Spatical-temporal Distribution Of Catch Rate And Relations To Marine Environment For The Bigeye Tuna(Thunnus Obesus) In Atlantic Ocean

Bigeye tuna(Thunnus obesus)was one of the main target species caught by longline fishery.It had an positive significance on the development of tuna longline fishery for China.It was important research content of fishing forecast,that the spatial-temporal distribution and relations to marine environment for bigeye tuna(Thunnus obesus)were analyzed.Based on the data on the catch of bigeye tuna longline fishery in Atlantic Ocean and Sea Surface Temperture(SST),Chlorophyll a concentration(Chl-a)and Sea Surface Height Anomaly(SSHA)by remote sensing,we analyzed the spatial-temporal distribution of Catch Per Unit Effort(CPUE)of bigeye tuna fishing grounds and their relations by using Arc Gis and mathematical statistic methods.Meanwhile this present study analyzed rate of contribution on the spatical-temporal and environmental factors to the fishing grounds distribution of bigeye tuna(Thunnus obesus)using Generalized Additive Model(GAM).The results are summarized as follows:1)Temporal change of bigeye tuna longline fishery in the Atlantic Ocean was analyzed.The results showed that,in the spatical series the bigeye tuna fishery mainly distributed in the sea near 10°S~8°N,17°W~28°W and 5°N~10°N,34°W~40°W.And the catch high-yield area most Concentrated in the northern latitudes;The catch gravity central of fishing vessels appear a full ups and downs bylatitude,and little change by longitude.The second quarter and fourth quarter the vessel produte in the northern latitudes and the third quarter produte in the southern latitude.The catch gravity central changed from southeast to northwest in Atlantic Ocean from fourth quarter to the first quarter.The Span is larger by longitude and latitude.Meanwhile,Analyzed the CPUE of bigeye tuna fishing grounds in the temporal series,results shows that the catch of bigeye tuna in Atlantic Ocean were caught through the year,and the CPUE of the first quarter is significantly higher than others.The rich catch of biheye tuna in Atlantic Ocean appeared from January to March and the highest catch appeared during the mid-January to mid-February.2)The results showed that the SST of bigeye tuna fishing center ranged from 25.2 to 28.9?,the optimum SST ranged from 27.5~28.5?,the frequency percentage achieve 95% in this area,and the catch was 56% of the total produced.There were significant differences of theopimum SST during different period: From January to April the CPUE of fishing grounds was relatively high and the optimum SST was 27.5~28.5?,from May to August,the optimum SST was 27~28? and the CPUE of this period was lower.From September to November,the optimum SST was 25.2~26? the CPUE also at the lowest value of the year.In December the fishing grounds from low temperatures area to the high temperatures area.3)The results showed that the SST of bigeye tuna fishing center ranged from 0.1 to 0.18mg/m3,The chl-a of fishing grounds in the northern latitudes showed a downward trend in April and may.From May to June,the Chl-a ranges were 0.07~0.12mg/m3.During July to August,the fising grounds most in the morthern latitude and the suitable ranges of Chl-a were 0.11~0.16mg/m3.From September to October,the ranges of Chl-a was 0.06~0.15 mg/ m3,but the CPUE was lower in this sea area.During January to March,the CPUE of bigeye tuna was high,the optimum ranges were 0.10~0.15mg/m3.4)The results indicated that the SSHA of bigeye tuna fishing grounds mainly ranges 8~12cm.Some high CPUE grounds will appeared in the-2~2cm.The number of fishing grounds showed a trend of increasing and decreasing by the growth of SSHA,in the one year.From January to march the high CPUE appeared between The high-value region and low-value region of SSHA,During July to August,the fishing grounds between the mid-value region and high-value region,but the number of productions was small in this area.In general,the SSHA lower near the equator from Ffrom February to July,and at high altitudes the SSHA lower from August to January.5)Selected the week,the latitude,the longitude,the SST,the Chl-a and the SSHA,we analyzed the relations between CPUE and the six factors.the results of stepwise GAM showed that week was the most significant influence to the CPUE,in the other factors,the longitude was the second,and then was the latitude.In the environment factors,the SST was the most significant influence to the CPUE,then the SSHA was the second,and then was the Chl-a.