| Overfishing and marine pollution have led to a dramatic deterioration of the marine environment,the destruction of fishing grounds,the depletion of fisheries resources and the desertification of fishing waters,and the urgent need to protect and restore marine fishing grounds.Against this backdrop,marine ranching has emerged.The construction of artificial reefs is a key part of the construction of marine pastures.Floating reefs,as a type of artificial reef,have unique advantages in the conservation of pelagic fish in the South China Sea,where water depths are large,but research on the conservation effects of floating reef resources in China is scarce.This study investigated the fish collection effect and bait supply capacity of floating reefs placed in the marine pasture waters of Wuzhizhou Island,Sanya,Hainan.one single floating reef was placed in June 2021 in the north and one in the southwest of Wuzhizhou Island,and four sets of floating reefs were rearranged in April 2022,where three sets of single floating reefs formed a single unit floating reef,which was studied in comparison with another single floating reef.The data collection was divided into two main phases.The first phase of the survey was carried out in November 2021,March 2022,June and October 2022 to obtain data on the distribution of fishery resources and the biomass of floating reefs attached to the Wuzhizhou Island marine pasture area.The surveys were conducted using acoustic surveys of fisheries resources,underwater camera surveys and underwater sampling by divers to accurately assess the amount of fisheries resources in the Wuzhizhou Island marine pasture area,the amount of fisheries resources in the floating reef area,the composition and number of species,and the species and number of organisms attached to floating reefs.The second phase will be carried out in August 2021 and August 2022,using simultaneous fisheries acoustic resource surveys and swimmer trawl surveys to analyse the fishery resources,species composition and distribution range of the Wuzhizhou Island Marine Ranch and its adjacent waters,and to analyse the changes in fishery resources before and after the placement of sunken reefs in the same waters and the distinction between floating and sunken reef resources in the same season.The effect of floating reefs and submerged reefs on the conservation of fishery resources was evaluated through the changes in fishery resources before and after the deployment of submerged reefs in the same area and the distinction between floating and submerged reefs in the same season.Based on the above studies:(1)The unit area fish population,FPUA,in winter,spring,summer,and autumn of 2021,2022 were 15.79 ind/m2,14.07 ind/m2,20.23 ind/m2,and 24.44 ind/m2,respectively.In winter,compared with the non-floating reef area,the FPUA of the individual floating reef on the north and southwest sides increased by 12.9% and 66.8%,respectively.In spring,the FPUA of individual floating reefs on the north and southwest sides increased by 170.3% and 249.6%,respectively,compared with the non-floating reef area.In summer,compared with the nonfloating reef area,the FPUA of individual floating reefs decreased by 12.0%,but the FPUA of unit floating reefs increased by 114.5% when compared with the non-floating reef area.In addition,the FPUA of unit floating reefs increased by 244% compared with that of individual floating reefs.In autumn,the FPUA of individual and unit floating reefs increased by 30.6%and 135.9%,respectively,compared with the non-floating reef area.Furthermore,the FPUA of unit floating reefs increased by 181% compared with that of individual floating reefs.The fish species that appeared around the floating fish reefs in all four seasons of this study were Siganus guttatus,Pterocaesio digramma,Siganus fuscescens,and Plagiotremus spilistius.The fish species that appeared around the floating fish reefs in three seasons were Caranx ignobilis,Heniochus acuminatus,Gnathanodon speciosus,and Pempheris vanicolensis.(2)Research on the attached biological communities of floating reefs in different seasons revealed that 16,18,23,and 25 species of attached organisms were identified during winter,spring,summer,and autumn quarters,respectively,resulting in a total of 28 species.Among them,there were 2 species of cnidarians,11 species of mollusks,4 species of annelids,10 species of arthropods,and 1 species of echinoderms.Balanus trigonus was consistently the dominant species throughout all seasons,while Alectryonella plicatula,Saccostrea mordax,Hydroides elegans,Stenothoe sp.,Hyastenus diacanthus,Thalamita coeruleipes,and Ophiactis savignyi were important components of the community.In the four surveys,the distribution range of the diversity index H’ for the quantity density of attached organisms was 0.741 to 1.312,with an average of 1.020,with summer>spring>winter>autumn;the distribution range of the evenness index J’ for quantity density was 0.160 to 0.292,with an average of 0.236,with spring>summer>winter>autumn;the distribution range of the abundance index d for quantity density was 1.302 to 1.927,with an average of 1.668,with autumn>summer>spring>winter;the distribution range of the singularity index C for quantity density was 0.677 to 0.826,with an average of 0.742.According to the biodiversity threshold grading evaluation standard,the diversity level of attached organisms on the floating fish reefs of Wuzhizhou Island is classified as general(0.6<H’<1.5).(3)A comparative study was conducted on the differences in fishery resources in the reef area before and after the deployment of traditional concrete sinking reefs,and a comparative analysis was also conducted with the floating reef area.The results showed that: In the summer of 2020,the overall average quantity density of fishery resources on Wuzhizhou Island was 1.52×107 individuals/km~2,with an average resource density of 35.76 t/km~2;in the summer of 2021,the overall average quantity density of fishery resources on Wuzhizhou Island was 1.64×107 individuals/km~2,with an average resource density of 41.49 t/km~2.The quantity and resource density of fishery resources in the benthic reef area increased by 49.3%and 61.2%,respectively,compared to before the deployment of artificial reefs.The average quantity density and resource density of fishery resources in the floating reef area were 224%and 243% higher,respectively,compared to those in the benthic reef area.The number of fish species in the marine ranch increased from 66 species of 41 families in 10 orders in 2020 to 93 species of 49 families in 11 orders in 2021.The common dominant fish species in both surveys were Trachiocephalus myops,Saurida undosquamis,Upeneus japonicus,and Uranoscopus oligolepis.In the same season,sinking reefs had a significant attraction effect on lower fishery resources compared to floating reefs and blank controls,with the proportion of acoustic integral value of lower sinking reefs being 23.3% compared to 15.2% for blank controls and17.3% for floating reefs;compared to sinking reefs and blank controls,floating reefs had a significant attraction effect on upper fish(p<0.05),with the proportion of acoustic integral value of upper fish reaching 30.2% compared to 14.4% for blank controls and only 9.1% for sinking reefs.The proportion of the acoustic score of pelagic fish reached 30.2%,compared with 14.4% in the blank control group and only 9.1% in the sinking reef.Compared with the blank control group,the proportion of acoustic integral values of floating reefs in the mesopelagic layer decreased significantly(p<0.05),indicating that the floating reefs may have concentrated mesopelagic fish in the mesopelagic layer after placement.This series of research shows that floating reefs in Hainan near-shore waters to collect fish effect is significant,compared with sinking reefs floating reefs in the pelagic fish resources aggregation conservation effect is obvious,bait supply effect is good,indicating that it is suitable for Hainan near-island marine pasture waters to put in order to carry out fishery resources conservation. |
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