| Skipjack tuna is under the jurisdiction of the Western and Central Pacific Fisheries Commission(WCPFC),and due to the increasing fishing pressure on skipjack tuna in the Western and Central Pacific Ocean in recent years,the amount of skipjack tuna has tended to decline.China’s mainland tuna purse seine has formed a certain scale through the accelerated development in the past ten years,and the growth of China’s mainland purse seine fleet has improved China’s participation in sharing the high seas and oceanic fishery resources,and has also played a positive influence on the enhancement of China’s status in the international fishery.However,in recent years,tuna purse seine fishery enterprises have faced increasing unit prices for Vessel Day Scheme(VDS)operating days in the Western and Central Pacific Islands,and increasingly strict regulations by regional fisheries management organizations on the use of Fish Aggregation Devices(FAD)by fishing vessels,FAD(Fish Aggregation Devices)regulations by regional fisheries management organizations are becoming stricter,and changes in the marine environment are affected by extreme atmospheric changes(e.g.,El Ni?o and La Ni?a)that are difficult to predict.By grasping the center of fishing grounds and their distribution,we can help fishery companies to improve their fishing efficiency and thus solve these situations to a certain extent.This paper is based on the production data of the vessels"Jinhui 18"and"Jinhui58"from 2017 to 2021 of Shanghai Kai Chuang Ocean fisheries Co.Ltd and combined with my practical experience in offshore production for two years from 2020 to 2021.By comparing and analyzing the distribution of fishing grounds、Catch Per Unit Effort(CPUE)and three marine environmental factors including Sea Surface Temperature(SST),Chl-a Concentration(Chl-a)and Sea Surface Height(SSH)on the spatial-temporal distribution of fishing grounds,and then obtain the spatial-temporal distribution of fishing grounds and the relationship between the three marine environmental factors and the distribution of fishing grounds of the two vessels,in order to provide a reference for the relevant fishery enterprises to improve the fishing efficiency by grasping the central fishing grounds.The main findings of this study are as follow:1.In terms of the distribution of production center of gravity,in 2017,the production center of gravity of both vessels was distributed in the sea west of 174°E,mainly in the Exclusive Economic Zone(EEZ)of Kiribati,with a longitudinal span of 12°and 10°,respectively,and mainly within 4°south of the equator.The center of gravity of production of both vessels in 2018 is contracted in the longitudinal direction,and production center of gravity is concentrated in the EEZ of Kiribati,and the distribution of production center of gravity in 2019 is clearly shifted to the east in the longitudinal direction.From the distribution of the latitudes of the two vessels,it can be concluded that the operating area is mainly concentrated around 1.5°S,with less distribution north of the equator.The change of production center of gravity in latitude,Jinhui 18 ships are mainly distributed within 1.5°S,with a trend of moving northward in the first half of the year and southward in the second half of the year;Jinhui 58 ships are more distributed in southern latitude,with the range north of 1°S.The center of gravity of production of the two vessels overlaps in the longitude range of 170°E～174°E,but the span in longitude upward is greater for the Jinhui 58.2.From the CPUE distribution of both ships,in longitude upward span is larger,reaching 27°and 22°respectively,while in latitude upward both ships CPUE are distributed within the area of 4°north and south latitude.If the Kiribati Gilbert Islands are used as a distinction,we can see that the CPUE of both ships are mainly distributed in its west side.CPUE distribution of both ships shows a trend of eastward and southward migration during 2018.CPUE distribution of both ships shows a trend of north-south latitude contraction and east-west longitude expansion,and mainly shows a southward contraction and eastward expansion during 2019.2020 shows the opposite situation compared to 2019.Most of the CPUEs are distributed south of the equator,and the CPUEs of the two vessels in Nauru increase significantly and the operating range shrinks significantly.2021 CPUEs of the two vessels show a clear north-south distribution,and the range expands from 4°S in 2017 to 10°S,and the distribution sea area is still dominated by Nauru and Kiribati EEZ.3.Based on the marine environmental factors of yield data and satellite remote sensing data,the correlation test of each factor on the CPUE of the two vessels was analyzed using the generalized additive model(GAM)).The results showed that the explanation rate of the total deviation of CPUE in the GAM model of 18 rounds was8.20%,and the best model was selected according to the AIC and P-value:Ln(CPUE+1)～s(month)+s(Longitude)+s(latitude)+s(SSH)+s(Chl-a)+s(SST)+ε;the explanation rate of the total deviation of CPUE in the GAM model of 58 rounds was 11.20%.The explanation rate of the total deviation of CPUE in the model is11.80%,and the best model is selected according to the AIC and P-value:Ln(CPUE+1)～s(year,k=5)+s(month)+s(Longitude)+s(latitude)+s(SSH)+s(Chl-a)+s(SST)+ε.Among the explanation rates of each factor environmental factors were higher compared to the spatio-temporal factors explained,with the contribution of SST being the highest in the GAM models of both vessels,4.87%and 5.90%,respectively.4.Based on GIS spatial and temporal analysis,the sea surface temperature range of the two boats of skipjack tuna CPUE distribution area is 28.31～31.18℃;sea surface height range is 0.52～0.83 m;chlorophyll a concentration range is 0.15～0.21mg/m~3 and 0.14～0.22 mg/m~3,respectively,in the area where chlorophyll a concentration is greater than 0.22 mg/m~3,there is almost no distribution of the two boats of skipjack tuna CPUE.region,the CPUE of skipjack tuna was almost not distributed in both vessels. |
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