Investigation On The Biology And Habitat Distribution Of Bigeye Tuna In The Western And Central Pacific High Seas

Bigeye tuna?Thunnus obesus?is a species of high economic value and one of the major targets of our pelagic fishery.The western and central Pacific has the largest annual tuna production in the world's oceans,there are many Chinese tuna longline fishing vessels are production in the Western and Central Pacific High Seas,so the investigation on the biology and habitat distribution of the bigeye tuna has a positive effect to Chinese pelagic fishery enterprise production in the Western and Central Pacific High Seas.In this investigation,using the bigeye tuna samples collected in the Western and Central Pacific High Seas?2°03?S?11°17?S,163°14?E?173°35?E?from May 2018 to March 2019studied and analyzed the biology of bigeye tuna.During the Marine survey,DST?centi-TD?was used to collect the fishing gear depth data and water temperature data of tuna longline fishing vessels during production operations,and analyzed the vertical habitat distribution of bigeye tuna.In addition,by collecting the production data of tuna longline fishing fleet in the Western and Central Pacific High Seas in 2018,combined with the satellite remote sensing data,using generalized additive model?GAM?analyze the relationship between distribution and different factors in bigeye tuna fishery.The main results of this investigation are as follows:1.Investigation on biological characteristics of bigeye tunaThe overall fork length of bigeye tuna ranged from 55.00 to 195.00cm,with an average fork length of 120.98cm?s.d.=26.12,n=1040?.The processed weight ranged from8.00 to 139.00kg,with an average processed weight of 35.25kg?s.d.=13.84,n=886?.The relation between the fork length and the processing weight was W=4.364×10^-5FL^2.7877?R²=0.9552?.The gastric contents mainly included shrimp,fish,cephalopods and other unidentified species,and the degree of stomach contents was mainly 0,1 and 2,accounting for 77.54%of the total.The sex ratio of male to female is 1.85:1?n=877?.Maturity of fish gonads mainly?,?,?period,accounting for 89.62%of the total.The weight of male gonads ranged from 5.00 to 900.00g,with an average weight of247.94g?s.d.=144.18,n=569?.The weight of the female gonads ranged from 10.00 to2350.00g,with an average weight of 583.91g?s.d.=488.18,n=308?.The male gonad index ranged from 0.05 to 3.10,and the mean value was 1.02?s.d.=0.52,n=569?.The female gonad index ranged from 0.19 to 7.87,with an average of 2.61?s.d.=1.81,n=308?.2.Investigation on the vertical distribution of bigeye tunaThe fishing depth of bigeye tuna ranged from 49.92 to 461.26m,with an average fishing depth of 258.24m?s.d.=90.03,n=692?.The range of fishing water temperature was8.41?29.97?,with an average fishing water temperature of 15.80??s.d.=5.65,n=692?.The highest water layer of CPUE is 300.00?350.00m,and the corresponding CPUE value is 3.86 tails/1000 hooks.The highest water temperature range of CPUE is12.00?14.00?,the corresponding CPUE is 4.46 tail/1000 hook.In the Western and Central Pacific High Seas,the water layer of bigeye tuna is 200.00?350.00m and the water temperature range is 10.00?16.00?.The upper boundary depth of the thermocline ranges from 115.89 to 175.49m,with an average depth of 153.12m.The temperature range is 25.62?28.77?,and the average temperature is 27.31?.The depth of the lower boundary of the thermocline ranges from 234.14 to 324.91m,with an average depth of 286.69m.The temperature range is 10.52?14.91?,and the average temperature is 12.51?.3.Investigation on the relation between distribution of bigeye tuna fishery and different factorsGAM model was used to study the relation between CPUE and different factors in bigeye tuna.The results showed that all factors except sea surface temperature and chlorophyll a concentration had significant effects on the CPUE of bigeye tuna?P<0.05?.The high CPUE area of the bigeye tuna fishery in the Western and Central Pacific High Seas is mainly close to the western part of the fishery and the equatorial region.When the surface temperature was 29.27?30.40?,the CPUE of bigeye tuna increased with the sea surface temperature.When the sea surface temperature was greater than 30.40?,the CPUE of bigeye tuna decreased gradually with the sea surface temperature rising.The change of chlorophyll a concentration had little effect on the CPUE of bigeye tuna.When the sea surface salinity was 33.43?34.25,the CPUE of bigeye tuna increased with the increase of sea surface salinity.When the sea surface salinity was greater than 34.25,the influence of sea surface salinity on the CPUE of bigeye tuna was weakened.When the sea surface height anomaly was-0.01?0.05m,the CPUE of bigeye tuna increased with the increase of sea surface height anomaly.When the sea surface height anomaly was 0.05?0.15m,the influence of the sea surface height anomaly on the CPUE of bigeye tuna was weakened.When the sea level anomaly is greater than 0.15m,the CPUE of bigeye tuna decreases gradually with the increase of the sea level anomaly.This paper study on the biological characteristics,vertical distribution and the fishing ground distribution of the bigeye tuna in the Western and Central Pacific High Seas,obtained overall conclusion that the bigeye tuna's main habitat water layer is 200.00?350.00 m,main habitat water temperature is 10.00?16.00?,the optimum range of sea surface temperature is 29.75?30.40?,the optimum range of sea surface salinity is34.25?35.50,the optimum range of sea surface height anomaly is 0.05?0.15 m,which provides reference for tuna longline fishing boats to find the center of bigeye tuna fishery and improve the catch rate of bigeye tuna in our country.