东海区小黄鱼空间格局的地统计学分析

Geostatistical analysis on spatial patterns of small yellow croaker (Larimichthys polyactis) in the East China Sea

运用地统计学原理和方法,分析2002年东海区小黄鱼(Larimichthyspolyactis)分布的空间变异特征,并用Kriging法对不同时期的小黄鱼分布进行空间插值成图。结果显示,不同时期东海区小黄鱼种群的变异函数均可拟合为球状模型,秋季的空间变异程度最高,冬季随机性变异占总变异的比例最低,具有最好的空间自相关特性,而夏季的空间自相关范围最小。小黄鱼空间结构的季节变化与其繁殖、索饵、洄游等生态习性和人为捕捞影响密切相关。

Small yellow croaker(Larimichthys polyactis) is the warm-temperate and economic fish of bottom layer,distributed in the Bohai Sea,the Yellow Sea and the East China Sea in China. It is the mainly catching target of fishery in China. The resource has been declining because of over-catching during 1960's-1980's. After the 1990's,especially the forbidden fishing zone,forbidden fishing period and summer close season were brought into effect,the spawning ground and recruitment of small yellow croaker in the East China Sea got effective maintenance,and the output obviously went up. To take reasonable advantage of this fishery resource,it is necessary to know spatial distribution characteristics of the small yellow croaker. Its spatial distribution in the sea is very complex. In this paper,Geostatistical theories and methods were used to analyze spatial heterogeneity of the small yellow croaker in the East China Sea in 2002. The measurement was made at 121 stations within 122°00′-127°00′E and 27°00′-34°00′N. Each station was arranged at intervals of 0.5°. The biomass resources in the stations were measured by CPUEs per reef with bottom trawl survey. We describe the spatial variation in small yellow croaker in April,June,September and December respectively by calculation of semivariogram,which shows the average variance at increasing distance interval. Spherical model was used to fit the form of semivariogram,then some parameters such as nugget,sill,range and fractal dimension were estimated. With Kriging in the sampling area,the spatial pattern of the small yellow croaker at different seasons was expressed in two dimensions as well.The results showed that the semivariogram of small yellow croaker could be described by spherical model. The spatial heterogeneity in autumn was the greatest with the highest sill. There was the lowest ratio of random variance (21.6%) and the highest proportion of spatial structured variance(78.4%) to total variance in winter,suggesting the most significant spatial autocorrelation. These values were about 50% for other seasons;random variance was found less then 50?km;structured variance was found within distances from 50?km to 170?km. This indicated that the small-scale ecological processes would have attention in the course of the seasons. Fractal dimension of four seasons also showed the same conclusion. And the small yellow croaker in winter had the highest values in the range of spatial autocorrelation of 196?km. Spring and autumn in the range of 170?km follow it,while winter was the lowest value,83?km. The seasonal variability of spatial structure of the small yellow croaker can be explained by the ecological habits of spawning,feeding,migration and so on,as well as anthropic factor.