Relationship between catch per unit effort and density of Japanese common squid Todarodes pacificus under squid jigging boat

Night-time squid jigging operations were conducted by the R/V Hakusan-maru (167 gross tons) equipped with 78 metal halide lamps (234 kW) in the Sea of Japan, and the changes in catch per unit effort (CPUE) and density of Japanese common squid Todarodes pacificus under the boat during operations were investigated. The squid density was measured using a quantitative echosounder. CPUE increased with increasing squid density during operations, but the increase of CPUE slowed down when CPUE was extremely high. The rise in CPUE with increasing squid density greatly differed by operation. The relationship between CPUE and squid density (S) was expressed as CPUE =A . SI (B-1+S), where A is an upper limiting CPUE and B is catchability of the squid. This relationship suggested that CPUE would hardly decrease under considerably high squid density conditions even though the squid density was somewhat decreased by reduced lighting, so additional operations were conducted to test this prediction. The squid density was increased by reducing the number of lit lamps in the middle of operation and CPUE was often increased. These results indicate that reduced lighting is effective to save energy (fuel) without reducing squid catch.