A Comparison of Alternative Circle Hook (Kahle Hook) and J-Style Hook Performance in Experimental Pelagic Longline Fishery in Turkey

摘要

In recent years, circle hooks have been encouraged as an alternative to traditional J-hooks in pelagic longline fisheries to minimize by-catch mortality and injury to sea turtles and other marine wildlife. Prior to this study, circle hooks had not been used by domestic commercial pelagic longliners in Turkey. The main objective of the study was to evaluate the efficiency of kahle hook comparing with J-style hook baited with sardine (Sardina pilchardus) in pelagic longline fishery in the Aegean coast of Turkey (Kusadasi Bay). We used conventional J-style hooks (Mustad 2315DT-4/0) and kahle hooks (Eagle Claw 142A-6/0) for each fishing operation and compared catch rates, catch compositions of target and non-target species. The relative performance of kahle and traditional J-style hooks was tested during 22 valid pelagic longline fishing operations between August 2010 and December 2012. A total of 2200 hooks were used equally among kahle and J-style hooks consecutively. Captured fish were identified, total and fork lengths were measured, weighed, the time of haul back, and hook type as well as by-catch fish were recorded. A total of 78 fish were caught belonging to 13 species during the samplings. The overall CPUE was 4.73 fishes per 100 hooks for kahle hooks and 2.46 fishes for J-style hooks. For the CPUE of all fishes, the difference was statistically significant (Z = -1.977; P<0.05), in favour of the kahle hook being almost two times greater than the J-style hook. Likewise CPUE was 17007.69 g per 100 hooks for kahle style hooks and 4807.27 g for J-style hooks (Z = -1.997; P<0.05). While no difference was found between two hook models on by-catch species, kahle hooks were more efficient in comparison to J hooks on discard species. Swordfish (Xiphias gladius) had the highest CPUE (2.82) among all species for kahle hooks followed by silver scabbard fish (Lepidopus caudatus), 0.64. For J-style hooks, silver scabbard fish catch had the highest CPUE (0.64) followed by swordfish (0.55).