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Donnan Dialysis (DD) is developed in this study for continuous removal of fluoride from Antarctic krill by using seawater or concentrated seawater as the receiving solution. Results show that RO concentrate (1.0 mol L−1 NaCl) got the highest fluoride removal efficiency (93.66% ± 0.81%) with three stages at 0.01 cm s−1 flow velocity. Afterwards, fluoride removal experiment with a real krill solution showed 89.34% ± 0.55% under the optimized conditions. The product has fulfilled the fluoride content of US FDA standard and Canadian Food Inspection Agency in fish and fish products. Results also showed a lower loss of amino acids and proteins in comparison of conventional methods. Finally, a techno-economic evaluation showed that 4.0 USD per ton of Krill solution can be expected by this DD process. This study proves that Donnan Dialysis may be a sustainable defluorination process in removing high fluoride content of seafood by seawater or concentrated seawater.

Cleaner production in the textile industry may be realized by replacing certain synthetic substances with natural materials, especially those that are industrial by-products, which offer the added benefit of increasing the value of the textiles. Since natural materials generally pose a low risk to both the human health and the environment owing to their biodegradability, the wastewater released from their manufacturing processes is less polluting, and therefore, it requires less resources and energy for treatment compared to wastewater loaded with synthetic substances. Herein, we report the use of a protein by-product recovered from the oil extraction process of Antarctic krill (Euphausia superba) to replace traditional mordanting agents in the dyeing of cotton with tannin-rich natural dye extracted from the bark of Xylocarpus granatum. Antarctic krill protein pretreatment successfully improved the dyeability of the fabrics through the formation of insoluble complexes between the protein and tannin. The color parameters of the dyed samples were measured based on the CIE L*a*b* system. The obtained reddish-brown fabrics exhibited mostly good to excellent color fastness ratings in response to washing and other wet treatments. They also displayed durable UV protection properties, with the UPF rating reaching the maximum (50+) level, despite being washed for 50 cycles. Both the Antarctic krill protein and tannin contributed to improved UV protection efficiency due to the presence of UV-absorbing moieties and slight changes in the resulting fabric thickness and cover factor.

Krill, a small shrimp-like crustacean, is actually being exploited commercially in the Antarctic waters. In order to evaluate the offals generated during the processing of krill to food and feed products, as commercial sources of chitin, three kinds of shell waste were analysed. Depending upon the method of krill processing applied the shell waste contained 49–60% of proteinaceous material. The content of crude chitin in the dried deproteinised shells ranged from 34 to 49%. About 60% of the salt mixture impregnating the shells was phosphates and carbonates of calcium and magnesium.

The extent to which marine species avoid survey vessels is the subject of considerable debate, with stimuli such as noise and pressure waves receiving particular attention. By some estimates, avoidance behaviour is a major bias in the assessment of pelagic species distribution and density. Surveyors of the marine environment are increasingly using autonomous platforms; thus the question of avoidance of these novel platforms must be considered. A long-duration, underwater glider with an integrated echo-sounder was deployed to measure the density and distribution of Antarctic krill. We show that krill reacted to the glider, despite the low-noise profile of the platform. The weighted-mean depth of krill swarms was observed to deepen when a glider came within 30 m. In addition, we observed a near-range decrease in depth-integrated acoustic backscatter and we demonstrate that this effect is not explained by the instrument's acoustic footprint. The potential triggers for these behaviours are discussed. The list of sensors available for use on a glider is increasing, with some producing sound, light or other potential stimuli for behavioural response. Our paper demonstrates that caution should be used when designing mission payloads and in the interpretation of acoustic data for animal density from gliders. A key consideration for surveyors may be the factoring in of an exclusion zone from their analyses.

The net position and the spreading performance are crucial for hydrodynamic performances of Antarctic krill trawl, which determine its fishing efficiency. In this paper, the hydrodynamic performance of an Antarctic krill trawl system (including trawler, cable, otter board and trawl) was studied by means of numerical simulation combined with full-scale measurement at sea. The numerical model was established based on finite element method and the principle of minimum potential energy was employed to determine the equilibrium configuration of the trawl system in uniform current. The Newton–Raphson method was applied to solve the equilibrium equation. A multi-wing vertical cambered otter board was designed and a series of wind tunnel model tests were carried on in order to explore the hydrodynamic performance (drag coefficient, lift coefficient and lift-drag ratio) of the otter board. By comparing the simulated results and the simulated results after correction with the experimental results at sea, the modified Tauti's law and the accuracy of the numerical method were verified. The results showed that the fishing vessel, the trawl and the otter board matched well on hydrodynamics. The effects of the warp length, the leg length, the towing speed and the angle of attack of the otter board on the net position, the spread of otter board and the spreading performance of net opening were analyzed. Scientific suggestions on the setting of each component of the trawl system were given based on the numerical simulation study. This paper could be regarded as a scientific reference for Antarctic krill trawl fishing operation.

Euphausiids are vital components of many oceanic foodwebs. Due to their large size, they are key prey species for many vertebrates, and several species are subject to commercial fisheries. The best studied euphausiid species is Antarctic krill (Euphausia superba), and a considerable literature exists documenting its ecology. The abundance of Antarctic krill varies enormously over multiple time and space scales in the Southern Ocean. This variability is driven partly by physical processes, but also by the behaviour of the animals as individuals and as groups. It is likely that such variability also affects the populations of other large euphausiid species. In order to understand this variability, particularly in the context of rapid environmental change and expanding fisheries interests, we need to shift emphasis from conventional point- and transect-sampling conducted from brief research cruises—usually in summer—to basin-scale observations over extended time periods. Future studies of the large-scale biology of krill of all species will also need to consider how their growth, reproduction and behaviour might alter in response to predicted environmental changes such as decline in sea ice cover, rising temperature and acidification of the ocean. Paradoxically, to answer many outstanding questions in krill biology, there also needs to be a shift towards examining the three-dimensional dynamics of krill aggregations on very small space and timescales. This paper outlines some of the approaches that might enable us to make progress in understanding these key organisms at multiple spatial and temporal scales, approaches that in turn may leave us better able to manage krill populations into the future. Whilst the paper’s focus is primarily on Antarctic krill, the findings are applicable generally to other large, schooling euphausiid species.

Antarctic krill (Euphausia superba) is one of the most abundant commercial species in the world and still has great potential for further development and utilization. It is, however, very important that the resource is utilized in a sustainable manner in terms of efficiency and selectivity, which can be enhanced through proper design of pelagic trawls that are used for harvesting the species. Pelagic trawls rely heavily on hydrodynamic forces acting on the netting to form desirable shapes. It is thus crucial to understand hydrodynamic forces acting on the trawl to predict its performance. A large Antarctic krill trawl with a net opening circumference of 200 m was designed for a fishing vessel (2855 kW) and analyzed by numerical simulation and physical model tests. A numerical model of Antarctic krill trawl was established based on the finite element method. The principle of minimum potential energy was employed to determine the equilibrium configuration and the tension distribution of the trawl in a uniform current. The Newton–Raphson method was applied to solve the equilibrium equation. A series of physical model tests were conducted in a flume tank to verify the result from numerical simulation. The results showed that the trawl with a net opening circumference of 200 m had superior hydrodynamic performance and could be well matched with fishing vessels of the class for the efficient production of Antarctic krill. This paper demonstrates the use of scientific methods for the design of large Antarctic krill trawls and the application of numerical simulation to study the hydrodynamic performance.

Antarctic krill is a vital part of the food web and supports a significant fishery in the Southern Ocean. Shifts in historical fishing grounds and spatial distribution of catches have occurred as a result of recent changes in fishery practices. To understand these shifts, fishery spatial dynamics and fishing fleet behavior evaluated on different spatial and temporal scales are critical. We examine the catch distribution on three spatial-temporal scales. At the Western Antarctic Peninsula (WAP) scale, we assessed the fleet’s southward expansion, identifying the Bransfield Strait (BS) as the main current fishing ground, replacing the historical Drake sector. At the BS scale, we identified fishing hotspots (FHs) that concentrated 48%–57% of the total catch over a period of 2–6 months and had high catch densities (2.2–30.3 ton km−2). At the FH scale, we tracked the spatial distribution of the fleet within FHs, demonstrating a shift of fishing vessels to contiguous zones as a result of a decrease in daily catch rates (CPUE). Such shifts (allowing the fleet to increase CPUE) occurred every 4–17 days. Previously exploited fishing grounds were revisited based on FH persistence and sea ice conditions. This paper concludes with a discussion of the potential impact of fishing fleet behavior and catch concentration, considering the recent spatial shift towards less-exploited areas, the overlap with critical zones for predator feeding, and several implications for fisheries management.

This study conducted a bibliometric analysis of 1251 articles related to Antarctic krill from 1960 to 2015, based on the Core Collection in Thomson Reuters’ Web of Science. We analyzed the results from four aspects: annual distribution, Web of Science categories and the major journals, international collaboration and author keywords. The Antarctic krill research has developed rapidly since 1978, with an increasing article output. The studies mostly focused on the fields of marine and freshwater biology, oceanography, and ecology. Polar Biology, Marine Ecology-Progress Series and Deep-Sea Research Part II-Topical Studies in Oceanography, were the top three journals to publish the Antarctic krill-related papers. Although Russia is the earliest state to report Antarctic krill, U.S.A. and England were leaders with the largest output quantity and the highest cooperation frequencies. The researches in PR China have taken a blooming since 2009 and will play a more and more important role in the world. Th...

Antarctic krill, Euphausia superba , is a highly abundant and ecologically important zooplankton species in the Southern Ocean. Regions of elevated Antarctic krill biomass exist around Antarctica, often as a result of the concentrating effect of bathymetry and ocean currents. Such areas are considered biological hotspots and are key foraging grounds for numerous top predators in the region. A hotspot of Antarctic krill biomass exists off the southern extent of Anvers Island, Western Antarctic Peninsula, and supports a population of Adelie penguins that feed almost exclusively on it, as well as numerous other top predators. We investigated the spatio-temporal variability in Antarctic krill biomass and aggregation structure over four consecutive summer seasons, identifying environmental factors that were responsible. We identified three distinct krill aggregation types (Large-dense, Small-close and Small-sparse), and found that the relative proportion of each type to total aggregation numbers varied significantly between survey days. Large-dense aggregations occurred more frequently when westerly winds predominated and when the local mixed tide was in the diurnal regime. Small-close aggregations were also more frequent during diurnal tides and were negatively correlated with phytoplankton biomass. Small-sparse aggregations, on the other hand, were more prevalent when the mixed tide was in the semi-diurnal phase. We suggest that, under certain conditions (i.e. diurnal tides and westerly winds), the biological hotspot in the nearshore waters off Palmer Station, Anvers Island, functions as a zone of accumulation, concentrating krill biomass. Our findings provide important information on the dynamics of Antarctic krill at the local scale.

A one-dimensional, temperature-dependent model was used to simulate the descent–ascent cycle of the embryos and early larval stages of Antarctic krill to determine which regions of the western Antarctic Peninsula (wAP) continental shelf support successful completion of this cycle under present environmental conditions and those projected to occur as a result of climate change. The transport and fate of the embryo and larva under present and modified conditions was investigated with Lagrangian particle tracking simulations. The two modeling studies were implemented using temperature and density (embryo–larva model) and circulation distributions (Lagrangian particle tracking) obtained from a high resolution version of the Regional Ocean Modeling System configured for the wAP shelf region. Additional simulations used temperature and circulation distributions obtained from simulations that were forced with increased wind speed and increased transport of the Antarctic Circumpolar Current (ACC), both projected to possibly occur with climate change in the wAP region. Simulations using present conditions showed that successful completion of the descent–ascent cycle occurred along the outer shelf and on the shelf in regions with bottom depths of 600–700 m. Estimated residence times for the shelf regions that support success of the embryo and larva were 20–30 days. Thus, krill spawned in the mid and inner shelf regions can be retained in these regions through development to the first feeding stage (calyptopis 1). Increased winds and ACC transport resulted in more onshelf transport of Circumpolar Deep Water (CDW), which increased the volume of warm (1–1.5 °C) water at depth. These conditions supported a moderate increase in success of the krill embryo and larva, but only for limited areas of the shelf where hatching depths decreased by 10–30 m (

Net-based data on the abundance, distribution, and demographic patterns of Antarctic krill are quantified from a contemporaneous two ship survey of the Antarctic Peninsula during austral summer 2011. Two survey areas were sampled focussed on Marguerite Bay in the south, and the tip of the Antarctic Peninsula in the north. Data from 177 stations showed that the highest concentrations of krill were found in the southern sampling area. Differences between areas were associated with a few large catches of one year old krill found in anomalously warm and productive waters in Marguerite Bay, and small krill catches in the less-productive, offshore waters in the north. Estimated krill density across the survey area was 3.4 krill m � 2 , and was low compared to the long-term average of 45 krill m � 2 for the Elephant Island area. Overall recruitment between the two survey regions was similar, but per capita recruitment was about 60% lower than historical mean recruitment levels measured at Elephant Island since the late 1970s. Demographic patterns showed small krill concentrated near the coast, and large krill concentrated offshore on the shelf and slope all along the survey area. The offshore distribution of adult krill was delineated by the warm (� 1 1C), low salinity (33.8) water at 30 m, suggesting that most krill were present shoreward of the southern boundary of Antarctic Circumpolar Current Front. Distributions of larvae indicated that three hotspot areas were important for the production of krill: slope areas outside Marguerite Bay and north of the South Shetland Islands, and near the coast around Antarctic Sound. Successful spawning, as inferred from larval abundance, was roughly coincident with the shelf break and not with inshore waters. Given the rapid changes in climate along the Antarctic Peninsula and the lower per capita recruitment observed in recent years, studies comparing and contrasting production, growth, and recruitment across the Peninsula will be critical to better understand how climate change will impact krill populations and their dependent predators in the Scotia Sea.

Pathways and rates of ocean flow near the Antarctic Peninsula are strongly affected by frontal features, forcings from the atmosphere and the cryosphere. In the surface mixed layer, the currents advect material from the northwestern Weddell Sea on the eastern side of the Peninsula around the tip of the Peninsula to its western side and into the Scotia Sea, connecting populations of Antarctic krill (Euphausia superba) and supporting the ecosystem of the region. Modelling of subsurface drifters using a particle tracking algorithm forced by the velocity fields of a coupled sea ice-ocean model (ORCA025-LIM2) allows analysis of the seasonal and interannual variability of drifter pathways over 43 years. The results show robust and persistent connections from the Weddell Sea both to the west into the Bellingshausen Sea and across the Scotia Sea towards South Georgia, reproducing well the observations. The fate of the drifters is sensitive to their deployment location, in addition to other factors. From the shelf of the eastern Antarctic Peninsula, the majority enter the Bransfield Strait and subsequently the Bellingshausen Sea. When originating further offshore over the deeper Weddell Sea, drifters are more likely to cross the South Scotia Ridge and reach South Georgia. However, the wind field east and southeast of Elephant Island, close to the tip of the Peninsula, is crucial for the drifter trajectories and is highly influenced by the Southern Annular Mode (SAM). Increased advection and short travel times to South Georgia, and reduced advection to the western Antarctic Peninsula can be linked to strong westerlies, a signature of the positive phase of the SAM. The converse is true for the negative phase. Strong westerlies and shifts of ocean fronts near the tip of the Peninsula that are potentially associated with both the SAM and the El Nino-Southern Oscillation restrict the connection from the Weddell Sea to the west, and drifters then predominantly follow the open paths to South Georgia and the east. Over the 43-year time series, the number of drifters advected into the Bellingshausen Sea decreases significantly by 23% and the travel time to South Georgia shortens significantly by 19% which corresponds to 56 days. We propose that these trends are linked, at least in part, to the increasingly positive trend in the SAM and, as such, this suggests an additional anthropogenic source of change to the regional ecosystem.

In this study we examined the hypothesis that, under conditions of replete macronutrients and iron in the Southern Ocean, phytoplankton abundance and specific N uptake rates are influenced strongly by the processes of grazing and NH(4) regeneration. NH4 and NO(3) uptake rates by marine phytoplankton were measured to the northeast and northwest of the island of South Georgia during January-February 1998. Mean specific uptake rate for NO(3) (vNO(3)) was 0.0026 h(-1) (range 0.0013-0.0065 h(-1)) and for NH(4) (vNH(4)) was 0.0097 h(-1) (0.0014-0.0376 h(-1)). vNH(4) was related positively with NH(4) availability, which ranged from 0.1 to 1.5 mmol m(-3) within the upper mixed layer. Ambient NH(4) concentrations and vNH(4) were both positively related to local krill biomass values, computed from mean values along acoustic transect segments within 2 km of the uptake measurement stations. These biomass values ranged from similar to 1 g krill fresh mass m(-2) in the northwest to >4 kg krill wet mass m(-2) in the northeast. In contrast to the variability found with NH(4) concentrations and uptake rates, vNO(3) was more uniform across the sampling sites. Under these conditions, increasing NH(4) concentration appeared to represent an additional N resource. However, high vNH(4) tended to be found for stations with lower phytoplankton standing stocks, across a total range of 0.24-20 mg chlorophyll a m(-3). These patterns suggest a coupling between phytoplankton biomass, vNH(4) and krill in this region of variable but high krill biomass. Locally high concentrations of krill in parts of the study area appeared to have two opposing effects. On the one hand they could graze down phytoplankton stocks, but on the other hand, their NH(4) excretion supported enhanced uptake rates by the remaining, ungrazed cells. (C) 2011 Elsevier Ltd. All rights reserved.

Glacier ice released to the oceans through iceberg formation has a complex effect on the surrounding ocean waters. We hypothesized that phytoplankton communities would differ in abundance, composition and production around or close to an iceberg. This paper tests the influence of individual icebergs on scales of meters to kilometers, observed through shipboard oceanographic sampling on March-April 2009. Surface waters (integrated 0-100 m depth, within the euphotic zone) sampled close to the iceberg C-18a ( 10 μm and the salps on smaller cells, 3-10 μm. The iceberg's main influence in the austral fall is measured not so much by phytoplankton accumulation but by reactivation of the classic Antarctic food chain, facilitating diatom growth and sustaining high Antarctic krill populations.

This paper describes growth and maturation of individual Antarctic krill for a complete annual cycle in an artificially controlled environment. Antarctic krill were kept individually and maintained under temperature regimes of −1, 1 and 3 °C, while light conditions simulated natural seasonal conditions for the 14 months of the experiment starting in April. The growth increment (GI), instantaneous growth rate (IGR), daily growth rate (DGR), intermoult period (IMP) and maturity scores (MS) were tracked by measuring the consecutively moulted exoskeletons and modelled using linear mixed models (LMMs). There was a clear seasonal trend in growth and maturity in the three different temperature treatments. Males generally reached peak growth rates and matured earlier than females, but females showed higher growth rates overall. Negative growth occurred towards the end of January for both males and females, coinciding with the regression of external sexual characteristics. There was, as expected, a significant decline in IMP with increasing temperature, which was moderated by increasing trends with total length (TL) and month for the −1 °C treatment. For the 1 and 3 °C treatments there was no relationship with TL and the season effect declined after October and December, respectively. For krill with a TL of 40 mm in October, the predicted mean IMP values at −1, 1 and 3 °C were 28 days, 24 days and 19 days, respectively. There was some evidence to suggest that 1 °C was optimum for growth, as the IMP was significantly lower than at −1 °C but the difference in GI between the two temperatures was not significantly different from zero, while all growth variables were significantly lower for the 3 compared to the −1 °C treatment. For the first time, this study has been able to confirm, by fitting a bivariate LMM, that compensation mechanisms do exist between IMP and IGR and to quantify the degree of compensation at both the between- and within-animal levels. This will allow modelling of growth trajectories in the wild to quantify the distribution of length given age.

Despite much research on Euphausia superba , estimates of their total biomass and production are still very uncertain. Recently, circumpolar krill databases, combined with growth models and revisions in acoustics have made it possible to refine previous estimates. Net-based databases of density and length frequency (KRILLBASE) yield a summer distributional range of ∼19×10 6 km 2 and a mean total abundance of 8×10 14 post-larvae with biomass of 379 million tonnes (Mt). These values are based on a standardised net sampling method but they average over the period 1926–2004, during which krill abundance has fluctuated. To estimate krill biomass at the end of last century we combined the KRILLBASE map of relative krill density around Antarctica with an acoustics-derived biomass estimate of 37.3 Mt derived for the Scotia Sea area in 2000 by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Thus the CCAMLR 2000 survey area contains 28% of the total stock, with total biomass of ∼133 Mt in January–February 2000. Gross postlarval production is estimated conservatively at 342–536 Mt yr −1 , based on three independent methods. These are high values, within the upper range of recent estimates, but consistent with the concept of high energy throughput for a species of this size. The similarity between the three production estimates reflects a broad agreement between the three growth models used, plus the fact that, for a given population size, production is relatively insensitive to the size distribution of krill at the start of the growth season. These production values lie within the envelope of what can be supported from the Southern Ocean primary production system and what is required to support an estimated predator consumption of 128–470 Mt yr −1 . Given the range of recent acoustics estimates, plus the need for precautionary management of the developing krill fishery, our net-based data provide an alternative estimate of total krill biomass.

Studies have documented effects of drag created by data-logging units attached to seals, but the effect of visual stimuli from such units has not been investigated. We evaluated potential effects of camera attachment including near-infrared flash operation by comparing the diving behaviour of 15 female Antarctic fur seals (Arctocephalus gazella) with cameras and 10 seals without cameras. Irrespective of the presence of the camera or flash, all seals exhibited an expected diel dive pattern with shallower, shorter dives, less time at the bottom of a dive, and slower ascent and descent rates at night following krill vertical migration. We also observed a previously unreported foraging trip dive pattern with faster ascents and descents near the end of trips. With cameras present, dive duration and bottom time increased and ascents were slower. During flash operation, dive duration increased and bottom time remained constant throughout the day contrary to the expected diel trend. Also during flash operation, bottom time was shorter at the beginning of a foraging trip and dives were deeper, with longer duration and bottom time later in the trip. We were unable to conclude whether the flash emission spectrum overlapped with the visual sensitivity of seals and Antarctic krill (Euphausia superba) since visual sensitivity data for seals and krill at longer wavelengths were not available. It is possible that the flash was bright enough for the seals or krill to detect; however, although there was a change in diving behaviour observed during flash operation this behaviour was within the range of values normally observed for these seals and should not cause ethical concern.

We simulate the formation of social aggregations in a turbulent fluid environment. The theoretical framework is employed to investigate the ecological consequences of spatial patchiness in the density distribution of krill, which often assemble in swarms or schools. We first describe the formation of aggregations resulting from the interplay of social forces and population dynamics, and then consider an idealized ecosystem model of zooplankton with social behavior who feed on phytoplankton; this is solved analytically for the initial growth of patches and numerically for the steady-state distributions of predator and prey biomass. Environmental variability changes the linear instability criterion for spontaneous aggregation. The second part of the paper addresses the evolution of social behavior in a population with density-dependent mating success. The model simulates the transmission of a gene controlling social behavior; natural selection determines whether the grouping or non-grouping type becomes dominant. It is found that the behavior can evolve when mixing occurs rapidly enough for resources to remain available to the clustered organisms. Turbulent advection prevents the grouping type from becoming dominant if the shear of the flow is strong enough to disrupt the patches; otherwise the aggregated zooplankton benefit from enhanced diffusion of resources by the turbulent flow.

Antarctic krill, Euphausia superba Dana, has a heterogeneous circumpolar distribution in the Southern Ocean. Krill have a close association with sea ice which provides access to a critical food source and shelter, particularly in the early life stages. Advective modelling of transport pathways of krill have until now been on regional scales and have not taken explicit account of sea ice. Here we present Lagrangian modelling studies at the circumpolar scale that include interaction with sea ice. The advection scheme uses ocean velocity output from the Ocean Circulation and Climate Advanced Modelling (OCCAM) project model together with satellite-derived sea ice motion vectors to examine the potential roles of the ocean and sea ice in maintaining the observed circumpolar krill distribution. We show that the Antarctic Coastal Current is likely to be important in generating the large-scale distribution and that sea ice motion can substantially modify the ocean transport pathways, enhancing retention or dispersal depending upon location. Within the major krill region of the Scotia Sea, the effect of temporal variability in both the ocean and sea ice velocity fields is examined. Variability in sea ice motion increases variability of influx to South Georgia, at times concentrating the influx into pulses of arrival. This variability has implications for the ecosystem around the island. The inclusion of sea ice motion leads to the identification of source regions for the South Georgia krill populations additional to those identified when only ocean motion is considered. This study indicates that the circumpolar oceanic circulation and interaction with sea ice is important in determining the large-scale distribution of krill and its associated variability.

The Harvard Ocean Prediction System (HOPS) is configured to simulate the circulation of the Scotia Sea and environs. This is part of a study designed to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia in the eastern Scotia Sea are sustained by import of individuals from upstream regions, such as the western Antarctic Peninsula. Comparison of the simulated circulation fields obtained from HOPS with observations showed good agreement. The surface circulation, particularly through the Drake Passage and across the Scotia Sea, matches observations, with its northeastward flow characterized by three high-speed fronts. Also, the Weddell Sea and the Brazil Current, and their associated transports match observations. In addition, mesoscale variability, an important component of the flow in this region, is found in the simulated circulation and the model is overall well suited to model krill transport. Drifter simulations conducted with HOPS showed that krill spawned in areas coinciding with known krill spawning sites along the west Antarctic Peninsula continental shelf can be entrained into the Southern Antarctic Circumpolar Current Front (SACCF). They are transported across the Scotia Sea to South Georgia in 10 months or less. Drifters originating on the continental shelf of the Weddell Sea can reach South Georgia as well; however, transport from this region averages about 20 months. Additional simulations show that such transport is sensitive to changes in wind stress and the location of the SACCF. The results of this study show that krill populations along the Antarctic Peninsula and the Weddell Sea are possible source populations that can provide krill to the South Georgia population. However, successful transport of krill to South Georgia is shown to depend on a multitude of factors, such as the location of the spawning area and timing of spawning, and variations in the location of the SACCF. Therefore, this study provides insight into which environmental factors control the successful transport of krill across the Scotia Sea and with it a better understanding of krill distribution in the region.

During January and February 2000 four research vessels,f rom Russia,t he UK, Japan, and the United States, conducted an oceanographic survey with 137 hydrographic stations within the Scotia Sea and adjoining waters as part of a survey sponsored by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to estimate the biomass and distribution of Antarctic krill in the Scotia Sea. Chlorophyll-a (Chl-a) measurements showed great variability in phytoplankton biomass within the Scotia Sea,wi th some areas having among the lowest Chl-a concentrations found in Antarctic waters (o0.1mgm_3 in surface waters) while other areas were among the richest with 410mgm_3. This paper describes the distribution and concentration of Chl-a in the upper 100m of the water column and relates the Chl-a profiles at individual stations to profiles of upper water-column stability,t o the depth of the upper mixed layer, and to the mixing of different water masses. The 58 stations with the lowest Chl-a values in surface waters also had low values for integrated Chl-a (33.9+-9.5mgm_2) and a Chl-a maximum at depths of between 70 and 90m,in contrast to all other stations where deep Chl-a maxima did not occur. The T/S diagrams at many of these stations were indicative of Antarctic Circumpolar Current (ACC) waters. The central Scotia Sea and areas to the west and north of South Georgia had significantly higher integrated Chl-a values (98.1+-46.0mgm_2, n ¼ 57),i n addition to five stations with very high Chl-a values (mean of 359+-270mgm_2). The mean rate of integrated primary production,wh ich was estimated using the Chl-a data and the mean incident solar radiation measured from previous cruises as well as from satellite data,w as estimated to be 994mg carbon m_2 day_1. The temperature profiles at these stations suggested that considerable interleaving and mixing of water types had occurred,w hich was also evident in the T/S diagrams,w hich indicated mixing of ACC waters with coastal waters originating from Bransfield Strait or theWeddell Sea. There was no significant correlation between integrated Chl-a values and the profiles of upper water column stability or the depth of the upper mixed layer. The spatial variability in phytoplankton biomass within the Scotia Sea is discussed in relation to the hypothesis that low iron concentrations are the major factor controlling phytoplankton biomass in these pelagic Antarctic waters and that concentrations of iron available for phytoplankton uptake are strongly influenced by fronts and the mixing of different water masses.

This paper summarises the results of krill demographic studies from BROKE—a large-scale survey off East Antarctica conducted in January – March, 1996. The survey progressed from 80°E in late January to 150°E in mid March. Krill varied in mean size across the survey area, and the various maturity stages showed some longitudinal and latitudinal trends. Males, early stage females, and juveniles were, on average, larger in the east of the survey area whereas gravid and spent females differed little in length across the survey area. Gravid females were only found north of the shelf break; juveniles, males and other stages of females were found throughout the latitudinal extent of the survey. Growth rate measurements resulted in comparable figures to other studies in the Indian Ocean and were greatest in February for all stages. Observed growth rates were sufficient to account for the changes in mean sizes of krill observed across the survey area. The mean density of krill revealed by nets (2.65 krill per 1000 m −3 ) was low compared to other areas that have been surveyed. Similarly, the overall estimates of proportional recruitment were below average when compared to the range of reported values. Krill larvae were moderately abundant in the survey area but were more frequently encountered in the east, which is probably a function of the lateness of the season when the larvae would be rising into the surface layer sampled by the net.

A unique Antarctic data set from four multidisciplinary cruises (spring, Nov 1991; summer, Jan–Feb 1993; fall, Mar–May 1993; winter, Aug–Sept 1993) was analyzed to provide a description of seasonal variability in the distribution and abundance of Antarctic krill, Euphausia superba, west of the Antarctic Peninsula. Analyses of acoustic observations revealed distinct seasonal variations in estimates of krill abundance, the dimensional parameters used to characterize individual krill aggregations, the geographic area over which krill were acoustically detected, and the depth distribution of krill biomass. Spatially averaged estimates of krill biomass were an order of magnitude higher in spring (32 g m-2) and summer (95 g m-2) compared to fall (12 g m-2) and winter (8 g m-2). In summer, krill were detected throughout the region and most of the krill biomass was associated with aggregations of small cross-sectional area ( 150 g m-3), which were positioned in the upper 50 m of the water column. Winter observations, in contrast, were characterized by the absence of krill throughout most of the region and aggregations occuring deeper than 100 m with large cross-sectional area (>10000 m2) and low mean biomass ( 50 g m-2) at selected locations on the inner shelf and the disproportionate contribution, in terms of total krill biomass (>80%), by a small number of aggregations ( 40 mm) krill positioned offshore of smaller krill (32–38 mm) in all seasons except winter. Synthesis of these data and historical observations suggest that there is a seasonal shift in the primary habitat of krill and that changes in krill behavior are an important factor affecting variations in krill distributions.

Acoustic Doppler current profilers (ADCPs) are being used increasingly to derive estimates of zooplankton and micronekton abundance. The absence of a practical means for users to perform ADCP calibration, however, makes the quantitative value of this approach questionable. In an attempt to evaluate ADCP- derived volume backscattering strength (S-c) data, and hence to assess the utility of such measurements for biomass estimation, a regularly calibrated Simrad EK500 scientific echo-sounder (operating at 38, 120 and 200 kHz) and an RDI narrowband ADCP (153.6 kHz) were similarly configured and run in synchrony on a transect in the Southern Ocean. Data were collected by both instruments from congruent depth (4 m) and time (2 min) bins in order to allow direct comparison of numerous discrete values without the need for further signal averaging. Echoes were recorded from the Antarctic krill, Euphausia super ba, in deep- ocean and on-shelf locations during day and night. ADCP-derived volume back scattering strength data from shallow, evenly distributed krill targets were well correlated with equivalent data from the EK500 (r(2) > 0.98), and the offsets between instruments conformed to those predicted for their respective operating frequencies by a theoretical model of sound scattering by krill (H-0: S-upsilon 153.6 kHz = S-upsilon 120 kHz + 2.3 dB, t(0.05(2),155) = 1.98, t = 0.74, P = 0.46). Data from deeper, more irregularly distributed targets differed significantly (P < 0.001). We conclude that under some ideal, but probably rare, circumstances data from the ADCP can be used to derive biomass estimates. The numerous uncertainties surrounding ADCP calibration and the current practical impossibility for users to monitor system performance should, however, preclude these instruments from being used as a matter of course to determine abundance estimates, a task that we believe should remain firmly within the domain of a well calibrated scientific echo sounder. (C) 1998 Elsevier Science Ltd. All rights reserved.

The diel vertical migration (DVM) of Antarctic krill ( Euphausia superba ) can greatly bias the results of qualitative and quantitative hydroacoustic surveys which are conducted with a down-looking sonar and irrespective of the time of day. To demonstrate and quantify these negative biases on both the estimates of biomass distribution and abundance, a time-depth-density analysis was performed. Data were collected, as part of the United States Antarctic Marine Living Resources Program (AMLR), in the vicinities of Elephant Island, Antarctica, during the austral summers of 1992 and 1993. Five surveys were conducted in 1992; two covered a 105 by 105 n.mi. area centered on Elephant Island, two encompassed a 60 by 35 n.mi. area immediately to the north of the Island, and one covered a 1 n.mi. 2 area centered on a large krill swarm to the west of Seal Island. The 1993 data include repetitions of the two small-area and two large-area surveys. Average krill volume densities were calculated for each hour as well as for three daily periods: day, twilight and night. These data were normalized and presented as a probability of daily average density. With spectral analysis to identify the frequencies of migration, a four-term periodic function was fitted to the probability density function of average daily biomass versus local apparent time. This function was transformed to create a temporal compensation function (TCF) for upwardly adjusting acoustic biomass estimates. The TCF was then applied to the original 1992 survey data; the resulting biomass estimates are an average of 49.5% higher than those calculated disregarding biases due to diel vertical migration. The effect of DVM on the estimates of krill distribution are illustrated by a comparison of compensated and uncompensated density maps of two 1992 surveys. Through this technique, high density kril areas are revealed where uncompensated maps indicated low densities.

Measurements on krill from distinct swarms and echo-sounder measurements of the same swarms have been analysed using multivariate methods. The analysis has addressed the problems of whether krill swarms in a small area may be of a limited number of types, and whether the biological characteristics of the krill could be related to the echo-sounder measurements of the swarm. The main sources of biological variation between krill in different swarms seemed to be related to size and maturity. Krill swarms did not appear to form groups based on biological similarity, and swarms caught in the same haul were as different as swarms caught in different hauls. However, swarms could be divided into groups on the basis of time of day and swarm depth. The biological features (size, maturity, sex ratio and moult stage) of krill in the swarms were not related to echo-sounder observations (horizontal and vertical extent, depth and density of swarms), although some degree of separation between swarms containing large and small krill may be possible if the shape of the swarms is considered. Information on biological characteristics of krill in swarms must still be collected using nets.

The results of morphometric and biochemical measurements of samples of Euphausia superba and Thysanoessa macrura were used to study krill longevity. On each individual, different measurements were taken, a differentiation index was calculated, and lipids and carotenoids analysed; the data were processed by principal component analysis (PCA). in Euphausia superba the analysis of six morphometric characteristics shows a separation into two groups for the males, but not for females. The analysis of a larger sample, using only four variables, shows an analogous, though less marked separation, suggesting a morphological evolution linked with age. When biochemical data were added, PCA shows a good separation into two groups for both males and females, and the same result was obtained using only the biochemical data and the differentiation index. No possible age groups, other than juveniles and adult males and females, could be identified by PCA for Thysanoessa macrura .

The effect of the ice edge zone on the abundance and distribution of Antarctic krill was investigated by acoustic and net sampling methods in the northwestern Weddell Sea during austral spring, 1983. The dominant acoustic target was Euphausia superba which occurred over the entire study area in the upper 100 m of the water column, either in aggregations or loosely defined layers. The vertical depth distribution under the pack ice was similar to that of open water. Average krill biomass under the ice ranged from 1 to 68 g m −2 and in open water range from 10 to 100 g m −2 . Another euphausiid, Thysanoessa macrura , appeared to be ubiquitous but was much less abundant than E. superba. T. macrura also formed aggregations. All stages were found in open water, but only adults and juveniles under the ice. A few adults and larvae of a third euphausiid, E. frigida , were found only in open water. Salps, which were abundant in open water, were not present under the pack ice. The pack ice directly influenced the abundance and distribution of young krill. Juvenile E. superba were much more abundant under the ice than in open water north of the ice edge. Numerous observations were made of juvenile krill feeding on the undersurface of ice floes where chlorophyll concentrations were much greater than in the water column below. These observations appear to indicate that the pack ice serves as a giant nursery area for young krill, providing a refugium from predators as well as a vast food resource that may be critical to the survival of overwintering juvenile E. superba .

An extremely low abundance of the Antarctic krill, Euphausia superba, was observed in the Scotia Sea during the austral winter of 1983. The decline could not be attributed to any of the environmental factors investigated, including phytoplankton biomass which was higher than expected. One effect of the reduced krill population, observed during the 1983 to 1984 summer, was a much lower than average breeding success for bird and seal predators of krill on Bird Island, South Georgia. Historical evidence suggests that drastic reductions in krill abundance may not be uncommon, and will have profound consequences for the developing krill fishery.

The sinking rates of embryos of the Antarctic krill, Euphausia superba , were measured during development in the laboratory. The sinking rates were determined at two hydrostatic pressures, 10 and 1000 dbar. There was no significant difference in the sinking rates of the eggs measured at the two pressures at any time during development. The two possible effects of hydrostatic pressure—increasing the density of the seawater and compressing the embryo—are antagonistic and of the same relative magnitude. In a static water column, the effect of the physical environment on the developmentaltime and not the sinking rate appears to be the most important factor determining the depth where the embryos of E. superba hatch.

The dry weight of cast exoskeletons of Euphausia superba was found to be log-linearly related to the dry weight of the post-moult animal, a relationship similar to that obtained for other species of euphausiids. The moult of this species represented an average of 7.5% of the post-moult dry weight of the animal, which is twice the estimate of other authors. The moults sank at rates ranging from 0.06 to 1.18 cm s −1 and the sinking rate was a function of the moult weight and of its surface area. Freshly shed exoskeletons had a mean carbon to nitrogen ratio of 5.6 and a mean organic content of 73.2% of the high dry weight. Fluoride levels in the cast exoskeleton were high (mean 5.44 ppt), and the fluoride was shown to leach out following ecdysis. The rate of fluoride loss was most rapid in the first 2 days following moulting and showed markedly in the following 3 days. The effect of these processes on the transport of organic matter and fluoride from the Antarctic surface waters is discussed.