| The mesopelagic fishes—the small nektonic organisms,inhabiting in the middle-level sea areas at depths between 200 and 1000 m,It is the most abundant organism and widely distributed in the world open ocean,from the Arctic to the Antarctic.Diel vertical migration(DVM)habit is one of the most prominent ecological characteristics of mesopelagic fish,migrating to the upper layer for feeding at the night,and down to the middle-level of the ocean for emission in the day.The migration pattern mainly includes four kinds: strong migration,semi-migration,passive migration and non-migration for mesopelagic fishes.DVM is important to maintain the stability of the deep sea ecosystem by transferring the material and energy from the upper layer to the deep sea.The study of DVM has lasted for 50 years,however,no such study has ever been undertaken in China and understanding of the phenomenon and mechanisms is incomplete.This paper summarized the main research progress and results of DVM of mesopelagic fishes by worldwide.Major potential mechanisms governing the DVM and its research statusare described,in this paper,the diurnal and vertical migration habits of fish in the northern South China Sea were studied.According to the fisheries resources data collected from the northern South China Sea(18°00?N~22°00?N,111°00?E~120°00?E)in August and November 2015,we investigated the community structure,dominant species and diversity of fishery resources in this area.The results showed that 210 fishery species in August,mainly of fishes and crustaceans.The index of relative importance(IRI)is used to measure ecological dominance of species to decide the role each species plays in the community.Diaphus brachycephalus,Ceratoseopelus warmingii,Diaphus Phillipis and Oplphorus typus were identified as the moninant species in summer.The species with value of IRI between 100 and 500 is viewed as the major species.The ranges of catch rates in weight were 0.36-1.77kg/h in the study areas,of which the average catch rates was 0.95 kg/h.The ranges of catch of individual numbers were 182-755 ind./h in the study areas,of which the average individual numbers of catch was 393 ind./h.The average Shanon-Wiener diversity index(H'),Pielou evenness index(J')values and Margalef richness index(D)of fishery resources in summer were 4.34?0.70 and 3.41,and they were 5.42?0.79 and4.03 in winter.The fish in the study area had obvious diurnal and vertical migration habits.According to the data of trawl,There are 52 types of fishing,the catch were 1.22 kg of daytime surface(200m light),There are 43 types of fishing,the catch were 4.52 kg of daytime surface(200m light);the day 350-550 m water catches a total of 40 species,a total of 1491 catches for tail,2.46 kg forweight,night 350-550 m water catches a total of 59.A total of 852 tail,2.67 kg for weight;day700m to deep layer catches a total of 36 species,a total of 435 catches for tail and 2.26 kg for weight,night 700 m to deep catch a total of 76 species,a total of 445 catches for tail,2.30 kg for weight;0-200 m on the surface of the bottom trawl fishery day was less,the night catches increased significantly,especially in the small fish as the representative of lantern fish,and some relatively small fish such as Zeidae and(Melamphaidae)and remains in the water layer.Acoustic data show middle fish habitat in 250-500 m and water during the day,the evening of most fish species up to 100-200 m middle layer and 100 m in shallow water,that most fish species are middle diel vertical migration behavior obviously.In order to fishery system and ecological resources development functions of the northern South China Sea sea provide scientific reference. |
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