Raja clavata, , Linnaeus, 1758

McAllister, Mia, Fraser, Shaun & Henry, Lea-Anne, 2024, Population ecology and juvenile density hotspots of thornback ray (Raja clavata) around the Shetland Islands, Scotland, Journal of Fish Biology 104 (3), pp. 576-589 : 577-578

1.4 | Stock status of R. clavata in the North Sea

R. clavata is classified as near-threatened on the IUCN Red List of Threatened Species ( Ellis, 2016) and is also of conservation concern to the Regional Seas Convention OSPAR, listed as a threatened and/or declining species ( OSPAR, 2010). Updated status assessments of R. clavata showed improving indicators in parts of the Greater North Sea Region (includes Shetland, OSPAR Region II; OSPAR, 2021), but experts maintained that much uncertainty in stock estimates remains, thus population trends in each OSPAR region are fairly inconclusive.

The International Council for the Exploration of the Seas ( ICES) provides fisheries advice for skates and rays, informing annual changes to the total allowable catches (TACs) that aim to regulate exploitation.

ICES recently indicated stable/increasing R. clavata stocks for the Greater North Sea Subarea 4 (includes Shetland), which underpinned advice to increase landings by 9% for 2022 and 2023 ( ICES, 2021a).

However, both OSPAR and ICES identified important knowledge gaps, including locations of nurseries and other habitats where juvenile R. clavata are regularly found, and population demographic data more generally ( ICES, 2020, 2021b; OSPAR, 2021).

Existing population knowledge for R. clavata is based on data from surveys such as ICES' standardized International Bottom Trawl Survey ( IBTS). However, the large size of the vessels and areas involved in the IBTS mean that the coverage in inshore areas is restricted and data for R. clavata are limited. For example, results from the 2022 North Sea IBTS Quarter 3 showed zero catches of R. clavata in the entirety of Area 1, which covers a large part of the northern North Sea, including Shetland ( DATRAS; https://www.ices. dk/data/data-portals/Pages/ DATRAS.aspx). This highlights the difficulty in analysing data from large-scale surveys in cases where the species' habitat preference is not fully covered by the surveys targeting depths, especially when these data are used to inform management decisions. This applies to R. clavata where they are thought to be most abundant in coastal areas at 10 – 60 m depth, commonly up to 100 m ( OSPAR, 2010). In this instance, smaller-scale surveys that provide more intensive coverage, including in shallow waters, are preferential.