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Wetlands are dynamic environments where aquatic organisms are affected by both predictable and unpredictable changes in hydrology. Understanding how abundant large-bodied predators respond to these changes is especially important in context of wetland restoration. We used satellite telemetry to investigate how individual (e.g., sex, size, body condition) and environmental factors influenced movement behaviors of American Alligators [Alligator mississippiensis (Daudin, 1801)] in a managed freshwater marsh ecosystem of the Florida Everglades. We quantified space use, movement activity, and habitat selection of animals (n = 18) across hydrological seasons and the breeding period and performed stable isotope analyses to infer seasonal dietary changes. Though individual animals did not change space use across seasons, movement activity was lower for some individuals and δ15 Nitrogen isotopic values were higher in the dry season possibly reflecting greater foraging opportunities when marsh dry down concentrates prey. Alligators may be using canals as foraging sites which have abundant prey year-round and shallow sawgrass habitats as spots for basking. Based on our findings, ongoing restoration of water inflow will likely change the distribution and movement behavior of alligators. [ABSTRACT FROM AUTHOR]

Background: Hurricanes can have catastrophic effects on coastal ecosystems. To minimize negative impacts of storms, animals may seek shelter in place, move to a nearby refuge, or evacuate long-distances. Crocodilians can be important predators in estuarine habitats, but little is known about how they respond to extreme weather events. We investigated the movement behaviors of eight acoustically tracked American alligators (Alligator mississippiensis) before, during, and after Hurricane Irma in 2017 within the Shark River Estuary of Everglades National Park, USA. Using tracking data, we compared their movements and habitat use before and after the hurricane to similar timeframes in other years without major storms. Results: We observed considerable variation in movement tactics and responses to the hurricane. Of eight animals that we tracked, two showed no changes in movement or habitat use throughout the study. Two animals ceased upstream excursions that they were regularly making before the hurricane with one of these animals reducing the distance ranged across the river system. Another animal moved upstream from the lower river to the mid-estuary immediately after the hurricane despite having not done this in the 60 days prior. Two other animals moved from the marsh and mangrove forest habitats to river channels several days after the hurricane. One animal shifted to commuting downstream from its upstream habitat shortly before the storm and continued this behavior for the rest of the 2017 and 2018 wet seasons. Conclusions: We found considerable variability in behavioral responses to the hurricane, ranging from no discernable changes in movements to one animal exhibiting a complete shift in movement tactics not observed by any animal in the long-term tracking of this population. Our research provides insight into alligator movement behavior and ecology in the context of a major hurricane disturbance. [ABSTRACT FROM AUTHOR]

Animal dietary information provides the foundation for understanding trophic relationships, which is essential for ecosystem management. Yet, in marine systems, high‐resolution diet reconstruction tools are currently under‐developed. This is particularly pertinent for large marine vertebrates, for which direct foraging behaviour is difficult or impossible to observe and, due to their conservation status, the collection of stomach contents at adequate sample sizes is frequently impossible. Consequently, the diets of many groups, such as sharks, have largely remained unresolved. To address this knowledge gap, we applied metabarcoding to prey DNA in faecal residues (fDNA) collected on cotton swabs from the inside of a shark's cloaca. We used a previously published primer set targeting a small section of the 12S rRNA mitochondrial gene to amplify teleost prey species DNA. We tested the utility of this method in a controlled feeding experiment with captive juvenile lemon sharks (Negaprion brevirostris) and on free‐ranging juvenile bull sharks (Carcharhinus leucas). In the captive trial, we successfully isolated and correctly identified teleost prey DNA without incurring environmental DNA contamination from the surrounding seawater. In the field, we were able to reconstruct high‐resolution teleost dietary information from juvenile C. leucas fDNA that was generally consistent with expectations based on published diet studies of this species. While further investigation is needed to validate the method for larger sharks and other species, it is expected to be broadly applicable to aquatic vertebrates and provides an opportunity to advance our understanding of trophic interactions in marine and freshwater systems. [ABSTRACT FROM AUTHOR]

Within oligotrophic ecosystems, resource limitations coupled with interspecific variation in morphology, physiology, and life history traits may lead to niche partitioning among species. How generalist predators partition resources and their mechanisms, however, remain unclear across many ecosystems. We quantified niche partitioning among upper trophic level coastal and estuarine species: American alligators ( Alligator mississippiensis), bull sharks ( Carcharhinus leucas), common bottlenose dolphins ( Tursiops truncatus), common snook ( Centropomus undecimalis), and Atlantic tarpon ( Megalops atlanticus) in the Shark River Estuary of the Florida Coastal Everglades, USA using acoustic telemetry, stable isotope analysis, and visual surveys, combined with published diet and life history demographic information. Spatial and isotopic niche overlap occurred among most species, with variability in partitioning among interspecific interactions. However, seasonal variability in habitat use, movements patterns, and trophic interactions may promote coexistence within this resource-limited estuary. Beyond guild-level niche partitioning, predators within the Shark River Estuary also exhibit partitioning within species through individual specializations and divergent phenotypes, which may lead to intraspecific variability in niche overlap with other predators. Niche differentiation expressed across multiple organizational levels (i.e., populations and communities) coupled with behavioral plasticity among predators in oligotrophic ecosystems may promote high species diversity despite resource limitations, which may be important when species respond to natural and human-driven environmental change. [ABSTRACT FROM AUTHOR]

Deep-water sharks are abundant and widely distributed in the northern and eastern Gulf of Mexico. As mid- and upper-level consumers that can range widely, sharks likely are important components of deep-sea communities and their trophic interactions may serve as system-wide baselines that could be used to monitor the overall health of these communities. We investigated the trophic interactions of deep-sea sharks using a combination of stable isotope (δ 13 C and δ 15 N) and stomach content analyses. Two hundred thirty-two muscle samples were collected from elasmobranchs captured off the bottom at depths between 200 and 1100 m along the northern slope (NGS) and the west Florida slope (WFS) of the Gulf of Mexico during 2011 and 2012. Although we detected some spatial, temporal, and interspecific variation in apparent trophic positions based on stable isotopes, there was considerable isotopic overlap among species, between locations, and through time. Overall δ 15 N values in the NGS region were higher than in the WFS. The δ 15 N values also increased between April 2011 and 2012 in the NGS, but not the WFS, within Squalus cf. mitsukurii . We found that stable isotope values of S. cf. mitsukurii , the most commonly captured elasmobranch, varied between sample regions, through time, and also with sex and size. Stomach content analysis ( n =105) suggested relatively similar diets at the level of broad taxonomic categories of prey among the taxa with sufficient sample sizes. We did not detect a relationship between body size and relative trophic levels inferred from δ 15 N, but patterns within several species suggest increasing trophic levels with increasing size. Both δ 13 C and δ 15 N values suggest a substantial degree of overlap among most deep-water shark species. This study provides the first characterization of the trophic interactions of deep-sea sharks in the Gulf of Mexico and establishes system baselines for future investigations. [ABSTRACT FROM AUTHOR]

While extreme climatic events (ECEs) are predicted to become more frequent, reliably predicting their impacts on consumers remains challenging, particularly for large consumers in marine environments. Many studies that do evaluate ECE effects focus primarily on direct effects, though indirect effects can be equally or more important. Here, we investigate the indirect impacts of the 2011 "Ningaloo Niño" marine heatwave ECE on a diverse megafaunal community in Shark Bay, Western Australia. We use an 18‐year community‐level data set before (1998–2010) and after (2012–2015) the heatwave to assess the effects of seagrass loss on the abundance of seven consumer groups: sharks, sea snakes (multiple species), Indo‐pacific bottlenose dolphins (Tursiops aduncus), dugongs (Dugong dugon), green turtles (Chelonia mydas), loggerhead turtles (Caretta caretta), and Pied Cormorants (Phalacrocorax spp.). We then assess whether seagrass loss influences patterns of habitat use by the latter five groups, which are under risk of shark predation. Sharks catch rates were dominated by the generalist tiger shark (Galeocerdo cuvier) and changed little, resulting in constant apex predator density despite heavy seagrass degradation. Abundances of most other consumers declined markedly as food and refuge resources vanished, with the exception of generalist loggerhead turtles. Several consumer groups significantly modified their habitat use patterns in response to the die‐off, but only bottlenose dolphins did so in a manner suggestive of a change in risk‐taking behavior. We show that ECEs can have strong indirect effects on megafauna populations and habitat use patterns in the marine environment, even when direct effects are minimal. Our results also show that indirect impacts are not uniform across taxa or trophic levels and suggest that generalist marine consumers are less susceptible to indirect effects of ECEs than specialists. Such non‐uniform changes in populations and habitat use patterns have implications for community dynamics, such as the relative strength of direct predation and predation risk. Attempts to predict ecological impacts of ECEs should recognize that direct and indirect effects often operate through different pathways and that taxa can be strongly impacted by one even if resilient to the other. [ABSTRACT FROM AUTHOR]