| With the depletion of China's offshore fishery resources,the Antarctic marine biological resources show great potential,especially the Antarctic krill,as the key link of energy flow in the south ocean ecological environment system,its commercial value and potential have attracted the attention of many countries.Because of its complex environment and unclear mechanism of sea condition change of fishing ground,Antarctic krill fishery has become a major research hotspot in the current Antarctic fishery.At present,satellite remote sensing technology is widely used to study the spatial-temporal distribution of Antarctic krill and its relationship with environmental factors,which is of great significance for the development and utilization of Antarctic krill fishery resources,However,there are few reports on the spatial-temporal variation of long-time series and the establishment of multi parameter discriminant method in the central fishery of Antarctic krill.In this study,FAO 48 areas,the main fishing area,are taken as the research site.Combined with the fishing statistics and marine environment remote sensing data from2010 to 2018,mathematical statistics and geographic information software are used to analyze the spatial-temporal distribution and environmental characteristics of Antarctic krill fishery.Adopted the generalized additive model to analyze the correlation between the spatiotemporal and environmental data and the catch per unit of effort(CPUE)of Antarctic krill.This paper attempts to construct a multi parameter identification method for Antarctic krill central fishing ground,to screen the suitable fishing ground location for continuous fishing and to determine the stable fishing ground of year,month and week.According to the analysis results of GAM model,three environmental factors(sea surface temperature,chlorophyll concentration,sea ice density)with high correlation with Antarctic krill were selected to determine the appropriate environmental indicators for stable fishing ground,which laid a foundation for future exploration of the variation law of Antarctic krill fishing ground.The main results are as follows:(1)From the perspective of interannual change,the average CPUE of Antarctic krill is on the rise year by year,and the proportion of operation times is also on the rise;from the perspective of monthly change,the average CPUE of Antarctic krill is on the seasonal change,high in summer and autumn,low in winter and spring,high from December to May of the next year,highest in April,low from June to October,and the lowest is in October;The average CPUE of Antarctic krill first increased and then decreased,reaching the highest value in the 14th week(the 1st week of April)and the lowest value in the 49th week(the 1st week of December).According to the change of the center of gravity of the krill fishery,the center of gravity of the krill fishery is mainly distributed in the sea of34°W?54°W,52°S?64°S,and in the sea near the South Shetland Islands and South Orkney Islands(46°W?64°W,60°S?64°S)from the 1st to the 24th week(the 1st week of January to the 2nd week of June),and then in the sea area near the South Georgia Islands(35°W?37°W,53°S?55°S)from the 25th to the 34th week(the 3rd week of June to the 3rd week of August).After the 35th week(the 4th week of August)or so,the center of gravity of the krill fishery moved to the Southwest(54°W?64°W,60°S?66°S).(2)The sea surface temperature range of Antarctic krill fishing ground is-1.8?3.0?,the high CPUE area is-1.7?2.3?,the highest frequency of sea surface temperature of Antarctic krill operation point appears in the range of-1?0.5?,at this time,the average CPUE is relatively high;the chlorophyll concentration range is 0.03?3.3mg/m~3,and the high CPUE area is 0.04?0.67 mg/m~3,Chla value frequency highest value appears in the range of 0.1?0.2 mg/m~3,at this time the average CPUE is at the highest value;krill mainly gather in the sea area of 0?10%sea ice concentration,it shows seasonal change,from January to August sea ice range from small to large,August to December sea ice concentration gradually reduced.(3)The GAM model simulation results show that the influence of each factor on the spatial-temporal distribution of CPUE is in order of cycle(5.94%),latitude(5.62%),sea ice density(5.47%),month(4.64%),sea surface temperature(4.07%),longitude(3.85%),chlorophyll(1.7%),year(1.44%),current(0.16%),and the total interpretation deviation rate of all factors is 32,According to F test,there was a significant correlation between CPUE and year,week and sea surface temperature(P<0.05).Specifically,the most suitable fishing week is from the 10th to the22th week(the 1st week of March to the 4th week of May;the most suitable fishing longitude and latitude ranges are 61.5°S?63.5°S,56°W?62°W;the SST range suitable for krill fishery is-0.5?1?;the krill fishery is concentrated in 0.15?0.25mg/m~3,the most suitable fishing sea ice concentration is 0?1%,and the most suitable current velocity in the range of 0?0.2m/s,in this range the CPUE is slowly decreasing.The second gam model analysis of the significant correlation factors(year,week,SST)shows that the confidence interval of the three factors is obviously reduced,and the suitable fishing range is more refined.With the increase of the year,the fitting degree is higher and higher,and the CPUE also shows an increasing trend;with the change of the week,the CPUE first rises and then falls,and the fitting degree is higher around 5-15 weeks;with the change of SST,the fitting degree is about-1?CPUE at-0.5?and 0.5?1?showed an upward trend and a high degree of fit.(4)If the CPUE of krill per hour in three consecutive days is?20t,and the space distance is relatively close,within the space range of 0.5°×0.5°,then the fishery is suitable for continuous fishing,and is defined as the center fishery.From the suitable continuous fishing,three levels of stable fishery are screened again,namely yearly stable fishery,monthly stable fishery and weekly stable fishery.Yearly stable fishery is defined as:three consecutive years and above a certain sea area range;monthly stable fishery is defined as:continuous 3 months and above a certain sea area range;weekly stable fishery is defined as:continuous 3 weeks and above a certain sea area range.The main operation area of Antarctic krill is located in the sub areas of 48.1,48.2 and 48.3.According to the analysis,there are suitable continuous fishing grounds in all three sub areas,and the better stable fishing grounds are located in the sub area of 48.1.The southwest area of South Shetland Islands is the largest high-yield fishing ground in the 48 fishing areas.From October to May of the next year,there are higher catches,while those in the sub areas of48.2 and 48.3 are suitable small and medium-sized continuous fishing grounds In addition,the operations in sub region 48.3 are generally concentrated from June to September,which is suitable for small and stable fishing grounds with long-term operations,while those in sub region 48.2 are suitable for continuous fishing,with less operation time and short continuous time.The range of yearly stable fishery is 58.2°W?59.2°W,63.1°S?63.3°S(48.1 sub area),35.6°W?36°W,54°S?54.4°S(48.3 sub area),The range of monthly stable fishery is 58.2°W?59.6°W,63°S?63.4°S(48.1 sub area),35.6°W?36°W,54.1°S?54.2°S(48.3 sub area),The range of weekly stable fishery is 58.4°W?59.8°W,63°S?63.3°S(48.1 sub area),35.6°W?36°W,54°S?54.4°S(48.1 sub area),The stability index of 48.3 sub area is higher than that of 48.3 sub area.The main environmental range is:chlorophyll concentration is 0.1?0.3mg/m~3,sea ice density is 0?40%,sea surface temperature is-1.8?1.5?.The innovative results of this study are as follows:(1)The spatial-temporal distribution of krill trawlers in the long time series(9 years)and large spatial scale(48.1,48.2 and 48.3 subregions)was analyzed.It was found that the environmental patterns in the high CPUE area(CPUE>20t/h)were-1.7?2.3?(sea surface temperature range),0.04?0.67 mg/m3(chlorophyll concentration range)and 0?60%(sea ice density range),respectively.(2)For the first time,GAM model was used to analyze the correlation and optimum range of CPUE with cycle,sea ice density and current.The optimum fishing cycle was 10-22weeks,the optimum sea ice density was 0-1%,and the optimum current velocity was 0-0.2m/s.(3)For the first time,the multi parameter identification of Antarctic krill central fishing ground was carried out.The area with CPUE?20t per hour in three consecutive days and spatial distance within 0.5°×0.5°was defined as the central fishing ground suitable for continuous fishing,and the method of judging the stability of the central fishing ground(operation times and CPUE weight method)was proposed. |
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