Abstract:Salpa thompsoni is an important tunica filter feeder in the Southern Ocean, which plays a significant role in the Antarctic marine food web. S. thompsoni and Antarctic krill (Euphausia superba) compete for similar diets. Therefore, in order to study the factor influencing food composition of S. thompsoni in the fishing ground of Antarctic krill fishery, based on the specimens collected from the Bransfield Strait from March to April 2020, this study identified the food composition of this species, and further analyzed the difference in feeding habits between months and life history stages. The results showed that S. thompsoni mainly fed on diatoms and zooplankton, and a small number of ciliates and protozoa. C. pennatum is dominant in the diet of S. thompsoni. Seasonal differences occurred in diet of S. thompsoni. Specifically, the feeding quantity of diatom, i.e., C. pennatum, which is dominant in March, decreased significantly at the end of April. The diet composition of S. thompsoni changed significantly between solitary and aggregating stages. This study is expected to provide a reference for the study of feeding habits of S. thompsoni in the Southern Ocean, and to provide basic information for clarifying the trophic relationship between S. thompsoni and Euphausia superba.

Abstract:Recently the fishing vessel has been widely used to collect acoustic data to provide information on the distribution and abundance of Antarctic krill (Euphausia superba). One basic assumption of the acoustic survey is that the effective range detection limit (RDL) of the echo sounder could cover the major distribution layer of Antarctic krill. However, due to the lack of noise mitigation design, the background noise levels of fishing vessel are usually higher than the research vessels, which may seriously degrade the RDL of the echo sounder system. In order to facilitate the use of fishing-vessel-based acoustic data, in the present study, a method was introduced to estimate the RDL of scientific echo sounder based on the background noise estimates obtained using post-processing technique. Furthermore, taking the Antarctic krill fishing vessel “Fu Rong Hai” as a case study, the background noise levels and RDLs of the Simrad EK 60 echo sounder system (38, 70 and 120 kHz) onboard were estimated at various vessel speeds. Results indicated that the RDL was not only related to echo sounder specifications and backscattering strength of the survey target, but also to the background noise level and the vessel speed. For “Fu Rong Hai”, the background noise levels of the acoustic data collected by the EK60 system increased markedly with increasing vessel speed and resulted in decreased RDLs for all the three frequencies. At a vessel speed of 8 kn and a signal-to-noise ratio (SNR) of 10 dB, the RDLs for all the three frequencies were estimated to be larger than 300 m for the Antarctic krill with a S_v threshold of −70 dB , while the RDL decreased to be around 100 m at 70 kHz which could not meet the requirement of depth coverage (250 m) for Antarctic krill acoustic survey when the vessel speed was increased to 12 kn. The results proved that the vessel speed may have significant impact on the performance of effective range detection limit of echo sounder system, and this study may provide valuable reference for the use of fishing vessels to conduct acoustic survey particularly the vessel speed and data processing.

Abstract:An 8-week feeding experiment was conducted to evaluate the effects of replacing fish meal (FM) with krill meal (KM) on the growth performance, serum immune indexes and muscle quality of Pelteobagrus fulvidraco [initial body weight (10.51±0.13) g]. Five experimental diets consisted of different proportions of FM that were replaced with KM, corresponding to dietary inclusion levels of 0% (KM0), 2.5% (KM2.5), 5% (KM5), 7.5% (KM7.5), and 10% (KM10). The results showed that there was no significant difference in growth performance, survival rate, intestinal amylase and lipase activities with the increase of the substitution proportion of krill meal. Compared with KM0 group, trypsin activity in each substitution group decreased significantly. Compared with KM0 group, the content of serum complement 3 in each substitution group increased significantly, and immunoglobulin M in KM5 group increased significantly. When the substitution level exceeded 5%, the activity of serum alkaline phosphatase decreased significantly. With the increase of the substitution ratio of krill meal, the muscle adhesiveness, springiness and gumminess decreased, the cohesiveness increased, and the hardness and chewiness increased first and then decreased. Compared with KM0 group, muscle adhesiveness, springiness and gumminess in KM10 group decreased significantly, and cohesiveness increased significantly. With the increase of the proportion of KM instead of FM, the content of total delicious amino acids and total non-essential amino acids in muscle hydrolyzed amino acids increased first and then decreased. In conclusion, the substitution of KM for FM has no negative effect on the growth performance, which can enhance immune function to a certain extent, and affect the muscle textural parameters and total delicious amino acids in the appropriate ratio.

Abstract:Since the promotion of Antarctic governance, particularly the establishment of Antarctic Marine Protection Areas (AMPAs), involves diverse factors, the roles and functioning of parties are differed in those processes. Non-governmental organizations (NGOs), as multiple actors in Antarctic governance, have significant effected on the promotion of AMPAs with their ability in providing scientific data, active participation and public attention. The role of NGOs in Antarctic governance has influenced, to some extent, the promotion of AMPAs and the effective management of Antarctic krill fishery. By analyzing the works of four NGOs, including the Antarctic and Southern Ocean Coalition (ASOC), the Association of Responsible Krill Harvesting Companies (ARK), the Pew Charitable Trusts (PEW) and the Oceanites, to explore their roles in the promotion of AMPAs and Antarctic krill fishery management. At present, China can enrich China Antarctic scientific research database by using multi-party data, use NGOs to tell China's stories within its legal framework. The government and NGOs interact to form a virtuous cycle to improve the scientific nature of AMPAs research and Antarctic krill fishery management, thus improving the overall level of Antarctic governance and contributing China wisdom to the protection of the Antarctic ecological environment.

Abstract:Euphausia superba is rich in astaxanthin, which is a good source of natural astaxanthin. Shrimp meal is one of the most important processed products of E. superba. In the shrimp meal processing, the cooking and drying processes involve heat treatment. Astaxanthin is a heat-sensitive substance with poor structural stability, and it is easy to be degraded and isomerized at high temperature, which results in the changes of astaxanthin content and antioxidant capacity. In order to understand the changes of astaxanthin content, structure and antioxidation ability during the processing of E. superba meal, the content and structure of astaxanthin in each stage were determined by high-performance liquid chromatography, the antioxidant activity of astaxanthin in different processing stages was compared, and the correlation between astaxanthin structure and its functional activity was analyzed. The results showed that the content of astaxanthin in E. superba was 110.6 mg/kg, of which the content of all-trans astaxanthin was 90.7% , the content of 13-cis astaxanthin and 9-cis astaxanthin were 4.7% and 4.6% respectively, and after cooking and drying, the content of astaxanthin was 88.7 and 52.1 mg/kg, the proportion of trans astaxanthin was 76.2% and 72.2% , the proportion of 13-cis astaxanthin was 19.9% and 21.9%, and the proportion of 9-cis astaxanthin was 3.9% and 5.9%. The content of three optical isomers such as 3S, 3’S, 3S, 3’R, 3R, 3’R in astaxanthin of E. superba were 16.8, 17.9 and 72.1 mg/kg respectively, the content were 12.0, 25.5 and 55.3 mg/kg after cooking，and were 2.8, 8.1 and 12.4 mg/kg after drying. The scavenging capacity of astaxanthin to DPPH free radical was stronger than Vc. In the scavenging experiment of hydroxyl free radical, the antioxidation ability of astaxanthin after cooking and drying was better than krill material. In FRAP iron reduction experiment, the antioxidation after cooking and drying also showed greater reduction ability. The results showed that the geometric isomerization of astaxanthin mainly took place in the cooking stage, and the optical isomerization mainly took place in the drying stage. This study can provide a theoretical basis and technical reference for the optimization of the processing technology of E. superba meal and the extraction and utilization of astaxanthin.

Abstract:It’s difficult for accurate quantification of astaxanthin esters because of their multiple forms, and hydrolysis of astaxanthin esters to free astaxanthin is the key to solve the problem. In this work, Antarctic krill (Euphausia superba) was used as a representative specie for the study of astaxanthins. The mono- and di-esters of astaxanthin were prepared from Antarctic krill by column chromatography, and the composition and content of them were clarified using high-resolution mass spectrometry with ultraviolet detection. The astaxanthin monoesters and the astaxanthin diesters were then taken as the typical research samples, the enzymatic hydrolysis conditions of which were optimized through single factor and orthogonal experiments, and the accuracy and applicability of the method were evaluated. Results showed that: (1) 8 astaxanthin monoesters and 13 astaxanthin diesters were prepared and identified as typical characteristic compounds from krill. (2) For the astaxanthin monoesters, as the substrate concentration was 0.5 μg/mL, the enzyme concentration of the reaction system was 1.14 U/mL, the reaction temperature was 25 ℃, and the reaction time was 75 mins, the yield of free astaxanthin could reach (94.56±1.24)%; And for the astaxanthin diesters, as the substrate concentration was 1.0 μg/mL, the enzyme concentration of the reaction system was 0.92 U/mL, the reaction temperature was 25 ℃, and the reaction time was 75 minutes, the free astaxanthin yield reached (98.28±0.84)%. (3) Enzymatic hydrolysis at room temperature was applied to the analysis of actual samples, the astaxanthin content was (265.09±20.35) mg/kg in Antarctic krill oil, and the content was (21759.36±90.19) mg/kg in Haematococcus pluvialis. In order to verify the accuracy, the enzymatic hydrolysis method was compared with the standard methods from SC/T 3053—2019 and GB/T 31520—2015. The determination results were 260.42±11.57 mg/kg and 21752.54±100.00 mg/kg respectively, and the deviations of the results were all less than 10%. Then the results were further verified by adding a standard solution of all-trans astaxanthin to the sample matrix was tested, the recovery rate of free astaxanthin was 95.24% in Antarctic krill and 98.56% in Haematococcus pluvialis, RSD was 2.03% and 0.75%, respectively. It proved that the enzymatic hydrolysis method has good accuracy and precision. Studies have shown that the enzymatic hydrolysis method has good stability and high repeatability, reduces the oxidation of astaxanthin in the reaction process, and maximizes the conversion of ester astaxanthin into free form, which is suitable for accurate quantification of esterified astaxanthin. Therefore, the scientific basis for the comprehensive utilization of astaxanthin resources could be provided from this study.

Abstract:Antarctic krill (Euphausia superba) is a key species in the Antarctic marine ecosystem with important potential for commercial exploitation, however, significant heterogeneity in type and distribution of krill swarms increases the difficulty of biomass estimation and also brings the challenges for at-sea operation and working plan to fishing company. Therefore, using acoustic data collected from fishing vessels, the spatial and temporal distribution characteristics, diel differences, and swarm structures of Antarctic krill swarms in the fishing grounds of the Bransfield Strait were analysed with the aim of improving fishing efficiency. The results indicated that, in the Bransfield Strait, krill swarms were primarily located in the southern shelf waters in autumn 2020, and that the number of krill swarms increased over time in autumn. Most krill swarms can be found in water layers between the surface and the depth of 150 meters, but some swarms also occur close to the bottom. The diel distribution of krill swarms varied, with a general tendency of reversed diel vertical migration that moves up to the surface in the daytime but sinks to the deeper layer at night. The layered type of swarm with a high density is dominant in the daytime, while scattered type of swarm with low density occupies a high proportion at night. The density within swarms is correlated positively with swarm length. In general, the daytime layered type of swarms within the Bransfield Strait are suitable for fishing vessels. Understanding krill swarm distribution is beneficial to understanding their formation characteristics of krill fishing ground as well as enhancing the productivity of fishing vessels.

Abstract:Due to richness in essential amino acids, phospholipids, astaxanthin and omega-3 polyunsaturated fatty acids (PUFAs), Antarctic krill (Euphausia superba) which was abundant and had high nutritional value was considered to have great development value. At present, the analysis of fatty acid contents in Antarctic krill and its products mainly focused on the determination of total fatty acid contents. Owing to the effect of bioavailability for PUFAs in different esters, it was necessary to accurately quantify the content of fatty acid in different types of esters in Antarctic krill and its products. In order to clarify the content of phospholipids (PL) fatty acids in Antarctic krill oil, a gas chromatography analysis method for the content of fatty acids in PL in Antarctic krill oil was established based on solid phase extraction. After optimizing the various conditions of the impact analysis, under the optimal conditions, the recoveries of the standard addition measured by this method were between 84.22%-94.45%, and the intra-day and inter-day precision were between 0.79%-6.09%. This method was applied to measure the changes in the content of various PL fatty acids of Antarctic krill oil during storage. The results showed that the content of PL fatty acids decreased during the 21-day storage process, and the degradation rate increased with increasing temperature. The present study provided methodological support for the study of lipids in Antarctic krill.

Abstract:Antarctic krill (Euphausia superba) is a type of crustacean living in Antarctic waters and is an important strategic marine living resource. Currently, the research on the safety of Antarctic krill is mainly focused on fluorine and arsenic, while the study on Antarctic krill sensitization is rarely reported. How to prevent and control the food allergy caused by Antarctic krill has become urgent work. In order to explore the sensitization problem of Antarctic krill, the main allergens were screened, identified, isolated and purified from Antarctic krill, and the properties of major allergens were studied. Antarctic krill proteins were extracted by salt buffer; Allergens were screened by SDS-PAGE and Western blot (WB); The primary structure of these allergic proteins were identified using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS); Major allergens were separated and purified by isoelectric precipitation, ammonium sulfate salting out and anion exchange column chromatography. The heat resistance and the digestive stability of Antarctic krill major allergens to simulated gastrointestinal fluid were analyzed by SDS-PAGE and WB. Results showed that the protein bands of sarcoplasmic protein (SP) and myofibrillar protein (MF) extracted from Antarctic krill were rich and the range of the molecular weight (MW) was wide. Antarctic krill proteins could react with the serum IgE of shrimps/crabs allergic patients, and at least four proteins had positive reactions. The protein with the strongest immune reaction had a MW of about 35 ku and could be recognized by the serum of all allergic patients. This allergic protein was identified as Antarctic krill tropomyosin (TM) by LC-MS/MS. The optimum saturation of ammonium sulfate was 50% for the salting out Antarctic krill TM. After separation and purification, TM with high purity was obtained, which could have a strong immunoreactivity with the serum IgE of shrimps/crabs allergic patients. The measured isoelectric point of Antarctic krill TM was 4.4, and it had good thermal stability. With the extension of digestion time of simulated gastric fluid (SGF), MW of TM gradually decreased and finally stabilized at about 33 ku, and the abundance of degradation fragments with MW of 15 ku and 12 ku gradually increased and existed stably. These degradation bands could still have strong immunoreactivity with the serum IgE of allergic patients. With the extension of digestion time of simulated intestinal fluid (SIF), the original band of TM gradually decreased until disappeared, and finally completely degraded into smaller polypeptide. The immunoreactivity of TM degradation products was greatly reduced after digestion by SIF. The results obtained above indicate that there are allergens in Antarctic krill, and TM is the main allergen with immunoreactivity. TM also has the general characteristics of allergens, such as high temperature resistance, pepsin digestion resistance and partial stability of trypsin digestion.

Abstract:To further study the temporal and spatial distribution characteristics of Antarctic krill (Euphausia superba) aggregations in the waters near the South Shetland Islands, based on the acoustic surveys of Chinese E. superba production fishing vessels and commercial fishing data in the 2018/2019 fishing seasons, the center depth, water temperature and morphology of E. superba aggregations were analyzed. The results showed that there were significant temporal and spatial differences in the depth of E. superba aggregations center, the temperature at the depth of Antarctic krill aggregations and aggregations morphology in the waters near the South Shetland Islands (P<0.05). The average aggregations center depth, whose variation range was 34.39 to 86.12 m, showed an increasing trend from April to July, the difference between day and night was small (P=0.325), and the peak periods were sun rising (SRS) and night (NIT), which were 64.06 and 65.32 m respectively. The low value range of average aggregations center depth was 62.75°−63.75°S and 58.25°−59.75°W, and the high value range was 61.75°−62.25°S and 60.25°−61.75°W. The average temperature at the depth of E. superba aggregations, whose variation range was −1.71 to −1.50 ℃, showed a decreasing trend from April to July. The peak period was NIT and evening twilight (ETW), which were −1.46 ℃ and −1.40 ℃ respectively. The low value range of average aggregations water temperature was 62.75°−63.75°S and 61.25°−61.75°W, and the high value range was 61.75°−62.25°S and 58.25°−60.75°W. The cluster shape was mainly stripped from April to May and scattered from June to July. The cluster shape was mainly horizontal band from day to afternoon (AFT), and the cluster shape was mainly scattered from sunset (SST) to morning (MRN). The results showed that there were obvious temporal and spatial differences in the depth of E. superba cluster center, cluster water temperature and cluster shape in the waters near the South Shetland Islands. The difference between months was greater than that between day and night, and had relative consistency in spatial variation.

Abstract:Antarctic krill oil (AKO) refers to the lipid extracted from Euphausia superba. Recently, it has attracted great concerns from academia and industry due to its unique composition. However, the lack of standards, complex composition and differences in processing methods can easily lead to unstable quality of AKO products, which would further limit the in-depth research on its functional properties and restrict the development of the AKO industry. Thus, the fractional preparation of AKO and its quality analysis were conducted in this study. Firstly, the whole E. superba meal was used as the raw material, and soybean oil or medium chain triglycerides was used as the co-solvent carrier in conjunction with supercritical CO₂ extraction technology to prepare triglyceride-enriched oil (first grade oil). And then, the extracted E. superba meal was subjected to alcohol extraction to prepare a phospholipid-enriched oil (second grade oil). Considering the lipid composition, and content of phosphatidylcholine and phosphatidylethanolamine as the inspection indicators, 30% soybean oil was selected as the co-solvent carrier in conjunction with supercritical CO₂ extraction technology to prepare AKO. The results showed that, compared with the non-cosolvent group and the ethanol cosolvent group, the co-solvent carrier (30% soybean oil) group had the highest extraction rate of primary oil, suggesting the phospholipids of the first and second grade oils were effectively separated, and its polyene index, atherosclerosis index and thrombosis index were relatively low. The phospholipid content of AKO prepared by fractionation in the present study was significantly different, which not only enriched the types of AKO products, but also provided theoretical guidance for the selection and formulation of subsequent AKO extraction technology. It is suggested that the research of AKO in the future should focus on the influence of typical processes on the composition, structure and functional properties of AKO and their related mechanisms, which would be helpful to achieve precise regulation and efficient production of AKO with target functionalities.

Abstract:As a key species in the Antarctic ecosystem, distribution of Antarctic krill (Euphausia superba) resources demonstrates significant spatial-temporal heterogeneity. Different spatial scales may give different results when analyzing the spatial pattern of Antarctic krill. In order to analyze the influence of different spatial scales on the spatial pattern of Antarctic krill, based on the biomass data of Antarctic krill in the waters near the Antarctic Peninsula from 1996 to 2011, Moran’s I, Geary’s C and Ripley's K value were calculated to analyze the spatial pattern of Antarctic krill resources, and to detect changepoints of various spatial indicators at different spatial scales. The results showed that the value of global Moran’s I decreased as the increasing of spatial scales, the value of Geary’s C increased but then decreased. The results of the generalized estimation equation showed that both spatial scale and distance had a significant impact on the K' value. In general, Antarctic krill around the Antarctic Peninsula had a high-density cluster distribution. and the aggregation degree of Antarctic krill around Antarctic Peninsula decreased with the increasing of the spatial scales. The changepoint detection showed that 25'×25' was the spatial scale where multiple spatial indicators qualitative change. Therefore, this study suggests 25'×25' can be considered as the scale threshold for comparing the results of such studies within the scale of 1'×1'~60'×60'. This study explored the scale effect of the spatial distribution of Antarctic krill resources, which can provide a scientific basis for further research on the spatial and temporal distribution of local krill resources and the formation mechanism of fishing grounds.

Abstract:Pickering emulsion is a new type of emulsion system that uses solid particles to achieve the stability. Compared with traditional emulsions, Pickering emulsion has not only the basic characteristics of classic emulsions, but also better stability, higher safety and a wider range of applications. As a result, Pickering emulsion has received widespread attention. However, most researchers used inorganic particles or organic polymers to prepare Pickering emulsions. These particles have shortcomings such as low biocompatibility and poor degradability, which limit their use in the food industry. Therefore, seeking food-grade natural stabilizers has become a development trend. β-cyclodextrin is a cyclic oligosaccharide composed of seven glucose molecules. It has a unique structure of hydrophobic internal and hydrophilic external, and has good emulsifying properties. In the water-oil system, β-cyclodextrin can embed the oil phase in the inner cavity and adsorb the water phase on the outer wall, forming an interfacial film at the oil-water interface in the form of clathrate particles, thereby forming a stable emulsion system. In order to make the Antarctic krill oil Pickering emulsion stabilized by β-cyclodextrin and study its stability, the effects of different emulsification methods (ultrasonic, high-speed shearing, high pressure microfluidics), different oil phase volume fractions (30%, 40%, 50%, 60%, 70%), and different β-cyclodextrin mass fraction (1%, 2%, 3%, 4%, 5%) on the emulsion system (turbidity, centrifugal stability, particle size, ζ-potential) were studied and the preparation process of β-cyclodextrin stabilized Antarctic krill oil Pikering emulsion was determined. Then, the thermal sterilization stability, freeze-thaw stability and storage stability of the emulsion were investigated through the appearance, microscopic changes of the emulsion and the characteristic indexes. The results showed that a stable Antarctic krill oil Pickering emulsion was prepared with 60% oil volume fraction, 3% β-cyclodextrin mass fraction and high-speed shear emulsification. The turbidity, centrifugal stability, particle size and ζ-potential of the emulsion were 1.83, 85.12%, 110.5 nm and -28.39 mV, respectively. Thermal sterilization had no significant effect on the appearance and microstructure of the emulsion, and the characteristic index of the emulsion. Freezing and thawing process had a significant impact on the emulsion. After the freezing and thawing, serious precipitation and emulsification took place in the emulsion, and the emulsion was no longer in a uniform and stable state. After the emulsion was stored for 16 days, although the appearance structure, microstructure and characteristic indexes of the emulsion had changed, the emulsion still showed a uniform and stable state. In short, β-cyclodextrin as a stabilizer could be used to prepare Antarctic krill oil Pickering emulsion, which could have good thermal sterilization and storage stability (within 16 days), but no freeze-thaw stability.

Abstract:Antarctic krill (Euphausia superba) is a key species of Antarctic marine ecosystem and the main fishing object of Antarctic fishery, whose fishing ground has significant temporal and spatial distribution characteristics. In order to clarify the changes of krill fisheries in the northern waters of the Antarctic Peninsula, based on the statistical data of E. superba fisheries in China from 2010 to 2020, this study analyzed the temporal and spatial distribution characteristics of krill fisheries in this water area by using the global Moran's I index and hot spot analysis. The results showed that the spatial distribution of krill catches in the northern waters of the Antarctic Peninsula evolved from dispersion to concentration, and with gradual transition from the north of the South Shetland Islands (SSI) to the Bransfield Strait (BS), with high values distributed along the land. The high value of catch per unit effort (CPUE) mainly occurred in the north of SSI and the side near the Antarctic Peninsula in BS, which was distributed along the land. The krill fisheries in the northern waters of the Antarctic Peninsula showed significant spatial aggregation from 2010 to 2020, and the spatial autocorrelation in 2014, 2015, 2016, 2018 and 2020 was relatively weak. The temporal and spatial evolution characteristics of hot spots and cold spots in the distribution of krill fishing grounds were obvious. The hot spots gradually migrated from the north of SSI to BS, the north of SSI gradually changed from hot spots to cold spots, and the BS gradually changed from cold spots to hot spots. This study discussed the temporal and spatial distribution characteristics of krill fishery, which could not only provide a scientific basis for further research on krill population distribution and fishery formation mechanism, but also provided basic data for improving the production efficiency of krill fishery.

Abstract:In order to improve the antioxidant activity of Antarctic krill protein, a new polyphenol-protein complex (SAKP-rutin complex) was successfully prepared by grafting rutin onto soluble Antarctic krill proteins (SAKP). The antioxidant capacity of SAKP-rutin complexes was evaluated by measuring its ability to scavenge DPPH^- and hydroxyl radicals. Meanwhile, the protective ability of SAKP-rutin complexes against oxidative damage of HepG-2 cells was determined by using an H₂O₂ induced oxidative damage model. The results showed that the combination of rutin greatly enhanced the ability of SAKP to scavenge free radicals. Compared with natural SAKP, the SAKP-rutin complexes significantly increased the activity of cellular antioxidant enzymes (CAT, SOD and GSH-Px), decreased the production of lipid peroxidation products (MDA) in cells caused by oxidative stress, and finally reduced the damage of oxidative stress to cells. These findings suggest that SAKP-rutin complex is a novel protein resource which will hopefully be applied to developing functional protein food.

Abstract:Global warming has attracted more and more attention. As the key factors of climate change, Antarctic sea ice and wind field significantly affect the safety and economic efficiency of fishing vessels. Krill fishery is an important part of China's pelagic fishery. China generally uses traditional fishing vessels for krill fishing, which is more vulnerable to the external environment than continuous pumping fishing vessels. The changing environment has a more and more significant impact on Antarctica. However, there has been no regional study on sea ice and wind field in Bransfield Strait. According to the adaptability of krill fishing, based on the sea ice concentration data of the National Snow and Ice Data Center of the United States and the wind field data of the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1989 to 2020, this study obtained the distribution and variation trend of sea ice concentration and wind in the Bransfield Strait, Antarctica within the Subarea 48.1 of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) under climate change. The results show that under the background of global warming, the sea ice and wind speed in Bransfield Strait in Subarea 48.1 showed a decreasing trend, compared with CCAMLR Subarea 48.2, 48.3, and 48.4, Subarea 48.1 was more suitable for krill fishing. According to the distribution of fishing vessels’ operating positions, the fishing operation area was mainly concentrated in central basin (CB) area and eastern basin (EB), and the sea ice concentration was 0.15-0.2 and in areas with large wind force (wind force level reached level 6 and above) for 50-70 days. For the characteristics of sea ice and wind field from 1989 to 2020, the suitable operation days under the influence of sea ice in Bransfield Strait (the days with sea ice density <0.2) increased; the wind direction in this area was mainly to the west, and the number of days with large wind force was less, and the trend was mainly increasing. Due to the low Beaufort scale in the study area, the suitable operation days of traditional fishing boats in the study area were greatly affected by sea ice. Therefore, combined with the changes of sea ice and wind in the Strait in the past 32 years and their impact on traditional fishing operation, our study showed that the suitable operation days of traditional fishing vessels will increase in the future, but the variation in krill resources derived from the change of sea ice and wind needs to be considered in the future study.

Abstract:In order to meet the needs of Antarctic resource development, in order to solve the problems of the disorderly development of the deshelling processing mode in the current shipborne processing of Euphausia superba, and the lack of key technology for proportioning process of E. superba and seawater, which results in poor operation stability of the deshelling processing equipment, in this study, according to industrial development needs of E. superba processing and E. superba deshelling production line on a domestic E. superba professional fishing and processing ship, a standardized processing mode has been established by using mechanism analysis method. Using mechanism analysis method, the law of conservation of mass, Dixon's criterion and data fusion filtering algorithm, etc., the data processing method of the acquisition signal of the feeding system in E. superba deshelling process , the mathematical model of the feeding system’s dynamic proportioning process of E. superba and seawater, the control model and workflow of E. superba to seawater were established, and using the E. superba deshelling processing equipment on a domestic E. superba professional fishing and processing ship, the research on the application effect of the key technology of proportioning process of E. superba and seawater was carried out. The results showed that based on the process parameters set in the experiment, the value of proportioning process of E. superba and seawater fluctuated around the preset value, and the maximum change was controlled within ±2%. Among them, in the starting state, the regulation time of seawater flow and E. superba’s mass rate was about 119 seconds, and both can operate stably according to the preset parameters. In the running state, the regulation time of seawater flow and E. superba’ s mass rate was about 32 seconds, and then it showed periodic and stable changes with the change of liquid level. The deviation of seawater flow rate was –0.48 to 0.42 m³/h, and the deviation of shrimp mass rate is –0.48 to 0.42 m³/h., meat yield increased by 0.7%. The results indicated that the key technology of proportioning process of E. superba and seawater for E. superba deshelling processing in the standardized shipborne processing mode of this study can ensure the stable value of proportioning process of E. superba and seawater. The maximum change of the proportioning process of E. superba and seawater in this research was controlled within ±2%, meat yield increased by 0.7%. This technology can ensure the stable operation of proportioning process of E. superba and seawater deshelling processing, and meet the needs of E. superba deshelling process development.

Abstract:Species Distribution Models (SDM) are important tools for exploring future changes in global biodiversity. However, relatively few studies have applied multi-model approaches to assess biogeographic changes globally, especially in marine environments. Antarctic krill (Euphausia superba) is a key species in the Southern Ocean marine ecosystem, but researches on its habitat are still limited, which hampers the understanding of its distribution and resource management. To this end, based on the resource density data of Antarctic krill and five environmental factors including Sea Surface Temperature, Sea Surface Chlorophyll, Sea Surface Height, Net Primary Productivity and Sea Ice Coverage, through ensembled models of 12 algorithms, we analyzed the habitat of Antarctic krill. Our results showed that, of the 8 algorithms, the Support Vector Machines, Random Forests, Multivariate Adaptive Regression Splines, Classification and Regression Trees, Multi-Layer Perceptron, and Recursive Partitioning and Regression Trees consistently outperformed the others; while the Bioclim, Domain, and Maxlike had poor performance, although they also differed among months. Besides, there was a link between inter-annual environmental variability and the spatial and temporal patterns of potential habitat for Antarctic krill. The results showed that the suitable habitat for Antarctic krill is mainly located in the central Bransfield Strait. The prediction of Antarctic krill habitat by ensembled model is helpful for the conservation of Antarctic krill resources, and for the exploration of the best fishing ground for Antarctic krill and the space of important fishing area in the future.

Abstract:Beam trawl is an important part of Antarctic krll (Euphausia superba) continuous fishing system. In order to further understanding the gear performance under different conditions, a series of model test were designed to study the effect of gear structure and sinker on gear performance. The gear structures include 3 kinds of belly width and 2 types of knitting for each belly width, represented by A, B, C, AA, BB and CC respectively. Modified Tauti’s law was used to designed beam trawl models. The full scale was 20, mesh size or twine diameter scale was 10. Based on the energy efficiency coefficient, vertical opening and resistance, the performance of different gear structure were compared. The result showed that: the performance of different gear structure was in the order of BB>CC>C>A>B> AA, but the difference was not obvious (P>0.05). Less total line area of net can effectively improve the vertical opening of the beam trawl and reduce the energy efficiency coefficient, especially under the high trawling speed. Sinker weight was significantly correlate with gear resistance and vertical opening, and not significantly correlate with energy efficiency coefficient. In order to keep good performance in vertical opening of test nets, heavier sinker were needed under higher trawling speed. According to the model test, sinker weight should not be less than 3.05 t at the trawling speed of 1.5 m/s for test nets; a power function was observed between net resistance and trawling speed, and the index ranged from 1.49 to 1.64. These conclusions can be used as reference for the performance optimization of E. superba beam trawl and promote the development of E. superba fishery.