| Chilean jack mackerel(Trachurus murphyi)is height migratory,and widely distributed,fishery resources and the centre of fishing ground changes have large interannual differences, distributed across the entrie South Pacific, occupied a very important position in the world’s economy marine fishes. With the increased of fishing intensity and effects of climate change,its resources has been decreased. In recect years Chilean jack mackerel is the main specie of fishery. Fishery assessment of recent years have indicated that the resources have been declining, and fishing ground is hard to be found. In this case, Chilean jack mackerel resource conservation has become an important topic. Study on fertility and biological characteristics provides reference for the forecast of reproductive growth level and stock abundance. Affiliation study among the gonad development level, growth character and early development history and so on was made to determine fisheries management measures such as fishing season closure, area closure and catchable size. Aims to quota management, will strive for the initiation of science and technology for resource assessment and quota management of China’s view at the sprfmo, formed our country characteristic of Chilean jack mackerel catch and management policy,promote the power position in world fishery organization in our country.There is a famous research found that,from Chile to New Zealand. Especially in the region between 78°W to 160°W, Chilean Jcak Mackerel is abundant. North of the sea area,fish school turns the migration path towards west to the center part of Southwest Pacific.Meantime, fish school also migrates towards south and north. Chilean Jack Mackerel is growing in the migrating period towards west.According to 2500 samples of Chilean jack mackerel(Trachurus murphyi)collected from March to September in 2012, April to August in 2014 and April to July in 2015 in the south eastern Pacific Ocean,analyzed relationship between fork length and body weight, 750 otoliths were taken to do age determination, and estimated the von Bertalanffy relationship of Chilean jack mackerel. Histological analysis on the samples was made to observe jack mackerel gonads in order that we can have a detailed description of the gonad development characteristics jack mackerel. Statistical analysis methods was used to study the first sexual maturity fork length, 50% sexual maturity, the gonad maturation level.According to one-way ANOVA test, there is a significant difference in the fork length composing between male and female jack mackerel(F=35.997,P<0.01). The range body length for female is from 182 to 516 mm, the dominant fork length range is 320 to 380 mm. The range fork length for male is from 178 to 521 mm, the dominant fork length is 320 to 380 mm. According to one-way ANOVA test, there is also a significant differences in body weight composition(F=19.14,P<0.01), The range body weight for female jack mackerel is from 59 to 1284 g, with the average of 608.4±199.0g(confidence interval is 95%), the dominant body weight group is 400~600g. The range body weight for male jack mackerel is from 54 to 1520 g, with a average of 603.9±199.0g(confidence interval is 95%), the dominant body weight is 400~600g. Based on ANCOVA(analysis of covariance) test, it showed that relationship between fork length and body weight of Chilean jack mackerel should be followed as: W = 2.435×10-5L2.9539(r2 = 0.8959,n=2500) There are no significant differences between female and male skipjack tuna(F= 0.027, P> 0.05). Maximum and minimum observed age for jack mackerel was 2 and 9 years respectively. Growth parameters,L∞,k and to for female jack mackerel were 1330.4mm,0.0385 and-3.222,respectively.Growth parameters,L∞,k and to for male jack mackerel were 817.0mm,0.0896 and-1.261,respectively.The development process of jack mackerel oocyte is divided into five phases. in phaseⅠ, mitosis occurs actively, the number of cells increased rapidly from phase Ⅱ to Ⅳ, the accumulation of cytoplasmic substances happens gradually, yolk and fat bubble increase slowly; in the Ⅴphase, nuclear moves to the pole of the mature oocyte, little fat vesicles fuse into a big one. Based on the combination of visual observation and analysis of tissue sections for samples from outheastern Pacific Ocean, the smallest mature fork length of jack mackerel is 30.8cm for male, and 46.7cm for femal, 50% maturity fork length is 383.113 mm for male, and 378.641 mm for female. Selected the ovaries which maturity is above Ⅲ,and conducted a study on its individual fecundity and relationship between individual fertility and biological indicators. The results show that absolute fecundity is between 52211 ~305305 eggs, average fecundity is 154905±54878 eggs; relative fecundities based on folk length were176~687 eggs / mm, with an average of 396±109 eggs / mm; relative fecundities based on body weight were 138~349 eggs / g, with an average of 220±34 eggs /g. There were significantly positive correlation between absolute fecundity and fork length, body weight, net weight and gonad weight and other biological indicators. When the fork length is from 320 to 440 mm, there is no significant difference among sex ratio. When the fork length is small, male amount for dominant, with the fork length increased, female individuals has a significant dominance. |
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