Studies on the habitat suitability index based on the vertical structure of water temperature for skipjack Katsywonus pelamis purse-seine fishery in the Western-central Pacific Ocean

According to the catch data and fishing times of skipjack in the purse-seine fishery in the Western-central Pacific Ocean(WCPO)(20°N-25°S,120°E-175°W),and the environment data of different water layer temperature(sea surface temperature,water temperatures of 12.5 m,237.5 m and 287.5 m layer,temperature difference per meter between 137.5 m and 187.5 m layer),the relative ratio of fishing times with high yield was considered as the habitat suitability index(SI),and SI model with single variable is established by nonlinear regression methods.Five methods(Continued product,Minimum,Maximum,Arithmetic mean and Geometric mean) were used to establish the multi-factor habitat suitability index(HSI) model.The results indicated that when Continued product and Minimum method were applied,the yield of skipjack was mainly located in the area with HSI0.5.When Geometric mean and Arithmetic mean method were applied,the yield of skipjack was mainly distributed in the area with HSI ranging from 0.3 to 0.8.When Maximum method was used,the yield of skipjack was mainly located in the area with HSI0.8,which occupied 87%of the total catch.We found that the Maximum method could best fit the fishing ground of skipjack distribution.Based on the data of water temperature in 2003,the monthly HSI was estimated by the Maximum method and verified by the catch distribution of skipjack,which showed that it was feasible to forecast the fishing ground with HSI method.