scholarly journals New target-strength model indicates more krill in the Southern Ocean

2005 ◽  
Vol 62 (1) ◽  
pp. 25-32 ◽  
Author(s):  
David A. Demer ◽  
Stéphane G. Conti
Keyword(s):  
Southern Ocean ◽  
Euphausia Superba ◽  
Target Strength ◽  
Scotia Sea ◽  
Biomass Estimate ◽  
Antarctic Marine ◽  
Survey Results ◽  
The Antarctic

Abstract Antarctic krill, Euphausia superba, comprises the foundation of the foodweb in the Southern Ocean and is the target of a large fishery. Recently, the total abundance of krill in the Scotia Sea was estimated from an international echosounder and net survey (CCAMLR 2000) to be 44.3 million metric tonnes (Mt; CV 11.4%) (Hewitt et al., 2002). The new biomass estimate prompted the Antarctic Treaty's Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to revise the precautionary catch level for krill in the area from 1.5 to 4 Mt (SC-CAMLR, 2000). These survey results are based on the total echo energy attributed to krill, scaled by the Greene et al. (1991) model of krill acoustical reflectivity or target strength (TS). Presented here is a re-analysis of the CCAMLR 2000 data incorporating recent improvements in the characterization of krill TS. The results indicate that the estimated krill biomass in the Scotia Sea may be as high as 192.4 Mt (CV = 11.7%), or as low as 109.4 Mt (CV = 10.4%), depending solely on the expected distribution of krill orientations. The new Stochastic, Distorted-Wave, Born-Approximation (SDWBA) TS model solved with an empirically estimated distribution of in situ orientations leads to a krill-biomass estimate that is nearly 2.5 times the previous estimate. In consequence, revisions may be warranted of the standard krill TS model, the CCAMLR 2000 biomass estimate, and the associated precautionary catch level for krill in the Scotia Sea.

scholarly journals Experimental determination of reflectance spectra of Antarctic krill (Euphausia superba) in the Scotia Sea

2021 ◽  
pp. 1-13
Author(s):  
Anna Belcher ◽  
Sophie Fielding ◽  
Andrew Gray ◽  
Lauren Biermann ◽  
Gabriele Stowasser ◽  
...  
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Reflectance Spectra ◽  
Spectral Signature ◽  
Absorption Feature ◽  
Scotia Sea ◽  
Surface Ocean ◽  
Measuring Surface ◽  
Ground Truthing

Abstract Antarctic krill are the dominant metazoan in the Southern Ocean in terms of biomass; however, their wide and patchy distribution means that estimates of their biomass are still uncertain. Most currently employed methods do not sample the upper surface layers, yet historical records indicate that large surface swarms can change the water colour. Ocean colour satellites are able to measure the surface ocean synoptically and should theoretically provide a means for detecting and measuring surface krill swarms. Before we can assess the feasibility of remote detection, more must be known about the reflectance spectra of krill. Here, we measure the reflectance spectral signature of Antarctic krill collected in situ from the Scotia Sea and compare it to that of in situ water. Using a spectroradiometer, we measure a strong absorption feature between 500 and 550 nm, which corresponds to the pigment astaxanthin, and high reflectance in the 600–700 nm range due to the krill's red colouration. We find that the spectra of seawater containing krill is significantly different from seawater only. We conclude that it is tractable to detect high-density swarms of krill remotely using platforms such as optical satellites and unmanned aerial vehicles, and further steps to carry out ground-truthing campaigns are now warranted.

CCAMLR and its approaches to management of the krill fishery

Polar Record ◽  
1991 ◽  
Vol 27 (162) ◽  
pp. 229-236 ◽  
Author(s):  
Stephen Nicol
Keyword(s):  
Southern Ocean ◽  
Antarctic Krill ◽  
Euphausia Superba ◽  
Management Plan ◽  
Conservation Measures ◽  
Antarctic Marine ◽  
Central Resource

AbstractThe Commission for the Conservation of Antarctic MarineLiving Resources has met annually since 1982, with the task of implementing the Convention on the Conservation of Antarctic Marine Living Resources; the treaty which was designed to manage rationally the exploitation of resources in the Southern Ocean. The central resource of the region is Antarctic krill (Euphausia superba Dana) and despite nine years of meetings the Commission has yet to adopt any conservation measures to protect krill. This article examines the published work of the Commission, seeking to determine how the Commission has dealt with the krill fishery and why it has not yet developed a krill management plan.

scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

2018 ◽  
Vol 15 (6) ◽  
pp. 1843-1862 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Global Ocean ◽  
Field Observations ◽  
Scotia Sea ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium-carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterised. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarised micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for E. huxleyi morphotype B/C in the Antarctic zone waters in 2001–2002; (2) coccoliths captured by the traps experienced weight and length reduction during summer (December–February); (3) the estimated annual coccolith weight of E. huxleyi at both sediment traps (2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted for approximately 2–5 % of the annual deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic zone. They provide a baseline against which to monitor coccolithophore responses to changes in the environmental conditions expected for this region in coming decades.

scholarly journals Estimating the Four-Dimensional Structure of the Southern Ocean Using Satellite Altimetry

2011 ◽  
Vol 28 (4) ◽  
pp. 548-568 ◽  
Author(s):  
A. J. S. Meijers ◽  
N. L. Bindoff ◽  
S. R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Satellite Altimetry ◽  
Velocity Structure ◽  
Velocity Fields ◽  
Optimal Interpolation ◽  
Dimensional Structure ◽  
Strongly Correlated ◽  
Circumpolar Current ◽  
The Antarctic

Abstract A gravest empirical mode (GEM) projection of temperature and salinity fields over the circumpolar Southern Ocean is presented and is used in combination with satellite altimetry to produce gridded, full-depth, time-evolving temperature, salinity, and velocity fields. Optimal interpolation of historical hydrography, including Argo floats, is used to produce GEM projections of the circumpolar temperature and salinity fields. Parameterizing these fields by dynamic height allows the use of altimetric SSH values from 1992–2006 to create synoptic temperature and salinity fields at weekly intervals on a ⅓° grid at 36 depth levels. The satellite-derived temperature and salinity fields generally capture over 90% of the property variance below the thermocline, with RMS residuals of 1.16°C and 0.132 in salinity at the surface, decreasing to less than 0.45°C and 0.05 below 500 dbar. The combination of altimetry with the GEM fields allows the resolution of the subsurface structure of the filamentary fronts and eddy features. Velocity fields derived from the time-evolving temperature and salinity fields reproduce the Antarctic Circumpolar Current (ACC) velocity structure well, and are strongly correlated (r > 0.7) with in situ measurements from current meters and drifters, with RMS velocity residuals of 4.8–14.8 cm−1 in the Subantarctic Front.

Circumpolar occurrence of eugregarinid protozoanCephaloidophora pacificaassociated with Antarctic krill,Euphausia superba

2008 ◽  
Vol 20 (5) ◽  
pp. 437-440 ◽  
Author(s):  
Kunio T. Takahashi ◽  
Masaki Kobayashi ◽  
So Kawaguchi ◽  
Junko Saigusa ◽  
Atsushi Tanimura ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Krill ◽  
Geographical Location ◽  
Protozoan Parasite ◽  
Euphausia Superba ◽  
Maturity Stage ◽  
Syowa Station ◽  
Frequency Distributions ◽  
The Mean ◽  
The Antarctic

AbstractThe geographical distribution of protozoan parasiteCephaloidophora pacificaAvdeev (Order Eugregarininda) associated with Antarctic krill,Euphausia superba, was examined in samples collected from the vicinity of the Antarctic Peninsula, near Syowa Station, and Pacific and Indian sectors of the Southern Ocean.Cephaloidophora pacificawas found at all stations around the Antarctic, with 96.4% of the euphausiids infected (n = 195). The numbers ofC. pacificaper krill ranged from 0 to 8089 krill-1, and the average was 350.0 ± 787.8 (mean ± SD). The frequency distributions ofC. pacificashowed an overdispersed parasite population (i.e. the variance was greater than the mean) at all locations. Statistical analysis showed that whilst the geographical location did not have a significant effect on intensity ofC. pacificathe maturity stage of krill did, with an increasing intensity of infection as krill matures. The infestation ofE. superbaby eugregarinid protozoan is considered to be a circum-Antarctic phenomenon, and it occurs equally throughout the Southern Ocean.

scholarly journals Functional characterization of the circadian clock in the Antarctic krill, Euphausia superba

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Alberto Biscontin ◽  
Thomas Wallach ◽  
Gabriele Sales ◽  
Astrid Grudziecki ◽  
Leonard Janke ◽  
...  
Keyword(s):  
Circadian Clock ◽  
Antarctic Krill ◽  
Functional Characterization ◽  
Euphausia Superba ◽  
The Antarctic ◽  
Antarctic Krill Euphausia Superba

scholarly journals Copepod faecal pellet transfer through the meso- and bathypelagic layers in the Southern Ocean in spring

2017 ◽  
Vol 14 (6) ◽  
pp. 1511-1525 ◽  
Author(s):  
Anna Belcher ◽  
Clara Manno ◽  
Peter Ward ◽  
Stephanie A. Henson ◽  
Richard Sanders ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Size Distribution ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Faecal Pellet ◽  
Copepod Community ◽  
Scotia Sea ◽  
Faecal Pellets ◽  
A Minor

Abstract. The faecal pellets (FPs) of zooplankton can be important vehicles for the transfer of particulate organic carbon (POC) to the deep ocean, often making large contributions to carbon sequestration. However, the routes by which these FPs reach the deep ocean have yet to be fully resolved. We address this by comparing estimates of copepod FP production to measurements of copepod FP size, shape, and number in the upper mesopelagic (175–205 m) using Marine Snow Catchers, and in the bathypelagic using sediment traps (1500–2000 m). The study is focussed on the Scotia Sea, which contains some of the most productive regions in the Southern Ocean, where epipelagic FP production is likely to be high. We found that, although the size distribution of the copepod community suggests that high numbers of small FPs are produced in the epipelagic, small FPs are rare in the deeper layers, implying that they are not transferred efficiently to depth. Consequently, small FPs make only a minor contribution to FP fluxes in the meso- and bathypelagic, particularly in terms of carbon. The dominant FPs in the upper mesopelagic were cylindrical and elliptical, while ovoid FPs were dominant in the bathypelagic. The change in FP morphology, as well as size distribution, points to the repacking of surface FPs in the mesopelagic and in situ production in the lower meso- and bathypelagic, which may be augmented by inputs of FPs via zooplankton vertical migrations. The flux of carbon to the deeper layers within the Southern Ocean is therefore strongly modulated by meso- and bathypelagic zooplankton, meaning that the community structure in these zones has a major impact on the efficiency of FP transfer to depth.

scholarly journals Nexus and Imbroglio: ccamlr, the Madrid Protocol and Designating Antarctic Marine Protected Areas in the Southern Ocean

2015 ◽  
Vol 30 (4) ◽  
pp. 727-764 ◽  
Author(s):  
Laurence Cordonnery ◽  
Alan D. Hemmings ◽  
Lorne Kriwoken
Keyword(s):  
Southern Ocean ◽  
Protected Areas ◽  
Marine Protected Areas ◽  
Legal Context ◽  
Antarctic Marine ◽  
National Jurisdiction ◽  
Complicating Factors ◽  
The Antarctic ◽  
The Relationship ◽  
Global Oceans

The paper examines the process and context of international efforts to designate Marine Protected Areas (mpas) in the Southern Ocean. The relationship between the Convention on the Conservation of Antarctic Marine Living Resources (camlr Convention) and the Madrid Protocol is examined in relation to legal, political and administrative norms and practices. A contextual overview of the Antarctic mpa system is considered, followed by an analysis of the overlapping competencies of the camlr Commission (ccamlr) and the Madrid Protocol. The Antarctic mpa debate is placed in a wider international legal context of the management of global oceans space in areas beyond national jurisdiction. We provide an analysis of the politico-legal discourse and point to complicating factors within, and external to, the Antarctic system. The concluding section suggests options for breathing new life into the Southern Ocean mpa discourse.

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