The Relationship Between Surface Marine Environment Factors And The Fishing Ground Of Skipjack Tuna(Katsuwonus Pelamis) In Waters Near Gilbert Islands

Skipjack tuna is the main target of tuna purse seine fishing. Statistics shows that skipjack tuna is accounts for 78 percent in the catch composition of the Western and Central Pacific tuna purse seine fishing from 2012 to 2014. Skipjack tuna purse seine fishing as the most efficient mode of operation begins at fifties and sixties of the last century. Since 2001, China has engaged in the Western and Central Pacific tuna purse seine fishing that develops rapidly and achieves good economic benefits. In recent years, the production of skipjack tuna continues to increase. But by the cost of fishing continues to increase and the fish prices continue to slump, the economic benefits associated with the production of fishing enterprises have not increased correspondingly. Therefore, grasping the central fishing ground accurately and purchasing and using the operating days properly will effectively reduce the production costs to the high production costs of seine fishing of skipjack tuna. According to the statistics, 38 percent of skipjack tuna production of Shanghai Kaichuang deepsea fisheries Co. Ltd seine fleet comes from the Gilbert Islands waters from 2012 to 2015. Therefore, to carry out the research of fishing ground distribution can provide a reference for the number of fishing days in this waters which fishing enterprises is going to purchase and contributes to the production ship grasp the central fishing ground.The research is based on the production data of Shanghai Kaichuang deepsea fisheries Co., Ltd seine Fleet which is combined with data of three marine environmental factors: Sea surface temperature(SST), Sea surface chlorophy11-a(Chl-a) and Sea Surface Salinity(SSS). This paper is to research the relationship between spatial and temporal distribution of the Gilbert Islands waters fishery and surface marine environmental factors. The main conclusions are as follows:(1)Based on the years, months, longitude, latitude, SST, Chl-a and SSS of production data and satellite remote sensing data. Using the Generalized Additive Models(GAM) can analysis the relevance of CPUE. The results show that GAM model’s explanation was 7.82% to CPUE,the factor that provides the largest contribution is SST. Factors in order of importance: SST>Chl-a> years> latitude> longitude> months>SSS. Based on the AIC, the optimal model:Ln(CPUE+c)~s(year,k=4)+s(month)+s(latitude) +s(sst)+ε(2)The change of monthly production from 2012 to 2015 shows roughly 10-12 months for a period of change law. From each corresponding monthly average, the maximum average catch is in May. The highest average CPUE is in November.(3)Except in January, catchr of weight position concentration in range of 1.5 ° S ~ 1.5 ° N, 171 ° ~ 174 ° E. Catch of weight position moves back and forth in longitude direction no obvious regularity; on the latitude, in the first half of the year is roughly move from north to south, while the second half of the year move back and forth in a small scale.(4)On the latitude the weight position of CPUE is in weight position of catch 1.5°to the south in January.In other months the CPUE of weight position moves in the latitude and longitude roughly consistent with the distribution of the catch of weight position. In comparison, the deviation in the longitude is smaller than in the latitude between the catch of weight position and the CPUE of weight position.(5)Distribution of skipjack tuna fishing grounds does not tend to a fixed range of SST, but with the changes in the sea SST varies. SST in the range of 29.4-30.6 ℃ skipjack tuna production accounts for 99.3% of total production. The maximum of SST average CPUE is at 30.1 ℃.(6)Mainly catch of skipjack tuna distributed in Chl-a in the range of 0.01-0.22 mg/m3 and SSS in the range of 33.6-35.4,but the effect of Chl-a and SSS on the CPUE is not obvious.