Original Article Fisheries

Fisheries Science

, Volume 77, Issue 2, pp 161-167

Swimming angle and target strength of larval Japanese anchovy (Engraulis japonicus)

  • Yusuke ItoAffiliated withLaboratory of Marine Ecosystem Change Analysis, Graduate School of Environmental Science, Hokkaido University Email author 
  • , Hiroki YasumaAffiliated withLaboratory of Marine Ecosystem Change Analysis, Field Science Center for Northern Biosphere, Hokkaido University
  • , Reiji MasudaAffiliated withFisheries Research Station, Kyoto University
  • , Kenji MinamiAffiliated withFisheries Research Station, Kyoto University
  • , Ryuichi MatsukuraAffiliated withNational Research Institute of Fisheries Engineering, FRA
  • , Saho MoriokaAffiliated withFisheries Research Institute, Tokushima Agriculture, Forestry and Fisheries Technology Support Center
  • , Kazushi MiyashitaAffiliated withLaboratory of Marine Ecosystem Change Analysis, Field Science Center for Northern Biosphere, Hokkaido University

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Abstract

The swimming angle of larval Japanese anchovy (Engraulis japonicus) was measured in a tank, and target strength (TS) was calculated using a theoretical scattering model. The mean swimming angle was 12.8° (SD ±22.1). Increased speeds of flow led to increased mean swimming angles. The mean swimming angle at flow of 5 cm s−1 was higher than at other speeds. TS values were estimated using a distorted-wave Born approximation model for two cases. Average values were 1–3 cm s−1 (11.5° ± 22.1) and 5 cm s−1 (16.6° ± 21.7) for cases 1 and 2, respectively. For case 1, TS ranged from −92.0 to −74.7 dB with a mean of −79.4 dB at 120 kHz. For case 2, TS ranged from −92.2 to −75.2 dB with a mean of −79.9 dB. The mean TS in case 2 was lower than that in case 1, with the maximum difference being 1.0 dB at 120 kHz (standard length 22.0 mm). However, there were no significant differences between the regression lines of cases 1 and 2. Thus, changes in flow speed altered the swimming angle of larval Japanese anchovy, but had little influence on TS.

Keywords

Larval Japanese anchovy Swimming angle Target strength