The influence of fishing methods on catch size, catch rate, and size distribution of Octopus cyanea (Gray, 1849) in Zanzibar, Tanzania

Abstract

Octopus cyanea (Gray, 1849) is a benthic and diurnally active species found in tropical and subtropical reefs. It is harvested for commercial and subsistence purposes, but some factors in Zanzibar challenge its catch. This study was conducted to determine variations in O. cyanea catch between on-foot and dive fishing methods in Zanzibar. Information from this study would help in the establishment of management plans, which are still challenging in Zanzibar. The catch size, catch rate, and individual size of octopuses from dive and on-foot fishing were determined. Results revealed that about 54.11 % of all octopuses were caught by on-foot fishing and 45.89 % by dive fishing. However, the average catch size (by weight and length) was lower for on-foot fishing than for dive fishing. Moreover, the catch size and catch rate per fisher were higher for dive fishers than for on-foot fishers. The proportion of octopuses weighing ≥ 1000 g constitutes 49 % and 26 % of the total catch by dive and on-foot fishing, respectively, indicating that dive fishing captures a significantly higher percentage of larger individuals than on-foot fishing. Therefore, the concentrated on-foot fishing in shallow water could affect more recruits and juveniles, while high fishing efforts in deep water by dive fishers could impact more spawners and brooders found in these areas. Given these observations, this study emphasizes the necessity of conducting long-term research to accurately identify the peak breeding, spawning, and recruitment seasons.