Distribution Of Main Species Of Stow Net In The South Yellow Sea Based On Gam And Preliminary Study Of Characteristics Of Ichthyoplankton Assemblages In Haizhou Bay

Section one: Spatial and temporal distribution of catch CPUE and environmentalfactors analysis of stow net fisheries in the southern Yellow Sea in spring.Stow net fishery is one of the important fishing methods in the southern YellowSea. Based on the data collected from stow fishery resources survey in the southernYellow Sea in spring during2006-2009, the generalized linear model (GLM) andgeneralized additive models (GAM) were used to quantitatively describe therelationships between catch distribution of Larimichthys polyactis, Lophius litulon,Setipinna taty and environmental factors such as year, position, depth and sea surfacetemperature (SST). The results indicated that GAM model could explain therelationship between spatial and temporal distribution of CPUE(catch per unit effort)of the three species and environmental factors better than the GLM model. The CPUEof the two species were significantly correlated (P<0.01). L. polyactis’s CPUEshowed a trend of decreasing from north to south along the longitude direction,especially smaller around the Yangtze River estuary. Lophius litulon’s CPUE was alsolower near the Yangtze River estuary. The CPUE of the two species both showed ahighly significant correlation with SST. The calculated optimal scale of SST for L.polyactis and L. litulon were9-11℃and9-14℃, respectively. In time, Setipinnataty’s CPUE was in a downtrend annually. In space, Setipinna taty’s CPUE showed atrend of decreasing from north to south along the longitude direction, especiallysmaller around the Yangtze River estuary. Setipinna taty’s CPUE showed a significantcorrelation with depth and was higher in20meters to30meters. Setipinna taty’sCPUE showed a highly significant correlation with SST. The calculated optimal scaleof SST of Setipinna taty was7.2℃-12.4℃. Section two: Correlation study between spatial distribution of ichthyoplankton andenvironmental factors in Haizhou Bay during summerThe categories composition and distributional patterns of ichthyoplanktonsurveys were carried out investigated by horizontal tows associated with vertical towswith a zooplankton net (mouth diameter50cm,140cm in length, mesh size0.50mm)in waters of Haizhou Bay in summer2011.The relationships between spatialdistribution of ichthyoplankton and environmental factors are analyzed usinggeneralized additive model(GAM).According to the investigation results,2579eggsand325larvae of fishes belonging to11taxa were collected, of which,10taxa wereidentified as species, belonging to10genera,7families and4orders. Thepreponderant species were Stolephorus commersonnii and Cynoglossusjoyneri.Bottom temperature was significant for effects of density selected by stepwiseregression and pearson correlation. Model2with bottom temperature was fitter toexplain the temporal and spatial pattern of spawning in the west of Haizhou Bay.TheGAM plots showed that density was greater in waters where distance from coast wasabout40km, depth was about10m and bottom temperature was25.5℃.Section three: Spatial patterns of ichthyoplankton assemblages in Haizhou BayThe Haizhou Bay as a typical fishing waters was a traditional fishing grounds inthe central Yellow Sea, while it was also the spawning grounds and feeding groundsof many of our economic fishery biology. Surveys were conducted in five voyages(March, May, July, September and December) in Haizhou Bay, to determine theichthyoplankton composition, abundance and assemblage characteristics. A total of7825eggs and269fish larvae were collected sorted from110zooplankton sampleswith a zooplankton net (mouth diameter50cm,140cm in length, mesh size0.50mm),in which at least16families,37species of fsh eggs and9families,12species of fshlarvae were identifed. The results showed that, May and July were the peak of mostof fish spawning in Haizhou Bay. Unique topography of Haizhou Bay had a greatimpact on the spatial distribution of temperature and salinity, and then affected thecharacteristics of spatial patterns of ichthyoplankton. Overall, the seasonal turnover ofsea temperature determined the seasonal changes of the type and quantity of ichthyoplankton; and spatial distribution of ichthyoplankton in each month wasmainly affected by other factors such as salinity, currents and topography in HaizhouBay. Based on hydrological and topographical features in Haizhou Bay, the waterscould be divided into three regions (nearshore bay, middle bay and edge of bay). Itwas feasible that the stratified random sampling method according to the water depthand latitude was used to set up the site. Bray-Curtis index clustering analysis was usedto study the assemblage characteristics of fish eggs in May and July, and the resultsshowed that the dividing line of NBA and MBA was20meters isobath in both twomonths. In short, the distribution of nutrients and other oceanic elements wereaffected by the unique mechanism of circulation currents, tidal currents and residualcurrents and strong tidal fronts mad eggs gathered into dense plaques. Complexseabed topography and sediment provided better living environment for many fishspawning, so Haizhou Bay became one of the important spawning grounds in YellowSea.