| At present,fishery resources worldwide have been greatly reduced,and high-trophic large fish have been gradually replaced by low-trophic invertebrates and pelagic planktonic fish.Potential fish stocks,while enabling the country to maintain high catches,have had a negative impact on the biodiversity of Marine ecosystems and our fisheries may also face collapse if appropriate fisheries management policies are not implemented.In order to deal with the fishery crisis,our country strengthened the construction of Marine ranch to build the blue granary.However,the construction and management of Marine Ranching is still immature,and there are still some problems to be studied.In this study,the national Marine Ranching Demonstration area in the west of Furong Island in Shandong Province was taken as an example to analyze the composition of fish species,explore the biodiversity and functional diversity of fish community species in this area,and discuss the diversity changes in different areas and seasons.Based on the above fishery survey data and with limited data,a size spectrum model was established to develop the prediction technique of the maximum sustainable yield(MSY)of the target species in the small-scale ecosystem of Marine Ranching.The results of this study are as follows:(1)A total of 16 fish species belonging to 3 orders and 11 families were identified in the three quarterly(spring,summer and autumn)surveys in the Laizhou Bay Marine Ranching.Perciformes accounted for 50%of the total fish species.There are 9 species in summer,9 species in autumn and 7 species in spring.Black rockfish(Sebastes schlegelii)and fat greening(Hexagrammos otakii)were caught in all three seasons.The largest number of fish species were caught in autumn,with 10 species,in summer,with 9 species,and in spring,with only 7 species.According to regional statistics,S.schlegelii is captured in wind power fusion area and reef area.A total of 10 fish species were captured in the wind power fusion area,9 in the reef area and 11 in the control area.Black rockfish is the dominant species in three seasons.(2)From the perspective of seasons,the mean value of Shannon-Wiener index is summer>spring>autumn,Pielou index is spring>summer>autumn,and Gini-Simpson index is spring>summer>autumn.The three indices in autumn were all low,the relative density of species was low,and the resource situation was not good.The trend shows a decrease from summer to autumn and an increase from autumn to spring.From the survey area,Shannon-Wiener index mean wind power fusion area>reef area>control area,Pielou evenness index mean control area>reef area>wind power fusion area,wind power fusion area>reef area>control area,and Gini-Simpson index mean wind power fusion area>reef area>control area.Compared with the three regions,the three indexes in the summer reef area are the highest,while in autumn and spring they are the lowest.The Pielou index of the three regions in spring is close to each other,but there is no great difference.The index of control area was higher in autumn,but had no obvious advantage in the other two seasons.(3)Functional richness(FRic)calculation requires more than 3 functional populations,and the reef area in spring does not meet the calculation requirements,while the spring wind power fusion area has the highest functional richness.The seasonal average of functional evenness(FEve)was spring>summer>autumn,ranging from 0.536 to 0.755.The mean reef area was>wind power fusion area>control area,ranging from 0.553 to 0.619.Functional richness and functional evenness decreased from summer to autumn and rose in spring of the following year.The functional uniformity of reef area is significantly higher than that of the other two areas.Functional differentiation(FDiv)ranges from 0.679 to 0.970,and is generally high.The seasonal mean values of functional differentiation were autumn>summer>spring,ranging from 0.769 to 0.879.Mean reef area>control area>wind power fusion area,ranging from 0.762 to 0.861.Functional dispersion(FDis)ranges from 0.144 to 0.343,and is generally low.The seasonal mean of functional dispersion was spring>summer>autumn,and the range was 0.239～0.324.The average wind power fusion area was>reef area>control area,ranging from 0.222 to 0.263.(4)Taking the Laizhou Bay Marine Ranching as the research object,a size spectrum ecosystem model was established to simulate the equilibrium state of the multi-species size spectrum model within 15 years under the current stable fishing effort(taking the current fishing effort as the standard and setting the fishing death coefficient as 1,that is,F=1/yr).The total biomass(B),mean body weight(meanW)and large fish index(LFI)of the fish community showed similar trends and decreased with the increase of fishing effort.The total biomass ranged from 1615.5t to 3633.9t.Average body weight ranged from 35.9g to 86.8g.The index of large fish ranged from 0.59 to 0.81.The slope of community biomass spectrum showed a simple linear relationship with fishing effort,ranging from-0.54 to-3.82.The output of three enhancement species,S.schlegelii,H.otakii and Rapana venosa,all increased with the increase of F.The yield slopes of S.schlegelii and H.otakii reached their maximum at F values of 2.5/yr and 1.5/yr,with the yields of 44.8t/yr and 61.6t/yr,respectively.When F=5(the maximum fishing effort set),the maximum sustainable yield of R.venosa was not reached,and the yield was 138.1t.To sum up,Laizhou Bay Marine Ranching and nearby Furong Island artificial fish reef area are still in the development stage,the ecosystem is not mature,the number of fish species and resources are not high.The number of species in Laizhou Bay Marine Ranching is relatively small,and the species diversity index is high,but the actual species diversity level is low and the ecosystem is immature,and the anti-interference ability is relatively weak.The functional groups are few and single,the competition of fish community is high,and the ecological niche space is not fully utilized.The effect of artificial reefs on fish aggregation is still positive and may attract other pelagic fish in the future.The multi-species mass spectrum model can be established in the Marine pasture ecosystem with small data amount and scale.Through parameter setting and adjustment,the future fish community status can be further simulated,the changes of ecological indicators with fishing pressure can be monitored,and the production of enhancement species can be predicted.The maximum sustainable yields of S.schlegelii,H.otakii and R.venosa were 44.8 t/yr,61.6 t/yr and 138.1 t/yr,respectively.Maximum sustainable yield is best evaluated after sufficient data has been accumulated to achieve better simulation results. |
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