Relationship between lunar phase, water depth and operation time and CPUE of purpleback flying squid (Sthenoteuthis oualaniensis) in South China Sea in spring

According to the yield data of the Sthenoteuthis oualaniensis in the southern and northern sea areas of the South China Sea in spring in 2015 and 2016, the present research was carried out to analyze the relationship between depth, working time and moon phases and CPUE under the condition of operation. From the GAM model analysis, we knew that the effect of operation time and lunar day on CPUE was significant. The results showed that CPUE is relatively low at the depth of 0-999 m under the water in the bright moonlight. When there was nomoonlight, the CPUE in each water layer changed little, and the CPUE at the depth of 2 500-2 999 m was relatively higher. When the working time in the first half of the night (21:00—24:00), the CPUE was higher, which wan up to 399.4 kg/net at most, and the CPUE gradually decreased in the second half of the night (0:00—5:00). There was a great difference in the yield between the bright moonlight and moonless night, which were respectively 267.0 kg/net and 321.6 kg/net. El Niño has impact on the changes of the S. oualaniensis resources in various water layers to a certain extent. The research on the effect of operational conditions on CPUE of the S. oualaniensis can provide reliable suggestions for fishing ground.