长江口中国花鲈食性分析

Abstract

Lateolabrax maculatus,an estuary migratory species with high commercial value,is widely distributed in waters of the west Pacific Coast and in the Yangtze Estuary.However,collapse has been occurring of L.maculatus stocks after overfishing and habitat destruction for the extra activity of the human beings.Furthermore,the collapse stocks are impacting on the ecological function of broad water area near Yangtze Estuary.L.maculates,being on the trophic levels of food chain,importantly affects regulation of animals at lower trophic level of Yangtze Estuary.Similarly,the remove of L.maculates from the estuary will certainly cause a trophic cascading effect on the community,and possibly alter the abundance of species which maintain the whole food chain. In order to investigate the composition of prey species,265 samples of L.maculatus were collected from July to October,2010,of Yangtze Estuary.Stomach contents of each fish were examined.The result showed that stomachs of 18.11% fish were empty.Cumulative prey curves for the entire sets from Yangtze estuary,sample sets from points of Tuanjiesha and Dongwangsha,are all fitting better with logistic curve than with a linear relation.Therefore the sample size was considered sufficient to describe the diet of L.maculates.The results also showed that,the diet of L.maculatus consisted of 27 prey items from a widely array of biological groups which belongs to 6 kinds of Fishes,Shrimps,Crabs,Stomatopoda,Isopoda and Veneroida.Results of the resource indices indicate a diverse diet: prey diversity,H′=2.484;prey evenness,J′=0.7535;prey dominance,D=0.1262. The importance of the different prey items were evaluated by the frequency of occurrence,abundance and mass followed with using these dates to calculate the Index of Relative Important(IRI) for each taxonomic category,and the Index of Preponderance(Ip) which did not incorporate N into the formula.Percent Index of Relative Important values indicated that the three most important kinds in 217 stomachs of L.maculatus were Fishes(82.63 IRI%),Shrimps(10.78 IRI%) and Isopoda(4.02 IRI%).Index of Preponderance values indicated that Fishes(94.48 Ip) is the most important kind,Shrimps(4.08 Ip) is the second kind,Crabs(1.28 Ip) is the third one.Combining the values of two indices,Liza haematocheila was the dominant species in both terms of IRI%(41.89) and Ip(53.20).Exopalaemon annandalei and Gnorimosphaeroma rayi were dominant food items in terms of IRI% but showed a very low Ip.Saurogobio dumerili and Lateolabrax maculatus were dominant food items in terms of Ip but shows a smaller data.Combining with other indices,it is found that the main contribution for fishes to the feeding habit of L.maculatus was their large weight,and the main contribution for other species was their abundance.In the present study,the importance of different prey items could not be evaluated by any single index.Based on above facts,five species mentioned above were all dominant food items of L.maculatus. The value of prey diversity measured for L.maculatus was 2.484 which are considered moderate level,thus making fairly easy to find anyone of the 27 prey items from samples of L.maculatus′s.The result of feeding habits for L.maculatus is unlike previous studies,and there were obvious changes among the dominant species.According to analysis of the dates of PCA,differences of food items for two sampling points and the entire sets of Yangtze Estuary were being emerged.There were significant dietary shifts among samples from points of Tuanjiesha,Dongwangsha and the entire sets of Yangtze River estuary.According to principal components analysis,it is speculated that the difference is mainly caused by Coilia spp.,Glossogobius giuris,Exopalaemon carinicauda and Gnorimosphaeroma rayi.