Study On Long-term Variations In The Abundance Of Japanese Anchovy(Engraulis Japonicus) And Pacific Herring(Clupea Pallasii) And Their Driving Mechanisms In The Yellow Sea

Knowledge of marine fish population dynamics is key for us to understand the evolution processes of marine ecosystems,and achieve the goal of scientific management and sustainable development and utilization for fishery resources.In particular,small pelagic fishes,also known as forage fishes,such as anchovies,sardines,herrings,etc.,have shown great plasticity in growth,survival and other life history characteristics,making them be ideal indicators to examine variations in marine ecosystems with a warming world.In the early years,numerous studies have shown that small pelagic fish populations fluctuated drastically on the centennial-scale even millennial-scale,with frequent fluctuations between rise and fall,brought great challenges for normal fishery activities.Therefore,it is particularly urgent to clarify the reasons behind the long-term variations in fish abundance.Unfortunately,the progresses of appropriate research have been relatively slow,because of the lack of data in catches before large-scale industrial fishing.Fortunately,as precious archives,both historical documents and marine sediment records can be used to help us build a bridge between fish population dynamics and marine ecosystems,to discuss the present from the past and predict the future.This study was carried out from the following four parts.First,we tried to raise phisical-biological mechanism for elucidating anchovy(Engraulis japonicus)fluctuations over the past 150 years(1860-2005 AD),based on the combination with fish Scale Deposition Rate(SDR)and biogeochemical proxies in the central Southern Yellow Sea(SYS).Second,we used the SDR to further extend the length of the time series of the anchovy population(1620-2005 AD)to verify reliability of the proposed hypothesis.Third,we compared the anchovy in the YS with northern anchovy(Engraulis mordax)in the California Current Ecosystem(CCE)and Peruvian anchovy(Engraulis ringens)in the Humboldt Current Ecosystem(HCE),and to explore possible teleconnections between them.Fourth,the time series of the herring in the YS was reconstructed for nearly 600 years(1417-2004 AD)based on historical records,and to further examine the hypothesis by comparing with the anchovy in the YS.The primary results were as follows:(1)Before the 1980s,the anchovy population had a good agreement with phytoplankton and zooplankton abundance,while this consistency was completely disturbed by overfishing after the 1980s.(2)There were differences in seasonal Sea Surface Temperature(SST)for anchovy during different growth stages.Specifically,summer SST was very important for early recruitment of the anchovy,while winter SST had greater impacts on overwintering anchovy.In particular,anchovy was negatively correlated with North Pacific Gyre Oscillation(NPGO)in summer;while anchovy was positively correlated with Pacific Decadal Oscillation(PDO)in winter.(3)δ15N(proxy for stratification)and long-chain alkenone(proxy for haptophyte)had the potential to predict future fluctuations for anchovy abundance in the YS.(4)For the past 400 years,there have been seven peak intervals for anchovy in the YS:1630-1650 AD,1680-1700 AD,1740-1760 AD,1800-1820 AD,1850-1870 AD,1910-1930 AD,1970-1990 AD.In addition,there was a weak positive correlation with PDO with cycle of about 50-60 years.(5)The northern anchovy,Peruvian anchovy,and Japanese anchovy exhibited synchronous fluctuations in the Pan-Pacific,though the three subspecies of anchovy were geographically separated by hundreds or even thousands of kilometers.(6)The herring population in the YS fluctuated with low-frequency at higher abundance during the Little Ice Age(LIA);after the LIA,herring fluctuated with high-frequency at relatively low abundance.For the past 600 years,herring fluctuated with an average period of about 65 years.Also,there was a weak negative correlation with PDO,and a strong positive correlation with Drought/Flood(DF).(7)For the past 150 years,anchovy and herring alternated in the YS to varying degrees,while this phenomenon disappeared on a longer time scale..By comparing the responses of anchovy and herring populations in the YS to fishing and environmental stress,we discussed the reasons behind their long-term variations,and raised potential driving mechanisms.It is crucial to emphasize that future fisheries management strategies should not be considered solely from the perspective how to limit fishing efforts,but should incorporate both climate and fishing,and timely adjust fishing efforts to obtain better earnings.The results can fill gaps in related fields and provide a scientific basis for future development of fishery management strategies,thereby promoting the scientific management and sustainable development for fishery resources in the YS.