北大西洋大青鲨渔业生物学初步研究

Preliminary analysis of fisheries biology of the blue shark, Prionace glauca, in the North Atlantic Ocean

大青鲨(Prionace glauca)是金枪鱼延绳钓渔业中最主要的兼捕鱼种之一,作为海洋生物链的顶端物种对海洋生态系统的稳定性和多样性起到了重要作用。作者根据中国金枪鱼渔业科学观察员在北大西洋海域(3°~55°N,15°~40°W)采集的2 112尾大青鲨数据,按不同性别对其渔业生物学特征进行初步研究。结果表明:雌、雄大青鲨的优势叉长组分别为180~220 cm、190~230 cm,雄性叉长均值显著大于雌性,雌、雄性比符合1︰1;大青鲨叉长-全长、尾凹长-全长的线性关系分别为L_F=0.8008L_T+7.3361,L_P=0.7576L_T–1.8479;北大西洋热带海域(3°~13°N)兼捕的大青鲨群体组成以大个体为主(180~240 cm),冰岛附近海域(48°~51°N)兼捕的大青鲨群体组成以小个体为主(100~210 cm);大青鲨叉长和质量关系式为W_R=7×10^(–6)L_F^(2.9994);大青鲨肝脏为性腺的发育提供能量,成熟个体的肝质量指数显著小于未成熟个体;热带海域兼捕的大青鲨以性成熟个体为主(96.9%),冰岛海域兼捕的大青鲨以未成熟个体居多(77.1%);50%雌性性成熟个体对应的叉长为178.7 cm,50%雄性性成熟个体对应叉长为173.6 cm;雌性怀仔大青鲨的叉长与其怀仔数量线性关系为L_S=0.419×L_F–49.7(R^2=0.3905),幼仔雌雄性比符合1︰1;胃含物中以沙丁鱼和鱿鱼出现频率最高。作者的研究有助于更好地了解北大西洋大青鲨的生物学特征,为区域性渔业管理组织评估大青鲨种群资源状态提供数据参考。

The blue shark, Prionace glauca, is usually one of the key by-catch species in tuna longline fishery. As a top species of the oceanic food chain, it plays a vital role in maintaining the stability and diversity of the marine ecosystem. However, the biological information of this shark is limited for the availability of its samples. In this study, we described and analyzed the fisheries biology of the blue shark based on a total of 2 112 samples collected by China＇s national tuna fisheries observers in the North Atlantic Ocean（3°-55°N, 15°-40°W）. The results indicated that the dominant fork lengths of males and females were 180–220 cm and 190–230 cm, respectively, and the mean fork length of the male was significantly larger than that of the female. The female–male ratio of the captured sharks was almost 1︰1. The relationships between fork length and total length and pre-caudal length and total length could be described as L_F = 0.8008 LT ＋ 7.3361 and LP = 0.7576LT-1.8479, respectively. The larger individuals（180–240 cm） were primarily distributed in the tropical waters（3°-13°N）, while the smaller individuals（100–210 cm） were primarily captured around the Iceland waters. The relationship between fork length and round weight was described as W_R =7×10^–6LF^2.9994. The hepatosomatic index（HSI） of mature individuals was obviously smaller than that of immature individuals because of the energy expenditure for gonad development. Among the by-catch blue shark, mature individuals were dominant comprising 96.9% in the tropical waters, while immature individuals were dominant in the Iceland waters, comprising 77.1%. Fork length at 50% maturity was 178.7 cm for females and 173.6 cm for males. The relationship of LS-LF was LS = 0.419×LF-49.7（R^2 = 0.3905）, and the female–male ratio of juveniles was also almost 1︰1. Sardines and squids were predominantly found in the stomach of the blue shark. This study contributed to a better understanding of fisheries biology of the blue shark and could be useful for evaluating the shark＇s resources.