北部湾秋季底层鱼类多样性和优势种数量的变动趋势

根据1992年、2001年和2006年秋季在北部湾进行的底拖网调查数据,对该海域鱼类的种类组成、物种多样性、优势种及其数量的变动趋势进行分析。1992年共记录鱼类171种,隶属17目77科;2001年记录鱼类156种,隶属18目71科;2006年记录157种,隶属17目67科。3个年代记录的鱼类均以鲈形目的种类数最多,其中1992年为96种(占56.14%)、2001年90种(占57.69%)和2006年89种(占56.69%)。鱼类的Pielou均匀度指数(J')和Shannon-Wiener多样性指数(H')的变化趋势一致:以2001年最高,为0.72和3.64;其次为1992年,为0.64和3.27;2006年最低,分别为0.52和2.64。丰富度指数(D)呈逐年下降的趋势:为1992年的21.03,2001年的20.74和2006年的19.61。建立非线性回归模型对北部湾3个年代出现的6种共有优势种(发光鲷Acropoma japonicum、带鱼Trichiurus haumela、二长棘鲷Parargyrops edita、黄斑鲾Leiognathus bindus、竹荚鱼Trachurus japonicus和黄带绯鲤Upeneus sulphureus)的数量变化趋势进行分析。结果表明:北部湾鱼类中的经济价值较高的优势种逐渐被低值和小型的鱼类所替代,但繁殖力较强和寿命较短的鱼类变动较小。在6种共同优势种中,黄斑鲾和发光鲷的渔获率呈上升趋势;带鱼和黄带绯鲤的渔获率呈下降趋势;而二长棘鲷和竹荚鱼的渔获率基本保持不变。研究结果表明,北部湾鱼类的优势种更替明显,总体变化趋势是k选择种类(以红笛鲷和黑印真鲨等为代表)逐渐被r选择种类(发光鲷、鲾科和天竺鱼科等为代表)所替代,即寿命长、个体大和营养级高的鱼类数量减少,寿命短、个体小和营养级较低的种类增多。

Dynamics of demersal fish species diversity and biomass of dominant species in autumn in the Beibu Gulf, northwestern South China Sea

The Beibu Gulf is a semi-enclosed gulf located in the northwestern South China Sea and surrounded by the land territories of China and Vietnam. The region has a tropical to subtropical climate. Thousands of fish and shellfish species have been identified in the Beibu Gulf and support some very important fisheries throughout the year in the region. Large scale resource surveys have been conducted over the last few decades to assess fisheries resources in the Beibu Gulf, and a large quantity of biological and environmental data have been collected. Such scientific data are perfect for evaluating changes in the ecosystem and answers questions such as what changes have occurred over the last few decades to the fisheries ecosystem in the Beibu Gulf? In the study, we analyzed data collected in otter trawl surveys in the Beibu Gulf in autumn 1992, 2001 and 2006 to evaluate fish species composition and diversity, dominant species, and their biomasses. The analysis showed that 171 fish species caught in the 1992 autumn survey in the Beibu Gulf Gulf belonged to 77 families and 17 orders, a total of 156 fish species belonging to 71 families and 18 orders were found in the 2001 survey and 157 species belonging to 67 families and 17 orders were identified in 2006. Perciformes had the highest number of fish species, 96 species (accounting for 56.14%) in 1992, 90 species (57.69%) in 2001 and 89 species (56.69%) in 2006. The Pielou evenness index (J') had the same temporal trend as the Shannon-Wiener diversity index (H'). Both indices were the highest in 2001, followed by those in 1992 and 2006. The Margalef richness index (D) reduced from 21.03 in 1992 to 20.74 in 2001 and to 19.61 in 2006. Nonlinear regression models were developed to quantify the temporal trends of biomass of the 6 dominant species (Acropoma japonicum, Trichiurus haumela, Parargyrops edita, Leiognathus bindus, Trachurus japonicas and Upeneus sulphureus) in the Beibu Gulf. The dominant species were found to shift from the high-value fish species to the low-value species, but no significant changes for fish species with high reproduction rates and short life spans. The catch rates increased during the survey period for A. japonicum and L. bindus, decreased for T. haumela and U. sulphureus, and remained similar for P. edita and T. japonicus. This study shows an apparent succession of the dominant species with an overall trend of the K-selection species (such as Lutjanus sanguineus and Carcharhinus menisorrah) being replaced by the r-selection species (such as A. japonicum,Leiognathus, and Apogonichthys). The abundance of fish species with long life span, large size and high trophic levels decreased, while short-lived and small-sized fish species in low trophic levels increased their abundance over the time period covered by the survey. The study provides important evidence of changes occurring in the Beibu Gulf ecosystem.