热带中西太平洋黄鳍金枪鱼栖息水层空间分析

Spatial Analysis of Suitable Habitat for Yellowfin Tuna in the Tropical Central and Western Pacific Ocean

为了解热带中西太平洋黄鳍金枪鱼(Thunnus albacares)延绳钓适宜水层的空间分布,分析黄鳍金枪鱼垂直空间分布对渔获率的影响,采用Argo浮标剖面温度数据挖掘热带中西太平洋17℃和距海洋表层水温8℃(Δ8℃)的月平均等温线场,网格化计算17、Δ8℃等温线深度值和下界深度差,量化黄鳍金枪鱼游动水层,并结合中西太平洋渔业委员会(the Western and Central Pacific Fisheries Commission,WCPFC)黄鳍金枪鱼延绳钓商业生产数据,以高渔获率评估黄鳍金枪鱼索饵水层空间分布及其对延绳钓渔获率的影响。空间分布结果表明,高单位捕捞努力量渔获率(catch per unite of effort,CPUE)出现的海域17℃等温线深度值在180~279 m之间,平均深度为228 m,深度值超过300 m的海域CPUE较小。Δ8℃等温线高值CPUE出现的海域深度值主要在130~239 m之间,平均深度为186 m。在5°N—10°S纬向区域,全年月平均CPUE均较高,该区域17℃等温线深度值在200~240 m之间;Δ8℃等温线深度值在150~220 m之间。全年在5°N—10°S纬向区域,高渔获率的垂直分布深度更加集中。Δ8和17℃等温线分布影响热带大西洋黄鳍金枪鱼的垂直下游深度;温跃层下界温度影响黄鳍金枪鱼的索饵水层。研究初步得出了热带大西洋黄鳍金枪鱼适宜的水平和垂直深度分布区间,有助于辅助渔情预报,为热带中西太平洋黄鳍金枪鱼实际生产作业和资源管理提供参考依据。

In order to investigate the distribution of the yellowfin tuna(Thunnus albacares)fishing grounds in the tropical Central and Western Pacific Ocean,the isothermal distribution of subsurface temperatures in the yellowfin tuna fishing grounds was evaluated. The depths of 17 and 8 ℃ isotherm from the sea surface temperature(SST)(Δ8 ℃)were plotted on spatial overlay maps using data collected on a monthly basis from Argo buoys and monthly CPUE data(catch per unit effort)from Thunnus albacares long-lines supplied by the Western and Central Pacific Fisheries Commission(WCPFC). In addition,the differences in depth between the 17/Δ8 ℃ isolines and the lower boundary of the thermocline were computed to determine the relationship between Thunnus albacares vertical distribution and thermocline depth. The overlay maps suggested that the distribution of Δ8 ℃ isothermal depth showed obviously seasonal variation,roughly in the zonal striped distribution on the annual mode. The spatial distribution of the Δ8 ℃isothermal depth was deep in winter and shallow in summer. The catches per unite of effort(CPUE)were highest in areas where the 17 ℃ isothermal depth ranged from 180 to 279 m with the average depth 228 m. If the depth of 17 ℃isothermal was greater than 300 m or shallower than 150 m,the CPUE tended to be lower. Similarly,the highest CPUEs were observed in areas where the Δ8 ℃ isothermal depth ranged from 120 to 239 m with the average depth186 m. The horizontal distribution of high hook rates was concentrated in the area between 5°S and 10°N. The vertical distribution of Thunnus albacares in the Central and Western Pacific Ocean was affected by the 17 and Δ8 ℃isothermal depth,and the foraging depth of Thunnus albacares was affected by the low boundary temperature and depth of the thermocline. At last the optimum ranges of subsurface factors were computed by the frequency analysis and the empirical cumulative distribution function. The optimum ranges for 17 and Δ8 ℃ isothermal depths were 160~300 m and 160~240 m,respectively. The optimum ranges of depth difference were 0~70 m for 17 ℃ isothermal depths and 30~109 m for Δ8 ℃ isothermal depths. The results were confirmed by using the Kolmogorov-Smirnov test. The distribution interval and vertical depth range for the central fishing ground of Thunnus albacares were documented,and the results provided a reference for improving the efficiency of long-line fleet and resource management.