Spatial and temporal patterns of elasmobranch diversity around Jersey, Channel Islands

Over-exploitation has caused many elasmobranch populations to decline within temperate waters. However, these species are difficult to monitor without reliance on invasive or extractive techniques. A non-invasive method of studying oviparous (egg-laying) elasmobranchs involves mapping the abundance and distribution of their eggcases, which often wash ashore and are easily identifiable to species-level. Here, we identify spatial and temporal patterns of elasmobranch eggcases around Jersey, Channel Islands to infer elasmobranch presence and distribution. A total of 15,985 eggcases were collected by citizen scientists across 44 locations around Jersey between 2012 and 2018. A total of eight elasmobranch species were identified, with undulate ray (Raja undulata) and blonde ray (Raja brachyura) eggcases found in highest abundance. χ² Tests showed significant spatio-temporal patterns in eggcase occurrence. Eggcases were most abundant on the east and west coasts of the island (predominantly at Fauvic and La Pulente) during winter and spring. Drivers of these patterns likely relate to species-specific life histories, seasonal weather conditions, and distribution of survey effort. Whilst nursery grounds cannot be confirmed at this point due to the potential for eggcases dispersing in currents, Jersey likely represents an area of biological importance for several elasmobranch species. Further work to confirm this would be valuable, including increased participation in the existing citizen science project and integration of scientific surveys (e.g., baited video and tagging programmes). This would inform management strategies, such as the placement of Marine Conservation Zones (MCZs) to protect elasmobranch nurseries during this static, vulnerable phase of their lifecycle.