Target strength of the lanternfish, Stenobrachius leucopsarus (family Myctophidae), a fish without an airbladder, measured in the Bering Sea

Abstract

This paper reports theoretical values of target strength (TS) for the lanternfish Stenobrachius leucopsarus, a fish without an airbladder, which dominates the Subarctic marine mesopelagic fish community. Two models for liquid-like slender bodies, the general prolate-spheroid model (PSM) and the deformed-cylinder model (DCM), were used to compute the TS of the fish relative to its orientation. The relative mass density g and the sound speed h in seawater were measured and used in both models. To confirm the appropriateness of the models, tethered experimental measurements were carried out at 38 kHz for five specimens. The value of g measured by the density-bottle method was very low (1.002–1.009) compared with that of marine fish in general. The value of h measured by the time-average approach was 1.032–1.039 at the water temperature at which S. leucopsarus is found. TS-fluctuation patterns against fish orientation (the TS pattern) estimated from the DCM and PSM were in good agreement in the area of their main lobes. Both models reproduced the main lobes of the measured TS patterns in near-horizontal orientation (<±20°), and they were considered to be effective in measuring the TS of S. leucopsarus in a horizontal (swimming) position. After these comparative experiments, we computed the TS of 57 fish (27.8–106.9 mm) at 38, 70, 120, and 200 kHz, using the DCM. A plot of body length (in log scale) against TS showed a non-linear relationship at all frequencies. S. leucopsarus had a very low TS (<−85 dB, TScm), suggesting that acoustic assessment would be highly sensitive, especially when the proportion of small fish is high (e.g. L/λ < 2), and an appropriate frequency should be considered that takes into account both the length composition and the depth of occurrence

A review on mesopelagic fishes belonging to family Myctophidae

“…However, acoustic methods are considered more reliable for biomass estimation. Some studies using acoustic surveys like High Sonar multibeams and Acoustics Doppler Current Profiler (ADCP) showed that trawl biomass usually did not match the acoustic data (Benoit-Bird et al 2001Yasuma et al 2006). A reason could be that the fishes showed net avoidance by detecting the gear visually or by sensing turbulence in water.…”

“…Survey in the western Indian Ocean estimated the presence of 97 species of myctophids belonging to 23 genera (Nafpaktitis 1982). Stenobrachius leucopsarus is one of the abundant and dominant non-airbladder lanternfish in the Subarctic Pacific including the Bering Sea and Sea of Okhotsk (Yasuma et al 2006). Around 43 species belonging to 16 genera were recorded potentially in the southern ocean, out of which 7 species: Electrona antarctica, Gymnoscopelus braueri, G. ophisthopetrus, G. nicholski, Krefftichthys anderssoni, Protomyctophum bolini and P. tensioni were considered true representatives of regions of south of the Antarctic Polar Front (Hulley 1985;Kozlov 1995).…”

Measurements of density contrast and sound-speed contrast for target strength estimation of Neocalanus copepods (Neocalanus cristatus and Neocalanus plumchrus) in the North Pacific Ocean

“…A density-bottle method [12,14,21] was used for measuring body-mass density. In this method, body-mass density was determined by evaluating the buoyancy of each specimen.…”

“…Yasuma et al [21]. The mass density of seawater (ρ sw ) was calculated as a function of mean temperature, salinity, and pressure [22] that observed depth range where the net tows were conducted.…”

Broadband and statistical characterization of echoes from random scatterers : application to acoustic scattering by marine organisms

“…For example, the class of models developed for fluidlike zooplankton have been applied to predict the scattering from a variety of animals with fluidlike, weakly-scattering material properties, such as squid, fish without swimbladders, and other gelatinous zooplankton (Brierley et al, 2004;Kang et al, 2006;Warren and Smith, 2007;Wiebe et al, 2010;Yasuma et al, 2006Yasuma et al, , 2010. However, direct application of existing models should be treated with caution, since the scattering from any given animal may be strongly influenced by taxon-specific organs or structures.…”