleye pollock Gadus chalcogrammus . Within the Strait of Georgia, both male and female harbour seals consumed more hake and walleye pollock in areas and seasons in which they were more abundant. Harbour seals consumed a wide size range of prey that also varied by species, season, and region. These results indicate that harbour seal foraging is influenced by both the local abundance and composition of prey. Attempts to model the impact of predation on species of concern risk bias in their estimates and underrepresenting uncertainty if spatial and temporal variation in the diet is not accounted for.
... Their size and longevity allow great whales to exert strong effects on the carbon cycle by: (i) storing carbon more effectively than small animals [7], (ii) ingesting extreme quantities of prey [7], and (iii) producing large volumes of waste products [8]. Considering that baleen whales have some of the longest migrations on the planet [9], they potentially influence nutrient dynamics and carbon cycling over ocean-basin scales [10][11][12]. ...
... Previous studies on sharks and tunas have shown increased catch rates near steep DO gradients, suggesting that OMZs are an important area for actively fishing vessels (Prince et al., 2010;Prince & Goodyear, 2006;. Reductions in the populations of ecologically important marine predators can lead to cascading changes that propagate across the marine ecosystem, including top-down effects (Hammerschlag et al., 2019;McCauley et al., 2015). The loss of biodiversity can also have a number of other negative consequences, including the alteration of patterns in biogeochemical cycling, a reduction in cross-system connectivity, and decreased ecosystem stability (McCauley et al., 2015). ...
Article
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Global climate‐driven ocean warming has decreased dissolved oxygen (DO) levels (ocean deoxygenation) leading to expansions of hypoxic zones, which will affect the movements, behaviour, physiology and distributions of marine animals. However, the precise responses of animals to low DO remains poorly understood because movements and activity levels are seldom recorded alongside instantaneous DO in situ. We describe a new animal‐attached (dissolved oxygen measuring, DOME) archival tag with an optical oxygen sensor for recording DO, in addition to sensors for temperature and depth, a triaxial accelerometer for fine‐scale movements and activity, and a GPS for tag recovery. All sensors were integrated on a single electronic board. Calibration tests demonstrated small mean difference between DOME tag and factory‐calibrated DO sensors (mean relative error of 5%). No temporal drift occurred over a test period three times longer than the maximum deployment time. Deployments on four blue sharks (Prionace glauca) in the central North Atlantic Ocean showed regular vertical oscillations from the surface to a maximum of 404 m. Profiles from diving sharks recorded DO concentrations ranging from 217 to 272 μmol L⁻¹, temperatures between 13°C and 23°C, and identified an oxygen maximum at ~45 m depth, all of which were consistent with ship‐based measurements. Interestingly, the percentage of time sharks spent burst swimming was greater in the top 85 m compared to deeper depths, potentially because of higher prey availability in the surface layer. The DOME tag described blue shark fine‐scale movements and activity levels in relation to accurately measured in situ DO and temperature, with the potential to offer new insights of animal performance in low oxygen environments. Development of a tag with physico‐chemical and movement sensors on a single electronic board is a first step towards satellite relay of these data over broader spatiotemporal scales (months over thousands of kilometres) to determine direct and indirect responses of marine animals to heatwave and deoxygenation events.
... All three subspecies are listed in the IUCN Red List of Endangered species in the Endangered (harbour porpoise and bottlenose dolphin) and Vulnerable (common dolphin) categories [12][13][14] and are protected by national legislations of the six Black Sea coastal states as well as by international law. Being apex predators in the marine ecosystem of the Black Sea, cetaceans fulfil key ecological, economic and cultural functions [15]. ...
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Cetacean strandings are valuable sources of data about their life history, health status, population trends, and impact of threats. We examined the strandings along the Bulgarian coast of the Black Sea for a period of 13 years from 2010 to 2022. A total of 1528 cetacean strandings of all three species inhabiting the basin were recorded: 1031 harbour porpoises Phocoena phocoena, 199 bottlenose dolphins Tursiops truncatus, 97 common dolphins Delphinus delphis, 19 delphinids and 182 unidentified. The highest numbers were observed in 2016 and 2022. Monthly peaks for harbour porpoise and bottlenose dolphin were in July and August and for common dolphin in May. An unusually high mortality of porpoise neonates was recorded in 2015 and 2016. The overall sex ratio showed a slightly higher share of males at 120:100. This bias was the most pronounced for males of common dolphins. Spatial distribution varied interspecifically but was predominantly along the southern coast. Bycatch signs were detected in 80 animals including during the turbot fishing ban period, suggesting the existence of illegal fishing operations. All of this highlights the need for better reinforcement and control to ensure both the conservation of endangered cetaceans and the sustainability of fisheries. Improvement in data collection is needed to improve the quality of information.
... Sharks are functionally important components of coastal and oceanic food webs as they can exert top-down pressure on food webs at large spatial scales through the direct and indirect effects of predation 10,11 . They are also well researched, meaning that their abundance and diversity is well understood in many settings 8,12 . ...
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Human impacts lead to widespread changes in the abundance, diversity and traits of shark assemblages, altering the functioning of coastal ecosystems. The functional consequences of shark declines are often poorly understood due to the absence of empirical data describing long-term change. We use data from the Queensland Shark Control Program in eastern Australia, which has deployed mesh nets and baited hooks across 80 beaches using standardised methodologies since 1962. We illustrate consistent declines in shark functional richness quantified using both ecological (e.g., feeding, habitat and movement) and morphological (e.g., size, morphology) traits, and this corresponds with declining ecological functioning. We demonstrate a community shift from targeted apex sharks to a greater functional richness of non-target species. Declines in apex shark functional richness and corresponding changes in non-target species may lead to an anthropogenically induced trophic cascade. We suggest that repairing diminished shark populations is crucial for the stability of coastal ecosystems.
... Top predators are instrumental in nutrient cycling, carbon sequestration, habitat engineering, and counterbalancing biological invasions. Their value is also linked to socio-economical aspects, e.g., fishery sustainability, tourism, and bioinspiration Doughty et al., 2016;Haas et al., 2017;Hammerschlag et al., 2019). In addition, marine top predators can be used as sentinels of marine ecosystem status (Hazen et al., 2019;Coll et al., 2019b), and changes in their abundance can act as an early warning of decreasing marine health and trigger species and ecosystem conservation interventions. ...
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The conservation and management of marine ecosystems hinge on a comprehensive understanding of the status and trends of top predators. This review delves into the ecological significance of marine top predators, examining their roles in maintaining ecosystem stability and functioning through an integrated analysis of current scientific literature. We first assess the efficacy of various monitoring methods, ranging from traditional field observations to cutting-edge technologies like satellite tracking and environmental DNA (eDNA) analysis and evaluating their strengths and limitations in terms of accuracy, spatial coverage, and cost-effectiveness, providing resource managers with essential insights for informed decision-making. Then, by synthesizing data from diverse marine ecosystems, this study offers a comprehensive overview of the trends affecting top predator populations worldwide. We explore the multifaceted impacts of human activities, climate change, and habitat degradation on the abundance and distribution of these key species. In doing so, we shed light on the broader implications of declining top predator populations, such as trophic cascades and altered community structures. Following a thorough assessment of successful strategies for reversing the decline of top predators, a compilation of recommendations is presented, encompassing effective governance interventions. A crucial aspect of effective ecosystem-based management is the implementation of robust monitoring strategies. Mitigation measures are imperative to reverse the adverse impacts on marine top predators. We present a comprehensive array of mitigation options based on successful case studies. These include the establishment of marine protected areas, the enforcement of fisheries regulations, and the promotion of sustainable fishing practices. We deepen the synergies between these strategies and their potential to mitigate human-induced stressors on top predator populations to safeguard their pivotal role in maintaining marine ecosystem structure and function. By examining marine top predators’ ecological significance, analyzing population trends, discussing monitoring techniques, and outlining effective mitigation strategies, we provide a comprehensive resource for researchers, policymakers, and stakeholders engaged in fostering ecosystem-based management approaches. We conclude that integrating these insights into current management frameworks will be essential to safeguard both top predators and the broader marine environment for future generations.
... Indeed, many freshwater megafish species such as blue catfish, flathead catfish, African catfish, and wels catfish, are predators with a wide prey spectrum enabling them to affect many different taxonomic groups of native species (Carol et al., 2009;Cucherousset et al., 2012;Hammerschlag et al., 2019;He et al., 2024;Martino et al., 2011;Vagnon et al., 2022;Winemiller et al., 2015). For example, wels catfish prey on birds, fish, reptiles, mammals, amphibians, and insects (Carol et al., 2009;Cucherousset et al., 2012;Martino et al., 2011;Vagnon et al., 2022). ...
Article
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Freshwater megafish species, such as sturgeons, salmonids, carps, and catfishes, have a maximum reported weight ≥30 kg. Due to their charisma and economic value, they have been widely introduced outside of their native ranges. Here, we provide a comprehensive overview of the introduction of freshwater megafish and an assessment of their environmental impacts. Of the 134 extant freshwater megafish species, 46% have been introduced to new environments, and of these, 69% have established self-sustaining alien populations. These introductions affect 59% of the world's main basins, with the USA and western Europe being particular hotspots of megafish introductions. The common carp (Cyprinus carpio) is the most widely introduced species. Using the Environmental Impact Classification for Alien Taxa (EICAT and EICAT+) frameworks, we assessed the severity and type of negative and positive impacts posed by alien megafish on native species. Alien megafish caused negative impacts through nine different mechanisms, with predation being the most frequently reported mechanism, followed by herbivory and competition. Moreover, 58% of the alien megafish species with sufficient data to evaluate the severity of their impacts caused declining populations of native species, or worse, extirpations of native species populations. The positive environmental impacts of alien megafish were far less frequently documented. They include biotic interactions that benefit native species, and the provision of trophic resources or habitats. Widely introduced or extensively studied species are more likely to have documented severe impacts on native species. There is a clear trade-off between the economic benefits associated with megafish introductions and the severe adverse impacts they have on native biodiversity. Our study highlights the need for comprehensive risk assessments to evaluate the potential environmental impacts of megafish. More research and long-term monitoring schemes are required to inform management actions to protect biodiversity, particularly in the Global South.
... At a time of global biodiversity crisis (Knapp et al., 2021;Lees et al., 2020;Rull, 2022;Tian et al., 2020;Wagner, 2019), top predators are critically endangered by human activity, threatening key ecosystem functions and services (Hammerschlag et al., 2019;Rizzari et al., 2014). In the seas, shark extinction risk is rising with over one third of species endangered globally (Baum and Blanchard, 2010;Boussarie et al., 2018;Davidson and Dulvy, 2017;Edgar et al., 2014;Graham et al., 2010;Jorgensen et al., 2022;Juhel et al., 2018a), mostly due to ever increasing fishing pressure, habitat loss, climate change and pollution (Barone et al., 2022). ...
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Given the global biodiversity crisis, there is an urgent need for new tools to monitor populations of endangered marine megafauna, like sharks. To this end, Baited Remote Underwater Video Stations (BRUVS) stand as the most effective tools for estimating shark abundance, measured using the MaxN metric. However, a bottleneck exists in manually computing MaxN from extensive BRUVS video data. Although artificial intelligence methods are capable of solving this problem, their effectiveness is tested using AI metrics such as the F-measure, rather than ecologically informative metrics employed by ecologists, such as MaxN. In this study, we present both an automated and a semi-automated deep learning approach designed to produce the MaxN abundance metric for three distinct reef shark species: the grey reef shark (Carcharhinus amblyrhynchos), the blacktip reef shark (C. melanopterus), and the whitetip reef shark (Triaenodon obesus). Our approach was applied to one-hour baited underwater videos recorded in New Caledonia (South Pacific). Our fully automated model achieved F-measures of 0.85, 0.43, and 0.72 for the respective three species. It also generated MaxN abundance values that showed a high correlation with manually derived data for C. amblyrhynchos (R = 0.88). For the two other species, correlations were significant but weak (R = 0.35-0.44). Our semi-automated method significantly enhanced F-measures to 0.97, 0.86, and 0.82, resulting in high-quality MaxN abundance estimations while drastically reducing the video processing time. To our knowledge, we are the first to estimate MaxN with a deep-learning approach. In our discussion, we explore the implications of this novel tool and underscore its potential to produce innovative metrics for estimating fish abundance in videos, thereby addressing current limitations and paving the way for comprehensive ecological assessments.
... Apex predators fulfill essential functions regarding ecosystem health (Estes et al., 2016;Fleming et al., 2016). They are considered sentinels of climate change (Hazen et al., 2019) and provide several ecosystem services, such as habitat engineering and nutrient cycling (Hammerschlag et al., 2019). Large sharks play key roles in marine systems' ecosystem structure and functioning (Ferretti et al., 2010;Heithaus et al., 2008;Heupel et al., 2014;Roff et al., 2016). ...
Article
The broadnose sevengill shark (Notorynchus cepedianus) is classified as Vulnerable by the IUCN, and its population in the Southwest Atlantic is declining. Despite some progress in understanding the ecological requirements of the sevengill shark, there are still several information gaps. Essential aspects of its trophic ecology, such as main prey items or key feeding grounds, remain uncertain and this information is essential for developing effective conservation strategies. Stable isotopes and spontaneous regurgitations were analyzed to describe the trophic ecology of sevengill sharks within a marine protected area (MPA) of Península Valdés in Patagonia, Ar-gentina. Analysis of spontaneous regurgitations revealed that the southern elephant seal (Mirounga leonina) was the primary prey item (70%) for the sevengill shark, during abundance peaks of both species in the MPA. However , the stable isotope analysis indicated that the teleosts were the main prey item, and the overall contribution of the elephant seal to the diet of the sevengill shark was around 30%. In addition, the contribution of each prey group varied with the size of the individuals. The estimated trophic position was 4.43, placing the species among the apex predators of the region. This study confirmed the use of the MPA as an essential foraging ground and contributed to identifying its main prey items. Also, it reflects the need to expand conservation tools beyond this particular coastal protection.
... Cetaceans represent an important component of the marine biodiversity of the Mediterranean region supporting the ecosystem functioning and providing several ecosystem services (Pace et al. 2015;Kiszka et al., 2022). They play the role of keystone predators in the food web contributing to stability of the ecosystem structure (Hammerschlag et al., 2019;Kiszka et al., 2022), and in climate regulation mechanisms mitigating global warming (Roman et al., 2014). At the same time, as charismatic species, they help to promote ecotourism and citizen science activities, which represent an important recreational ecosystem service (Mazzoldi et al., 2019). ...
... Predation stands as a fundamental biological process that plays critical roles in maintaining the equilibrium and stability of marine ecosystems, namely in controlling marine organisms' abundance and distribution, promoting biodiversity and enhancing ecosystem functioning (Hammerschlag et al., 2019). However, in invaded ecosystems, the introduction of non-indigenous marine species (NIS) can disrupt this delicate balance by altering food web dynamics, which can lead to NIS out performing or outcompeting native species (Geburzi and McCarthy, 2018). ...
Article
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Non-indigenous species (NIS) spread from marinas to natural environments is influenced by niche availability, habitat suitability, and local biotic resistance. This study explores the effect of indigenous fish feeding behaviour on NIS proliferation using fouling communities, pre-grown on settlement plates, as two distinct, representative models: one from NIS-rich marinas and the other from areas outside marinas with fewer NIS. These plates were mounted on a Remote Video Foraging System (RVFS) near three marinas on Madeira Island. After 24-h, NIS abundance was reduced by 3.5 %. Canthigaster capistrata's preference for marinas plates suggests potential biotic resistance. However, Sparisoma cretense showed equal biting frequencies for both plate types. The cryptogenic ascidian Trididemnum cereum was the preferred target for the fish. Our study introduces a global framework using RVFS for in-situ experiments, replicable across divers contexts (e.g., feeding behaviour, biotic resistance), which can be complemented by metabarcoding and isotopic analysis to confirm consumption patterns.
... The acquisition of these information is even more urgent for those species whose ecological role is not locally assessed, such as the case of the monk seal. This measure would enable the implementation of efficient conservation measures, deepening the local food web dynamics, and supporting the processes needed to preserve ecosystem services [54]. ...
Conference Paper
The Mediterranean population of Mediterranean monk seal (Monachus monachus) is reported as "Critically endangered" by IUCN Red List and its spatial distribution seems to be fragmented in colonies, mainly found around the Ionian and Aegean islands. Monk seals are proved to be highly affected by human pressure such as boat traffic and fishery. Previous studies highlighted the occurrence of net depredation and interactions with artisanal small-scale fisheries. Accordingly, a source of concern is the little quantitative information on various aspects of the Greek small-scale fisheries. Thus, the landings composition of the Marathokampos Bay’s fleet between 2009 and 2011 has been analysed. Then, a dietary overlap index and multivariate analysis were used to analyse the overlap between resources exploited by fisheries and those consumed by monk seals.Results show that for a total of 565 days at sea, 57 % of those fishing days were performed with Trammel nets, 11.3 % with 8-9 mm Gillnets, 18.4 % with Longline, 12.6 % with Boat seine, 0.5 % with Kalami and 0.2 % for the Purse seine. The total landing biomass of 14.3 tons was composed of 68 species. Monk seal’s diets considered in the analysis showed the highest resource overlap with the Boat seines and the lowest with the Purse seines. Results of the cluster analysis showed that the similarity at 0.2 similarity level revealed a big group composed only by fishing métiers (Longline, Trammel net, Purse seine and total fleet). This study suggests that filling this gap of knowledge could support the implementation of conservation actions. Furthermore, some preliminary results regarding the characteristic of the Marathokampos Bay’s fishing fleet are provided, and the need to gather further data able to better quantify the impacts of both monk seals and fishery on the resources is underlined.
... Lentic freshwater environments are home to spatially and temporally diversified dynamic communities of aquatic consumers, which maintain strong and complex trophic interactions (Brönmark, Dahl & Greenberg, 1997). The structure and regulation of such communities is partially driven by some key organisms such as high-rank predators, which trigger direct and indirect top-down effects on organisms of lower trophic rank (Thorp, 1986;Hammerschlag et al., 2019). However, freshwater predators exhibit various foraging characteristics (Cooper, Smith & Bence, 1985), which may influence the way they shape aquatic communities (Wellborn, Skelly & Werner, 1996). ...
Article
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Freshwater vertebrate predators can exert trophic control over aquatic and littoral communities. Among these predators, post‐metamorphic anurans exhibit a biphasic trophic spectrum by foraging in both terrestrial and aquatic habitats. Many studies have described their diet through the classical taxonomic classification of prey. However, these singular diet habits imply a complex, time‐dependent, realised trophic niche in which predation pressure occurs over many consumers that fill diverse functional roles throughout the aquatic and terrestrial interface of ponds. Among anurans, marsh frogs ( Pelophylax ridibundus ) have been introduced outside their range in many countries and are now invading nationwide areas, particularly in western Europe. Focusing on their foraging specificities will therefore further the understanding of the trophic role of these alien taxa in pond environments that are highly colonised. We collected stomach contents from 761 marsh frogs from introduced populations in 19 ponds in southern France once a month over 4 months of their active period in the spring. The populations of marsh frogs were studied in a geographic area that was devoid of native water frogs and their origin tracks back as far as south‐eastern Europe (i.e., more than 1,000 km from the studied sites, as evidenced previously by genetic analyses). Marsh frogs exhibited generalist and opportunistic feeding strategies. The trophic niche was strongly asymmetrical and broader in the terrestrial environment than in the aquatic environment. However, predation occurred in communities of large freshwater macroinvertebrates and amphibians. Whereas the composition of the terrestrial diet exhibited strong seasonal variations, predation pressure was continuously exerted on the same aquatic organisms over time. Primary consumers and consumers at higher trophic levels frequenting aquatic benthic, vegetated, pelagic, and surface microhabitats were preyed upon, underlying the multidimensional extent of the predation spectrum. The diversified feeding strategies of alien marsh frogs highlight the extent of potential ecological control by predation on pond communities. Because of their wide trophic niche, they exert predation pressure on most pond organisms, triggering possible top‐down control of the overall aquatic communities. Our results show that the integration of the functional traits and microhabitats of consumed prey may aid in a better understanding of how predation by anurans may target specific components of pond communities. More particularly, this study raises concerns about the predatory role of introduced anurans in the context of biological invasions.
... Para cada una de las visitas realizadas por isla, se estimó la riqueza específica, la abundancia de individuos y la diversidad alfa mediante los índices de Shannon (basado en la equidad), de Margalef (basado en la riqueza específica) y de Simpson (basado en la dominancia;Moreno, 2001), utilizando el programa Past (Versión 3.16;Hammer et al., 2001).Estas islas sirven de zonas de alimentación, anidación, reposo y refugio de diversas especies de aves(Vilca-Taco et al., 2021) que cumplen a su vez, un rol importante en el ciclo de nutrientes y el control de plagas a través de las cascadas tróficas, dispersan semillas y contribuyen al valor científico y económico(Tàbara, 2006;Latta, 2012;Hammerschlag et al., 2019). Además, involuntariamente en sus patas o plumas transportan algas, crustáceos, huevos y estructuras reproductivas de diferentes organismos(Martínez, 1993).Para conocer la composición de las comunidades de aves presentes, se recorrieron a pie las seis islas del PNSAV, sumando seis desembarques en cada isla, de abril de 2021 a abril de 2022. ...
Article
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Antecedentes. Estudios previos en el Parque Nacional Sistema Arrecifal Veracruzano (PNSAV) han reportado que 48 % de las aves son migratorias de invierno y 52 % son residentes. Sin embargo, no se ha analizado previamente la estructura de las comunidades de aves de sus islas. Objetivos. Analizar la estructura de las comunidades de aves de las islas Sacrificios, Verde, Salmedina, Polo, de Enmedio y Santiaguillo. Métodos. Se realizaron seis censos de aves en cada isla de abril de 2021 a abril de 2022. Con los datos obtenidos se determinó la riqueza específica, la abundancia y la diversidad alfa mediante los índices de Shannon, Margalef y Simpson. Adicionalmente, luego de clasificar a las aves en marinas, acuáticas o costeras, rapaces y terrestres, se calculó el número de especies y la suma de máximos de estos grupos para cada isla. Con toda la información se analizó la conformación de las comunidades de aves para cada isla y sus variaciones en cuanto a la diversidad a lo largo del año de estudio. Resultados. La isla de Enmedio presentó los mayores valores de diversidad (abril y octubre 2021). Octubre 2021 fue el mes de mayor diversidad para Sacrificios, Verde y Santiaguillo. Salmedina y Polo presentaron mayor diversidad en julio 2021 y en enero 2022, en estas dos islas solo se observaron aves marinas y costeras, en las demás islas predominaron especies terrestres. En Polo, las aves marinas presentaron una elevada abundancia a pesar del reducido tamaño de la isla. Conclusiones. Parece existir una gran presión antrópica sobre los hábitats de reposo y reproducción de las aves marinas. Existe poca información de las islas, generarla es relevante para un manejo integral del PNSAV.
... Sharks play a key ecological role within and between marine ecosystems; yet, they are under increasing pressure from anthropogenic impacts, particularly fishing (Hammerschlag et al. 2019, Dulvy et al. 2021, Pacoureau et al. 2021). In addition, many shark species are especially vulnerable to population declines due to their conservative life history characteristics, complicating efforts to improve conservation outcomes for these species (Frisk et al. 2005, Pardo et al. 2016, Pacoureau et al. 2021. ...
Article
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Migratory sharks play a key ecological role through movements within and among marine ecosystems, yet many populations are declining. Addressing the decline is especially challenging for wide-ranging species, as they may undertake movements between countries with disparate conservation priorities. To investigate the transboundary migrations of threatened sharks between neighbouring South Africa and Mozambique, we tracked 4 commonly occurring carcharhinid species (bull, blacktip, tiger and grey reef sharks). A total of 102 individuals were fitted with long-life acoustic transmitters and monitored for 4 yr (2018-2022) on an acoustic receiver network of 350 receivers. During this period, 63% of tagged bull sharks (n = 19), 87% of blacktips (n = 13), 94% of tiger (n = 16) and 25% of grey reef sharks (n = 3) undertook transboundary movements. The frequency of mean transboundary movements per year ranged between 1.3 ± 1.5 (SD) for grey reef sharks and 81 ± 35.6 for tiger sharks. Blacktip, bull and tiger sharks all undertook long-distance transboundary migrations ranging from 980 to 2256 km. These data confirm high connectivity between neighbouring countries by threatened sharks undertaking persistent transboundary movements. This study emphasizes the need for collaborative transboundary cooperation between the 2 countries and the alignment of regional management plans and interventions to address declining shark populations in this region of the Western Indian Ocean.
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Red Sea elasmobranch populations are facing alarming declines. Effective conservation efforts require management strategies informed by extensive datasets and by developing an understanding of distribution patterns within the basin, which is currently lacking. This study introduces CERSE (Central and Eastern Red Sea Elasmobranchs), a comprehensive compilation of elasmobranch observations in the central and eastern Red Sea basin following the route of the Red Sea Decade Expedition. The data set was curated from surveys conducted during two scientific cruises, a time-series survey within Red Sea Global project areas (Tabuk province), and observations extracted from peer-reviewed literature. Through the use of diverse methodologies, we provide a holistic view of elasmobranchs distribution in the region, for a total of 2,847 sightings recorded. By consolidating dispersed information from across the region, this dataset forms a comprehensive foundation for future research and monitoring endeavors focused on elasmobranch fauna, and will serve as a cornerstone for informing targeted conservation initiatives aimed at safeguarding endangered elasmobranch species in this region.
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As the world faces the threats of multiple compounded and worsening crises, scientists are racing to gather the knowledge necessary to safeguard entire ecosystems and species. Technological advances are continuously facilitating more in-depth studies to understand the mechanisms driving species functioning and variations among and within populations, communities, and individuals. New methods are providing insights into difficult to access environments and species such as the open ocean. The following thesis uses theoretical and empirical approaches to understand the drivers of variation in ecological niches of large marine predators. One of the methods commonly used to study a species resource use is stable isotope analysis (SIA). However, the relationship between variation in stable isotope values in the tissues of consumers and their diet is often misconstrued or over-simplified. Here, we lay out the underlying factors that influence stable isotope ratios and how these can be accounted for when designing an ecological study. I then review new advances in stable isotope technologies and how compound-specific SIA can be used to ask questions about the life-history of a broad range of species. Having shown the value in combining biochemical methods with other disciplines, I apply this approach to study the ecology of large marine vertebrates in Ireland. By using fatty acid analysis in combination with reproductive hormone analysis, biologging, morphometrics and observations, I investigate the ecology and physiology of blue sharks, Prionace glauca, in Ireland. This population of predominantly female individuals in varying stages of maturity show indications of a seasonal change in resource use between the June and November, possibly indicating opportunistic foraging on abundant gelatinous or planktonic prey. Finally, I present the results from our tagging efforts on mature female porbeagle sharks, Lamna nasus, caught in Donegal (Ireland) in April 2022. As I have followed these two individuals over the past nine months, both have crossed many environmental and jurisdictional boundaries but have displayed high inter-individual variation. I argue the need for increased and continued cross-country collaboration in the Northeast Atlantic to study and manage this critically endangered species. The work carried out here emphasises the value in moving our field from uni- and multidisciplinary approaches towards more holistic interdisciplinary approaches, particularly when our aim is the sustainable preservation of large oceanic migrators.
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Marine mammals are integral to global biodiversity and marine health through their roles in coastal, benthic, and pelagic ecosystems. Marine mammals face escalating threats from climate change, pollution, and human activities, which perturb their oceanic environment. The diverse biology and extreme adaptations evolved by marine mammals make them important study subjects for understanding anthropogenic pressures on marine ecosystems. However, ethical and logistical constraints restrict the tractability of experimental research with live marine mammals. Additionally, studies on the effects of changing ocean environments are further complicated by intricate gene-environment interactions across populations and species. These obstacles can be overcome with a comprehensive strategy that involves a systems-level approach integrating genotype to phenotype using rigorously defined experimental conditions in vitro and ex vivo. A thorough analysis of the interactions between the genetics of marine mammals and their exposure to anthropogenic pressures will enable robust predictions about how global environmental changes will affect their health and populations. In this perspective, we discuss four challenges of implementing such non-invasive approaches across scientific fields and international borders: 1) practical and ethical limitations of in vivo experimentation with marine mammals, 2) accessibility to relevant tissue samples and cell cultures; 3) open access to harmonized methods and datasets and 4) ethical and equitable research practices. Successful implementation of the proposed approach has the potential impact to inspire new solutions and strategies for marine conservation.
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Amid escalating environmental challenges confronting marine ecosystems, the proliferation of coastal and marine protected areas (MPAs) has emerged as a pivotal strategy for mitigating biodiversity loss and fostering sustainable resource management. This research advocates for a paradigm shift towards a trait-based approach to assess functional diversity (FD) within MPAs, with a specific focus on the ecologically crucial Austrochlamys natans banks in Parry Bay, MPA Almirantazgo Sound. By surveying 28 invertebrate species across eight phyla, a PCA using fuzzy-coded functional traits revealed five distinct groupings primarily based on feeding, movement, and reproductive modes. Mobile predators and scavengers clustered distinctly from sessile suspension feeders and limited-mobility grazers, indicating a scarcity of mobile predator species in Parry Bay, which impacts the ecosystem's dynamics. FD indices highlighted low functional α-diversity, emphasizing trait redundancy that enhances resilience but relies heavily on a few unique and specialized species. The potential extinction or migration of these species could directly affect unique ecosystem properties. While revealing the resilience of the benthic community, this research underscores its dependence on a handful of species that are crucial for both ecological functions and regional commercial significance. Urgent conservation and management measures are imperative to protect these species and maintain the delicate balance of this ecosystem.
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Background Studying habitat use and vertical movement patterns of individual fish over continuous time and space is innately challenging and has therefore largely remained elusive for a wide range of species. Amongst sharks, this applies particularly to smaller-bodied and less wide-ranging species such as the spurdog (Squalus acanthias Linnaeus, 1758), which, despite its importance for fisheries, has received limited attention in biologging and biotelemetry studies, particularly in the North-East Atlantic. Methods To investigate seasonal variations in fine-scale niche use and vertical movement patterns in female spurdog, we used archival data from 19 pregnant individuals that were satellite-tagged for up to 365 days in Norwegian fjords. We estimated the realised niche space with kernel densities and performed continuous wavelet analyses to identify dominant periods in vertical movement. Triaxial acceleration data were used to identify burst events and infer activity patterns. Results Pregnant females frequently utilised shallow depths down to 300 m at temperatures between 8 and 14 °C. Oscillatory vertical moments revealed persistent diel vertical migration (DVM) patterns, with descents at dawn and ascents at dusk. This strict normal DVM behaviour dominated in winter and spring and was associated with higher levels of activity bursts, while in summer and autumn sharks predominantly selected warm waters above the thermocline with only sporadic dive and bursts events. Conclusions The prevalence of normal DVM behaviour in winter months linked with elevated likely foraging-related activity bursts suggests this movement behaviour to be foraging-driven. With lower number of fast starts exhibited in warm waters during the summer and autumn months, habitat use in this season might be rather driven by behavioural thermoregulation, yet other factors may also play a role. Individual and cohort-related variations indicate a complex interplay of movement behaviour and habitat use with the abiotic and biotic environment. Together with ongoing work investigating fine-scale horizontal movement as well as sex- and age-specific differences, this study provides vital information to direct the spatio-temporal distribution of a newly reopened fishery and contributes to an elevated understanding of the movement ecology of spurdog in the North-East Atlantic and beyond. Graphical Abstract
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Per- and polyfluoroalkyl substances (PFAS) enter the marine food web, accumulate in organisms, and potentially have adverse effects on predators and consumers of seafood. However, evaluations of PFAS in meso-to-apex predators, like sharks, are scarce. This study investigated PFAS occurrence in five shark species from two marine ecosystems with contrasting relative human population densities, the New York Bight (NYB) and the coastal waters of The Bahamas archipelago. The total PFAS (∑PFAS) concentrations in muscle tissue ranged from 1.10 to 58.5 ng g-1 wet weight, and perfluorocarboxylic acids (PFCA) were dominant. Fewer PFAS were detected in Caribbean reef sharks (Carcharhinus perezi) from The Bahamas, and concentrations of those detected were, on average, ~79% lower than in the NYB sharks. In the NYB, ∑PFAS concentrations followed: common thresher (Alopias vulpinus) > shortfin mako (Isurus oxyrinchus) > sandbar (Carcharhinus plumbeus) > smooth dogfish (Mustelus canis). PFAS precursors/intermediates, such as 2H,2H,3H,3H-perfluorodecanoic acid and perfluorooctanesulfonamide, were only detected in the NYB sharks, suggesting higher ambient concentrations and diversity of PFAS sources in this region. Ultra-long-chain PFAS (C≥10) were positively correlated with nitrogen isotope (δ15N) and total mercury in some species. Our results provide some of the first baseline information on PFAS concentrations in shark species from the northwest Atlantic Ocean and correlations between PFAS, stable isotope, and mercury further contextualize the drivers of PFAS occurrence.
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En la actualidad, nos enfrentamos a una crisis ambiental sin precedentes, donde la alteración de los ecosistemas del planeta Tierra está acelerando la tasa de extinción a un ritmo alarmante. En este contexto, comprender los mecanismos que sostienen la biodiversidad se vuelve una tarea clave en la ecología. El río Paraná se encuentra entre los ríos más grandes del planeta y se caracteriza por presentar extensas áreas de humedales. En su tramo medio, el río Paraná desarrolla una extensa llanura de inundación con una gran heterogeneidad ambiental y una fuerte influencia del pulso de inundación sobre los procesos ecosistémicos. Estas condiciones ambientales, y su ubicación en la región neotropical, determinan una gran biodiversidad que en el caso de los peces supera las 300 especies. Dentro de estas especies, los depredadores tienen un rol central en la estructuración de las tramas tróficas ya que regulan las poblaciones de sus presas, conectan los distintos compartimentos de la red y determinan el ciclo de nutrientes, entre otras funciones. En esta tesis, nos proponemos a describir las propiedades estructurales de las redes tróficas y de ocurrencia del Río Paraná medio y evaluar los posibles mecanismos que determinan estas propiedades, centrándonos en las principales especies de peces piscívoros como objeto de estudio. El estudio se desarrolló en dos áreas de la llanura aluvial del río Paraná entre las ciudades de Santa Fe y Paraná. Se muestrearon las comunidades de peces y las variables ambientales en 27 ambientes acuáticos a lo largo de 10 años, considerando distintos tipos de hábitats y distintas condiciones estacionales, y se seleccionaron 16 especies de depredadores ictiófagos. Las redes de ocurrencia (o espaciales) se construyeron con 3009 interacciones (depredadores por sitio) en 149 comunidades (sitios por fecha) mientras que la red trófica se construyó con 1300 interacciones (depredador-presa) distribuidas en 114 presas. Posteriormente, las redes fueron analizadas con distintas herramientas de redes para analizar las estructuras, la asociación con los atributos y los mecanismos que subyacen a la organización de la biodiversidad. Para evaluar los patrones estructurales como la modularidad y el anidamiento, se construyeron modelos nulos para confrontar contra los valores observados en la red trófica y la red de ocurrencia. A su vez, mediante el concepto de roles topológicos, analizamos el papel que tiene cada depredador en la conexión de distintos compartimentos de las tramas tróficas y de las redes de ocurrencia, considerando como afectan los atributos corporales (por ejemplo, tamaño corporal, morfología del cuerpo). Luego, examinamos como se relacionan la similitud funcional, el solapamiento de nicho trófico y el uso del espacio a nivel de especies infiriendo los mecanismos que promueven la coexistencia. Además, analizamos la manera en la cual la similitud funcional, uso de ambientes y capturas de presas determina la congruencia entre los módulos de las distintas redes. Por último, se generaron tramas tróficas simuladas para cada ambiente utilizando un modelo basado en los patrones de consumo de presas de cada especie, la co-ocurrencia entre depredadores y presas y las necesidades energéticas de los depredadores. Con estos datos, analizamos las relaciones entre la riqueza, las principales variables estructurales de las tramas tróficas (modularidad, conectancia, anidamiento, fuerza de interacciones y conexión intermodular) y la biomasa en pie mediante un análisis de vías. Nuestros resultados indican que tanto la red trófica como la red de ocurrencia presentan un patrón modular (subgrupos de especies interactúan mucho entre ellos, pero poco con el resto de la red), donde los módulos emergen por una coincidencia entre rasgos y se orientan al uso de diferentes tipos de presas o de sitios. La estructura modular de las redes se mantuvo consistentemente estable a lo largo del tiempo a pesar de una gran variación en la composición de la comunidad en distintas situaciones climáticas. A su vez, observamos que las distintas situaciones hidroestacionales afectan la capacidad de conectar módulos de los depredadores, donde las especies van cambiando su importancia como conectores de las redes de interacción. En este sentido, observamos que el tamaño corporal cumple un rol diferentes en ambas redes; donde se asocia de manera positiva con la conexión de los módulos tróficos, pero negativamente con la conexión espacial. Además, se observó que la captura de presas y el uso de hábitats se asocia de manera positiva con la similitud funcional. Dentro de los módulos las especies que tienden a compartir los mismos sitios tienden a capturar presas similares. Por último, observamos que la riqueza y la estructura de las redes tróficas están estrechamente relacionadas, y ambas afectan el funcionamiento ecosistémico. Específicamente, la riqueza de especies junto con la organización modular y la eficiencia de las redes (gran cantidad de conexiones / conectancia) promueve la biomasa en pie en las comunidades del Río Paraná. Considerados globalmente, nuestros resultados son un paso hacia adelante para comprender los mecanismos que sostienen nuestra diversidad biológica, brindando información necesaria para elaborar proyectos de conservación eficientes, en un contexto de rápida pérdida de la biodiversidad.
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Humans have dramatically transformed ecosystems over the previous millennia and are potentially causing a mass extinction event comparable to the others that shaped the history of life. However, only a fraction of these impacts has been directly recorded, limiting conservation actions. Conservation paleobiology leverages geohistorical records to offer a long-term perspective on biodiversity change in the face of anthropogenic stressors. Nevertheless, the field's on-the-ground contributions to conservation outcomes are still developing. Here, we present an overview of directions in which paleobiological research could progress to aid conservation in the coming decades using elasmobranchs (sharks, rays, and skates)—a highly threatened group with a rich fossil record—as a model. These research directions are guided by areas of overlap between an expert-led list of current elasmobranch conservation priorities and available fossil and historical records. Four research topics emerged for which paleobiological research could address open questions in elasmobranch science and conservation: (1) baselines, (2) ecological roles, (3) threats, and (4) conservation priorities. Increasingly rich datasets and novel analytical frameworks present exciting opportunities to apply the elasmobranch fossil record to conservation practice. A similar approach could be extended to other clades. Given the synthetic nature of these research topics, we encourage collaboration across timescales and with conservation practitioners to safeguard the future of our planet's rapidly disappearing species.
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An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention’s progress to reduce the impact of global Hg pollution on people and the environment.
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1- Elasmobranchs, encompassing an array of sharks and rays, confront a threat of extinction on a global scale. The Sea of Marmara (SoM) stands out as a critical refuge for these endangered species. 2- This study harnesses data derived from comprehensive trawl surveys, representing the first area-based evaluation of the elasmobranchs inhabiting the SoM. Sampling protocols were carried out at 10 separate stations along the 980-km coastline of the SoM, each bounded by different ecological characteristics and anthropogenic influences. 3- A total of eight shark species and six ray species were caught in the towed area of the entire the SoM. Notably, Scyliorhinus canicula and near-threatened Raja clavata constitute more than 50% of the total abundance. Additionally, rare, and critically endangered species, including the Oxynotus centrina, Squatina squatina, Dipturus batis, and Myliobatis aquila, were documented, expanding our knowledge of their presence in the region. 4- Spatial distribution heterogeneity was pronounced within species. 5- Size distributions were species-specific, and the presence of both juvenile and adult individuals suggested successful reproduction and growth. 6- Records expand the known size range in the SoM for six shark and three ray species. It also provides first-size information based on the total length of the S. stellaris and D. batis. 7- Additionally, the urgent need for field-based conservation efforts is highlighted, citing a previously unidentified important sensitive areas located in the southern part of the SoM.
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Freshwater megafauna, such as sturgeons, giant catfishes, river dolphins, hippopotami, crocodylians, large turtles, and giant salamanders, have experienced severe population declines and range contractions worldwide. Although there is an increasing number of studies investigating the causes of megafauna losses in fresh waters, little attention has been paid to synthesising the impacts of megafauna on the abiotic environment and other organisms in freshwater ecosystems, and hence the consequences of losing these species. This limited understanding may impede the development of policies and actions for their conservation and restoration. In this review, we synthesise how megafauna shape ecological processes in freshwater ecosystems and discuss their potential for enhancing ecosystem restoration. Through activities such as movement, burrowing, and dam and nest building, megafauna have a profound influence on the extent of water bodies, flow dynamics, and the physical structure of shorelines and substrata, increasing habitat heterogeneity. They enhance nutrient cycling within fresh waters, and cross‐ecosystem flows of material, through foraging and reproduction activities. Freshwater megafauna are highly connected to other freshwater organisms via direct consumption of species at different trophic levels, indirect trophic cascades, and through their influence on habitat structure. The literature documenting the ecological impacts of freshwater megafauna is not evenly distributed among species, regions, and types of ecological impacts, with a lack of quantitative evidence for large fish, crocodylians, and turtles in the Global South and their impacts on nutrient flows and food‐web structure. In addition, population decline, range contraction, and the loss of large individuals have reduced the extent and magnitude of megafaunal impacts in freshwater ecosystems, rendering a posteriori evaluation more difficult. We propose that reinstating freshwater megafauna populations holds the potential for restoring key ecological processes such as disturbances, trophic cascades, and species dispersal, which will, in turn, promote overall biodiversity and enhance nature's contributions to people. Challenges for restoration actions include the shifting baseline syndrome, potential human–megafauna competition for habitats and resources, damage to property, and risk to human life. The current lack of historical baselines for natural distributions and population sizes of freshwater megafauna, their life history, trophic interactions with other freshwater species, and interactions with humans necessitates further investigation. Addressing these knowledge gaps will improve our understanding of the ecological roles of freshwater megafauna and support their full potential for facilitating the development of effective conservation and restoration strategies to achieve the coexistence of humans and megafauna.
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River otters ( Lontra canadensis ) are key predators in North Carolina's aquatic systems, but they are often seen as competitors by anglers and fish hatcheries. River otter diets typically consist of fish and crayfish, but also include occasional herpetofauna, mammals, and birds. While standard diet studies focus on identification of prey through manual examination of stomach contents and feces, metabarcoding DNA analysis has become more popular to determine the presence or frequency of species that are often missed, misidentified, or underestimated. We collected river otter carcasses from licensed trappers and fur dealers across North Carolina from the 2009–10 trapping season through the 2015–16 season. We conducted necropsies and analyzed the stomach contents using standard observational methods and metabarcoding DNA analysis. We manually examined 522 river otter stomachs, of which 377 contained prey items. Decapods (crustaceans) were identified in 41% of stomachs and made up similar percentages within each Furbearer Management Unit (FMU). The order Perciformes composed the majority (62%) of fish prey across all stomach samples. Coastal Plain river otters primarily consumed crustaceans (50%) and fish (40%). Piedmont and Mountain river otters consumed fish (32% and 42%, respectively) most often followed by crustaceans (62% and 50%, respectively). Prey selection was similar between the sexes. Out of 368 samples, metabarcoding DNA examination was able to reliably match 164 prey items to species, 5 classes, 18 orders, 25 families, and 42 genera. Fishes made up 33% of the identifications, particularly Perciformes (13%), Cypriniformes (7%), and Siluriformes (5%). Twelve percent of identifications was made up by Amphibia, split evenly by Anura and Urodela. No birds or reptiles were detected in the Mountain or Piedmont FMUs, and no mammals were detected in the Coastal Plain or Mountain FMU. Overall, river otters in North Carolina consume a large variety of prey that varied regionally. The manual examination provided identifications that were not provided by the DNA examination (i.e., crayfish, brown snakes), while the DNA examination provided a more accurate identification of the broad array of prey items. To understand the composition of annual river otter diets we encourage managers to expand research to evaluate river otter diets year‐round and incorporate additional noninvasive methods (e.g., scat surveys) throughout the year.
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The social-ecological systems framework (SESF) is arguably the most comprehensive conceptual framework for diagnosing interactions and outcomes in social-ecological systems (SES). This article systematically reviews the literature applying and developing the SESF and discusses methodological challenges for its continued use and development. Six types of research approaches using the SESF are identified, as well as the context of application, types of data used, and commonly associated concepts. The frequency of how each second-tier variable is used across articles is analyzed. A summary list of indicators used to measure each second-tier variable is provided. Articles suggesting modifications to the framework are summarized and linked to the specific variables. The discussion reflects on the results and focuses on methodological challenges for applying the framework. First, how the SESF is historically related to commons and collective action research. This affects its continued development in relation to inclusion criteria for variable modification and discourse in the literature. The framework may evolve into separate modified versions for specific resource use sectors (e.g., forestry, fisheries, food production, etc.), and a general framework would aggregate the generalizable commonalities between them. Methodological challenges for applying the SESF are discussed related to research design, transparency, and cross-case comparison. These are referred to as "methodological gaps" that allow the framework to be malleable to context but create transparency, comparability, and data abstraction issues. These include the variable-definition gap, variable-indicator gap, the indicator-measurement gap, and the data transformation gap. A benefit of the framework has been its ability to be malleable and multipurpose, bringing a welcomed pluralism of methods, data, and associated concepts. However, pluralism creates challenges for synthesis, data comparison, and mutually agreed-upon methods for modifications. Databases are a promising direction forward to help solve this problem. In conclusion, future research is discussed by reflecting on the different ways the SESF may continue to be a useful tool through (1) being a general but adaptable framework, (2) enabling comparison, and (3) as a diagnostic tool for theory building.
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Trophic cascade theory predicts that predator effects should extend to influence carbon cycling in ecosystems. Yet, there has been little empirical evidence in natural ecosystems to support this hypothesis. Here, we use a naturally-occurring trophic cascade to provide evidence that predators help protect sedimentary organic carbon stocks in coral reef ecosystems. Our results show that predation risk altered the behavior of herbivorous fish, whereby it constrained grazing to areas close to the refuge of the patch reefs. Macroalgae growing in “riskier” areas further away from the reef were released from grazing pressure, which subsequently promoted carbon accumulation in the sediments underlying the macroalgal beds. Here we found that carbon stocks furthest away from the reef edge were ~24% higher than stocks closest to the reef. Our results indicate that predators and herbivores play an important role in structuring carbon dynamics in a natural marine ecosystem, highlighting the need to conserve natural predator-prey dynamics to help maintain the crucial role of marine sediments in sequestering carbon.
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We summarise current understanding of consumer recycling in lake nutrient cycles and expand on it by integrating emerging knowledge from food web ecology. The role of consumer nutrient recycling (CNR) is initially framed in the wider context of lake nutrient cycling, which includes hydrodynamic and biogeochemical processes, and their responses to global environmental change. Case studies are used to demonstrate that effects of CNR on lake ecosystems range widely, from reduced nutrient cycling rates to exacerbation of eutrophication. CNR depends on consumer biomass, body size and diet, remaining relatively consistent through the year and becoming important as other fluxes seasonally ebb. Universal patterns in food web structure, for example, consumer–resource biomass ratios, body size scaling and relationships between trophic level and diet breadth, are used to demonstrate the predictability of CNR effects. Larger, mobile, top predators excrete nutrients at a lower rate but over a wider range, linking nutrient cycles across habitats. Smaller-bodied, lower trophic level consumers have strong localised nutrient cycling effects associated with their limited mobility. Global environmental-change drivers that alter food web structure are likely to have the greatest impact on CNR rates and should direct future studies.
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The availability of iron controls primary productivity in large areas of the Southern Ocean. Iron is largely supplied via atmospheric dust deposition, melting ice, the weathering of shelf sediments, upwelling, sediment resuspension, mixing (deep water, biogenic, and vertical mixing) and hydrothermal vents with varying degrees of temporal and spatial importance. However, large areas of the Southern Ocean are remote from these sources, leading to regions of low primary productivity. Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean. The aim of this review is to provide a quantitative and qualitative assessment of the current literature on pelagic iron recycling by marine animals in the Southern Ocean and highlight the next steps forward in quantifying the retention and recycling of iron by higher trophic levels in the Southern Ocean. Phytoplankton utilize the iron in seawater to meet their metabolic demand. Through grazing, pelagic herbivores transfer the iron in phytoplankton cells into their body tissues and organs. Herbivores can recycle iron through inefficient feeding behavior that release iron into the water before ingestion, and through the release of fecal pellets. The iron stored within herbivores is transferred to higher trophic levels when they are consumed. When predators consume iron beyond their metabolic demand it is either excreted or defecated. Waste products from pelagic vertebrates can thus contain high concentrations of iron which may be in a form that is available to phytoplankton. Bioavailability of fecal iron for phytoplankton growth is influenced by a combination of the size of the fecal particle, presence of organic ligands, the oxidation state of the iron, as well as biological (e.g., remineralization, coprochaly, coprorhexy, and coprophagy) and physical (e.g., dissolution, fragmentation) processes that lead to the degradation and release of fecal iron. The flux of dissolved iron from pelagic recycling is comparable to other sources in the region such as atmospheric dust, vertical diffusivity, vertical flux, lateral flux and upwelling, but lower than sea ice, icebergs, sediment resuspension, and deep winter mixing. The temporal and seasonal importance of these various factors requires further examination.
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Animal movements can facilitate important ecological processes, and wide-ranging marine predators, such as sharks, potentially contribute significantly towards nutrient transfer between habitats. We applied network theory to 4 years of acoustic telemetry data for grey reef sharks (Carcharhinus amblyrhynchos) at Palmyra, an unfished atoll, to assess their potential role in nutrient dynamics throughout this remote ecosystem. We evaluated the dynamics of habitat connectivity and used network metrics to quantify shark-mediated nutrient distribution. Predator movements were consistent within year, but differed between years and by sex. Females used higher numbers of routes throughout the system, distributing nutrients over a larger proportion of the atoll. Extrapolations of tagged sharks to the population level suggest that prey consumption and subsequent egestion leads to the heterogeneous deposition of 94.5 kg d−1 of nitrogen around the atoll, with approximately 86% of this probably derived from pelagic resources. These results suggest that sharks may contribute substantially to nutrient transfer from offshore waters to near-shore reefs, subsidies that are important for coral reef health.
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Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels, and may again act as a top-down regulatory force on marine ecosystems. Also the harbour seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960's, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbour seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in faecal samples and published estimates on the seal's daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbour seals from the Dutch Wadden Sea fed predominantly on demersal fish, e.g. flatfish species (flounder, sole, plaice, dab), but also sandeel, cod and whiting. Total fish biomass in the Wadden Sea was insufficient to sustain the estimated prey consumption of the entire seal population year-round. This probably explains why seals also acquire prey further offshore in the adjacent North Sea, only spending 13% of their diving time in the Wadden Sea. Still, seal predation was estimated to cause an average annual mortality of 43% and 60% on fish in the Wadden Sea and adjacent coastal zone, respectively. There were however large sources of uncertainty in the estimate, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down control by harbour seals on demersal fish. However predation by seals may also alleviate density-dependent competition between the remaining fish, increasing fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could potentially become an important component in the functioning of shallow coastal systems.
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Prey responses to predation risk can affect multiple phenotypic traits that have significant implications for population‐to‐ecosystem‐level properties. The general stress paradigm (hereafter GSP ) proposes integrating the principles of ecological stoichiometry and prey physiological plasticity in response to predation risk to provide an explicit mechanistic framework to evaluate the direct influence of predation risk on ecosystem functioning. However, theoretical attempts evaluating the GSP have focused on only one component of phenotypic plasticity, neglecting the fact that multiple phenotypic responses can affect nutrient demand and consumption, and therefore, the overall animal effect on nutrient cycling rates and stoichiometry. In this study, we used a dynamic state variable model to examine how variation in predation and starvation risk on a landscape of patch types that vary in food quality affects the behavioural and physiological phenotypic responses of prey and the linked nutrient and carbon recycling. We found that the stress imposed by predation risk promotes prey carbon limitation, which leads to increased nutrient release and carbon uptake due to a stoichiometric mismatch between an animal's demand and food stoichiometry. Such effects can be altered by prey shifting spatially to carbon‐ or nutrient‐rich patches. However, the abilities of prey to cope with new physiological demands can be affected by absolute stress level or the predation risk distribution on a spatially implicit landscape of stoichiometric‐divergent patch type availability. Overall, starvation risk can act as a selective force favouring individuals that maximize their growth, thus reducing their nutrient release, but increasing their exposure to predation risk. Our results provide an important connection between predator‐induced stress ecology and ecosystem functioning, linking organism nutrition and ecological stoichiometry to fitness outcomes, thus improving our understanding of how non‐consumptive predator effects can scale up to ecosystems. A plain language summary is available for this article.
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More than half the fish in the sea As the human population has grown in recent decades, our dependence on ocean-supplied protein has rapidly increased. Kroodsma et al. took advantage of the automatic identification system installed on all industrial fishing vessels to map and quantify fishing efforts across the world (see the Perspective by Poloczanska). More than half of the world's oceans are subject to industrial-scale harvest, spanning an area four times that covered by terrestrial agriculture. Furthermore, fishing efforts seem not to depend on economic or environmental drivers, but rather social and political schedules. Thus, more active measures will likely be needed to ensure sustainable use of ocean resources. Science , this issue p. 904 ; see also p. 864
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