Are Marine Protected Areas Better Than Size Limits for Halting the Decline of the North Sea Thornback Ray Raja Clavata?

A key challenge of the ecosystem approach to fisheries management is to sustain viable populations of large-bodied less-productive vulnerable elasmobranchs that are the bycatch of fisheries that target more productive species. The North Sea population of thornback ray Raja clavata is now mainly confined to the Thames Estuary and surrounding SW North Sea, which is subject to a flatfish trawl fishery. We explore the relative effectiveness of seasonal closures versus size-based landing restrictions using a four-season age-structured model. More than a third of adult thornback rays are currently removed by fishing each year, and without effective management, a further 90% decline within 30 years is likely. A three-season closure of the Thames Estuary was the shortest closure that ensured thornback ray recovery and minimal loss of fishery yield. Minimum and maximum landing size restrictions are nearly as effective at recovering thornback rays but less so at improving yield. While long seasonal closures and full marine protected areas are more effective at ensuring the recovery of thornback rays, length restrictions may be simpler to implement under the current institutional framework and may have less impact on the multispecies trawl fisheries operating in the area.