An assessment of post-capture condition and survival of Rajidae caught in fixed nets

Abstract

Skates (Rajiformes: Rajidae) are commercially and ecologically-important elasmobranchs captured in targeted and mixed fisheries globally. Many species are of conservation concern and are subject to high levels of discarding. They are currently exempt from the European Union’s landing obligation due to evidence of high discard survival, although the bulk of this evidence comes from mobile gear fisheries. Improved evidence on survival after discarding from fixed gears is necessary. We assessed immediate survival rates and post-capture condition (injury, reflex impairment, and vitality) of four skate species commonly discarded from seasonal Dover sole, Solea solea and plaice, Pleuronectes platessa gillnet fisheries in the Irish Sea and Bristol Channel, UK. We also modelled the relationship between a suite of environmental and operational fishing variables to the condition of thornback skate, Raja clavata. This is the dominant skate captured as bycatch and is classified as near threatened by the IUCN due to declining populations trends. At-vessel survival on gear hauling was high for all species (R. clavata = 99.43%, R. montagui = 100%, R. microocellata = 100%, R. brachyura = 100%). Post-capture condition of R. clavata was size-dependent, with larger skates demonstrating higher levels of injury and reflex impairment and poorer vitality. Higher vitality in smaller individuals and strong negative effects of aerial exposure on skate vitality highlight the likely benefits of prioritising discarding of unwanted catch upon gear hauling. This may maximise survival and future reproductive potential and facilitate population recovery.