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1

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Sampling biological characteristics of krill: Effect of heterogeneous nature of swarms (1990)

Watkins, J. L. ; Morris, D. J. ; Ricketts, C. ; [et al.]

Springer

Marine biology 107 (1990), S. 409-415

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract An effect of the very patchy distribution of Antarctic krill (Euphausia superba Dana) in various forms of aggregation is that a single swarm may not provide an unbiased estimate of population parameters such as mean length of krill in the local area. Here, we analyse the number of samples required to estimate the characteristics of a local population as precisely as if there were no differences between krill swarms in terms of their biological composition. Krill were intensively sampled over different spatial and temporal scales around South Georgia in 1981 and 1982, and in the Bransfield Strait in 1985. These varied from replicate hauls at a single station over 24 h and repeat sampling in restricted areas over periods of 6 to 14 d to regional surveys around South Georgia and in the Bransfield Strait. Various biological characteristics were measured such as length, maturity, moult stage and feeding state. Depending upon the biological characteristic examined and the area covered by the sampling programme, the number of samples needed to obtain the same degree of precision as would be found in the absence of heterogeneity varied from 3 to 〉 80 samples. This has important implications for the design of net-sampling programme for monitoring krill populations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01313422

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2

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Concordance of interannual fluctuations in acoustically estimated densities of Antarctic krill around South Georgia and Elephant Island: biological evidence of same-year teleconnections across the Scotia Sea (1999)

Brierley, A. S. ; Demer, D. A. ; Watkins, J. L. ; [et al.]

Springer

Marine biology 134 (1999), S. 675-681

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Acoustic estimates of the densities of Antarctic krill, Euphausia superba, in areas around South Georgia (SG) and Elephant Island (EI) were compared for seven austral summers between 1981 and 1997. Estimated densities of krill at SG were most often lower than at EI, although this may simply have been a function of differences in the survey and data-analysis techniques used at each site. More interestingly, the magnitudes of density and between-year gradients of density at each site were mirrored by those at the other location; for example 1991 and 1994 were years of very low krill density at both SG and EI. There was no apparent lag in changes in density between sites, and ranked between-year gradients in density at both locations were closely correlated. These pronounced similarities suggest that densities of krill at both locations are linked directly, and may be impacted by the same gross physical and biological factors (e.g. recruitment, dispersal and environmental variability) acting over the same temporal and spatial scales. The observed concordance also implies that the pelagic ecosystems at these widely separated sites (≃1500 km distant at opposite sides of the Scotia Sea) are not operating in isolation. Fluctuations in krill density were investigated with reference to cyclical variations in sea ice extent, and in air and sea-surface temperature. The resulting model suggests that the 1999/2000 austral summer will be one of low krill density.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002270050583

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3

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Moult in relation to some aspects of reproduction and growth in swarms of Antarctic krill,Euphausia superba (1996)

Buchholz, F. ; Watkins, J. L. ; Priddle, J. ; [et al.]

Springer

Marine biology 127 (1996), S. 201-208

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract In a 14-d period 38 swarms of Antarctic krill,Euphausia superba Dana, were sampled in an area 55.5 x 55.5 km to the southwest of Elephant Island, at the north of the South Shetland Islands. Moult stage, maturity stage, and size of ca. 100 krill from each swarm were measured. Each of the characteristics varied greatly between swarms. Moulting krill were found in most swarms, but in one swarm all of the krill were just about to moult. Ways in which moulting may act as a possible sorting mechanism are discussed. Data for all the analysed krill (ca. 3000 specimens) were used to investigate the interdependence of moult rate, sexual maturation and growth. While all immature krill moulted at approximately the saine rate in the study, there were significant differences in the moulting rates of mature male and female krill. Gravid female krill continued to moult, although less frequently than mature males. As a consequence males had to attach spermatophores to females after each moult. It is likely that variation in moult rate of females and males was related to the energy expenditure required for ovary development in females and spermatophore production and searching behaviour in males. Spawning and moulting were only partly coupled in gravid females. Spawning appeared to take place predominantly during Moult Stage D2. There was no evidence of intermoult growth by intersegmental dilation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00942104

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4

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Layers of Antarctic krill, Euphausia superba : are they just long krill swarms? (1998)

Watkins, J. L. ; Murray, A. W. A.

Springer

Marine biology 131 (1998), S. 237-247

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Antarctic krill, Euphausia superba Dana, a major component in the southern ocean food web, typically occur in aggregations that range from small, discrete swarms and schools through to layers and superswarms that extend horizontally for several kilometres. A large Longhurst–Hardy plankton recorder has been used to obtain high-resolution serial samples from within two layers (up to 4 km in length) that were found near Elephant Island, north of the Antarctic Peninsula. Krill length, sex and maturity stage, net and acoustic estimates of number density are shown to vary significantly within these large layers. The variation occurring within a single layer is comparable with that occurring in a set of 38 swarms sampled contemporaneously with the layers. Thus, unlike a krill swarm, a whole krill layer may account for a substantial amount of the variation in the local krill population, although individual parts of the layer cannot be considered in this way. The layers play an important role in the ecology of the krill within the area. Firstly, these large layers may contain a significant proportion of the biomass within an area. Secondly, the structure of the layers gives some insight into the ways in which krill swarm formation and dispersal may be occurring.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002270050316

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5

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Conductive sphere in a radio frequency field: Theory and applications to positioners, heating, and noncontact measurements (1996)

Jackson, H. W. ; Watkins, J. L. ; Chung, S. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 3370-3384

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: An electrically conductive spherical sample located in an electromagnetic field excited by rf (radio frequency) current in a system of coaxial coils is treated theoretically. Maxwell's equations are solved exactly and all integrals in the formulas for the fields are evaluated analytically for the case where the sphere is on the axis and the coil system is modeled by a stack of filamentary circular loops. Formulas are also derived for electromagnetic force exerted on the sphere, excess impedance in the coil system due to the presence of the sphere, and power absorbed by the sphere. All integrals in those formulas have been evaluated analytically. Force measurements are presented and they are in excellent agreement with the new theory. A low-power electromagnetic levitator that is accurately described by the theory has been demonstrated and is discussed. Experimental measurements of excess impedance are presented and compared with theory, and those results are used to demonstrate an accurate noncontact method for determining electrical conductivity. Theoretical formulas for power absorption are evaluated numerically and their usefulness in both rf heating and in making noncontact measurements of a number of thermophysical properties of materials is discussed. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.361419

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6

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Krill biomass in the Atlantic (1995)

Trathan, P. N. ; Everson, I. ; Miller, D. G. M. ; [et al.]

[s.l.] : Nature Publishing Group

Nature 373 (1995), S. 201-202

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] SIR - Acoustic target strength (TS)1 is an important parameter when using acoustic survey data to estimate the abundance of Antarctic krill (Euphausia superba Dana). Recently, when the TS of krill was reassessed2,3, it emerged that the previous values had been too high, leading to unrealistically ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/373201b0

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7

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Nocturnal changes in the mean length of a euphausiid population: vertical migration, net avoidance, or experimental error? (1985)

Watkins, J. L. ; Morris, D. J. ; Ricketts, C.

Springer

Marine biology 86 (1985), S. 123-127

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The lengths of 9 421 Antarctic krill, Euphausia superba Dana, from 144 net samples from 4 depth ranges at the same location (north east of South Georgia) were measured over a period of 6 d. While the mean lengths showed differences between each depth range in each time period of each day, the only consistent difference occurred in the period 00.00 to 04.00 hrs local time, when the mean lengths of krill were up to 2 mm greater than those found at other times. While vertical migration may have contributed to this nocturnal change in mean length, differences in measurement techniques between observers were also implicated. Controlled laboratory experiments confirmed that there were significant differences between measurements of the same krill analysed by six different observers while there were no significant differences in replicate measurements made by a single observer. These results have important implications for future studies involving length and length-frequency analysis, and suitable precautions and experimental protocols are suggested.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00399017

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8

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Differences between swarms of Antarctic krill and some implications for sampling krill populations (1986)

Watkins, J. L. ; Morris, D. J. ; Ricketts, C. ; [et al.]

Springer

Marine biology 93 (1986), S. 137-146

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Antarctic krill, Euphausia superba Dana, were sampled from 28 discrete swarms in a small area south west of Elphant Island, South Shetlands, over a period of 14 d (24 February-9 March 1985). Four biological characteristics of the krill (length, sex, moult, gut fullness) were examined in a study of variation between swarms. Analysis of these characteristics indicated extensive differences between swarms and no single characteristic, or combination of characteristics, emerged as consistently accounting for the observed heterogeneity. There was no relationship between the degree of heterogeneity and the physical or temporal proximity of swarms. The variability between even close swarms strongly suggests that swarms are the basic unit of organization of krill populations. This conclusion has important implications for sampling programmes aimed at estimating population parameters. Thus, in the population studied here, we calculate that it was necessary to sample 23 swarms to estimate mean length and 10 swarms to establish a reliable estimate for the proportion of females in the population.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00428662

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