热带中西太平洋大眼金枪鱼的繁殖生物学特性

Reproductive biology of bigeye tuna(Thunnus obesus)in the tropical western and central Pacific Ocean

利用漂流金枪鱼延绳钓作业方式,于2018年5月—2019年3月对热带中西太平洋海域(WCPO,2°03′~11°17′S,163°14′~173°35′E)的大眼金枪鱼进行了取样,对其中886尾进行了繁殖生物学测定。使用广义线性模型(GLM)和多元有序Logistic回归模型,结合圆形统计方法,分析个体叉长等生物因素、渔获水深和月度等时空因素对繁殖生物学参数的影响。结果显示,雄性和雌性平均叉长分别为(132.2±19.1)cm和(125.4±16.8)cm。取样群体中,雌雄比为0.54±0.74,且叉长与雌雄比具有负相关(r=−0.263,P=0.016),叉长大于140 cm后,雄性占主导。GLM模型结果显示,性腺指数(GSI)与叉长之间存在显著的二次方关系,即个体GSI随着叉长增加,当雄性和雌性叉长分别达到130~140 cm和140~150 cm后,GSI随叉长下降。基于圆形统计发现,月度对个体GSI具有显著影响,其中雄性GSI上半年较下半年高(正弦显著,P<0.001),而雌性GSI年末和年初高于年中(余弦显著,P=0.021)。有序多元Logistic模型结果显示,性腺成熟度随叉长显著增加(P<0.001),雄性性腺成熟度在5—7月较高(余弦显著,P=0.004)。此外,栖息水层对雄性个体的性腺成熟度具有显著的影响(正相关,P<0.001)。雄性和雌性个体50%性成熟叉长分别为(96.13±1.24)cm和(104.93±2.60)cm。研究结果可为更好地了解热带WCPO大眼金枪鱼的繁殖生物学特征、科学养护热带WCPO大眼金枪鱼资源提供参考。

Understanding the reproductive biology of bigeye tuna(Thunnus obesus)and quantifying size-specific parameters provides the means for accurately predicting the effects of fishing on the reproductive potential of stock and the basis for improving the assessment and management of bigeye tuna stocks.In this paper,a total number of 886 T.obesus were sampled by pelagic longline fishing in the tropical western and central Pacific Ocean(WCPO,2°3'-11°17'S,163°14'-173°35'E)from May 2018 to March 2019 and then their reproductive biology was investigated.The effect of biological factors,such as individual fork length,and temporal and spatial factors,such as fishing depth and month,on the reproductive traits of T.obesus was assessed by a generalized linear model(GLM)and polytomous logistic regression for the ordinal response model,combined with the circular statistics method.The results showed that the mean fork lengths of male and female T.obesus were(132.2±19.1)cm and(125.4±16.8)cm,respectively.The sex ratio(female:male)of sampled T.obesus was(0.54±0.74),and a significant negative correlation between fork length and sex ratio was detected(r=−0.263 P=0.016).Males would dominate the sample group when the fork length is greater than 140cm.The output of the GLM fit showed that there was a significant quadratic relationship between gonadosomatic index(GSI)and fork length(P<0.001),which means GSIs of T.obesus increased with fork length,peaked at a certain fork length(130-140 cm for males and 140-150 cm for females,respectively)and then decreased with fork length.Based on circular statistics,a significant effect of fishing months on GSIs was also detected.It is found that the GSIs of males in the first half of the year are higher than those in the second half(sine significant,P<0.001),while GSIs of females at the end and beginning of the year are higher than those at the middle of the year(cosine significant,P=0.021).The output of the ordered multivariate logistic model fit indicated that gonad maturity stages increased significantly with fork length(P<0.001)and gonad maturity stages of male T.obesus were relatively higher during May and July(cosine significant,P=0.004).In addition,fishing depth has a significant effect on the maturity stage of males(positive correlation,P<0.001).Fork lengths at 50%sexual maturity were(96.13±1.24)cm and(104.93±2.60)cm for males and females,respectively.The findings in this paper reduce uncertainty in current stock assessment models,which will ultimately assist the fishery in becoming sustainable for future generations and will contribute to scientific conservation and sustainable yield of this species.