Conservation relevant fine scale distribution and habitat associations of threatened elasmobranchs in temperate nearshore waters

Abstract

Elasmobranchs are globally threatened and experiencing ongoing declines. Understanding threatened elasmobranch distribution is critical for developing effective marine conservation strategies. However, our knowledge of fine scale elasmobranch habitat association and distribution in temperate nearshore systems is limited. Here, we examined the presence, relative abundance and habitat association of sharks, skates and rays using benthic baited remote underwater stereo-video systems (SBRUVs). From 772 deployments (682 total hours, 53 minutes average soak time) across three years (2021-2023) and two Scottish sea lochs and adjacent bays, elasmobranchs were detected on 31.2% of deployments (n = 241). Our surveys detected six species of elasmobranchs, representing 17.6% of the resident elasmobranch diversity reported to date in nearshore waters < 200 m depth in UK waters. The species detected include two species listed as globally Vulnerable on the IUCN Red List, spiny dogfish (Squalus acanthias) and porbeagle (Lamna nasus) and one Critically Endangered species, flapper skate (Dipturus intermedius). Critically Endangered flapper skate were detected in 5.2% deployments (n = 40) and were the only species recorded which did not show a relationship between the probability of presence and substratum type. Our findings provide critical data on the fine scale spatial distribution and habitat use of elasmobranchs, informing evidence-based conservation measures and supporting more consistent and targeted policy action for these species in Scotland.