Improved parametrization of Antarctic krill target strength models

Lawson, Gareth L.; Wiebe, Peter H.; Ashjian, Carin J.; Chu, Dezhang; Stanton, Timothy K.

doi:10.1121/1.2141229

Cited by 78 publications

(80 citation statements)

References 44 publications

(35 reference statements)

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“…By applying the more generous range of 2 to 16 dB, we increase the possibility of mistakenly accepting as krill the scattering from other small zooplankton, but allow for these sources of uncertainty associated with the measurements made at 43 kHz. Furthermore, the target strength model of Lawson et al (2006) employed here would predict that a difference in the mean volume backscattering strength between the frequencies of 120 and 43 kHz of 16 dB would correspond to a krill of length 8 mm, and so it does not seem unreasonable to use this value as the upper bound. Frequency (kHz) Figure 4.2 -Target strength (TS) in relation to acoustic frequency.…”

Section: 23b Distinguishing Krill Scattering From Other Sourcesmentioning

confidence: 99%

“…Additional details concerning acoustic data collection are found in Lawson et al (2004Lawson et al ( , 2006.…”

Section: 22a Acoustic Datamentioning

confidence: 99%

“…The acoustic analyses that follow all employed the theory-based krill target strength model of Lawson et al (2006). This model represents the krill's shape as an equivalent cylinder, defined on the basis of animal length measured from the anterior of the eye to the end of sixth abdominal segment.…”

Section: Acoustic Analysesmentioning

confidence: 99%

“…Predictions of target strength were made using physics-based models for 35 and 42 mm-long krill, a 1 mm diameter pteropod, a 1.5 mm diameter siphonophore pneumatophore (a gas-filled structure), and a 2 mm-long copepod. The krill target strength model of Lawson et al, (2006) was used for krill. Models and parameter values for the other animals are the same as in Lawson et al, (2004).…”

Section: 23b Distinguishing Krill Scattering From Other Sourcesmentioning

confidence: 99%

“…Chapters 2 and 3 repeat mostly verbatim the material of Lawson et al (2004) and Lawson et al (2006), respectively; the changes made here to the text of those publications were done in an effort to keep the language consistent with the rest of the thesis.…”

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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: 23b Distinguishing Krill Scattering From Other Sourcesmentioning

confidence: 99%

“…Additional details concerning acoustic data collection are found in Lawson et al (2004Lawson et al ( , 2006.…”

Section: 22a Acoustic Datamentioning

confidence: 99%

Section: Acoustic Analysesmentioning

confidence: 99%

Section: 23b Distinguishing Krill Scattering From Other Sourcesmentioning

confidence: 99%

mentioning

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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Individual‐based modeling explains the contrasted seasonality in size, growth, and reproduction of the sympatric Arctic (Thysanoessa raschii) and Nordic krill (Meganyctiphanes norvegica) in the St. Lawrence Estuary, eastern Canada

Benkort

Plourde

Winkler

et al. 2018

Limnology & Oceanography

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The Nordic krill Meganyctiphanes norvegica and Arctic krill Thysanoessa raschii both dominate the krill community within the Estuary and Gulf of St. Lawrence system where they are central forage species for its pelagic ecosystem. We developed a species‐specific physiological individual based model that implements the critical physiological processes of growth, molting, and reproduction of female adults as responses to environmental forcing. Key innovations of our approach were the decoupling between the molting schedule and growth, as well as considering two distinct sources of prey (phytoplankton and mesozooplankton). Our simulation results revealed that the details of the feeding process were critical for an accurate representation of the production dynamics of adult individuals from both species. Their specific feeding preferences on phytoplankton and mesozooplankton resulted in distinct species‐specific phenological patterns that reproduced observations. The present study highlights the importance of detailed knowledge of diet and feeding behavior of krill species to improve our understanding of population responses in a rapidly changing environment.

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Measuring the in situ tilt orientation of fish and zooplankton using stereo photogrammetric methods

Levine

Williams

Ressler

2018

Limnology & Ocean Methods

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Acoustic‐derived estimates of fish and zooplankton numerical and biomass density rely on knowledge of the sound scattered by an individual, known as target strength (TS). An important, but difficult to measure, factor in determining TS is the tilt orientation of animals in relation to the insonifying acoustic wave. Underwater stereo‐camera systems can provide in situ tilt measurements for fish and zooplankton. We describe a protocol to remove the effects of camera pitch and roll from tilt measurements using a low‐cost orientation sensor and a mathematical correction. A tank experiment indicated that tilt estimates made with corrected pitch and roll position data improved measurement accuracy as compared to those made with uncorrected position data. This experiment also provided empirical limits on the range of yaw values that allowed for accurate estimation of target tilt and length. We further tested this protocol using an in situ collection of krill stereo images collected in the Gulf of Alaska. Krill tilts calculated with pitch‐ and roll‐corrected position data were an average of 10° different than those collected with uncorrected position data. Our pitch‐ and roll‐correction improved the accuracy of stereo photogrammetric tilt estimation. Extending this method to appropriate spatial and temporal scales could allow for more accurate parametrization of TS models.

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Improved parametrization of Antarctic krill target strength models

Cited by 78 publications

References 44 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

Individual‐based modeling explains the contrasted seasonality in size, growth, and reproduction of the sympatric Arctic (Thysanoessa raschii) and Nordic krill (Meganyctiphanes norvegica) in the St. Lawrence Estuary, eastern Canada

Measuring the in situ tilt orientation of fish and zooplankton using stereo photogrammetric methods

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