| Hairtail fishes are important fishes in China and even the world,occupying an important position in global fisheries.Though the Chinese marine fisheries resources especially the traditional economic fishes gradually declined,the production of hairtail species maintaineda constant amount and have ranked the first in Chinese marine fishing for years.The haitail fisherymaintained a high yield of more than 1 million tons per year in the past two decades and contributed more than 80%to the global hairtail production.In view of the importance,hairtail could attract not only the scientific researches but also the governmental attentions.Considering the insufficient knowledge on fish spatial distribution in coastal waters of China,population structure,as well as feeding habits and trophic ecology,further researches are in urgent for resonalble exploitation,protection and recovery of hairtail fishery resources.A total of 2281 hairtail specimens were collected from 17 fishing ports along the coastal waters of China in every autumn from 2016-2018.Morphological methods and molecular biology techniques were used to identify the species,and the spatial distribution of the species was determined combining the sampling information.The status of the hairtail assemblage was studied based on the analysis of population structure by the measured biological data.Using stomach content analysis and stable carbon and nitrogen isotopic technology,feeding and trophic relationships between species were estimated according to the feeding habit and trophic ecology.The results are as follows:1.The common species of Trichiuridae in the coastal waters of China belong to 4 genera,6 species,including Trichiurus japanicus,Trichiurus nanhaiensis and Trichiurus brevis,Lepturacanthus savala,Eupleurogrammus muticus,and Tentoriceps cristatus.Among them,the occurrence frequency and number of T.japanicus are both the highest and widely distributed in 16 sites of 3 sea areas(Yellow and Bohai Sea(YBS),East China Sea(ECS)and South China Sea(SCS)).Following species L.savala appeared in 6 sites of YBS,ECS and SCS.Species of T.brevis and E.muticus distributed in the YBS and SCS,while T.nanhaiensis and Te.cristatus only distributed in SCS.2.The specimens of T japanicus were mainly composed of small and medium-sized individuals;Te.cristatus were mainly large individuals as well as a small amount of small sized individuals;more than 90%of the samples of the T.nanhaiensis,T.brevis,L.savala and E.muticus were small individuals.The b values of length-weight relationship of 6 hairtail species are all smaller than 3,indicating a negative allometric growth.The range of Fulton condition factor(Kn)of the six species was ranged from 0.61 to 1.72.Species Te.cristatus has the smallest Kn while the other species were similar,and difference between female and male was not significant.The sexual ratios of 6 species range from 0.23 to 1.69,and T.japanicus,T.nanhaiensis and T.brevis were all bigger than 1.0.The composition of the gonad maturity showed the immature individuals dominate in the samples(more than 60%).3.The age composition of 6 hairtail fishes in the coastal of China was 1-6 years old,dominated by 1-2 years old group.Species T.nanhaiensis,T brevis and L.savala were 1-3 years old with dominant group of age 1.Species T.japanicus were 1-6 years old with age 1-2 as the dominant age group.The VB growth functions of T japanicus were estimated as Lt=666(1-e-0.15(t+1.19))for the length and Wt-2590(1-e-0.22(t+0.38))3 for the weight.4.The 6 hairtail species in the coastal of China were similar in feeding habits as euryphagous and carnivorous.They fed on fish mainly and a small amount of crustaceans and cephalopods.The dominant fish species in food items were Bregmaceros rarisquamosus,Bregmaceros nectabanus,Diaphus sp.,T.japanicus,Stolephorus sp.,Sardinella sp.,Thryssa mystax,Trachurus japonicas,most of them belonging to pelagic fishes.The prey crustaceans and cephalopods were mostly from Sergia,Penaeus,Solenocera,Loligo,and Sepiida.Besides,the hairtail fishes showed cannibalism.The high feeding trophic levels(4.07<TL<4.57)indicated the hairtail species were medium-high grade carnivorous fishes.The feeding niche breadths ranged from 1.55 to 2.37,and the T japanicus showed the biggest breadth.The overlaps of feeding niche between T.japanicus and other species were obviously.Species of T.japanicus showed 1-2 feeding transitions during the growth.The length at feeding habit change were 270mm and 370mm in the YBS,271-310 mm in the ECS,190-210mm and 270-290mm in the SCS.5.The wide range for ?13C and ?15N of 6 hairtail fishes(-20.90?-14.72‰ and 5.81?17.55‰)indicated rich trophic sources and big span of trophic level.The average trophic level of 6 hairtail fishes were 3.17<TL<3.97,with T.japanicus belonging to the lowest and T.nanhaiensis belonging to the highest.One-way ANOVA showed that 813C and ?15N were significantly different(P<0.01)in different sea areas or sites or length groups of T.japanicus,T.nanhaiensis,T.brevis and L.savala.The isotopes and trophic levels of T.japanicus in the YBS and SCS were similar.With the increase of length,the ?13C of T.japanicus was relatively stable,while the 815N and trophic level showed a trend of gradual increase.The isotopes and trophic levels of T.nanhaiensis changed little in different sites,and the ?13C increased with the growth of length while the ?15N and trophic level declined.With the increase of latitude,the 813C of T.brevis showed a trend of gradual increase while the ?15N and trophic level did not change much.With the increase of body length,the ?13C change little while the ?15N and trophic level showed a gradual decline.The ?13C of L.savala showed significant difference in different sites but no regulation,and the ?15N declined with the increase of latitude.With the increase of length,the?13C of L.savala changed little but the ?15N and trophic level gradually increased.Corresponding to the increasing length,the ?13C of Te.cristatus did not change much,and the?15N and trophic level showed a trend of gradual decline.6.The total trophic niche(TA)of 6 hairtail fishes ranged from 2.07 in Te.cristatus to 35.77 in T.japanicus.The range of core niche(SEA)of 6 hairtail fishes was 0.80?6.90,highest in T.brevis and lowest in Te.cristatus.The range of trophic diversity(CD)of 6 hairtail fishes was 0.85?3.01,L.savala showing the highest and T.nanhaiensis showing the lowest.The trophic similarity(MNND)of 6 hairtail fishes varied between 0.12 and 0.33,and E.muticus was the highest and T.japanicus was the lowest.The range of trophic evenness(SDNND)of 6 hairtail fishes was 0.13?0.22,highest in L.savala and lowest in T.japanicus.The common species of Trichiuridae in the coastal waters of China comprised of 6 species.Though the resources of the hairtail fishes showed slight variation,the structure has improved as the increasing of length at mature and trophic level of T.japanicus.The abundant trophic sources and big span of trophic level indicated that the hairtail fishes played an important role in achieving energy transfer to marine ecosystem.Hairtail species showed high ecological niche overlap,but this could be relieved by increasing food sources diversity.Species T.japanicus and L.savala were the two most important populations constituting the trophic structure of hairtail.Species T.japanicus showed the strongest capacity on resource utilization and environmental adaptability. |
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