Simulation Study Of Ecosystem Dynamics Of Early Life History Of Chub Mackerel (Scomber Japonicus) In The East China Sea

Chub mackerel (Scomber japonica) is important pelagic fish resources inthe China Sea. Changes of fish resources are not entirely influenced byfishing, but the environment has a big effect on recruitment. Past researchhas focused on relatinship between environment and resource, but annualrecruitment is mainly determined by the survival in fish early life stage.Minor change of marine environment will have an impact on growth,surivival and recruitment of eggs and larvae, which is the most vulnerable inthe fish life stage. Application of based on individual-based model to studythe growth of fish early history has been relatively developed at abroad, butin China, relative research is not well developed.This project to make the interdisciplinary research, according to thephysical environment of the early growth mackerel, combined with itsgrowth characteristics, using ocean physical model, and developsphysical-ecological coupling model of early life history of chub mackerelbased on individual, and the research on the growth, transport, migration,connectivity and recruitment of chub mackerel eggs and larvae, explore theinner dynamics factor of population resources fluctuation, in order to accurately predict mackerel resource and realize biological resource recoveryin China Sea provide the scientific basis.Based on introduced individual-based model, this paper develops abio-physical dynamic model of early life history of chub mackerel in the EastChina Sea (ECS). The physical model is developed based on the FVCOM(Finite Volume Coast and Ocean Model) simulates the3-D physical fields,using3d,10km resolution march average temperature and salinity initialfields, eight main tidal constituent on the open boundaries. The biologicalmodel uses on individual-based models (IBM). Early life of chub mackerel isdefined by five stages according to age and length, parameterized early lifebiological process (spawn, growth, survival, etc) of chub mackerel of ECS.The eggs hatch time and larval metamorphosis time is the function of watertemperature in the model. Growth is the function of temperature and food.The mortality rate was a negative correlation with the length and a positivecorrelation with the growth rate. Food availability is calculated from thecoastal upwelling index. Estimated spawning ground is the southwest of theECS (Taiwan northeast). Spawning period is from March to June. Batchspawning eggs is released in the10m water layer. The physical field duringMarch-July yielded from the physical model is coupled with the biologicalmodel through the Lagrange particle tracking, considering the passive driftby current and random walk by turbulence. Using the super-individualtechnology, the individuals are grown when the particle drifts passively. The application of the model for normal climate, extreme climate and the changeof spawning ground study transport of eggs and larvae, to study dynamicsfactors of the changes effect. The main research results are as follows:The results of flow field under normal climatological forcing conditionshow that with the increase of water temperature in March, chub mackerelbegan to spawn. Eggs are distribution in between Taiwan Warm Current(TWC) and the Kuroshio, and transported to the northeast. In April with thewater temperature further raise, the spawning peak is coming. Eggs increasedrapidly. Eggs and larvae were divided into two parts by the influence ofTWC and kuroshio. One can follow TWC to northward transportation. Theother part can follow the Kuroshio to northeast direction to transport. Watertemperature continues to rise in May, the most mackerel spawn over. Thenumber of spawning increase is reduced, because of death. The number ofeggs and larvae is decrease. Some continue to transport north for ZhoushanIsland. There is very little has been transported to the Yangtze Estuary andthe Hangzhou Bay. The other part also continues to transport northeast. Thefarthest drift is in the western Goto-retto islands. Most of larvae are thedistribution in between50m and200m isobaths. But because of the kuroshiobarrier, it is difficult to break into, or through the kuroshio to larvea. Watertemperature continues to rise in June. Part of the larvae to transport northalso began to turn to the northeast transport with other along the100-200misoaths. Most of larvae was transported to northeast of ECS in end of June only a little of larvae stranded in the Yangtze Estuary and Zhoushan Sea.When larvae get to the Goto-retto islands, larvae are divided into two partsby tidal currents, and a part was broughted into Tsushima Strait by TsushimaStrait Warm Current (TSWC), the other part to go through western sea ofKyushu was quickly broughted into the Pacific by the Kroshio. In July, watertemperatures continue to rise. The simulation is coming to the end. The mostof larvae was transported to Cheju, Tsushima Strait, Kyushu Island and thePacific Ocean. Some has drift out calculation domain by the kuroshio.Larvae were rarely found in this time in other ECS. The transportation oflarvae is significantly influenced by complex hydrodynamic TWC, Kuroshioand TSWC.Statistical analysis showed that the mean water depth of larvae is deeperthan other three nursery grounds because of strong turbulence of nurseryground in the Pacific Ocean,. In end of July, average depth exceeds400m.Due to characteristics of the high temperature and salinity of the Kuroshio,the average water temperature is not the lowest. Juvenile basically can also isvery good to grow, that was transported into nursery ground in the PacificOcean.With the advance of time, the proportion of larvae reached each parts ofnursery ground will has variation. In the end of June, most of larvae weretransported from spawning ground in south ECS to nursery ground of ChejuIsland and Kyushu Island. In mid-july, the proportion of nursery of Cheju Island and Kyushu Island is decreased becase of transport into nurseryground of the Pacific Ocean and Tsushima Strait. In the end of the simulationin July, most of larvae were transported to north nursery ground of Kyushuand Tsushima Strait. But only a third of the total larvae were transported tothe south nursery ground of Pacific Ocean snd Kyushu.The spawning ground in the southern East China Sea made morecontributions to the recruitment to the fishing ground in northeast East ChinaSea, but less to the Yangtze estuary and Zhou-Shan Island. The transport ofeggs and larvae is the main mechanism of connection between spawningground and nursery ground. Connectivity is very similar to division of theocean currents system in ECS, divided into two parts. Northwest part(Section A) and Southwest part (Section B) of spawning ground had strongconnectivity with the nursery grounds of Cheju and Tsushima Straits.Northeast part (Section C) and Southeast part (Section D) of spawningground had strong connectivity with the nursery grounds of Kyushu andPacific Oceans. This is proof that physical factors impacts on connectivity.Flow field under the typhoon forcing drives IBM to study transportdistribution of eggs and larvae of chub mackerel. The result showed that nosignificant difference distribution of eggs and larvae is found forclimatological forcing condition after a typhoon pass. But the typhooninfluence on water layer and survival of larvae. In order to verify theauthenticity of the horizontal distribution, eliminate the stochastic and individual water depth. We do the idealistic experiment. The results showedthat the little impact of larval distribution is really. The reason is transportpath of lavae is in the area of the typhoon minimum affect. Typhoon sweptthe ECS is a short period. The cancellation of tide-induced anti-cyclonic andtyphoon-driven cyclonic currents reduced its influence on the low-frequencycurrents and thus on larval transport in this region. Some difference is foundin larval abundance and velocity of transport in back end of transport path,where high density larvae northeast drift and velocity of transport increased.The typhoon caused higth mortality, to move to deeper water layer. Addingan experiment of the longer the typhoon duration, we observe that typhooncertain effect to larval distribution.The change of position has great influence on transport distribution ofeggs and larvae. The west spawning ground was great influenced by Taiwanwarm current. Larval transport was northwest. A large amount of eggs andlarvae was retention and transit in coastal China in the process of transport.The most of larvae were finally transported to north nursery ground of ChejuIsland. The east spawning ground was great influenced by the Kuroshio.Larval transport was southeast. Almost no eggs and larvae was drift incoastal China. Speed of drift is very fast. A large amount of larvae werefinally transported to south nursery ground of Pacific Ocean. Transport speedof wast and east spawning ground was influenced by Taiwan warm currentand the Kuroshio. Survival and growth of normal spawning ground are the best in three spawning ground. The the change of spawning depth has noeffect on larval distribution and transport. But mortality rate of5m and15mdeep increases. Normal spawning depth (10m) is the best spawning depth.We set the movement rule and develop IBM including a swimmingabilities submodel. The result shows that larval swimming ability had littleinfluence in the early transport stage. With the increase swimming ability inthe later stage, larvae have appeared to shcool. Larval mortality is reduced.Speed of northeast transport is also reduced. The amount of transport to thePacific Ocean and the Janpan Sea is decline. Average water depth is lower,which is more suitable to grow. The change of spawning ground make thewest spawning ground was influenced by Taiwan warm current. Larvaeschool in west. East spawning ground was influenced by the Kuroshio.Larvae school in eest. It is to explain the physical environment and biologicalfactors will also have effect to transport of swimming ability of larvae.We study migration of adult spawning mackerel. The result show suitabledepth of mackerel is20m. School of mackerel in northeastern Taiwan wasmainly influenced by TWC, mainland coast water, the Kuroshio. There are alarge number of mackerel distributionn in the intersection front of TWC andcoast water. There are aslo a large number of mackerel distributionn in tidearea of coast water and the Kuroshio. The change position of spawningground is west spawning ground have large accumulation in front of TWCand coast water becase of large influenced by TWC, and east spawning ground have large accumulation in front of the Kuroshio becase of largeinfluenced by the kuroshio. Different locations of mackerel will affect theposition of school, it that explain the physical environment and biologicalfactors can influence on the migration and school of mackerel.