Krill Fishery Research Articles

Changing the focus: The need for cross-scale dynamic management in the Southern Ocean and implications for holistic conservation of Antarctic marine living resources

The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) establishes the regulatory framework for fisheries management and the establishment of Marine Protected Areas (MPA) in the Southern Ocean. Identifying foraging areas regularly used by penguins provides valuable information for the small-scale management of the krill fishery and the design of MPAs, currently under discussion in CCAMLR. We used geolocators to identify the areas used by Adélie penguins from Ardley Island (South Shetlands Islands) during the non-breeding season and Stable Isotope Analysis (SIA) (δ13 C and δ15 N) on feathers to study the trophic niche. Adélie penguins depended on resources available in CCAMLR subareas 48.1 and 48.5 during the post-breeding and molting stage, the subarea 48.5 during the post-molting stage and subareas 48.1, 48.2 and 48.5 during the pre-breeding stage, critical moments of the species’ annual cycle. The Domain 1, Weddell Sea and SOISS MPA proposal areas were extensively used. SIA results show the use of coastal and off-shore foraging areas in 2022, but principally off-shore areas in 2021. Adélie penguins dependence on resources from different subareas in different times of the year emphasizes the need of incorporating the temporal dimension of resources utilization when designing conservation measures in the Southern Ocean. With an increasing pressure on Adélie penguin colonies in the western Antarctic Peninsula, its long-term protection might depend on both 1) well designed and managed MPAs in the Domain 1 and the Weddell Sea, and 2) small-scale fisheries management that simultaneously consider activities undertaken in different small-scale management units.

Morphometric characteristics of Antarctic krill (Euphausia superba) and finfish bycatch in the krill fishery in the waters of South Orkney Islands during the 2022/23 fishing season

Determination of bar spacing of bycatch reduction devices (BRDs) should consider species composition and morphometric characteristics (particularly width) of target species krill and bycatch. This study conducted a scientific investigation of the finfish bycatch in the Antarctic krill (Euphausia superba) trawl fishery by the fishing vessel SHEN LAN in the waters surrounding the South Orkney Islands from December 24, 2022, to February 20, 2023. The results show that scientific observers sampled 676 individuals of finfish bycatch. Of these, 665 were identified to species (17 species from 8 families), while the remaining 11 specimen were juveniles of the Nototheniidae family that could not be identified to the species level. IRI (index of relative importance) calculations showed three dominant (IRI value greater than 1,000) finfish bycatch species (Champsocephalus gunnari, Pseudochaenichthys georgianus, and C. aceratus from the Channichthyidae family) and four important (IRI value between 1,000 and 100) finfish bycatch species (Electrona carlsbergi and Gymnoscopelus nicholsi from the Myctophidae family, Gobionotothen gibberifrons from the Nototheniidae family, and Notolepis coatsi from the Paralepididae family). Our study provides morphometric data (particularly body width) that is crucial to model the potential for bycatch reduction by use of bycatch reduction devices (BRDs) and to determine the appropriate candidate bar spacings for BRD sea trials. Predictions suggest that a 10 mm (the maximum body width of krill) bar spacing releases a significant amount of dominant and important bycatch species (93.94% of C. gunnari, 53.99% of P. georgianus, 76.25% of C. aceratus, and 100% of G. gibberifrons). Reduced fishing pressure would reduce the risks to dominant and important bycatch species to make the krill fishery sustainable. We recommend that future BRD sea trials should initially test a 10 mm bar spacing. If marked loss of krill is observed, wider spacings (e.g. 15 mm) must be tested.

Factors impacting the timing of reproductive development in female Antarctic krill at the northwestern Antarctic Peninsula

The northwestern Antarctic Peninsula is an important spawning, recruitment, and overwintering ground for Antarctic krill. The region is warming rapidly, and the current impacts of climate and environmental variability on the reproductive cycle of krill remain unclear. Here, we examine the reproductive stage of female krill in the austral winter from 2012 to 2016 in relation to climate and environmental data to assess what factors influence the timing of reproductive development. We observed significant interannual variability in the degree of maturation in female krill, ranging from 48% of female krill measured at a station in 2016 to a maximum of 94% of female krill measured at a station in 2014. On average, across all five years, three-quarters of the female krill sampled were in the stage known as previtellogenesis, the point at which the onset of sexual maturity begins. The preceding spring, summer, and autumn Southern Annular Mode and the Multivariate El Niño Index explained most of the variance in the data and indicated a strong, preconditioning storm-related effect on environmental conditions leading up to winter, affecting krill maturation status at the end of the winter season. Results from our study can be used to improve krill population models that are necessary for the management of the krill fishery and for conservation at the northwestern Antarctic Peninsula.

Sensitivity of the stock assessment for the Antarctic krill fishery to time‐varying natural and fishing mortality

Sensitivity of the stock assessment for the Antarctic krill fishery to time‐varying natural and fishing mortality

Sustainability Activities in a Hard-to-Abate Industry—A Real-Life Example

Marine sources of omega-3, proteins, and other nutrients are in increasing demand, while supply is struggling to meet this demand increase. A key focus for meeting the need for marine ingredients for human and animal nutrition is ensuring sustainable sourcing for both the oceans as well as other production types. Aker BioMarine is harvesting and producing marine ingredients from krill and this communication is intended to showcase how the harvesting and production of such ingredients are performed in a sustainable way. This communication is written to describe the krill fisheries’ management, to provide demonstration cases from CO2 hot spotting, and show how results from these are used to target GHG emission reduction. The initiatives that are taken to ensure sustainable fishing and production, as well as examples of short- and long-term actions to reduce and minimize the impact of all activities, are provided.

At-sea distribution of marine predators around South Georgia during austral winter, with implications for fisheries management

The sub-Antarctic island of South Georgia is surrounded by highly productive waters, supporting dense aggregations of Antarctic krill (Euphausia superba), a vital food source for globally important seabird and marine mammal populations. These waters also support a commercial fishery for Antarctic krill. Regular monitoring of key krill predator species is undertaken at South Georgia to detect any changes in the ecosystem in response to harvesting activities. This monitoring provides essential data but is focused on land-breeding animals during the austral summer, whilst the krill fishery operates exclusively in winter. Here, we report the results of at-sea surveys to investigate abundance and distribution of krill-dependent predators from winter 2010 and 2011, which represented a “poor” krill year and “good” krill year, respectively. Correspondingly in 2011 higher numbers of krill predators were observed; notably Antarctic fur seals (Arctocephalus gazella) across the northern shelf. Spatial overlap between fur seals and the krill fishery occurred mainly within the krill fishery hotspot to the north-east, highlighting the potential for locally high levels of competition. Cetaceans were observed during both survey years, but in low numbers compared to recent studies. Gentoo penguins (Pygoscelis papua) were the most frequently observed penguin species, showing an inshore distribution and almost no overlap with the krill fishery. Diving-petrels (Pelecanoides spp.) were the most abundant flying seabirds, observed across all transects, with particularly high densities to the south in early winter 2010. In conclusion, this survey provides valuable baseline data on the distribution of South Georgia’s predators during the winter months.

Analyzing fishery data and exploring the resource status of Antarctic krill based on its environmental dependence

AbstractAntarctic krill Euphausia superba is a key species in the Southern Ocean ecosystem and has important ecological value. It is also one of the main fishery resources in the Southern Ocean with high economic value. In recent years, with the development of krill fishery and rapid climate change, the conservation and management of krill resources have faced unprecedented challenges. The krill resource is different from the general fishery resources. Due to the krill schooling characteristics, fishery data has some advantages over scientific survey data. Reviewing and analyzing the krill fishery data is necessary. Therefore, in this study, four fishery resource indices (FRIs) were calculated based on Antarctic krill fishery data, and based on the environmental dependence of Antarctic krill, the FRI with the strongest environmental dependence was screened by using the Gradient Forest Model, and the step changes of the FRI with strongest environmental dependence was examined by using the sequential t‐test analyses of regime shifts (STARS). The generalized additive model (GAM) to analyze the correlation between the FRI with the strongest environmental dependence and the main environmental factors, and then explore the resource status of Antarctic krill in the study area. The model results showed that the “FRI_hual” had the strongest environmental dependence and was a better indicator of the status of the Antarctic krill in the study area than the others. In the 2009–2010 year, “FRI_hual” had an obvious regime shift. The interaction of environmental factors “ice_area_2” and “SSH_1” has a great impact on “FRI_hual”. Methods used and results obtained in the study can provide new ideas and a scientific reference for future work, including integrated stock assessment of krill and krill resource monitoring, conservation, and management based on the ecosystem.

Investigating the influence of minor krill-predators on the krill-predator dynamics of the Antarctic ecosystem in the International Whaling Commission's Management Area II

Krill ( Euphausia superba), a small pelagic crustacean. is the largest food resource serving many predators in the Antarctic ecosystem. Given the recent slow expansion of the krill fishery, interest is increasing on how best to harvest krill without unduly impacting its natural predators. The Mori–Butterworth Antarctic ecosystem model attempted to explain the dynamics of the “major” predators through predator–prey interactions alone. That model considered blue, fin, humpback, and minke whales, and crabeater and Antarctic fur seals. Here, this model is expanded to include “minor” krill-predators, such as mackerel icefish. It focuses on a smaller scale, roughly corresponding to International Whaling Commission Management Area II. Results suggest a meaningful difference (historical abundance trajectories differing by more than 5% on average over time) when including “minor” predators. Hence, at an area-specific level, “minor” predators should be considered for further models of at least certain sectors of the Antarctic, as they may meaningfully influence the dynamics of krill and its “major” predators. This in turn could impact management decisions for the krill fishery, as regards optimal krill harvesting.

Seasonal acoustic presence of marine mammals at the South Orkney Islands, Scotia Sea.

Increased knowledge about marine mammal seasonal distribution and species assemblage from the South Orkney Islands waters is needed for the development of management regulations of the commercial fishery for Antarctic krill (Euphausia superba) in this region. Passive acoustic monitoring (PAM) data were collected during the autumn and winter seasons in two consecutive years (2016, 2017), which represented highly contrasting environmental conditions due to the 2016 El Niño event. We explored differences in seasonal patterns in marine mammal acoustic presence between the two years in context of environmental cues and climate variability. Acoustic signals from five baleen whale species, two pinniped species and odontocete species were detected and separated into guilds. Although species diversity remained stable over time, the ice-avoiding and ice-affiliated species dominated before and after the onset of winter, respectively, and thus demonstrating a shift in guild composition related to season. Herein, we provide novel information about local marine mammal species diversity, community structure and residency times in a krill hotspot. Our study also demonstrates the utility of PAM data and its usefulness in providing new insights into the marine mammal habitat use and responses to environmental conditions, which are essential knowledge for the future development of a sustainable fishery management in a changing ecosystem.

Spatial structuring in early life stage fish diversity in the Scotia Sea region of the Southern Ocean

AbstractThe fish community of the Scotia Sea is diverse and plays key roles in Antarctic food webs and biogeochemical cycling. However, knowledge of the spatial and community structure of their early life stages is limited, particularly in the region surrounding the South Orkney Islands. Here we examine the structure of the early life stage fish community in the epipelagic using data from a basin-scale survey conducted in early 2019, which sampled the top 200 m of the water column. 347 early life stage fish from 19 genera were caught in 58 hauls. A third of all specimens belonged to the genus Notolepis and the nine most common genera comprised over 90% of specimens. Cluster analysis revealed five distinct groupings, the most common were a group dominated by pelagic and shelf slope genera (Notolepis, Muraenolepis and Electrona) found mainly in oceanic waters (depth ≥ 1000 m), and a group dominated by species with demersal or benthopelagic adults (Chionodraco, Chaenocephalus and Nototheniops) found mainly in shelf waters. Bottom depth was the main environmental determinant of community structure, separating the diverse on-shelf assemblage at the South Orkneys from the less species-rich community of widespread oceanic taxa. Our results indicate the highest diversities of early life stages of endemic fish occur on the shelf and near-shelf areas. Dedicated monitoring is recommended to understand the seasonal differences in larval community assemblages and the implications of early life stages fish bycatch within the krill fishery.

Coupled dynamics of the moving Antarctic krill trawl structure and its hydrodynamics behavior using various catch sizes and door spreads based on wavelet-based and Fourier analysis

Antarctic krill is a key element of the complex ecology of the Antarctic Ocean and a target species for commercial fisheries for aquaculture supply, krill oil production, and as a major food source for various natural predators. Therefore, understanding the interaction between the fluid structures of the Antarctic krill trawl structure is the key factor in solving problems such as selectivity, energy efficiency, catchability, and ecological sustainability in this fishery. Thus, this study experimentally investigated the influence of catch sizes, door spread, and inflow velocities on the bridle tension, trawl motions, trawl deformation, and flow field inside and around a scaled trawl model in flume tank based on the electromagnetic current velocity meter measurements. Fourier analysis using power spectrum density and the continuous wavelet transform is used to analyze the time-frequency contents of the instantaneous flow velocities, bridle tension, and trawl motions; and in the interaction between the unstable turbulent flows and the fluttering trawl motions, wavelet coherency analysis was employed to detect coherent structures. Results indicated that the bridle tension and trawl motions increased as the catch size, door spread, and inflow velocity increased. Owing to the significant trawl deformation, a complex fluid–structure interaction occurred and a strong positive correlation between the bridle tension and trawl motions was obtained. Furthermore, a significant decrease in the flow field occurred inside and outside different parts of the trawl. Fourier and wavelet analysis results showed that the trawl motions and bridle tension are mainly of a low-frequency activity and of another component related to the unsteady turbulent flow street, and decreased with the increasing catch size and door spread. A complex fluid–structure interaction is then demonstrated where the hydrodynamics of the moving Antarctic krill trawl structure are an intricate interplay between trawl fluttering motions and unsteady turbulent flow influenced by catch size and door spread. The knowledge of such trawl hydrodynamic behavior is of great importance to understand and design the optimal structure of trawl nets to maintain the sustainability of the Antarctic krill fishery.

Evaluating threats to South Shetland Antarctic fur seals amidst population collapse

Abstract Antarctic fur seals (Arctocephalus gazella) are an iconic marine mammal, an important component of Antarctic ecosystems, and a key indicator species for regional fisheries management. Recent studies have demonstrated Arctocephalus gazella is composed of at least four distinct subpopulations, including one breeding on the South Shetland Islands. These South Shetland Antarctic fur seals (SSAFS) are the highest latitude population of otariids in the world. As such, this subpopulation faces a unique array of environmental and ecological challenges, harbours a disproportionately large reservoir of genetic diversity for the species, and has experienced catastrophic population decline in the last 15 years (2008–2023). We review the array of current and potential threats to the successful recovery of SSAFS. If decision makers wish to promote resilience and support a robust population of this species with future recovery potential, actions are needed to address threats ranging from uncertain to critical, including debris entanglement, climate change, incidental mortality, and resource competition with the krill fishery. In particular, the risks associated with overlap in the spatial and temporal distribution of the young of the year and the krill fishery should be addressed carefully. There is an urgent need for updated population estimates for all Antarctic fur seal subpopulations, analysis on the population viability of the SSAFS, and further characterising summer and winter foraging behaviours to better inform potential conservation actions.

Quantifying Antarctic krill connectivity across the West Antarctic Peninsula and its role in large-scale Pygoscelis penguin population dynamics

Antarctic krill (Euphausia superba) are considered a keystone species for higher trophic level predators along the West Antarctic Peninsula (WAP) during the austral summer. The connectivity of krill may play a critical role in predator biogeography, especially for central-place foragers such as the Pygoscelis spp. penguins that breed along the WAP during the austral summer. Antarctic krill are also heavily fished commercially; therefore, understanding population connectivity of krill is critical to effective management. Here, we used a physical ocean model to examine adult krill connectivity in this region using simulated krill with realistic diel vertical migration behaviors across four austral summers. Our results indicate that krill north and south of Low Island and the southern Bransfield Strait are nearly isolated from each other and that persistent current features play a role in this lack of inter-region connectivity. Transit and entrainment times were not correlated with penguin populations at the large spatial scales examined. However, long transit times and reduced entrainment correlate spatially with the areas where krill fishing is most intense, which heightens the risk that krill fishing may lead to limited krill availability for predators.

What is needed to implement a sustainable expansion of the Antarctic krill fishery in the Southern Ocean?

Policy differences amongst CCAMLR Members are increasingly affecting decision-making with regards to management of Southern Ocean fisheries. Major differences reflect differing interpretations of the Convention’s primary objective: the conservation of marine living resources, where conservation includes rational use. The best available science historically informed decisions, but policy objectives are increasingly coming to the fore. Resolving how scientific evidence is used in decision-making is essential, given this has consequences for all management topics. In the southwest Atlantic, scientific evidence and how it is used is central to the controlled development of the Antarctic krill fishery. Much work has already been undertaken to allow catches to increase, but more is needed, including ensuring that, as yet untested, management procedures work as intended. Precautionary development should therefore now focus upon ensuring ecosystem resilience is not compromised. Generally, the area managed by CCAMLR experiences relatively light human pressures, yet with newly proposed krill catch limits, this is set to change. Before catches increase, appropriate ecosystem monitoring is needed, and spatial management tools agreed to ensure that biodiversity is adequately maintained, especially given regional climate change. Without such constraints, the krill fishery should not expand. An integrated programme could help CCAMLR adapt. In implementing this, CCAMLR should focus upon areas where economic interests are most intense, that is, over shelf areas and areas of elevated bathymetry. Large-scale remote areas with little economic interest should be set aside as closed areas, until such future time that CCAMLR has agreed appropriate ecological impact assessments and monitoring for these largely unexploited areas.

Quantifying circumpolar summer habitat for Antarctic krill and Ice krill, two key species of the Antarctic marine ecosystem

AbstractAntarctic krill (Euphausia superba) and Ice krill (Euphausia crystallorophias) are key species within Southern Ocean marine ecosystems. Given their importance in regional food webs, coupled with the uncertain impacts of climate change, the on-going recovery of krill-eating marine mammals, and the expanding commercial fishery for Antarctic krill, there is an increasing need to improve current estimates of their circumpolar habitat distribution. Here, we provide an estimate of the austral summer circumpolar habitat distribution of both species using an ensemble of habitat models and updated environmental covariates. Our models were able to resolve the segregated habitats of both species. We find that extensive potential habitat for Antarctic krill is mainly situated in the open ocean and concentrated in the Atlantic sector of the Southern Ocean, while Ice krill habitat was concentrated more evenly around the continent, largely over the continental shelf. Ice krill habitat was mainly predicted by surface oxygen concentration and water column temperature, while Antarctic krill was additionally characterized by mixed layer depth, distance to the continental shelf edge, and surface salinity. Our results further improve understanding about these key species, helping inform sustainable circumpolar management practices.

Distribution and biomass estimation of Antarctic krill (Euphausia superba) off the South Orkney Islands during 2011–2020

Abstract Antarctic krill is a key species in the Southern Ocean and subject to the most extensive fishery in the Antarctic. The Norwegian Institute of Marine Research has conducted acoustic-trawl monitoring of krill off the South Orkneys annually since 2011 in collaboration with the krill fishing industry. Average krill biomass within the 60000 km2 survey area ranged from 1.4 to 7.8 million tonnes in the period 2011–2020, strongly supporting that this is among the regions in the Scotia Sea with consistently highest krill densities. There were no significant (p ≈ 0.18, non-parametric Mann–Kendall test) monotonic trends in estimated krill biomass over the 10 years. The highest krill densities were associated with the shelf edge and submarine canyons on the north side of the South Orkneys. Our comparison with the CCAMLR 9.3% reference exploitation rate suggests that management of the krill fishery in the South Orkneys region is precautionary. The monitoring is run on fishing vessels, so e.g. acoustic frequencies applied could not always be in compliance with the standard CCAMLR methodology. Estimated deviance in krill backscatter when comparing 38 kHz to the standard 120 kHz ranged from −1.1% to 12.8%. Our results show that industry-based surveys are cost-efficient approaches to high-quality monitoring of krill.

Antarctic krill (Euphausia superba) catch weight estimated with a trawl‐mounted echosounder during fishing

AbstractReporting reliable catch weight estimates is important for all fisheries management. This study explores the potential for precise and direct estimation of catch weight (green weight) for the Antarctic krill (Euphausia superba) fishery by employing a high frequency acoustic sensor in the trawl. Trials were performed off the coast of the South Orkney Islands during February 2020 using a scientific macroplankton trawl and echosounder providing a 18° beam pointing downwards across the fishing circle at the trawl mouth. The acoustically estimated catch weight and the observed catch weight had a linear relationship (R2 = 0.87, F(1,10) = 69.6, p < 0.000) where the acoustically estimated catch weight significantly predicted actual catch weight (β = 1.20, p = 0.000). The acoustic vertical densities of krill increased toward the center of the trawl opening suggesting that krill were herded during fishing. The current study demonstrates that acoustically based catch weight monitoring has the potential to be used for reporting total krill catch weight in each trawl, potentially in real‐time, and that similar methods could also be employed in similar types of trawl fisheries.

Using machine learning to alleviate the allometric effect in otolith shape-based species discrimination: the role of a triplet loss function

Abstract Species identification by fish otoliths is an effective and appropriate approach. However, the allometric growth of otoliths can cause discrimination confusion, particularly in juvenile otolith classification. In the Southern Ocean, Chionodraco rastrospinosus,Krefftichthys anderssoni,Electrona carlsbergi, andPleuragramma antarcticum are frequently caught together in krill fishery as bycatch species. Furthermore, the otolith shape of these four species is relatively similar in juvenile fish, making the identification of fish species difficult. In this study, we tried and evaluated many commonly used machine learning techniques to solve this problem. Eventually, by introducing a triplet loss function (function used to reduce intraspecific variation and increase inter-specific variation), the discrimination confusion caused by the allometric growth of otoliths was reduced. The classification results show that the neural network model with the triplet loss function achieves the best classification accuracy of 96%. The proposed method can help improve otolith classification performance, especially under the context of limited sampling effort, which is of great importance for trophic ecology and the study of fish life history.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Характеристики современного промысла антарктического криля Euphausia superba (период с 2010 по 2022 года) в Антарктической части Антарктики. Перспективы развития отечественного промысла криля

The authors discuss the state of the current krill fishery (2010 to 2022). Current trends in the development of the krill fishery in the CCAMLR Convention Area are analysed, including the spatial and temporal dynamics of the krill catch, the characteristics of the vessels participating in the krill fishery, the performance of the fishery, taking into account the trawl fishing technology (daily catch, number of days in the fishery, vessel processing of krill). Prospects for the resumption of the Russian krill fishery are being discussed, focusing on priority areas for the development and use of krill resources.