| With the increasing effects of climate change and human activities onmarine ecosystem, the dynamics of fishery resources are greatly changed. Theresponse of the biological characteristics of marine fishery stocks toenvironmental changes, as well as the redistribution of the fishery stocks underclimate change scenarios, are of great importance and guidance to the rationalexploitation of the fishery resources and the ecosystem-based fisherymanagement. As the key species in food web of the Yellow Sea, anchovyEngraulis japonicus plays a critical role in fish community, as well as to marineecosystem. Based on the fishery survey data in1985-1986and in2000-2010inthe central and southern Yellow Sea, the interannul variations in anchovybiological characteristics, its resources density and the correlations betweenresource density index (RDI) and climate index were analyzed. Furthermore, theredistribution of anchovy was evaluted using a modified dynamic bioclimateenvelope model under climate change scenarios. The main results were asfollows:The interannual variations in biological characteristics of anchovy: Averagebody length showed a decreasing trend in summer and autumn in1985,2000and2009while it decreased from1986to2001and then increased from2001to2010in winter and spring. The allometic factor b was significantly bigger than3(P<0.05), showing a strongly positive-allometric growth of anchovy, except thestock (both males and females) in spring2010and the male stock in autumn in 2009. Feeding intensity varied in1986,2001and2010. In winter and spring,compared to1986, the feeding intensity in2001changed slightly due to thechanges of the proportion in different feeding grade groups. The gastric vacuousrate indicated a declining trend from1986to2001, while the proportion of thefeeding grade groups increased at the same time. However, the situation in2010had totally changed; the gastric vacuous rate decreased sharply and was only10%, the feeding behavior seemed to last all the four seasons which was differentfrom that in1986and2001. Especially in winter, the individuals with the feedinggrades in stage II, III and IV still accounted for some certain proportion. The sexratio (♀:♂) showed either significantly more females (P<0.05) or no significantdifferences (P>0.05) to1:1, demonstrating that females might have a longer lifeexpectancy than males. In winter, the stage II individuals dominated in the stocksin1986,2001and2010, contributed to more than90%of the stock. No obviousdifferences (P>0.05) were found in the proportions of different gonadaldevelopment stages in spring. In summer, the stage V and VI individuals totallyaccounted for93%in the stock in1985, while the stage III individuals weredominant in2000with a proportion of82%, stage II and III individuals totallyaccounted for85%in2007, the similar results were found in autumn2009,except a few stage III and IV individuals. In addition, the condition factor in1986was smaller than that in2001and2010. Besides, the condition factorindicated an increasing trend from1986to2010in all seasons except winter.Interannual variations of the resources density of wintering anchovy stock:The occurrence frequency of anchovy was less than40%in1986while it wasbigger than60%since2000. In2001and2006, it peaked at93%and82%,respectively. However, the changing trend of RDI was not consistent withoccurrence frequency. The RDI values were relatively high in2000,2001and2009, accounting for63.5kg/km2,65.6kg/km2and66.5kg/km2, respectively.The RDI was36.4kg/km2in1986. While in other survey-years, it showed afluctuation trend, and reached the lowest value (1.9kg/km2) in2007. The RDI was positively correlated with the sea surface temperature (SST) of the YellowSea in January and the Southern Oscillation Index (SOI) while it showed thenegative correlation with the Pacific Decadal Oscillation (PDO) and Nino3.4index. However, no significant differences (P>0.05) were found in theabove-mentioned correlations. So did it to the occurrence frequency of anchovy.The larger anchovy individuals mainly occurred in the deeper sea area(123o-125oE,34o-37oN) while the smaller individuals mainly distributed in thecoastal waters.Redistribution of wintering anchovy stock under climate change scenarios:firstly, we evaluated the current distribution of the wintering anchovy stock inthe central and southern Yellow Sea; secondly, a habitant suitable function,consisting of SST and sea surface salinity (SSS), was used to demonstrate theimpacts of environment factors on the wintering anchovy stock; thirdly, fourclimate change scenarios were analyzed, including RCP2.6, RCP4.5, RCP6andRCP8.5, these came from Geophysical Fluid Dynamics Laboratory (GFDL)CM2.0, and represented the low, relative low, modest and the highest emissionscenarios; finally, based on a series of parameters, the redistribution of winteringanchovy was predicted using the modified dynamic biological envelope model.The resource barycenter was used to evaluate the reaction of wintering anchovyto different climate change scenarios. The wintering anchovy stock showed theobvious northward trend, reached as much as to2.5-2.7oin the next30years. Theaverage speed of shift to northward could be0.09oper year. There were nosignificant differences among the four climate change scenarios. In thesensitivity analysis, the scale constant k was not sensitive to the redistribution ofanchovy stock while the intrinsic rate of population increase r was closely relatedto its redistribution. |
PDF Full Text Request