No abstract

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.

1. The isotopic composition of tooth-bound collagen has long been used to reconstruct dietary patterns of animals in extant and palaeoecological systems. For sharks that replace teeth rapidly in a conveyor-like system, stable isotopes of tooth collagen (δ 13 C Teeth & δ 15 N Teeth ) are poorly understood and lacking in ecological context relative to other non-lethally sampled tissues. This tissue holds promise, because shark jaws may preserve isotopic chronologies from which to infer individual-level ecological patterns across a range of temporal resolutions.2. Carbon and nitrogen stable isotope values were measured and compared between extracted tooth collagen and four other non-lethally sampled tissues of varying isotopic turnover rates: blood plasma, red blood cells, fin and muscle, from eight species of sharks. Individual-level isotopic variability of shark tooth collagen was evaluated by profiling teeth of different ages across whole jaws for the shortfin mako shark Isurus oxyrinchus and sandbar shark Carcharhinus plumbeus.3. Measurements of δ 13 C Teeth and δ 15 N Teeth were positively correlated with isotopic values from the four other tissues. Collagen δ 13 C was consistently 13 C-enriched relative to all other tissues. Patterns for δ 15 N were slightly less uniform; tooth collagen was generally 15 N-enriched relative to muscle and red blood cells, but congruent with fin and blood plasma (values clustered around a 1:1 relationship). 4. Significant within-individual variability was observed across whole shortfin mako shark (δ 13 C range = 1.4‰, δ 15 N range = 3.6‰) and sandbar shark (δ 13 C range = 1.2‰-2.4‰, δ 15 N range = 1.7‰-2.4‰) jaws, which trended with tooth age.5. We conclude that amino acid composition and associated patterns of isotopic fractionation result in predictable isotopic offsets between tissues. Within-individual variability of tooth collagen stable isotope values suggests teeth of different ages may serve as ecological chronologies, that could be applied to studies on migration and individuallevel diet variation across diverse time-scales. Greater understanding of tooth replacement rates, isotopic turnover and associated fractionation of tooth collagen will help refine potential ecological inferences, outlining clear goals for future scientific inquiry.

Newcastle University ePrints -eprint.ncl.ac.uk Shipley ON, Olin JA, Polunin NVC, Sweeting CJ, Newman SP, Brooks EJ, Barker S, Witt MJ, Talwar B, Hussey NE. Polar compounds preclude mathematical lipid correction of carbon stable isotopes in deep-water sharks. Abstract 30Lipids affect isotope values in marine fishes, however such effects remain poorly 31 described for many extant shark taxa, especially deep-sea species. Here we report the effects 32 of lipid extraction (LE) on δ 13 C, δ 15 N, and C:N values of seven deep-sea sharks, generate 33 novel mathematical normalizations for δ 13 C based on the relationship between bulk and lipid 34 extracted values (δ 13 CBulk and δ 13 CLE)., and examine whether common normalized correction 35 models provide a robust method for addressing lipid-biasing effects in two species, the Cuban 36 dogfish (Squalus cubensis; n = 20), and Greenland shark (Somniosus microcephalus; n = 24). 37 LE generally resulted in an isotopic enrichment of 13 C and 15 N, but produced variable effects 38 on C:N across all species. Novel mathematical normalizations for δ 13 C were derived from the 39 pooled shark community, and a single species-specific correction was generated for the 40 Cuban dogfish, but could not be determined for the Greenland shark. Four common lipid 41 correction models used for teleosts, failed to accurately predict δ 13 C values statistically 42 similar to δ 13 CLE, in both Cuban dogfish and Greenland sharks, likely due to the confounding 43 effects of lipids and urea on C:N. These observations suggest that chemical lipid extraction 44 should be a mandatory procedure prior to interpreting stable isotope data for deep-sea sharks, 45 at least for those species where lipid effects are large. 46 47

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1. Mangrove creeks have a range of functional roles in tropical seascapes, but their use as feeding and refuge areas for commercially and ecologically important transient predators is poorly understood.2. This study used video cameras to investigate the diurnal use of three Bahamian mangrove creeks by transient predators during a 2-month period. More than 500 fishes from 10 species were recorded, including elasmobranchs, reef-associated fishes, and nearshore specialists. A multivariate analysis indicated that movement of the transient predator assemblage was not significantly linked to any abiotic variable and did not vary among creeks.3. Generalized linear mixed-effects models of the four most abundant transient predators demonstrated species-specific variations in creek use. Sightings of Caranx ruber and Negaprion brevirostris varied significantly among the three creeks. Furthermore, C. ruber was seen most frequently close to high tide, while N. brevirostris was seen more frequently with increasing time since sunrise and during higher tidal ranges. Sphyraena barracuda and Tylosurus crocodilus were seen most frequently just after low tide. All three creeks appear to be functionally important for transient predators, but these species exhibit considerable spatio-temporal variability in how they use this habitat.4. Mangrove creeks are threatened by a range of anthropogenic stressors, and are frequently a target of conservation initiatives. The species-specific spatial variability in creek use demonstrates that simply including representative creeks in marine protected areas could exclude functionally important areas. Furthermore, development that alters tidal cycles in creeks is likely to have significant impacts on transient predators, and underscores the need for restoration and conservation of hydrological flow.

Fisheries management strategies are needed that improve the survival of shark by-catch in longline fisheries. We quantified exercise intensity and physiological stress of longline-caught sharks to understand why different individuals fare better or worse upon release. Nurse sharks could improve their condition with added rest, unlike Caribbean reef sharks.

Overfishing is the most significant threat facing sharks and rays. Given the growth in consumption of seafood, combined with the compounding effects of habitat loss, climate change, and pollution, there is a need to identify recovery paths, particularly in poorly managed and poorly monitored fisheries. Here, we document conservation through fisheries management success for 11 coastal sharks in US waters by comparing population trends through a Bayesian state-space model before and after the implementation of the 1993 Fisheries Management Plan for Sharks. We took advantage of the spatial and temporal gradients in fishing exposure and fisheries management in the Western Atlantic to analyze the effect on the Red List status of all 26 wide-ranging coastal sharks and rays. We show that extinction risk was greater where fishing pressure was higher, but this was offset by the strength of management engagement (indicated by strength of National and Regional Plan of Action for sharks and rays). The regional Red List Index (which tracks changes in extinction risk through time) declined in all regions until the 1980s but then improved in the North and Central Atlantic such that the average extinction risk is currently half that in the Southwest. Many sharks and rays are wide ranging, and successful fisheries management in one country can be undone by poorly regulated or unregulated fishing elsewhere. Our study underscores that well-enforced, science-based management of carefully monitored fisheries can achieve conservation success, even for slow-growing species.