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Fisheries enforcement relies on visual catch identification and quantification at sea or when landed. Silage (fish dissolved in acid) and fish blocks (block frozen fish) are promising methods for on-board processing and storage of low-value catches. We examined the use of non-destructive sampling and two DNA-based methods, quantitative PCR (qPCR) and metabarcoding, to assess species composition and relative abundance in industrial grade experimental silage and fish blocks. We demonstrate the ability to identify and quantify DNA from fish species in both products. qPCR analysis of small silage samples collected over 21 days detected all target control species. DNA from one species (Atlantic wolffish) was consistently overrepresented while, for three species of gadoids (Atlantic cod, haddock and whiting), the DNA content matched input tissue proportions with high accuracy. qPCR and metabarcoding of fish blocks, sampled as run-off water and exterior swabs, provided consistent species detection, with the highest variance observed in quantification from swab samples. Our analysis shows that DNA-based methods have significant potential as a tool for species identification and quantification of complex on-board-processed seafood products and are readily applicable to taxonomically and morphologically similar fish. There is, however, a need for establishing DNA/weight calibration factors for primary fisheries species. [ABSTRACT FROM AUTHOR]

A crucial first step in assessing and managing the role and impacts of predators on their environment is knowledge on their foraging behaviour and diet. Here, we synthesize previously published and newly generated data on the diet of harbour seals, grey seals, and ringed seals in the Baltic Sea region. More than 45 000 otoliths recovered from 3147 samples of scats and digestive tracts were collected throughout all seasons and most Baltic Sea sub-basins from 1968 to 2013. The data revealed a large extent of interspecific, spatial, and seasonal variation in seal diet, implying that caution should be made when extrapolating from one species, area or season, to others. Still, a few fish species, including Atlantic herring, sprat, cod, and sandeels had high occurrence across seal species and locations. The compiled data provide the first overview of seal diet across the entire Baltic Sea region, but also comes with several limitations. Thus, while the data presented here constitutes an important reference for future inference, it also illustrates an urgent need for standardizing methodology across studies on the diet of seals and other aquatic predators. [ABSTRACT FROM AUTHOR]