Bycatch, Capture Mortality, and Release Condition in the Cypriot Pelagic Longline Fishery: A Multi-Year Observer-Based Assessment from the Levantine Sea

This study assessed bycatch composition, nominal catch rates, capture mortality and release condition in the Cypriot pelagic longline fishery targeting swordfish and albacore tuna. Observations covered 142 fishing days across 16 vessels during 2018–2024 and 335,340 hooks, recording 643 bycatch individuals from 23 species. Bycatch comprised 10.7% of the total catch biomass, with pooled rates of 1.92 individuals and 14.20 kg per 1000 hooks. Elasmobranchs accounted for 63.5% of bycatch individuals, and pelagic stingray alone accounted for 60.0%. Mean fishing-day bycatch biomass, expressed per 1000 hooks and 12 h, was 2.75 times as high in swordfish fishing as in albacore fishing (95% vessel-bootstrap confidence interval [CI] 1.53–3.68). Overall capture mortality was 26.4% (95% CI 23.2–30.0%), including 2.7% in elasmobranchs, 69.1% in teleost fishes and 60.7% in sea turtles. The low pooled elasmobranch mortality masked substantial taxonomic variation: 11 out of 22 sharks were dead at haulback (50.0%), whereas no deaths were observed among the 386 pelagic stingrays. Of the 406 individuals released alive, 396 (97.5%) were classified as Good for vitality, nine as Fair and one as Poor; all were coded as having Minor injury. Release condition remains a descriptive, uncalibrated indicator, and post-release survival was not measured. Sampling was partly opportunistic, and target fishery was partly confounded with year; results therefore describe the observed sample rather than the whole fleet. However, these findings establish a baseline for fishery-specific monitoring and mitigation and highlight the importance of distinguishing shark and stingray capture mortality.