Community Structure, Feeding Ecology And Movement Behaviors Of Demersal Fish Around Qiansan Islets

Since the 20 th century, overexploitation on marine organisms and developments of other marine industries, have caused the continuing marine defaunation around the globe. The fishery resource decay in coastal areas(e.g. Haizhou Bay) is notable in fish stocks declining and habitats lost. For sustainable fishery development, a great amount of stock recovery efforts, including the delineation of Marine Protected Area, deployments of artificial reefs to recover damaged habitats, and establishing measures on protective management, have been taken globally.The restoration of marine resources around Qiansan Islets in Haizhou Bay has been being carried out since 2005. However, after such restoration efforts, there was no systemic investigation of fishery resource around Qiansan Islets. A series of sampling survey on demersal fish around Qiansan Islets were taken from May 2013 to April 2014 and all caught fish were identified to 22 species 15 families 6 orders: perennial rockfish species(PRS), including Hexagrammos otakii, Sebastes schlegelii, Hexagrammos agrammus, Conger myriaster and etc. are dominant species; Chinese temperate sea bass Lateolabrax maculatus, pacific cod Gadus macrocephalus and species of Carangidae and Scombridae are seasonal migrational species(SMS). The results of canonical correspondence analysis(CCA), which was used to analyzed the effect of environmental factors on fish community structure, suggest that the distribution of fish are mainly influenced by bottom water temperature and dissolved oxygen in bottom water. The bottom water temperature has a positive effect on the biomass of H. agrammus, Pterogobius zacalles, Paralichthys olivaceus, Sebastes hubbsi, Scomber japonicus and Seriola dumerili. The biomass of both G. macrocephalus and H. otakii is of close relationship with dissolved oxygen in bottom water, and G. macrocephalus was only distributed in deep water of high dissolved oxygen in seasons of low temperature. Species of S. schlegelii, C. myriaster and S. pachycephalus were distributed widely in the study area.Through stomach analysis and stable carbon and nitrogen isotope analysis, we studyed the feeding ecology of H. agrammus, H. otakii, S. schlegelii(three rockfish species) and the migrational species L. maculatus. The results revealed that H. agrammus and H. otakii mainly fed on crabs, fish and amphipoda, and also ate shrimps and polychaeta. S. schlegelii and L. maculatus consumed a high proportion of fish and shrimps. Schoener’s index suggested no significant dietary overlap among the four species, and one way analysis of similarity(ANOSIM) indicated significant dietary differences among species. δ15N and δ13C of L. maculatus were significantly higher than the other three rockfish species, which indicate that the trophic niche differed significantly between L. maculatus and the rockfish species. The overlapped δ15N range and δ13C range, lower Schoener’s index(< 0.6) and significant food composition differences(by ANOSIM) among the three rockfish species, indicated that they had simmilary trophich niches, especially for S. schlegelii and H. otakii, but partitioned in prey resources.A short-term(with a tracking period of up to 46 d) acoustic tracking was conducted on the black rockfish S. schlegeli. The average residence index(the ratio of detected days to the total period from release to the last detection) in the study area was 0.92 ± 0.13, and most of the tagged fish were detected by only one region of the acoustic receiver array, suggesting relatively high site fidelity to the study area. Acoustic tracking also suggested that this species is more frequently detected during the day than at night in our study area. However, the diel detection periodicity(24 h) was only evident for certain periods of the tracking time, as revealed by a continuous wavelet transform. The habitat selection index of tagged S. schlegelii suggested that S. schlegelii preferred natural reefs, mixed sand/artificial reef bottoms and mixed bottoms of boulder, cobble, gravel and artificial reefs. The vertical movement of tagged S. schlegelii was mostly characterized by bottom dwelling behavior, and there was high individual variability in the vertical migration pattern. Our results have important implications for S. schlegelii catchability, the implementation of marine protected areas, and the identification of key species habitats, and our study provides novel information for future studies on the sustainability of this important marine resource in eastern China.