| Based on Janpanese catch statistic data from tuna purse seiner fleets and environment data which contains sea surface temperature anomaly(SSTA), sea surface temperature(SST) during the same period in the Eastern Pacific Ocean, the resource abundance of yellowfin tuna, spatial-temporal distribution of fishing ground and their relationships with various environment of middle scale climate just as in El Nino and La Nina condition are analyzed respectively by the means of Geography Information System(GIS)soft Marine Explorer4.0, gray correlation and statistical methods.The results are summarized as follows:(1) Through analyzing the SSTA in Nino3 sea area from 1975 to 2004, this paper determined the starting and ending years and months of El Nino and La Nina events.The results shown that the event of ENSO occurred frequently in 1980s and 1990s.The El Nino of 1997/1998 was the strongest event since the beginning data of history.(2) From monthly average SST from 1975 to 2004 in the Eastern Pacific Ocean(75～145°W,25°S～30°N),we can see that the change tendency of monthly average SST from 1975 to 2004 was almost the same.The change tendency of monthly average SST went up from January to April and declined from May to December.The monthly average SST between years changed a lot.Compared with normal year, the SST declined in El Nino condition and the value went up in La Nina condition.The total average SST in every longtitude had the same development tendency.The SST declined smaller from 118°W to 143°W and greatly from 73°W to 108°W.But the rise for SST occurd from 108°W to 118°W. The SST in every longtitude between years changed a lot. Compared with normal condition, the SST in every longtitude declined in El Nino condition and the value went up in La Nina condition. (3) This paper used GAM model to standardize CPUE of commercial yellowfin tuna fishery data collected in the Eastern Pacific Ocean,then compared normal CPUE with standardized CPUE,the result indicated that the variation trend of standardized CPUE was the same as normal CPUE annually and smoother than normal CPUE.(4) Evaluating yearly and monthly variation of yellowfin tuna resource abundance with the standardized CPUE of GAM method, the results indicated that the lowest yearly average CPUE was occurred in 1983,with the value of only 2.35 ton per day;the highest was occurred in 1988, with the value of only 4.82 ton per day.CPUE was among 2.35t/d and 3.18t/d from 1975 to 1983,among 3.43t/d and 4.82t/d from 1984 to 1994,among 2.74t/d and 3.4t/d from 1995 to 2004.The CPUE of the spring and summer was higher than the autumn and winter.(5) Spatial distribution was illustrated using the visualization function of GIS software based on resource abundance of yellowfin tuna in the Eastern Pacific Ocean. The results indicated that CPUE was distributed in 0～15°N,75～145°W and 0～10°S,75～95°W and based onⅠ,Ⅱ,Ⅲgrade level from 1975 to 1984.The distribution of CPUE from 1985 to 1993 was similar with from1975 to 1984, but CPUE was based onⅢ,Ⅳgrade level. The distribution of CPUE almost expanded to the entire area of 20°S～15°N,75～140°W,but CPUE was based onⅠ,Ⅱ,Ⅲgrade level from 1994 to 2004.(6) Spatial distribution was illustrated using the visualization function of GIS software based on fishing date of yellowfin tuna in the Eastern Pacific Ocean. Analysis and comparison on yellowfin tuna resource and operation position by time and area were made.The results by latitude were as follows: 1994 can be recognized as a boundary. The main fishing ground from 1975 to 1993 was concentrated in the coast and 5°S～15°N.After 1994,the fishing ground was widely distributed in 20°S～20°N,but mainly concentrated in 5°S～15°N. The main fishing ground from 1975 to 1993 was distributed in 75～135°W by longitude, but after 1994,distribution of fishing ground expanded to 145°W and no longer focused on coastal waters.(7) Based on monthly fishing gravity center,the results indicated that there was a siginifcantly regular annual change for the location of fishing gravity center. In the spring and summer, the fishing gravity center turned to the west and to the north, but it moved to the east and the south in the autumn and winter. The barycenter of fishing ground for yellowfin tuna were different in El Nino and La Nina condition from the other year. (8) Based on the analysis and research about the relationship between Nino3 index and fishing gravity center and CPUE of yellowfin tuna, preliminary results indicated that ENSO episodes affected the stock abundance and spatio-temporal distribution of yellowfin tuna significantly. During El Nino periods, the fishing gravity center moved to the east and the north, and to the west during La Nina periods. There was a negative relationship between Nino3 index and CPUE.(9) Based on the relationship between catch and SST,the yearly catch of yellowfin tuna in the Eastern Pacific Ocean from 1975 to 2004 was distributed in the waters with SST 18～30℃, and mainly came from 25～28℃,especially 27～28℃,the other temperature ranges had a low proportion.The SST for catch by months were as follows: 23～27℃in January, 25～27℃in February, 26～28℃in March, 26～29℃in April, 26～29℃in May, especially 28℃, 26～28℃in June, 27～28℃in July, 27～29℃in August, 27～28℃in September, 26～28℃in October, 26～28℃in November, 20～28℃in December, especially 26～27℃.(10) Relationship between the monthly average CPUE and SST was analyzed using GIS visualization. In normal condition,the area and strength of eastern Pacific warm pool(EPWP)reached peak in the spring and summer.At the same time,high CPUE concentrated in 0～10°N, 27～29℃. In the autumn,the area and strength of EPWP decayed and high CPUE moved to the south of equator.In winter, the area and strength of EPWP fell into the lowest. At the same time,high CPUE moved to 15°S to the south and distributed in 22～27℃.During the El Nino period, the average SST increased, the area enlarged,the western edge shifted to the westernmost position and the southern edge shifted to the southernmost position. At the same time, CPUE was distributed in 15°N～15°S,25～30℃, but high CPUE concentrated in 27～29℃. High CPUE decreased and moved to colder water during the strongest El Nino.During the La Nina period, the average SST reduced, the area lessened,the western edge shifted to the easternmost position and the southern edge shifted to the northernmost position. At the same time, CPUE was distributed in 15°N～20°S,20～29℃, but high CPUE concentrated in 27～29℃. High CPUE decreased or even disappeared during the strongest La Nina. |
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