Interpretation of the spectra of energy scattered by dispersed anchovies.
The spectra of backscattered energy by dispersed anchovies, which were reported by Holliday (1972), reveal several peaks at frequencies that correspond to theoretically calculated resonance frequencies of year classes of anchovies. Theoretical calculations are based on concurrent measurements of distributions of swim bladder dimensions and a modified form of Minnaert's (1933) equation. Differences between calculated and measured values of the mean lengths of the second-, third-, and fourth-year classes are within experimental uncertainties (+/-8%). The calculated mean lengths of juvenile anchovies are in good agreement with historical measurements of the bounds on this parameter (Butler, 1989). Matching of theoretical calculations and measurements of backscattered energy level versus frequency yields estimates of the total Q of the spectral line, QT, and the relative number density per year class. The resultant estimate of QT of adult anchovies is approximately 4.4. This value of QT is consistent with laboratory measurements of the Q of individual anchovies. Q0 (approximately 7 at 15 m) and measurements of length distributions of year classes and depth distributions. Resultant estimates of relative number densities of year classes were consistent with historical measurements of the relative number densities of year classes of anchovies in the Southern California Bight.
Diachok
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Naval Research Laboratory, Washington, DC 20375, USA. orest@wave.nrl.navy.mil
D000162:Acoustics; D000818:Animals; D004734:Energy Metabolism / Q000502:physiology*; D004735:Energy Transfer / Q000502:physiology*; D005399:Fishes / Q000502:physiology*; D008954:Models, Biological