Age and Growth of Japanese Spanish Mackerel in the Central and Western Waters of the Seto Inland Sea

Abstract

Age, growth and maturity of Japanese Spanish mackerel Scomberomorus niphonius were investigated based on 583 specimens collected from commercial landings, from May 1981 to June 1983, in the central and western waters of the Seto Inland Sea. Scales near the pectoral fin were used for analysis. The time of annulus formation was approximately during May and July. The mean fork lengths at each age and sex were compared by means of two methods of estimation, viz. the actual measurement of the specimens collected from May to July and the back-cal-culation. The results indicate discrepancies between the two procedures in both sexes at age 1 and in female at ages 2 and 3. The divergence at age 1 is presumably attributed to an inaccurate body-scale relationship used in the back-calculation. Von Bertalanffy growth equations derived from the mean observed fork lengths (mm) at each age are as follows: Males: Lt—804[1 — exp (—0.908(t—0.105)}], Females: 101 l[l-exp{-0.518(t+0.222)}]. The oldest male was 4 and female 6 years old, respectively. The spawning season of this species was found from May to July, and the maturity was attained at age 2. Length-weight relationships divided into four periods depending on the condition of maturity of the two sexes are: April: W=4.214.10-7. L3.434, May and June: W=1.054.10-5.L.2.943, July: W=4.2733.10-5. L2.713, From August to January: W= 5.686.10-5- L2.676, where weight in grams and L=fork length in millimeters. © 1985, The Japanese Society of Fisheries Science. All rights reserved.