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Environmental DNA (eDNA) detection of aquatic invasive species using quantitative polymerase chain reaction (qPCR) is a powerful tool for resource managers, but qPCR has traditionally been confined to laboratory analysis. Laboratory results often take days or weeks to be produced, limiting options for rapid management response. To circumvent laboratory delay, we combined a purpose‐built eDNA filtration system (Smith‐Root eDNA‐Sampler) with a field DNA extraction and qPCR analysis platform (Biomeme) to form a complete field eDNA sampling and detection process. A controlled laboratory study involving serial dilutions of New Zealand mudsnail (Potamopyrgus antipodarum; Gray, 1843) eDNA was conducted to compare the detection capabilities of the field system with traditional bench qPCR. Additionally, field validation studies were conducted to determine whether field eDNA analysis can be used to map mudsnail eDNA distribution and quantify temporal fluctuations. In the laboratory experiment, both qPCR platforms (Biomeme, bench qPCR) lost the ability to reliably detect mudsnail eDNA at the same dilution level, with starting quantity values as low as 21 DNA copies/reaction. A strong linear relationship was observed between the average quantification cycle values of the two platforms (slope = 1.101, intercept = −1.816, R2 = 0.997, p

Many marine mammal predators, particularly pinnipeds, have increased in abundance in recent decades, generating new challenges for balancing human uses with recovery goals via ecosystem-based management. We used a spatio-temporal bioenergetics model of the Northeast Pacific Ocean to quantify how predation by three species of pinnipeds and killer whales (Orcinus orca) on Chinook salmon (Oncorhynchus tshawytscha) has changed since the 1970s along the west coast of North America, and compare these estimates to salmon fisheries. We find that from 1975 to 2015, biomass of Chinook salmon consumed by pinnipeds and killer whales increased from 6,100 to 15,200 metric tons (from 5 to 31.5 million individual salmon). Though there is variation across the regions in our model, overall, killer whales consume the largest biomass of Chinook salmon, but harbor seals (Phoca vitulina) consume the largest number of individuals. The decrease in adult Chinook salmon harvest from 1975–2015 was 16,400 to 9,600 metric tons. Thus, Chinook salmon removals (harvest + consumption) increased in the past 40 years despite catch reductions by fisheries, due to consumption by recovering pinnipeds and endangered killer whales. Long-term management strategies for Chinook salmon will need to consider potential conflicts between rebounding predators or endangered predators and prey.

International audience; Accurately estimating predators’ diets at relevant spatial and temporal scales is key to understanding animals’ energetics and fitness, particularly in populations whose decline might be related to their diet such as northern fur seals Callorhinus ursinus. Our goals were to improve the accuracy of diet estimates and extend understanding of feeding ecology by combining 2 scat-based methods of diet determination (hard-part identification and DNA-metabarcoding) with stable isotope measurements and individual behavioural data. We collected 98 scats on a northern fur seal breeding colony. We also tracked 20 females with biologgers, and took blood samples to determine δ13C and δ15N values as proxies for seal foraging habitat and diet. Results show that diet composition from hard-parts analysis corresponded well with DNA results, with DNA yielding a greater diversity of prey species at a finer taxonomic level. Overall, scat-based methods showed that seals mostly fed on neritic shelf-associated prey. Cluster analyses of combined hard-parts and DNA results however identified 2 diet groups, one mostly neritic and the other mostly pelagic. Stable isotopes and behavioural data revealed that 40% of seals fed in oceanic waters on pelagic prey. This is more than indicated by scat-based analyses, which are likely biased towards animals foraging closest to the colony and underestimate some dietary specializations within the population. Consequently, the combination of multiple methods for diet identification with at-sea tracking of individuals can help identify and quantify specialist groups within a population and provide a wider spatial and temporal ecological context for dietary analysis.