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In fisheries, operational management units and biological data often do not coincide. In many cases, this is not even known due to the lack of information about a species' population structure or behaviour. This study focuses on two such species, the common ling Molva molva and the blue ling M. dypterygia , two Northeast Atlantic gadoids with overlapping geographical distribution, but different depth habitats. Heavily exploited throughout their ranges, with declining catches, little is known about their population structure. Genotyping-by-sequencing at thousands of genetic markers indicated that both species are separated into two major groups, one represented by samples from the coasts of western Scotland, Greenland, and the Bay of Biscay and the other off the coast of Norway. This signal is stronger for the deeper dwelling blue ling, even though adult dispersal was also identified for this species. Despite small sample sizes, fine-scale patterns of genetic structure were identified along Norway for common ling. Signatures of adaptation in blue ling consisted in signs of selections in genes involved in vision, growth, and adaptation to cold temperatures. [ABSTRACT FROM AUTHOR]

Due to global declines, skates and sharks have become a focus of marine conservation in recent years. Despite protective measures, they remain vulnerable to bycatch by fisheries, especially bottom-trawls and pose a problem for fisheries management measures that aim to eliminate discards in the future. In the mixed-species bottom-trawl fisheries of the North Atlantic catches can be increased by fitting a length of chain known as a "tickler" in front of the groundgear of the trawl. It was hypothesized that the tickler is especially effective at catching skates and rays that may otherwise escape beneath the net. A trial was undertaken with paired tows with and without the tickler chain. The trial demonstrated that the catch rate of skates and sharks can be significantly lowered by removing the tickler. A set of secondary nets (groundgear bags) attached behind the groundgear of the main net allowed the number offish escaping under the net to be estimated and showed that the reduction of skates and sharks in the main net was accompanied by an increase in number in the groundgear bags. This suggests that prohibition of the use of tickler chains in areas that are known to be especially important to skates and sharks could have conservation benefits. The removal of the tickler chain had little effect on catch rates of haddock, whiting, and flatfish, but caused a marked decrease in the catch rate of commercially valuable anglerfish. [ABSTRACT FROM AUTHOR]