热带印度洋大眼金枪鱼垂直分布空间分析

Vertical distribution of bigeye tuna Thunnus obesus in the tropical In-dian Ocean

为了解热带印度洋大眼金枪鱼(Thunnus obesus)适宜的垂直和水平空间分布范围,采用Argo浮标剖面温度数据重构热带印度洋10℃、12℃、13℃和16℃月平均等温线场,网格化计算了12℃、13℃等温线深度值和温跃层下界深度差,并结合印度洋金枪鱼委员会(IOTC)大眼金枪鱼延绳钓渔业数据,绘制了12℃、13℃等温线深度与月平均单位捕捞努力渔获量(CPUE)的空间叠加图,用于分析热带印度洋大眼金枪鱼中心渔场CPUE时空分布和高渔获率水温的等温线时空分布的关系。结果表明,从垂直分布来看,热带印度洋中心渔场延绳钓高渔获率区域垂直分布在温跃层下界以下,在表层以下150-400 m深度区间。从水平分布来看,12℃等温线,高CPUE区域大多深度值<350 m,众数为225-350 m;深度值超过500 m的区域CPUE普遍较低。13℃等温线,高值CPUE出现的地方大多深度值<300 m,众数为190-275 m;深度值超过400 m的区域CPUE普遍较低。全年在15oS以北区域,高渔获率的垂直分布深度更加集中。采用频次分析和经验累积分布函数,计算其最适次表层环境因子分布,12℃等温线250-340 m;13℃等温线190-270 m;12℃深度差30-130 m;13℃深度差0-70 m。研究初步得出热带印度洋大眼金枪鱼中心渔场适宜的水平、垂直深度值分布区间,可以辅助寻找中心渔场位置,同时指导投钩深度,为热带印度洋金枪鱼实际生产作业和资源管理提供理论支持。

We evaluated the isothermal distribution of subsurface temperatures in the bigeye tuna （Thunnus obesus） fishing grounds in the tropical Indian Ocean. We plotted the isothermal depths at 10, 12, 13, and 16℃ on a spatial overlay map using data collected on monthly basis from Argo buoys and monthly CPUE （catch per unit effort） from bigeye tuna long-lines. In addition, the differences in depth between the 12 and 13℃ isolines at the lower boundary of the thermocline were computed to determine the relationship between bigeye tuna vertical distribution and thermocline depth. Our analysis suggested that the vertical range of optimal temperatures （10 and 16℃） in the area of high CPUE was between 150 and 400 m, and was beneath the lower boundary depth of the thermocline. The overlay maps suggest that CPUE is highest in areas where the 12~C isothermal depth is shallower than 350 m （mode： 225-350 m）. Conversely, if the depth is 〉300 m, the CPUE tends to be low. Similarly, the highest CPUEs were observed in areas where the 13℃ isothermal depth was shallower than 300 m （mode： 190-275 m）, whereas CPUE was low when the depth exceeded 400 m. The vertical distribution of high hook rates was concentrated in the area to the north of 15°S. We used a frequency analysis and the empirical cumulative distribution function to compute the optimum range of subsurface factors. The optimum ranges for the12 and 13℃ isothermal depths were between 250-340 m and 190-270 m, respectively. The optimum depth difference ranges were 30-130 m for the 12℃ isothermal depth and 0-70 m for the13℃ isothermal depth. We documented the distribution interval and vertical depth range for the central fishing ground of bigeye tuna. Our results provide a reference for improving the efficiency of thelong-line fleet and aiding in resource management.