Spatio-temporal distribution and abundance of thornback ray (Raja clavata) in the North Sea and the Eastern English Channel

Stäudle, Timo; Poos, Jan Jaap; Parmentier, Bram


Presentations at EEA2021 conference Leiden.
Skates and rays are common bycatch species of fisheries, susceptible to overfishing because of their life
history characteristics. Their stock management suffers from data limitations and a lack of analytical stock
assessments. A global TAC, common for all Rajidae species as the current management measure, is often
reached through bycatch before the fisherie’s main target species quotas, such as for flatfish. This often
results in a substantial fraction of Rajidae being discarded to avoid a choke species effect, with limited
discard data available. Among Rajidae species, Raja clavata is the most landed species with the highest
commercial interest in the English Channel and North Sea (ECNS) area. Their stock has been depleted in the
1990s with trends of recovery of catches observed over the last decade. Due to its classification as a data
limited stock it is assessed by ICES with survey specific trend-based analysis methods.
The present study investigates a hierarchical Bayesian modelling (Integrated Nested Laplace Approximation)
to assess the spatio-temporal distribution of Raja clavata in the ECNS area and provide proxies of reference
points for relative population size and biomass. This approach allows to account for spatio-temporal
components across combined survey catch data from the International Bottom Trawl Survey, Beam Trawl
Survey and Channel Ground Fish Survey (1988-2020).
Preliminary results show an increase in the abundance and biomass of Raja clavata in the ECNS area in the
last decade. Furthermore, a notable expansion of the population abundance and distribution towards the
coast of the Netherlands can be observed over the last decade. The spatio-temporal consideration and the
combination of survey data across the ECNS area provide promising insights into past and present
distributions and reference points for analytical stock assessments for data limited marine populations.