Distribution and thermal niche of the common skate species complex in the north-east Atlantic

Temperature is one of the most significant variables affecting the geographic distribution and physiology of elasmobranchs. Differing thermal gradients across a species' range can lead to adaptive divergence and differing developmental times, an important consideration for recruitment rates of exploited species. The Critically Endangered common skate (formerly Dipturus batis) has been divided into 2 species, the flapper skate D. intermedius and blue skate D. batis, both of which have undergone dramatic population declines. Here we examine the environmental thermal and geographic distribution of these species, using observations from scientific trawling surveys and recreational angling around the British Isles. As similar-sized specimens of the 2 species can be confused, we validated species identity using molecular genetic techniques. Both species had more extensive geographic ranges than previously reported and different spatial patterns of abundance. The distribution of the blue skate appears to reflect its partiality to thermally less variable and warmer waters, while flapper skate were found in more variable and notably colder areas. The thermal range and current geographic distribution of these species indicate that future projected climate change could have a differential impact on distribution of flapper and blue skate in the north-east Atlantic.