Optical Characteristics of Snood in Tuna Longline Fishing

Abstract

The luminance and the spectral luminance from different snood materials in tuna longline fishing were measured to compare their optical characteristics with the background luminance constant. The luminance variation coefficient and inherent contrast of the zinc-plated wire were several times larger than that of nylon monofilament. The volumes of stimulation strengths reaching the tuna eye from nylon monofilament and red-colored wire smaller than those from zinc-plated and blue-colored wire were computed using spectral luminance reflectance, spectral irradiance and tuna spectral sensitivity. Since fish detect the presence of fishing gear by visual sense, it is considered that differences in optical characteristics between snood materials should have an effect on the tuna catch rate.