Shedding light on the extent and patterns of spurdog (Squalus acanthias) bycatch in the Norwegian coastal fisheries

• Main Author: Lind, Sophia
• Format: Master Thesis
• Language: English
• Published: 2023
• Subjects: spurdog; Bycatch; Northeast Atlantic; Squalus acanthias
• Online Access: http://hdl.handle.net/10852/103817

The spurdog (Squalus acanthias) is a common shark in the Northeast Atlantic. Through time, this species has been heavily exploited by fisheries which resulted in a gradually declining stock biomass. This led to the introduction of restrictive management measures in the 2000s. Even though fisheries targeting spurdog have been restricted for over 20 years, spurdog often end up as bycatch in commercial fisheries targeting other species, throughout the Northeast Atlantic, including in Norwegian waters. Bycatch can lead to unexpected harm to wild populations. If bycatch continues without the appropriate knowledge to trigger management actions, the exposed population might undergo increased vulnerability, which will delay recovery and, in the worst-case scenario, may lead to a population collapse. Therefore, quantitative methods for detecting the extent of bycatch are necessary. By using fishery-dependent data from the Norwegian Coastal Reference Fleet (CRF) and official landing statistics (sales notes) from the Directorate of Fisheries (FDir), this study investigates methods exploring the extent and patterns of spurdog bycatch in coastal gillnet fisheries along the Norwegian coast across time and space. Spurdog bycatch was estimated using two different approaches, both detecting possible bycatch drivers, and either detecting the probabilities for, or quantities of, spurdog bycatch. The results uncovered coastal areas with higher bycatch probabilities and quantities south of 62°N within the gillnet fisheries targeting a mix of coastal species. This study revealed that bycatch events and quantities of spurdog bycatch were higher compared to observed landings in the coastal gillnet fleet, probably as a result of discarding individuals at sea. There are however data gaps and uncertainties connected to the amount of spurdog discards in Norwegian waters, due to reporting gaps. Therefore, the additional mortality caused by bycatch, that is, landings plus discards, might leave the spurdog population in a heavier exploited ...