Lateral target strength of Antarctic krill

Hewitt, Roger P.; Demer, David A.

doi:10.1006/jmsc.1996.0038

Cited by 19 publications

(7 citation statements)

References 12 publications

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“…Measurements of Antarctic krill swimming freely in an enclosure and in situ observations (Hewitt and Demer, 1991) have yielded estimates of krill target strength consistent with the Greene et al (1991) model.…”

Section: Introductionmentioning

confidence: 66%

“…This difference likely stems from two sources. First, experimental error may tend to bias the empirical observations; the Hewitt and Demer (1991) in situ measurements, for instance, are thought to be positively biased by erroneous acceptance of multiple targets as individual target strengths (Demer and Conti, 2005), and the true target strengths for the krill they observed likely fall closer to the predictions of the present model.…”

Section: Discussionmentioning

confidence: 87%

“…(1992) review, Hewitt and Demer (1991) and Pauly and Penrose (1998) have also reported observations of krill target strength. Most of these earlier observations lie above our newly-parameterized scattering model (Figure 3.8).…”

Section: Discussionmentioning

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: Introductionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 87%

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

Lawson¹

2006

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“…O'Brien 1988, Demer & Hewitt 1995. Towing acoustic transducers pointed sideways or upward (Hewitt & Demer 1996, Probst et al 2009), towing video cameras (Veit et al 2008) with some type of lighting for night use, or towing multiple closing nets tripped at short distance intervals near the surface may provide important information on krill dispersion. Measurements of the patch structure of vertically migrating krill and copepods near the water surface at night are needed as a basis for foraging experiments and modeling for small auklets.…”

Section: Light Effects and Diel Vertical Migrationmentioning

confidence: 99%

Modeling profitability for the smallest marine endotherms: auklets foraging within pelagic prey patches

Lovvorn¹

2010

Aquat. Biol.

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Auklets (Alcidae) can be very abundant in north-temperate to arctic seas. Their numbers and trophic impacts in a given area depend on their ability to forage profitably as a function of the dispersion, depth, and density of prey patches. Thus, modeling these relationships is important when predicting the auklets' response to environmental change. This paper presents a simulation model of the foraging costs and intake rates of Cassin's auklets Ptychoramphus aleuticus (~170 g) and least auklets Aethia pusilla (~80 g) once they have located a patch of zooplankton prey. In the model, water temperature and dive depth (max. 20 m) have important effects on dive costs, mainly by affecting the duration and magnitude of costs during passive ascent. Within a prey patch, modeled intake rates are limited at relatively low prey densities by pursuit and handling time after a prey item is detected. Because intake rate is limited by capture time and not prey visibility, the model indicates that changes in light conditions over these depths have little direct effect on intake rates of zooplankton prey. However, vertical migration of prey in response to diel light cycles can strongly affect profitability (energy gain minus cost) by altering the depth of dives to prey patches. Because pursuit and handling time limit modeled intake rate, profitability cannot be increased further by finding patches of higher density, but rather by extending time in patches by swimming farther or slower. The model suggests that auklet dispersion should be insensitive to variations in patch density above a threshold that is relatively low compared to the very high densities that can occur. However, auklets may be attracted to higher-density patches because the patches themselves are more visible or predictable, or because other predators -from seabirds to whales -may gather in such patches and increase their visibility.

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“…Their observation that orientation is linked to swimming speed suggests observation in a natural environment may be important. Natural setting measurements of target strengths at differing ensonification angles, such as those conducted for E. superba by Hewitt and Demer (1996), might shed light on the orientation problem if interpreted by the best existing models.…”

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confidence: 99%

Scotian Shelf euphausiid and silver hake population changes during 1984–1996 measured by multi-frequency acoustics

Cochrane

Sameoto

Herman

2000

ICES Journal of Marine Science

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A 13-year time series of integrated acoustic volume backscattering strengths from Emerald Basin on the Scotian Shelf at 12, 50, 122, and 200 kHz are examined here, together with zooplankton data from net sampling. The three highest acoustic frequencies delineate relative abundances of the euphausiid Meganyctiphanes norvegica while the 12-kHz frequency primarily reflects abundances of pelagic silver hake. Euphausiid populations derived from acoustics fluctuate by a factor of 20 combining both seasonal and inter-annual variation components. Acoustically derived euphausiid populations correlate significantly with both net-sampled euphausiid populations and acoustically derived silver hake abundances, but show no clear long-term (multi-year) trends. The correlation between Emerald Basin euphausiid and migratory pelagic fish abundances suggests the ecological influence of the Shelf Basin euphausiid stocks extends to the surrounding shelf areas. International Council for the Exploration of the Sea

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Lateral target strength of Antarctic krill

Cited by 19 publications

References 12 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

Modeling profitability for the smallest marine endotherms: auklets foraging within pelagic prey patches

Scotian Shelf euphausiid and silver hake population changes during 1984–1996 measured by multi-frequency acoustics

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