DNA based monitoring of sharks, skates and rays, and risk-based evaluation of bycatch in Danish fisheries

Sharks and rays are important components of marine biodiversity. This together with their life history with slow growth, late maturation and large asymptotic size makes them candidates for biodiversity indicators under descriptor 1 of the Marine Strategy Framework Directive. However, the assessment of their abundance and occurrence in the fishery is complicated by expected poor species identification. Further, landings of skates and rays (Rajidae) have historically often been reported as “wings” in commercial landings, rendering the catches by species unknown. For sharks, many species are easier to identify visually, but some, such as Mustelus asterias (starry smoothhound) and Mustelus mustelus (common smoothhound) can be difficult to distinguish from each other. These difficulties mean that the Danish monitoring undertaken prior to the previous MSFD assessments could not support the evaluation of the impacts of fishing on individual species. This report aims to ensure that the species composition of sharks and rays in the Danish commercial fishery can be assessed going forward, and that Denmark can fulfil the obligations of the common fisheries policy and the marine strategy directive. This was approached through developing and testing DNA-based monitoring of by-catch of sharks and rays in the Danish commercial fishery and providing a knowledge base for risk-based management in relation to unintentional by-catch of sharks and rays. The project is divided into two components, mapping of the species composition of rays and selected sharks in the Danish fishery and an analysis of the catches of skates and rays in the Danish fishery. The mapping of species composition is confirmed by tissue samples from rays and selected shark species during observer trips on commercial fishing vessels and samples at landing sites. A risk-based analysis combines results from the genetic analysis with the observer and landing data to rank fisheries and gear