吉尔伯特群岛海域延绳钓渔场大眼金枪鱼的环境偏好

为了掌握基里巴斯吉尔伯特群岛附近海域大眼金枪鱼的环境偏好,2009年9月至12月,金枪鱼延绳钓船"深联成719"在该海域进行了调查。利用仪器获取海洋环境数据,结合每天渔获数据,应用逐步回归方法,建立钓钩深度预测模型,计算大眼金枪鱼在各水层、温度、盐度、叶绿素、含氧量、水平海流和垂直海流范围内的渔获率,渔获率最大的各环境因子范围为大眼金枪鱼偏好的环境。结果表明:(1)大眼金枪鱼偏好的水层、水温、盐度、叶绿素、含氧量、水平海流和垂直海流范围分别为200.0~240.0 m、14.0~15.0℃、35.00~35.10、0.24~0.26μg/L、3.0~4.0 mg/L、0.00~0.20 m/s和0.03~0.04 m/s;(2)一般情况下,接近成熟的大眼金枪鱼偏好的水温为14.0~17.0℃;(3)大眼金枪鱼的适盐性较广;(4)溶解氧高于门限值(0.8 mg/L)时,大眼金枪鱼的分布由其它环境因子决定。

Environmental preferences of Thunnus obesus near Gilbert islands: an application to longline fishery

To better understand the relationships between vertical distribution of bigeye tuna(Thunnus obesus) and water temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current,and to understand the environmental preferences of bigeye tuna in waters near Gilbert islands,thus to increase the catch rate of bigeye tuna,reduce the bycatch of non-targeting species and select the dominative environment variables as the input to the CPUE standardizing model,longliner Shenliancheng No.719,equipped with a super-spool,was used as the platform for sampling in waters near Gilbert islands from September to December in 2009.The data collected included CTD(XR-620),TDR(2050),and three dimensional current(ADCP2000) profiles,amount of fishing hooks,deploying position and time,course and speed,shooting speed of main line,number of hooks between successive buoys,the time interval between two hooks,beginning time and position of retrieving line,wind force and direction,the drifting speed and direction to the ground and hook code.The capture depth,water temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current of bigeye tuna area were anayzed.The methods adopted were as follows: ① Calculating the theoretical hook depth by the catenary curve hook depth equation;②Modeling the relationship between the theoretical hook depth and predicted hook depth by means of regression method;③ Calculating all the predicting hook depth based on the predicting hook depth model;④Obtaining a vertical profile reflecting the relationships between temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current and depth,recorded by XR-620 and ADCP2000,the profiles could be used for calculating temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current based on the predicted hook depth;⑤ Estimating the catch rate of bigeye tuna at different depths,temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current ranges based on the sample data.Results indicated that in tuna longline fishing grounds of waters near Gilbert islands,the depth,water temperature,salinity,chlorophyll-a,dissolved oxygen,horizontal current,and vertical current preference range of bigeye tuna was about 200.0-240.0 m,14.0-15.0 ℃,35.00-35.10,0.24-0.26 μg/L,3.0-4.0 mg/L,0.00-0.20 m/s,and 0.03-0.04 m/s,respectively.In general,subadult bigeye tuna prefers temperature from 14.0 to 17.0 ℃ in vast salinity range and at least 0.8 mg/L of dissolved oxygen.