Acoustical estimation of zooplankton populations1

Greenlaw, Charles F.

doi:10.4319/lo.1979.24.2.0226

Cited by 165 publications

(93 citation statements)

References 3 publications

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“…This congruence in acoustic and net estimates of krill length agrees with the results of previous studies that have attempted to invert multi-frequency acoustic observations of euphausiid aggregations and compare these to independent estimates of animal length available from other sources (e.g., Antarctic krill, Mitson et al, 1996, Azzali et al, 2004 submitted; Meganyctiphanes norvegica, Kristensen andDalen, 1982, Warren et al, 2003;Greenlaw, 1979). The consistently accurate estimation of animal length in the present work and these various earlier studies may relate in part to the shape of the scattering versus frequency relationship and particularly the transition from the Rayleigh to geometric scattering ranges which impart so much information in estimating length being less sensitive to uncertainty associated with calibrations, noise, and the exact scattering model employed.…”

Section: Acoustic Methodologiessupporting

confidence: 86%

“…Some previous studies employing inverse methods to estimate krill length and density have modeled the scattering from individual krill as that from a fluid-filled sphere of equivalent radius (Greenlaw, 1979, Mitson et al, 1996, Azzali et al, 2004, an approach that has been superceded by more sophisticated acoustic models with more realistic representations of the animal's shape (e.g., Stanton et al, 1998). We used the physicsbased target strength model of Lawson et al, (2006), which models the shape of the animal as a uniformly bent cylinder.…”

Section: Acoustic Methodologiesmentioning

confidence: 99%

“…Such 'inversions' must be approached with caution, however, as the number of taxa and size classes that can be solved for is limited by the number of frequencies employed and the problem can rapidly become very complicated for heterogeneous zooplankton communities of multiple scatterer types (Lavery et al, submitted). Nonetheless, studies of particular instances of euphausiid aggregations where only a single species was present with a single length mode have been able to estimate animal length with a high degree of accuracy (e.g., Antarctic krill, Mitson et al, 1996, Azzali et al, 2004 Meganyctiphanes norvegica, Kristensen andDalen, 1982, Warren et al 2003;Greenlaw, 1979). Such studies have also produced plausible density estimates, though often higher than suggested by independent net samples.…”

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

confidence: 99%

“…The abundance of animals spanning a range of size categories can be estimated on the basis of multi-frequency acoustic data alone, following what is referred to as an 'inverse approach' (Holliday 1977, Greenlaw 1979. Similar to the 6MVBS method described previously, the inverse method capitalizes on the fact that scattering from zooplankton is both size-and frequency-dependent (Figure 4.2).…”

Section: 23d Estimating the Mean Length And Density Of Krill In Imentioning

confidence: 99%

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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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Section: Acoustic Methodologiessupporting

confidence: 86%

Section: Acoustic Methodologiesmentioning

confidence: 99%

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

confidence: 99%

Section: 23d Estimating the Mean Length And Density Of Krill In Imentioning

confidence: 99%

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

Lawson¹

2006

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“…Acoustic estimation of underwater organisms can be made with one-frequency, twofrequency, or multifrequency methods (see Greenlaw 1979). Due to the restrictions of the experimental instrument, we adopted the onefrequency method at 200 kHz.…”

Section: Chaoborus Collected Inmentioning

confidence: 99%

A sound scattering layer in a freshwater reservoir

Jones¹,

Xie²

1994

Limnology & Oceanography

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A near‐surface sound scattering layer has been observed in a freshwater reservoir with a 200 kHz echosounder over the last 5 yr. Net sampling revealed that Chaoborus is the cause of the strong 200‐kHz sound scattering in this layer. With 50‐kHz sound, this layer cannot be distinguished from the background. Recent acoustic measurements have determined the target strength of a single Chaoborus larva and the frequency response of backscattering from Chaoborus in the reservoir so that an acoustic estimation of the Chaoborus population can be made. This population estimate is compared with simultaneous net‐sampling estimates.

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Observations of frazil ice formation and upward sediment transport in the Sea of Okhotsk: A possible mechanism of iron supply to sea ice

Ito

Ohshima

Fukamachi

et al. 2017

J. Geophys. Res. Oceans

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In the Sea of Okhotsk, sediment incorporation, transport and release by sea ice potentially plays important roles in the bio‐related material (such as iron) cycle and ecosystem. The backscatter strength data of bottom‐mounted Acoustic Doppler Current Profilers have suggested signals of frazil ice down to 30 m depth, and signals of upward sediment transport throughout the water column simultaneously in the region northeast of Sakhalin, with a water depth of ∼100 m. Such events occurred under turbulent conditions with strong winds of 10–20 m s−1. During such events, newly formed ice was present near the observational sites, shown by satellite microwave imagery. Sediment dispersion from the bottom occurred in association with strong currents of 1.0–1.5 m s−1. During these events, the mixed layer reaches near the bottom due to wind‐induced stirring, inferred from the high frequency component of vertical velocity. Thus the winter time turbulent mixing brings re‐suspended sediment up to near the ocean surface. This study provides the first observational evidence of a series of processes on the incorporation of sedimentary materials into sea ice: sedimentary particles are dispersed by the strong bottom current, subsequently brought up to near the surface by winter time mixing, and finally incorporated into sea ice through underwater interaction with frazil ice and/or flooding of sea ice floes. This wintertime incorporation of bottom sediment into sea ice is a possible mechanism of iron supply to sea ice which melts in spring, and releases bio‐reactive iron into the ocean.

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Acoustical estimation of zooplankton populations1

Cited by 165 publications

References 3 publications

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

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

A sound scattering layer in a freshwater reservoir

Observations of frazil ice formation and upward sediment transport in the Sea of Okhotsk: A possible mechanism of iron supply to sea ice

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