Dental microwear texture analysis as a tool for dietary discrimination in elasmobranchs

As abundant and widespread predators, elasmobranchs play influential roles in food-web dynamics of marine communities. Clearly, these trophic interactions have significant implications for fisheries management and marine conservation, yet elasmobranch diet is relatively understudied; for the majority of species little or no quantitative dietary data exist. This reflects the difficulties of direct observation of feeding and stomach contents analysis in wild elasmobranchs. Here, by quantifying the 3D surface textures that develop on tooth surfaces as a consequence of feeding, we show that tooth microwear varies with diet in elasmobranchs, providing a new tool for dietary analysis. The technique can be applied to small samples and individuals with no gut contents, and thus offers a way to reduce the impact on wild elasmobranch populations of analysing their dietary ecology, especially relevant in conservation of endangered species. Furthermore, because microwear accumulates over longer periods of time, analysis of texture overcomes the ‘snapshot bias’ of stomach contents analysis. Microwear texture analysis has the potential to be a powerful tool, complementing existing techniques such as stable isotope analysis, for dietary analysis in living and extinct elasmobranchs.

Feeding habits of Urotrygon microphthalmum (Myliobatiformes: Urotrygonidae) caught off northeastern Brazil

The feeding habits of Urotrygon microphthalmum, a Critically Endangered (CR) species, were investigated through stomach contents analysis from specimens caught on bottom double rigged otter trawls in Pernambuco state, Brazil, between March of 2010 and March of 2012. A total of 338 stomachs were analyzed, and 31 food items were identified in the diet of U. microphthalmum. The species ingests mainly shrimps. The diets between males and females were not different, and an ontogenetic diet shift was not observed. The estimated species’ trophic level is 3.5, classifying it as a secondary order consumer.

Diet of longnose stingray Hypanus guttatus (Myliobatiformes: Dasyatidae) in tropical coastal waters of Brazil

This study investigated the diet of longnose stingray Hypanus guttatus in the tropical waters of north-eastern Brazil. Samples were obtained from monthly sampling of artisanal fisheries from August 2007 to July 2008. A total of 258 specimens were examined, 127 females and 131 males, and stomach contents analysis suggested H. guttatus to be a generalist and opportunistic predator feeding on the most available prey in the environment. There was no significant difference in the diet composition of males and females, or between seasons. However, an ontogenetic dietary shift was observed with larger individuals having an increased proportion of molluscs in the diet, whilst smaller individuals predated primarily on small crustaceans.

Notes on the diet of adult Yellow Catfish Aspistor luniscutis (Pisces: Siluriformes) in northern Rio de Janeiro State, southeastern Brazil

Diet of adult specimens of Yellow Catfish Aspistor luniscutis (Valenciennes, 1840) was determined through stomach contents analysis. The specimens were target of commercial gillnet fisheries in northern Rio de Janeiro State, southeastern Brazil. In this region, A. luniscutis is a generalist benthophagous feeder, consuming most available prey species with crustaceans, especially penaeid shrimps, brachyuran crabs, and sciaenid fish dominating.

Inclusion of ecosystem information in US fish stock assessments suggests progress toward ecosystem-based fisheries management

The appetite for ecosystem-based fisheries management (EBFM) approaches has grown, but the perception persists that implementation is slow. Here, we synthesize progress toward implementing EBFM in the United States through one potential avenue: expanding fish stock assessments to include ecosystem considerations and interactions between species, fleets, and sectors. We reviewed over 200 stock assessments and assessed how the stock assessment reports included information about system influences on the assessed stock. Our goals were to quantify whether and how assessments incorporated broader system-level considerations, and to explore factors that might contribute to the use of system-level information. Interactions among fishing fleets (technical interactions) were more commonly included than biophysical interactions (species, habitat, climate). Interactions within the physical environment (habitat, climate) were included twice as often as interactions among species (predation). Many assessment reports included ecological interactions only as background or qualitative considerations, rather than incorporating them in the assessment model. Our analyses suggested that ecosystem characteristics are more likely to be included when the species was overfished (stock status), the assessment is conducted at a science centre with a longstanding stomach contents analysis program, and/or the species life history characteristics suggest it is likely to be influenced by the physical environment, habitat, or predation mortality (short-lived species, sessile benthic species, or low trophic-level species). Regional differences in stomach contents analysis programs may limit the inclusion of predation mortality in stock assessments, and more guidance is needed on best practices for the prioritization of when and how biophysical information should be considered. However, our results demonstrate that significant progress has been made to use best available science and data to expand single-species stock assessments, particularly when a broad definition of EBFM is applied.

Diet of invasive pikeperch Sander lucioperca: developing non-destructive tissue sampling for stable isotope analysis with comparisons to stomach contents analysis

Impact assessments of invasive piscivorous fishes usually rely on dietary analyses to quantify their predation pressure on prey communities. Stomach contents analysis (SCA), typically a destructive sampling method, is frequently used for this. However, many invasive piscivores are exploited by catch-and-release sport angling, with destructive sampling often not feasible. Stable isotope analysis (SIA) provides an alternative dietary analysis tool to SCA, with use of fin tissue, scales and/or epidermal mucus potentially enabling its non-destructive application. Here, the diet of a population of pikeperch Sander lucioperca, an invasive sport fish to Great Britain, was investigated by applying SIA to a range of tissues. Testing SI data of dorsal muscle (destructive sampling) versus fin, scale and mucus (non-destructive sampling) revealed highly significant relationships, indicating that the tissues collected non-destructively can be reliably applied to pikeperch diet assessments. Application of these SI data to Bayesian mixing models predicted that as S. lucioperca length increased, their diet shifted from macro-invertebrates to fish. Although similar ontogenetic patterns were evident in SCA, this was inhibited by 54% of fish having empty stomachs. Nevertheless, SCA revealed that as S. lucioperca length increased, their prey size significantly increased. However, the prey:predator length ratios ranged between 0.08 and 0.38, indicating most prey were relatively small. These results suggest that when non-destructive sampling is required for dietary analyses of sport fishes, SIA can be applied using fin, scales and/ or mucus. However, where destructive sampling has been completed, SCA provides complementary dietary insights, especially in relation to prey size.