Formation of Antarctic Krill Concentrations in Relation to Hydrodynamic Processes and Social Behaviour

Witek, Zbigniew; Kalinowski, J.; Grelowski, Alfred

doi:10.1007/978-3-642-73724-4_21

Cited by 35 publications

(31 citation statements)

References 4 publications

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“…BIOMASS, 1977;Everson & Goss, 1991;Murphy et al, 1997;Trathan et al, 1998). They are also often associated with oceanic fronts including the Southern Antarctic Circumpolar Current Front (SACCF) at South Georgia (Witek, Kalinowski & Grelowski, 1988;Miller & Hampton, 1989, Hofmann et al, 1998Trathan et al, 2003). Everson (1976Everson ( , 1977 suggested that enhanced primary productivity in regions of upwelling could be a key factor in krill distribution.…”

Section: (1) General Characteristicsmentioning

confidence: 99%

“…By contrast, Witek, et al (1988) suggested that behavioural reactions to water velocity gradients tended to concentrate krill in quiescent areas to the side of strong flow fields (see also Macaulay, English & Mathisen, 1984) where plankton abundance is often high, possibly as a consequence of the stable water conditions. Atkinson et al (2004) have shown that krill abundance in the Southern Ocean is spatially correlated with summer phytoplankton concentrations at a coarse scale.…”

Section: (1) General Characteristicsmentioning

confidence: 99%

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Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

Hill¹,

Murphy²,

Reid³

et al. 2006

Biol. Rev.

107

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The ecosystem approach to fisheries recognises the interdependence between harvested species and other ecosystem components. It aims to account for the propagation of the effects of harvesting through the food-web. The formulation and evaluation of ecosystem-based management strategies requires reliable models of ecosystem dynamics to predict these effects. The krill-based system in the Southern Models of the Southern Ocean ecosystem. 2Ocean was the focus of some of the earliest models exploring such effects. It is also a suitable example for the development of models to support the ecosystem approach to fisheries because it has a relatively simple food-web structure and progress has been made in developing models of the key species and interactions, some of which has been motivated by the need to develop ecosystem-based management. Antarctic krill, Euphausia superba, is the main target species for the fishery and the main prey of many top predators. It is therefore critical to capture the processes affecting the dynamics and distribution of krill in ecosystem dynamics models. These processes include environmental influences on recruitment and the spatially variable influence of advection. Models must also capture the interactions between krill and its consumers, which are mediated by the spatial structure of the environment. Various models have explored predator-prey population dynamics with simplistic representations of these interactions, while others have focused on specific details of the interactions. There is now a pressing need to develop plausible and practical models of ecosystem dynamics that link processes occurring at these different scales.Many studies have highlighted uncertainties in our understanding of the system, which indicates future priorities in terms of both data collection and developing methods to evaluate the effects of these uncertainties on model predictions. We propose a modelling approach that focuses on harvested species and their monitored consumers and that evaluates model uncertainty by using alternative structures and functional forms in a Monte Carlo framework.

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Section: (1) General Characteristicsmentioning

confidence: 99%

Section: (1) General Characteristicsmentioning

confidence: 99%

Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

Hill¹,

Murphy²,

Reid³

et al. 2006

Biol. Rev.

107

View full text Add to dashboard Cite

show abstract

“…The thin line represents the 2000-m isobath. The areas of consistent Antarctic krill spawning, as identified in Marr (1962) Transport of krill from these regions to South Georgia is thought to be accomplished by largescale ocean currents (Priddle et al, 1988;Witek et al, 1988;Murphy et al, 2004b).…”

Section: Introductionmentioning

confidence: 99%

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

Fach

Klinck

2006

Deep Sea Research Part I: Oceanographic Research Papers

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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. r

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“…A coastal current flows towards the southwest, which may serve to advect zooplankton into or out of the study region . In the case of krill, previous studies have suggested that abundance may be enhanced in regions of high velocity gradients such as frontal zones, meanders, and eddies (Witek et al, 1988;Ichii et Modeling and empirical studies have suggested that offshelf circumpolar deep water is pumped up onto the shelf by the action of the Antarctic Circumpolar Current (ACC) primarily at points where the deep troughs bisecting the shelf meet the shelf break and where the shelf break is strongly curved (Dinniman and Klinck, 2004;Klinck et al, 2004); horizontal blue arrows indicate such locations. Larger blue arrow indicates the direction of flow of the ACC.…”

Section: Southern Ocean Global Ecosystems Dynamics (So Globec) Programentioning

confidence: 98%

“…Qualitative examinations of krill abundance in relation to dynamic topography have previously led to the suggestion that high krill abundance may be associated with regions of high velocity gradients and the sluggish currents associated with eddies and meanders (Witek et al, 1988;Brinton, 1991;Ichii et al, 1998), and that retention may contribute to the formation of regions of enhanced krill abundance. The main known retentive feature in the present study region is a large and persistent gyre situated over the northern shelf, where krill biomass was low in fall.…”

Section: 42c Environmental Associationsmentioning

confidence: 99%

Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

Lawson¹

2006

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The physical and biological forces that drive zooplankton distribution and patchiness in an antarctic continental shelf region were examined, with particular emphasis on the Antarctic krill, Euphausia superba. This was accomplished by the application of acoustic, video, and environmental sensors during surveys of the region in and around Marguerite Bay, west of the Antarctic Peninsula, in the falls and winters of 2001 and 2002. An important component of the research involved the development and verification of methods for extracting estimates of ecologically-meaningful quantities from measurements of scattered sound. The distribution of acoustic volume backscattering at the single frequency of 120 kHz was first examined as an index of the overall biomass of zooplankton. Distinct spatial and seasonal patterns were observed that coincided with advective features. Improved parameterization was then achieved for a theoretical model of Antarctic krill target strength, the quantity necessary in scaling measurements of scattered sound to estimates of abundance, through direct measurement of all necessary model parameters for krill sampled in the study region and survey period. Methods were developed for identifying and delineating krill aggregations, allowing the distribution of krill to be distinguished from that of the overall zooplankton community. Additional methods were developed and verified for estimating the length, abundance, and biomass of krill in each acoustically-identified aggregation. These methods were applied to multifrequency acoustic survey data, demonstrating strong seasonal, inter-annual, and spatial variability in the distribution of krill biomass. Highest biomass was consistently associated with regions close to land where temperatures at depth were cool. Finally, the morphology, internal structure, and vertical position of individual krill aggregations were examined. The observed patterns of variability in aggregation characteristics between day and night, regions of high versus low food availability, and in the presence or absence of predators, together reinforced the conclusion that aggregation and diel vertical migration represent strategies to avoid visual predators, while also allowing the krill access to shallowly-distributed food resources. The various findings of this work have important implications to the fields of zooplankton acoustics and Antarctic krill ecology, especially in relation to the interactions of the krill with its predators.

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Formation of Antarctic Krill Concentrations in Relation to Hydrodynamic Processes and Social Behaviour

Cited by 35 publications

References 4 publications

Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

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