Publication Abstract

This study used electronic data storage tags and visual health assessments to quantify post-release survival for commercially caught thornback ray (Raja clavata), undulate ray (Raja undulata) and small-eyed ray (Raja microocellata) in UK inshore fisheries. Thornback ray were tagged and released from the English Channel trammel net fishery (n = 60), and the otter trawl fishery (n = 52) and longline fishery (n = 60) in the southern North Sea; Undulate ray (n = 65) from the English Channel otter trawl fishery and small-eyed ray (n = 68) from the English Channel otter trawl fishery. Depth and temperature measurements were logged on data storage tags from the point of release to the point of tag retrieval and used to infer the fate of the fish using a novel data classification method combined with data representing the normal behaviour of the skate species. Fish condition was visually assessed and assigned to ordinal classes of vitality, and reflex impairments and injuries recorded using a predefined assessment protocol for all or most of the skate caught (n = 1480). Vitality data were combined with the inferred fate of tagged skate to generate an indicative discard survival estimates for the fisheries. For thornback rays, survival is estimated at 94% for the trammel net fishery in the English Channel, 97% for the otter trawl fishery in the English Channel and 75% for the longline fishery in the southern North Sea. The survival rate is estimated at 83% for the undulate ray otter trawl fishery in the English Channel, and 55% for the small-eyed ray otter trawl fishery in the western English Channel. This study provides estimates of discard survival for European species of skate caught in inshore fisheries, which have immediate application to support regulations permitting the release of unwanted skate and ray catches and in enhancing the estimation of removals in stock assessments.

Serena R. Wright*, Ana Ribeiro Santos*, Ruth Hicks*, Peter Randall*, Joana Silva*, Victoria Bendall, Stuart Hetherington, Thomas Catchpole*