Effect of the depth-dependent target strength (TS) on biomass estimation of Japanese ahcovy was examined by using following four TS models: (1) TS = 20logLt-71.9, (2) TS = 20logLt-72.5, (3) TS = 20logLt-(20/3)log(1+z/10)-67.6 and (4) TS = 20logLt-(20/3)log(1+z/10)-64.7, where Lt and z represent total length (cm) and depth (m), respectively. (1) and (2) have been used in conventional fisheries resources surveys; (3) and (4) take account of depth-dependent TS. Because (1)-(3) were based on in-situ measurement, pitch angles of individuals used in the models were not known. Pitch angle is assumed 0° (±10° std) in (4). Biomass estimated by (3) was 82% and 73% of (1) and (2), respectively. Biomass estimated by (3) was 195% of (4). The results indicated that the effect of the pitch angle on the biomass estimation could be large even if the effect of the depth-dependent TS was taken account. Mean distribution depth can be used as a value for z.
Murase, Hiroto; Kawabata, Atsushi; Kubota, Hiroshi; Nakagami, Masayasu; Amakasu, Kazuo; Abe, Koki; Miyashita, Kazushi; and Oozeki, Yoshioki
"EFFECT OF DEPTH-DEPENDENT TARGET STRENGTH ON BIOMASS ESTIMATION OF JAPANESE ANCHOVY,"
Journal of Marine Science and Technology: Vol. 19:
3, Article 5.
Available at: https://jmstt.ntou.edu.tw/journal/vol19/iss3/5