In situ target strength measurements of the scyphomedusa Chrysaora melanaster

Abstract Bigeye tuna (Thunnus obesus) is an important commercial fish species, which aggregates around fish aggregating devices (FADs) together with other tropical tuna species. Acoustics is the main technology used by fishers and scientists for the location and quantification of tunas at FADs. However, currently it is not possible to reliably discriminate between the different tropical tuna species that are found together at FADs using acoustic methods, which hampers the development of selective fishing needed to preserve some of the tropical tuna species for which overfishing is occurring. One of the prerequisites for species discrimination is to know the target strength (TS) of each species at different frequencies. This paper measures in situ TS values and explores the frequency response of bigeye tuna at FADs in the central Pacific Ocean using three different acoustic frequencies. For the range of body length caught (40–100 cm), the obtained b20 values were −65, −66, and −72 dB for 38, 120, and 200 kHz, respectively. The decreasing frequency response pattern obtained for this swimbladder bearing species contrasts with the opposite pattern previously observed for skipjack tuna (bladder-less), the most abundant tuna species found at FADs, hence allowing the potential for discrimination between the two species.

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In situ target-strength measurement of young hairtail (Trichiurus haumela) in the Yellow Sea

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.07.010 ◽

2006 ◽

Vol 63 (1) ◽

pp. 46-51 ◽

Cited By ~ 16

Author(s):

Xianyong Zhao

Keyword(s):

Confidence Interval ◽

Yellow Sea ◽

The Yellow Sea ◽

Target Strength ◽

Abundance Estimation ◽

Strength Measurement ◽

The Mean

Abstract The target strength of hairtail (Trichiurus haumela) in the Yellow Sea was measured in situ with a 38 kHz, split-beam echosounder on 2 January 2001. The fish measured were of the 2000 year class, its anal length ranged from 62 to 115 mm, with a mean of 89.8 mm. The mean target strength of these young hairtail was estimated to be −49.2 dB, with a 95% confidence interval of (−49.4, −49.0) dB. This provided a rare and useful reference for the acoustic-abundance estimation of hairtail.

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Multifrequency target strength of northern krill (Meganyctiphanes norvegica) swimming horizontally

ICES Journal of Marine Science ◽

10.1093/icesjms/fsr170 ◽

2011 ◽

Vol 69 (1) ◽

pp. 119-130 ◽

Cited By ~ 5

Author(s):

Lucio Calise ◽

Tor Knutsen

Keyword(s):

Length Distribution ◽

Ex Situ ◽

Target Strength ◽

Acoustic Backscatter ◽

Acoustic Measurements ◽

Acoustic Beams ◽

Meganyctiphanes Norvegica ◽

Acoustic Identification ◽

Made In

Abstract Calise, L., and Knutsen, T. 2012. Multifrequency target strength of northern krill (Meganyctiphanes norvegica) swimming horizontally. – ICES Journal of Marine Science, 69: 119–130. Multifrequency acoustic measurements on ex situ horizontally swimming krill were made in a novel experimental setting. An ensemble of northern krill (Meganyctiphanes norvegica) was introduced to a large enclosure (a mesocosm), and acoustic backscatter was sampled using a multifrequency (70, 120, and 200 kHz) echosounder (Simrad EK60). Two submerged lamps were placed at opposite sides of the mesocosm and switched on and off to induce the krill, by light attraction, to swim horizontally through the acoustic beams. By tracking echoes, animal displacement, swimming speed, and target strength (TS) by frequency were estimated. The dominant and secondary modes of the total-length distribution were 21.8 ± 3.0 and 27.8 ± 2.7 mm, respectively. Although krill orientation was assumed stable and the ping rate was high, the range and inter-ping variability of the average TS values were large, decreasing and increasing with frequency, respectively. The overall TS frequency response observed and concurrent measurements at 120 and 200 kHz confirm the theoretical expectation that the acoustic backscatter from the investigated organisms were confined to the Rayleigh and Geometric scattering regions, a finding that might both aid acoustic identification and size-group separation of in situ northern krill.

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Determination of Composition and Vertical Structure of Fish Communities Using in situ Measurements of Acoustic Target Strength

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f94-012 ◽

1994 ◽

Vol 51 (1) ◽

pp. 99-109 ◽

Cited By ~ 13

Author(s):

M. Barange ◽

I. Hampton ◽

S. C. Pillar ◽

M. A. Soule

Keyword(s):

South African ◽

Size Structure ◽

Fish Communities ◽

Target Strength ◽

Small Scale ◽

Good Correspondence ◽

Structure And Dynamics ◽

Acoustic Target

A split-beam echo-sounder was used to estimate in situ acoustic target strengths (TS) of fish from a number of different fish communities on the South African continental shelf. The TS and size distributions (obtained by aimed trawling) were used to describe the size structure and vertical distribution of these communities. TS distributions obtained from several monospecific populations of juvenile Cape hake (Merluccius capensis), the dominant species present, were self-consistent, and there was good correspondence between modes in the TS and length distributions of juvenile hake, adult round herring (Etrumeus whiteheadi), anchovy (Engraulis capensis) recruits, pelagic goby (Sufflogobius bibarbatus), horse mackerel (Trachurus trachurus capensis), and ribbon fish (Lepidopus caudatus). Average TS values for all these species, both per individual and normalized by weight, are presented and compared with published values. The use of TS information in studies of the small-scale community structure and dynamics of fish populations is discussed. It is concluded that the method can be effective on low-density, multispecific assemblages such as those in our study, avoiding many of the pitfalls of conventional net sampling.

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In situ target strength estimates of optically verified southern blue whiting (Micromesistius australis)

ICES Journal of Marine Science ◽

10.1093/icesjms/fss177 ◽

2012 ◽

Vol 70 (2) ◽

pp. 431-439 ◽

Cited By ~ 4

Author(s):

Richard L. O'Driscoll ◽

Johannes Oeffner ◽

Adam J. Dunford

Keyword(s):

New Zealand ◽

Confidence Interval ◽

Fork Length ◽

Target Strength ◽

Blue Whiting ◽

Acoustic Target ◽

The Mean ◽

The Relationship ◽

Immature Fish

Abstract O'Driscoll, R. L., Oeffner, J., and Dunford, A. J. 2013. In situ target strength estimates of optically verified southern blue whiting (Micromesistius australis) – ICES Journal of Marine Science, 70: 431–439. Estimates of the acoustic target strength (TS) of southern blue whiting (Micromesistius australis) at 38 kHz were obtained using an autonomous acoustic–optical system (AOS) mounted on a demersal trawl. Data were collected from aggregations of spawning adult [mean fork length (FL) 34.4 cm] and immature (mean FL 24.6 cm) southern blue whiting south of New Zealand. Mean TS was estimated from 162 tracks containing 695 echoes from targets identified from video as southern blue whiting. The mean TS was –37.9 dB with a 95% confidence interval (CI) of –39.7 to –36.6 dB for 21 immature fish and –34.6 dB (95% CI –35.4 to –34.0 dB) for 141 adults. A logarithmic fit through the mean TS values produced a TS–fork length (FL) relationship from optically verified targets of TS = 22.06 log10FL – 68.54. This new relationship gives TS values within 1 dB of those estimated using the relationship recently adopted by ICES for blue whiting (Micromesistius poutassou) of TS = 20 log10TL – 65.2 (where TL is total length) obtained from in situ measurements, but higher values than those estimated from the previous relationship for southern blue whiting of TS = 38 log10FL – 97, which was based on swimbladder modelling.

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