Spatio-temporal Variation Of Fishery Resources In The Yellow Sea And Yangtze River Estuary

As an important component in agriculture,fishery provides high quality protein for human diet.Meanwhile,fishery plays vital roles in guaranteeing food supply,providing working opportunities and promoting the development of economy and trade.Applying the ecological theory reasonably to guide and solve the problems in the development of fishery is of great scientific significance to the rational utilization and adapative management of fishery resources.This thesis mainly focused on the spatio-temporal variation of fishery resources in the Yellow Sea and Yangtze River estuary.In terms of spatial aspect,different interpolation methods and algorithms of swept area methods were applied to the Yellow Sea fishery resources,respectively,and their performances were also compared.In temporal aspect,fish assemblage indices and multivariate analysis were used to study variations in fish diversity and community structure in the Yellow Sea.By establishing the indicatior system for fishery ecosystem health assessment,the health of the Yangtze River estuary was projected under different climate change scenarios.The results were as follows:Using the cross-validation diagnostic and visual examination,four methods in common use were tested to develop an appropriate interpolation method of determining fishery resources density in the Yellow Sea based on bottom trawl data in 2014-2015(August,October,January and May).The four spatial interpolation methods were inverse distance weighted interpolation(IDW),global polynomial interpolation(GPI),local polynomial interpolation(LPI)and ordinary kriging(OK).The results showed that the original data were not normally distributed.A log transformation was then used to make the data fit a normal distribution.During four survey periods,an exponential model was shown to be the best semivariogram model in August and October 2014,while data from January and May 2015 exhibited the pure nugget effect.Using a paired-samples t test,no significant differences(P >0.05)between predicted and observed data were found in all four of the interpolation methods during the four survey periods.Results of the cross-validation diagnostic demonstrated that OK performed the best in August 2014,while IDW performed better during the other three survey periods.The GPI and LPI methods had relatively poor interpolation results.With respect to the spatial distribution,OK was balanced and was not as disconnected as IDW nor as overly smooth as GPI and LPI,although OK still produced a few “bull's-eye” patterns in some areas.However,the degree of autocorrelation sometimes limits the application of OK.Based on bottom trawl data in 2014-2015 in the Yellow Sea,the resources density and biomass of demersal species were estimated using swept area method,and the effects of applying different swept area algorithms were compared.The results showed that three swept area algorithms nearly had the same performance to the aspect of estimation of biomass in all four seasons,while huge differences were found in calculating the variances of average resources density.The stratified algorithm and K-means clustering algorithm performed better and had a higher estimation precision than the ordinary algorithm.The average resources density of demersal fish in the Yellow Sea were high in summer and autumn,reaching 500 kg/km2,followed by spring(105 kg/km2)and lowest in winter,only 70 kg/km2.The sum of biomass of Liparis tanakae(Gilbert & Burke 1912)and Larimichthys polyactis(Bleeker 1877)accounted for nearly 50% of the total biomass of demersal fish;other high-biomass species were Lophius litulon(Jordan 1902)(11.10%),Trichiurus lepturus Linnaeus 1758(7.87%)and Gadus macrocephalus Tilesius 1810(7.41%).Based on data from bottom trawls in winter during 2003-2015,the status of fish community structure and diversity in the Yellow Sea were analyzed by methods including ecological diversity indices,multivariate analysis,size-spectra analysis and so on.Five fish assemblage indices all showed fluctuations without clear trends between 2003 and 2015,yet there were strong positive and significant correlations(P < 0.05)among them.The top-five dominant species,Japanese anchovy Engraulis japonicus Temminck & Schlegel 1846,anglerfish,Tanaka's snailfish,silver pomfret Pampus argenteus(Euphrasen 1788)and small yellow croaker,accounted for a high weight percentage(49.7 %-82.1%)in the annual fish catches.Multivariate analysis showed that two year groups could be pooled for the fish community: Group I consisted of the years 2006,2007,2008 and 2015 while Group II consisted of the years 2003,2004,2005,2009,2010 and 2014;the groups aggregated at 63.71% similarity,indicating a high level of similarity among all years.The multivariate dispersion values were 1.455 and 0.818 for Groups I and II,respectively,indicating greater variances in fish assemblage structure in Group I than in Group II.Size-spectra analysis revealed no consistent trend in the intercept and slope(P > 0.05);there was also no significant difference between the slope of the size-spectra and fishing effort.The CPUE and MIW analyses of the whole fish assemblage both showed a significantly decreasing trend over time.Based on the climate change scenarios from The Geophysical Fluid Dynamics Laboratory(GFDL)and projections of fish distribution under these scenarios(RCP2.6,RCP6 and RCP8.5)by the dynamic bioclimate envelope mode,the fishery ecosystem health in Yangtze River estuary was evaluated by hierarchical grey comprehensive evaluation model.The health evaluation system in Yangtze River estuary included environment,fishery community structure and ecosystem function and service.The fish abundance increment,particularly demersal fish abundance,increased with time under three climate change scenarios,and the increase level and the distribution were RCP8.5>RCP6>RCP2.6.In 2050,fish abundance increment migrated to the southern waters of Yangtze River estuary,and relatively less increment was found in offshore waters.The center of fish abundance increment mainly distributed in the Chongming Island coastal waters.During 2015-2050,the highest health index of Yangtze River estuary was found in RCP2.6 scenario then was RCP6 scenario,the lowest health index was found in RCP8.5 scenario.The health level gradually decreased with the increase of greenhouse gas emission levels.If the health index in 2050 was regarded as the final results,the health levels under RCP2.6 scenario were higher than those under the other scenarios.The health index under RCP2.6 scenario was 0.61,and it was 1.9 times and 1.8 times for RCP6 and RCP8.5 scenarios,respectively.