Structure and distribution of fish resources in the Yellow Sea off Shandong during spring and autumn 2006

Abstract

Marine ecosystems,particularly the structure of fish assemblages are increasingly affected by human activity.We evaluated the structure and distribution of fish resources using data collected by trawl surveys in May and October of 2006 in the Yellow Sea off Shandong(35o00?—38o00?N,120o30?—124o00?E).We collected sam-ples at 45 sites and standardized the survey data using the sweep area and capture coefficient.The capture coeffi-cient was set to 0.55 for pelagic fish,0.35 for demersal fish,and 0.25 for benthic fish.The abundance index was much higher in the coastal waters than in the deeper,offshore waters in spring.During this time,most species mi-grate to the coastal regions to spawn.In addition,winter-spawning species,such as pacific sandeel(Ammodytes personatus),were still feeding in the coastal waters during the time of the surveys.In autumn,the abundance in-dex was slightly higher in the coastal waters than in the offshore areas.The highest abundance index was meas-ured in Haizhou Bay,both in spring and autumn.We collected a total of 61 species,50 in spring and 50 in autumn.The structure of fish resources was analyzed based on economic value,habitat layer,and temperature-adapted components.The lower-valued species were dominant in spring and autumn.The lower-valued species constituted 91.0% of the biomass in spring and 80.9% in autumn.The demersal fish were dominant in spring(76.7% of the biomass) whereas pelagic fish,dominated in autumn(75.1% of the biomass).The biomass was dominated by cold-water species(75.0%) in spring and warm-water species(50.1%) in autumn.In spring,the top 10 species by biomass were pacific sandeel,Japanese anchovy(Engraulis japonicas),fang's blenny(Pholis fangi),pacific cod(Gadus macrocephalus),spotted mackerel(Scomberomorus niphonius),smallhead hairtail(Eupleurogrammus punctamanus),yellow croaker(Larimichthys polyactis),silver pomfret(Pampus argenteus),scaly hairfin anchovy(Setipinna taty),and grassfish(Liparis tanakae).Conversely,the assemblage was dominated by Japanese anchovy,Japanese sardinella(Sardinella zunasi),pacific sandeel,yellow croaker,rednose anchovy(Thrissa kammalensis),silver pomfret,gizzard shad(Konosirus punctatus),smallhead hairtail,spotted mackerel,and scaly hairfin an-chovy in autumn.We used the Normalized Biomass Size Spectra(NBSS) to compare the community composition between months and years.Species that contributed 0.01% to the total biomass were excluded.The slope was regressed by log2(total biomass of every weight class/10) to log2(upper limit of average individual weight class).The NBSS slope was ?1 in both spring and autumn,suggesting the biomass decreased as individual body weight increased.The average individual body weight was 2.36 g/individual in spring and 3.34 g/individual in autumn.The proportion of species whose average individual body weight was 10 g was 95.74% in spring and 82.09% in autumn.Compared with the 1980s,we conclude that: 1) The low-valued species are more dominant,2) though there has been a partial recovery in the fishery,the larger,high value species have not recovered at the same rate,and 3) the dominant species has changed significantly due to an increase in the number of fang's blenny.Given our results,we propose an earlier beginning to the closed fishing period during summer.