| Antarctic krill usually refers to the Euphausia superb Dana,which occupies a central position in the Antarctic ecosystem and is a key species in the Antarctic ecosystem.The reserves of Antarctic krill are very abundant.According to the recent acoustic assessment,the biomass of Antarctic krill is between 6.5 and 1 billion tons,and the conservative estimate is also 2.50 to 600 million tons,and biomass accounts for about 50% of plankton.The catchable capacity is more than double of the world's existing fishery production,and has great potential for development and utilization.In addition,Antarctic krill is rich in nutrients and is a potentially huge protein pool.China has always attached attention to the development and utilization of Antarctic krill,and it is the main target for the exploitation and utilization of Antarctic biological resources in China.The fishing method is mainly trawls,and the production vessels are generally large tail trawl trawl processing vessels.Antarctic krill mainly live in the Southern Ocean(south of south latitude 50 degrees)not far from the Antarctic continent,especially in the Weddell Sea.Sometimes krill group migration can form long and wide teams of several hundred meters.There are tens of thousands of krills per cubic meter,and the seawater is also discolored.That is,during the daytime,the sea surface appears light brown and is fluorescent at night.The traditional fishery of the krill involved in this article is the 48.1 area,which is the sea area around the South Shetland Islands.The collection tool for Antarctic krill is a Japanese four-piece single-vessel mid-tier krill trawl.In this paper,based on the fishery and observational data of the Antarctic krill exploration trawl survey conducted by the China Aquatic Products Co.,Ltd.in April-June2017,the unit fishing effort(CPUE)of Antarctic krill was used as an evaluation index.The temporal and spatial distribution of the resources of krill was statistically analyzed.The results showed that during the investigation,production of krill monthly decrease,between May CPUE little variation in the value of difference,but basically still showing a decreasing trend,from April to June the average CPUE of Antarctic krill were 14.76 ±0.61,13.12 ± 0.55,and 16.74 ± 0.80 t/h.On the whole,the CPUE value of Antarctic krill presented a leftward unimodal distribution,most of the nets were distributed on thesmaller side,the larger CPUE accounted for a small part,and the CPUE of the statistical period was 0.67~ 53.33 t/h,the average CPUE was 14.57±0.37 t/h.After one-way analysis of variance(ANOVA),the trawl depth,surface temperature(SST),and trawl time period all had significant influence on the CPUE of Antarctic krill.The effect of trawl speed on CPUE value was not significant.1.When the temperature is between-2.5 and-2.0 °C,the average CPUE is the highest,with a value of 15.4947±0.6252 t/h.When the temperature was between-0.5 and0 °C,the average CPUE of the Antarctic krill reached the lowest,with a value of8.75±1.25 t/h.In general,when the temperature varies from-2.5 °C to 0 °C,the CPUE value of Antarctic krill basically shows a gradually decreasing trend.2.The average resource level of Antarctic krill changes with the depth of trawling.Through the statistical analysis of the survey data of the “Dragon” survey,it can be concluded that the average CPUE of Antarctic krill gradually decreases as the depth of trawling increases.CPUE gradually decreased from 16.51±1.08 t/h at a towing depth of 0to 25 m to 9.23 t/h.3.Towing speed,as a fishing factor in the process of Antarctic krill fishing,has a great influence on the CPUE of Antarctic krill.During the survey,the speed was between1.7 and 3.2 kn,which was between 2.0 and 2.9 kn,accounting for 90% of the total network.Changes in drag speed have little influence on the CPUE of Antarctic krill.With the change of drag speed,CPUE basically remains unchanged.4.The average CPUE of the whole voyage Antarctic krill trawls showed an inverted“V” distribution by time period,with the maximum in the afternoon,which was17.31±0.85 t/h,and the lowest in the middle of the night,which was 12.56±0.55 t/h.It is necessary to know about the effects of salinity on the Antarctic krill under the situation of the global and the Antarctic ice and snow would melt.The survival rate and the slough rate of Antarctic krill(Euphausia superba)under abrupt and gradual changes in salinities were determined to evaluate the tolerance of Antarctic krill to salinity.The abrupt changes in salinity mean that the salinity was changed to 14,18,22,26,30,34,38,42,46,50 and 54 from 34,respectively.The gradual changes in salinity mean that the salinity was raised and reduced 4 every day for five days from 34.Put the survival Antarctic krill into the seawater whose salinity was 34,then observed the survival status of them after 24 hours.We observed 3 hours once,and then,we observed 12 hours after 24 hours.In 2016-2017,active Antarctic krill(Euphausiasuperba)which survived and were collected immediately in the capture by a pelagic trawl which made by Japan with the factory trawler “Longtong” near Shetland Island,towing speed was 3~4 knots,towing time was 20 minutes.There were no feeding food for Antarctic krill,and we kept the temperature in the range of 0.5 ~1.5?.The results showed that,in the treatments of abrupt changes,the influence of salinity on the Antarctic krill mortality was significant;the survival of krill was 0 when the salinity changed from 34 to lower than 22 and to 54,the survival rate of krill was 0 after 24 hours.However,when the salinity from 30 to 42,no krill was dead.After 14 days,the remaining alive krill's mortality was very low,and the mortality rates fell by 20% only when the salinity was 26.The slough phenomenon appeared in the salinity from 26 to 42,and the slough rate reached the maximum value88% when the salinity was 38.The slough phenomenon appeared under the salinity from26 to 42;the slough rate declined when the salinity decreased from 34,when it is 38,the slough rate had risen,then it declined when the salinity continued to rise.In the treatments of gradual changes,in the salinity from 14 to 22,the mortality of the Antarctic krill was73%,and the mortality of krill was 100% in the salinity from 14 to 18;otherwise,the mortality of krill was 0 in the salinity from 26 to 50;the mortality of krill was 100% again when the salinity was 54;and the influence of salinity on the Antarctic krill mortality was also significant with 24 hours.After 14 days,the remaining alive krill's mortality was very low,and the mortality individuals from the salinity of 50 accounted for 57% of all mortality individuals.There were some krill began to slough within 24 hours,in general,the slough rate reached the maximum 70% value when the salinity was 38.The slough tendency of gradual group was same with the abrupt group.Then we can draw a conclusion that had higher survival rate,and the optimum growth and development of the Antarctic krill was found at a salinity from 30 to 42 under gradual treatments.The slough rate would rise when the salinity rose in certain scope from 34,while,it would fall when the salinity reduce. |
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