Study On Fishery Resources And Fish Diversity In Minjiang River Estuary And Jiulong River Estuary And Their Adjacent Waters

The Fujian coastal waters locates in the Taiwan Strait, the junction of East China Sea and South China Sea, fishery resources are rich and distinctive characteristics. Studies on fishery resources in Fujian coastal waters were mainly focused on historical data collected from the 1980s to the 1990s, even some data were collected over 40 years ago, the fishery resource status and fish community structure were not fully addressed, particularly fishery resourse in major estuaries. So it is difficult to accurately assess the current status of fishery resources in Fujian coastal waters, and can not meet the national demand of"ocean development"and"construction on the west side of the Straits", so the study on spatio-temporal distribution of fish community and its diversity, fishery dynamics in this waters, not only enriched the research content of fishery resource, but also had the vital theoretical and practical significance to formulate rational fishery management and realize sustainable utilization of marine fishery resources.In this study, four bottom trawl surveys of fishery resources were carried out in the Minjiang River Estuary and the Jiulong River Estuary and their adjacent waters, including summer and winter, 2006, spring and autumn, 2007. Combined with the historical data, the studies were mainly involved in fish species composition, spatio-temporal distribution of fish community, biological characteristics of 22 key fish species and their suggested catchable size, and fishery dynamics. Furthermore, combined with fish species composition and their distribution in the Yangtze River Estuary, the Pearl River Estuary and their adjacent waters, a comparative geographical distribution study of fish community in four main estuaries of china southeastern coastal areas and their adjacent waters was studied. The result showed as follows:Firstly, A total of 222 fish species were collected in this survery, which belonged to 17 orders, 77 families and 140 genuses, including 17 elasmobranch species and 205 Actinopterygii species. Perciforms was species-richest, 109 species, accounted for 49.1%; then was Clupeiformes (20 species), accounted for 9.0%; species number in Anguilliformes, Scorpaeniformes, Pleuronectiformes, Mugiliformes, Tetraodontiformes was about 7-19, and not beyond 5 species in the other orders. Warm water species and warm temperate species were the main ingredients, accounting for 65.3% and 34.7%, respectively, and showed typical characteristics of subtropical fish fauna.Significant seasonal variations were found in the shift of dominant fish species and fishery dynamics. According to Pinkas index (IRI), there were 6 dominant fish species in spring, Harpadon nehereus, Leiognathus ruconius, Parargyrops edita, Setipinna taty, Thrissa kammalensis and Coilia nasus;Polydactylus sextarius, Johnius grypotus, Setipinna taty, Pennahia argentatus, Harpadon nehereus,and Leiognathus ruconius were dominant species in summer,; there were just 4 dominant species in autumn, Harpadon nehereus, Thrissa kammalensis, Wak tingiv and Polydactylus sextarius Harpadon nehereus, Collichthys lucida, Coilia nasus, Johnius grypotus, Trypauchen vagina, Thrissa kammalensis and Arius sinensis were dominant species in winter.It was just one dominant species Harpadon nehereus, occurred in four seasons. The abundance of fishery resource was not high, mean seasonal individual density of fishery resource was 43832 ind/km~2, mean seasonal mass density was 519.10kg/km~2; mean individual density and mean mass density were 34375ind/km~2 and 327.57kg/km~2 in spring, respectively; 28664ind/ km~2 and 467.18kg/ km~2 in summer, respectively; 99401ind/km~2 and 932.48kg/ km~2 in autumn, respectively; 39280ind/km~2 and 519.10kg/km~2 in winter, respectively. Fish diversity (Shannon-Wiener indexes) was low in summer and winter, and high in spring and autumn, particularly autumn.The characteristics of fish community structure were similar in four seasons by the cluster analysis and NMDS , fish community were divided into two assemblages , and the boundary between them was the Minjiang River mouth. Fish assemblage in the Jiulong River Estuary were dominated by Coilia nasus,Collichthys lucida,Trypauchen vagina, Harpadon nehereus, Polydactylus sextarius, and Arius sinensis; while Fish assemblage in the Mingjiang River Estuary were dominated by Johnius grypotu, Harpadon nehereus, Setipinna taty, and Polydactylus sextarius.Secondly, based on the survey data in the Minjiang River Estuary and its neighboring waters(25°42′-26°27′N, 119°42′-120°15′E), the swept-area method and Delta-distribution model-based method were used to assess the standing stock of fishery resource. The results showed the highest biomass density 2569.11kg·km~2 was found in autumn, then was 1120.23kg·km~2 in summer, the biomass density were low, 867.16 kg·km~2 and 553.60.29kg·km~2 in winter and spring, respectively. The current fishery resources in the Minjiang River Estuary and its neighboring waters were about 4599 t, while the fishery resources potential stock reached to 32451t. Based on the survey data in the Jiulong river estuary and its adjacent waters(about 2713km~2), the swept-area method was used to assess the standing stock of fishery resource. The results showed that the highest biomass density was found in autumn, 1261.39kg/km~2; then was winter and summer, 951.31kg/km~2 and 936.93kg/km~2 respectively; the least biomass density was found in spring, 778.24kg/km~2. The standing stock of fishery resources in the Jiulong River Estuary and its adjacent waters was about 2664.09t, while fishery resources potential stock reached to 16688t. The distribution of fishery resources in two study areas were closely linked to water temperature and water depth. Fish and crustaceans resources in two study areas were relatively high, while cephalopod resources was low.Thirdly, the biological characteristics of 22 fish species were analyzed, von Bertalanffy growth parameters, total mortality, natural mortality, fishing mortality and exploitation rates were evaluated by length based methods. The result were as follows: growth parameter of 22 species ranged from 2.5 to 3.5, most of them were over exploitation. Exploitation rates of 20 species were beyond 0.5, accounted for 90.1%, exploitation rates of 9 species were higher than 0.7, their resource were heavyly overexploited; exploitation rates of 11 species ranged from 0.5 to 0.7, were in slight overexploitation, only 2 species their exploitation rates were not beyond 0.5, were in not full exploitation, i.e. Chiloscyllium playiosum and Chrysochir aureus. The optimum catchable size of 22 species were suggested based on their ages at points of inflection, critical ages, as well as body length at first maturity. The catchable size for Trichiurus japonicus and Collichthys lucidus were 230 mm and 170 mm, respectively. The catchable size of Clupanodon punctatus, Thryssa kammalensis were suggested to increase, while catchable size of Setipinna taty, Thryssa vitrirostris were suggested to reduce, and catchable size in Trichiurus haumela, Collichthys lucidus and Odontamblyopus rubicundus were relatively stable. In order to realize the surtainable utilization and rational restoration of fishery resources, it was necessary to fully considered 22 main fish species as standard species to establish new legal catchable size and rational proportion of young fish in the catch.Furthermore, based on literature and survey data of fish composition collected by bottom trawl investigation from 2006 to 2007 in four main estuaries of China southeastern coastal areas and their adjacent waters, changes of the taxonomic diversity across spatial and temporal scales of fish community were analyzed by taxonomic diversity indices. The results are as follows: a total number of 1398 fish species (including some freshwater species), belonging to 2 classes, 42 orders, 186 families and 593 genera, were collected in the studied sea areas. The species richness increased with lower latitudes, particularly so with Perciformes. There were 339 fish species in the Yangtze River Estuary and its adjacent waters, belonging to 2 classes, 31 orders, 101 families and 231 genera. There were 535 fish species in the Minjiang River Estuary and its adjacent waters, belonging to 2 classes, 33 orders, 133 families and 323 genera. A total number of 803 fish species were collected in the Jiulong River Estuary and its adjacent waters, which belonged to 2 classes, 35 orders, 155 families and 419 genera. And 1021 fish species which belonged to 2 classes, 32 orders, 153 families, and 466 genera were collected in the Pearl River Estuary and its adjacent waters. The numbers of orders and families of fish species from the northern to the southern waters first increased and then decreased. The average variation in taxonomic distinctness (Λ~+) gradually decreased with lower latitudes in the four estuaries and adjacent waters. There were no significant differences in the average taxonomic distinctness (Δ~+) among the four estuaries and adjacent waters, and fish fauna were closely related with each other, and all of them belonged to the same zoogeographical fauna (Indian-Malaysia fauna). Fish composition in the Minjiang River Estuary and its adjacent waters was more similar to that in the Jiulong River Estuary and adjacent waters among the four estuaries. Compared with the historical data, the average taxonomic distinctness of fish community showed a great decrease in the Minjiang River Estuary and the Jiulong River Estuary and their adjacent waters.