The influence factors of spatial point patterns of purse seine free school in the Central Equatorial Pacific Ocean

There is one of the main areas of Chinese purse seine in the Central Equatorial Pacific Ocean. The fishing efforts for the free school fish stocks will be the trend of purse seine. To understand the environmental factors, which would affect the distribution of free school stock, is becoming more and more important. The free school stock is harder to catch than other types of fish, and the rate of failing sets is very high. This paper replaces the Catch per unit effort(CPUE)with the spatial points density as the index of stock abundance. The density of spatial points is treated as response variable, and we try to find out some significant variables from environmental factors based on the logbooks of Chinese Purse Seine fleets in 2015. Some factors are obtained as independent variables based on our experience or research articles, these variables are respectively: the distance to land (DIS), sea surface temperature (SST), net primary production (NPP) and mixed layer depth (MLD). First, the nonparametric estimate to these factors are calculated from relative covariate intensity function (rhohat) method. Second, using point process model (ppm) function of these factors, the intensity regression equation is given. The results show that: (1) The favorite environmental range of these variables, are 70–250 km in DIS, are 29.7–30.1 °C in SST, are 200–280 mg C/(m²·d) in NPP, and are 35.5–42 m in MLD, respectively. (2) There are positive relationships between the free school stock abundance with DIS within 0–70 km, SST within 28.5–29.8 °C, NPP within 150–280 mg C/(m²·d), and MLD within 30–37 m, while there are negative relationships between the free school stock abundance with DIS above 250 km, NPP above 280 mg C/(m²·d), MLD above 37 m. And there are a random relationship between the free school stock abundance with SST above 30.2 °C. (3)We get the optimal free school stock abundance regression equation of these factors through stepwise regression based on the AIC method. Among the environment factors that influenced the free school stock abundance, the order of importance factor is DIS>NPP>MLD>SST.