| Antarctic krill(Euphausia superba Dana 1850,refered to as krill abbreviation)is a kind of typical crustacean zooplankton species.It has rich resource,highnutritional value and not only plays a crucial role in the middle and upper ecosystem of the Southern ocean,but also is an important part of our country's pelagic fishery.Clustering behavior is a common feature of many marine organisms.Antarctic krill usually clusters at a certain time and place,and such a clustering behavior is vital in the life history of its natural population.For more than half a century,scholars from all over the world have carried out a lot of research on the formation mechanism,cluster type division,time and spatial structure of Antarctic krill clusters.However,due to the complex and changeable marine environment in the South Ocean and the short board of existing observation technology,many problems about krill clusters have been pending.With the popularization of acoustic survey technology and the continuous improvement of data analysis methods,the research of Antarctic krill colony based on acoustic data is of great help to us to understand its reproduction,distribution,migration and other contents.At the same time,the understanding of krill colony behavior will also help to identify krill fishery,improve yield and fishing efficiency.Based on the acoustic data collected during the survey of krill resources in South Orkney Islands from January to February 2018,this paper used Echoview software to post-process the acoustic data,and combined the biological information of krill samples obtained from trawling to obtain the eigenvalue information of krill clusters.The main results are as follows:Combining with principal component analysis and k-mean cluster analysis,this paper analyzed the characteristic values and types of krill clusters,and explored the temporal and spatial changes of the characteristic values of krill clusters.As a result,we found:(1)A total of 3224 krill swarms with swarm characters including swarm depth(96.00±64.33m),swarm length(218.52±455.66m),swarm thickness(11.19±13.98m),swarm area(1894.40±9345.72m~2)and packing density(114.11±159.60 ind/m~3)were extracted.(2)In different periods of a day,there were significant differences between swarm depth,swarm length,swarm thickness,swarm area and swarm density had no significant difference.In different depths of swarms,there were significant differences between swarm depth,swarm length, swarm area and there was no significant difference between swarm thickness and swarm area.(3)Three distinct krill aggregation types were classified.Type I had the biggest packing density(325.90±221.30m),smallest swarm area(379.64±433.73m~2)and deepest swarm depth(158.06±67.54m);type?had the longest swarm length (1089.60±1189.56m)and swarm area(15601.25±30243.33m~2)were much bigger than other two types;type?had the lowest swarm depth(78.91±52.88m)and smallest packing density(48.87±50.33 ind/m~3),but it had the largest numbers of swarms.Taking krill aggregation as the analysis object,using the marine area scattering coefficient(NASC)of krill to characterize its resource abundance,the study area is divided into 7 spatial scales according to longitude and latitude,including 10?×10?,20?×20?,30?×30?,40?×40?,50?×50?,60?×60?,70?×70?,and the geostatistics method is used to analyze and discuss the Antarctic phosphorus at different scales The spatial heterogeneity of shrimp resource abundance.The results show that:1.As a whole,with the increase of the spatial scale:(1)the nugget value and the block to base ratio decrease gradually,the nugget effect is weaker and weaker,and the influence of random factors on the total spatial variation degree is smaller;(2)the partial and base values decrease first,then increase and then decrease,and the spatial scale is 40?×40?,when the spatial structure variation has the most influence on the total spatial variation degree The results show that the spherical model has the best fitting effect when the spatial scale is 20?×20?and 50?×50?,the exponential model has the best fitting effect when the spatial scale is 10?×10?,the Gaussian model has the best fitting effect when the spatial scale is 30?×30?,40?×40?,60?×60?.The fitting results show that the resource abundance of Antarctic krill is the best 3.The spatial structure of krill resource abundance shows that,based on anisotropy,the difference of fractal dimension is the smallest when the scale is 50?×50?,the biggest when the scale is 60?×60?,the overall correlation is weak in the north-south direction(N0°)and the southeast northwest direction(n135°),the Northeast southwest direction(N45°)and the east-west direction(N90°)In the scale domain(30?,50?),the correlation is weak;based on isotropy,the fractal dimension value is the smallest when the scale is 60?×60?,the largest when the scale is 50?×50?,and the fractal dimension value decreases with the increase of scale in the scale domain(10?,40?). |
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