Preliminary Study On Growth,Mortality And Resource Status Of Pacific Saury In The Northwest Pacific Ocean

Cololabis saira mainly lives in the temperate waters of the northern Pacific Ocean and is one of the important economic fish species in China’s Marine fishery.Saury growth,death,and resources related to the current utilization of the research is relatively small,for the resource status of scientific evaluation and reasonable utilization of resources,based on the investigation on fishing in the north Pacific in 2019,saury biological data acquired using length frequency analysis method to explore the mackerel pike fish composition and growth parameters,The natural death coefficient M,fishing death coefficient F and total death coefficient Z were estimated by using the method of catch curve with varying body length and Pauly empirical formula.Based on the catch composition and biological characteristics of saury,the resource utilization situation of saury in the North Pacific was evaluated by combining the Beverton-Holt model,the catch contour per unit supplement,and the biological reference points F_0.1 and F_max,and the effects of fishing opening age and fishing death coefficient on the catch per unit supplement were analyzed.And put forward the relevant fishery management plan.The results are as follows:（1）The body length of saury ranges from 180-320mm,the dominant body length is 260-300mm,and the average body length is 272mm;Body weight range was 50-155g,dominant body weight was 80-125mm,and average body weight was 102mm.The relationship between body length and body weight was:W=2×10^-5L^2.7978（R²=0.8366,P<0.01）;The growth equation is:L_t=299×^{[1-e-0.33（t+1.68）]};W_t=171×[1-e^{-0.33（t+1.68）}]^2.7978;The maximum gross circumference of females ranged from 67 mm to 100mm,with an average gross circumference of 86mm.The maximum gross circumference of males ranged from 70 to104mm,with an average gross circumference of 85mm.The fitting function of body length and maximum circumference was C=0.249L+17.983,R²=0.81.The fitting function was C=0.2545L+18.418,R²=0.79.The proportion of grade 3 autumn saury was the highest,reaching 44%,followed by grade 2,accounting for about 40%.The proportion of grade 1 and grade 4 was the least,accounting for 11%and 6%,respectively.No individual with empty stomach was found in the samples.The average weight of gonad was0.488g（SD=0.52,SE=0.27）and 0.390g（SD=0.48,SE=0.25）.F test showed that there was significant difference in gonad weight between male and female（F=1.12,P<0.05）.The percentage of female gonad maturity from stageⅡto stageⅤwas 58.08%,33.08%,7.31%and 1.15%,respectively.Female mature individuals accounted for 8.46%,male gonad maturity stageⅡtoⅤaccounted for 63.8%,30%,5.88%,0.59%,and male mature individuals accounted for 6.47%,and no male and female individuals with gonad maturity stageⅥwere found in the samples.Female gonadal index ranged from 0.012 to 6.749,with an average of 0.54,0.34（SD=0.66,SE=0.05）at grade 2 and 0.63（SD=0.49,SE=0.05）at grade 3.It was 1.16（SD=0.56,SE=0.13）in grade 4 and 1.91（SD=0.65,SE=0.15）in grade 5.The male gonad index ranged from 0.01 to 4.654,and the average gonad index was 0.44.The gonad index was 0.32（SD=0.51,SE=0.03）at grade 2,0.6（SD=0.58,SE=0.06）at Grade 3,1.07（SD=0.7,SE=0.16）at Grade 4,1.6（SD=0.43,SE=0.13）at grade 5.The gonad index of male and female samples showed the same trend,that is,it increased with the increase of gonad maturity.（2）The total death coefficient Z and natural death coefficient M were estimated by using the body length curve method and Pauly empirical formula method.The total death coefficient Z was 1.302,the natural death coefficient M was 0.71,and the fishing death coefficient F was 0.59 and the development rate E was0.45.At present,the north Pacific autumn saury is not overexploited and the fishing pressure is at the sustainable development level.（3）Based on the Beverton-Holt model of catch per unit supplement and population dynamics model,the reference points and biological parameters were calculated to evaluate the resource status of saury.In this paper,the biological reference points F_0.1=0.48 and F_max=0.94 are calculated,and the current fishing death coefficient is 0.59,indicating that the autumn saury has not been overexploited.The current fishery point of autumn saury is t_c=0.84,F=0.59,and YPR is 32.9g.According to the analysis results of catch curve of unit supplementary amount,the current point of autumn saury is located between the optimal yield areas,indicating that the resource utilization of autumn saury is good.YPR first increased and then decreased with the increase of F and t_c.On the basis of comprehensive consideration of various factors such as fishing age,fishing death coefficient and fishery economic interests,the corresponding catch per unit supplement of autumn knife fish was 34.2g when F was increased to 0.96,an increase of 3.95%compared with the current fishing point.When F remained unchanged,When t_c is increased to 1.32yr,the catch of autumn saury per unit supplement is 34.6g,5.17%higher than the current fishing point,and the corresponding body length is 189mm.Therefore,the fishing age and intensity can be appropriately increased to ensure the rational utilization of autumn saury resources.