Variation in feeding ecology within the fish community in the north Yellow Sea

Abstract

Our objective was to evaluate ecosystem status before and after fishery enhancement.We analyzed the feeding habits,food consumption,and trophic level of the species constituting 90% of total biomass in bottom trawl surveys conducted in May and August of 2010.We compared the traits of the five dominant species(by total biomass) with those collected in 1985 and 2000.In addition,we evaluated decadal-scale variation in the mean TL of the fish community in the north Yellow Sea. The fish community in the north Yellow Sea was dominated by nine species,though these differed between May and August.The most dominant species in May included small yellow croaker Pseudosciaena polyactis,elongate eelpout Enchelyopus elongates,half-fin anchovy Setipinna taty,angler Lophius litulon,pointhead plaice Cleisthenes herzensteini,Pacific cod Gadus macrocephalus,and sea perch Lateolabrax japonicus.Conversely,in August the fishery was dominated by anchovy Engraulis japonicus,sea snail Liparis tanakae,small yellow croaker,elongate eelpout,and Pacific cod.Thus,the assemblage in May was characterized by a lack of nektivores,a decrease in the proportion of generalist predators,and an increase in the proportion of zooplanktivores relative to August.The mean trophic level of the fish community was 3.75 in May and 3.57 in August. The primary prey groups included euphausiids,copepods,hyperiid amphipods,crustacea larva,shrimps,ophiuroidea,bivalvia,polychaeta,and other fish species.We estimated the fish community consumed 0.5 million tons and 19.6 million tons of these prey items in May and August,respectively.Fish and shrimp were the dominant prey groups in May,accounting for 46.9% and 39.2% of the total food consumption,respectively.Similarly,fish,shrimp,and zooplankton were the dominant prey groups in August,accounting for 33.9%,31.4%,and 30.8% of the total food consumed,respectively.The primary prey species were Crangon affinis,Eualus sinensis,Euphausia pacifica,small yellow croaker,Johnius belengerii,and Ophiura sarsii in May.Consumption of these species equaled 0.3 million tons,accounting for 65% of the total food consumption.The primary prey species in August were C.affinis,E.sinensis,Themisto gracilipes,Calanus sinicus,and anchovy.Consumption of these species equaled 12.4 million tons,accounting for 62.9% of the total food consumption.Thus,as in the central and southern Yellow Sea,T.gracilipes,C.sinicus,C.affinis,E.sinensis,small yellow croaker,and anchovy were the most im-portant prey species in the north Yellow Sea. The mean trophic level of fish community declined from 4.26 in 1985 to 3.66 in 2010 in the north Yellow Sea,or 0.24 decade?1.This decrease was more rapid than in the Bohai Sea and central and southern Yellow Sea and was caused by a shift in the dominant species in the fish community.The percentage of nektivores decreased concomi-tantly with an increase in generalist predators between 1985 to 2010.The rate of change in trophic level has de-creased from 0.28 decade?1 between 1985 and 2000 to 0.18 decade-1 between 2000 and 2010,but has remained higher than the global rate.Given this,we recommend continuing efforts to enhance the fishery.