DNA barcoding unveils skate (Chondrichthyes: Rajidae) species diversity in ‘ray’ products sold across Ireland and the UK

Abstract

Skates are widely consumed across the globe, but many large species are subject to considerable concern regarding their conservation and management. Within Europe such issues have recently driven policy changes so that, for the first time, reports of skate landings now have to be made under species-specific names. Total allowable catches have also been established for many groups, which have been set to zero for a number of the most vulnerable species (e.g., Dipturus batis, Raja undulata and Rostoraja alba). Whilst accurate species identification has become an important issue for landings, the sale of skates is still usually made under a blanket term of “skate” or “ray”. The matter of identifying species of skate is further complicated by their morphologically conservative nature and the fact that they are commercially valued for their wings. Thus, before sale their bodies are usually discarded (i.e., “winged”) and often skinned, making morphological identification impossible. For the first time, DNA barcoding (of the mitochondrial COI gene) was applied to samples of skate wings from retail outlets across the British Isles, providing insight into which species are sold for consumption. A total of 98 wing samples were analysed, revealing that six species were sold; blonde ray (Raja brachyura), spotted ray (Raja montagui), thornback ray (Raja clavata), cuckoo ray (Leucoraja naevus) small-eyed ray (Raja microocellata) and shagreen ray (Leucoraja fullonica). Statistical testing demonstrated that there were significant differences in the species sold in the distinct retail groups which suggests complex drivers behind the patterns of sale in skates. The results also indicate that endangered species are not commonly being passed on to consumers. In addition, the practice of selling skate wings under ambiguous labels is highlighted as it makes it extremely difficult for consumers to exercise a right to avoid species of conservation concern. Interestingly, a single retailer chain labelled their wings as originating from three smaller-growing species (generally to be considered of lower conservation concern); of the six samples analysed from this company a third were mislabelled and originated from the thornback ray (a larger species that is currently undergoing population declines).

Mislabeling Seafood Does Not Promote Sustainability: A Comment on Stawitz et al. (2016)

“…The collated dataset is a heterogeneous mix of capture and farmed products, a collection of extensively studied species and less thoroughly investigated taxa, mostly grouped into ambiguous/"umbrella" terms (Griffiths et al 2013). The decision to standardize definitions to the US-FDA seafood list introduces additional ambiguities associated with such groupings (e.g., "bream," "flounder," "snapper," etc.…”

Resolving taxonomic uncertainty in vulnerable elasmobranchs: are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

“…The identification of species boundaries, fundamental for effective conservation management, is therefore challenging. This issue is reflected in market mis-labelling of commercial landings (Iglésias et al 2010;Griffiths et al 2013). Complementary molecular approaches can assist with defining these boundaries and verifying species identifications.…”

Skate-ing on thin ice: molecular ecology of longnose skates in the Southeast Pacific Ocean

“…In particular, longnose skate fisheries have unique challenges for conservation due to the convergence of morphological characters that hinder their identification (Robert & Hawkins, 1999;Stevens et al, 2000;Dulvy & Reynolds, 2002;Griffiths et al, 2013). Deep-water elasmobranchs, and particularly the skates, are among the marine organisms most vulnerable to extinction as a result of overfishing (Fowler et al, 2005;Dulvy et al, 2014).…”

“…Worldwide, skate fisheries are often accompanied by a lack of biological information necessary for adequate management (Ferretti et al, 2008(Ferretti et al, , 2010Griffiths et al, 2013;Dulvy et al, 2014). In particular, longnose skate fisheries have unique challenges for conservation due to the convergence of morphological characters that hinder their identification (Robert & Hawkins, 1999;Stevens et al, 2000;Dulvy & Reynolds, 2002;Griffiths et al, 2013).…”

“…The role of morphometrics, as applies to elasmobranch fishes, has been fundamental in the resolution of the identities of threatened species, especially in relation to their management and conservation (White & Last, 2012); however, morphologically-based taxonomic differentiation is not always clear, and under such circumstances molecular markers might provide a solution to the problem (Dudgeon et al, 2012). The recent development of molecular tools to assist in species identification has focused mainly on species complexes and cryptic species (White & Last, 2012;Cerutti-Pereyra et al, 2012;Tillett et al, 2012;Griffiths et al, 2013). The use of genetic markers has also allowed a better understanding of species dynamics and provided answers to questionings that have not been possible to resolve using traditional morphological methods (Schwartz et al, 2007;Ovenden, 2013).…”