Distribution, growth and mortality of young rough scad, Trachurus lathami, in the south-eastern Brazilian Bight

Distribution, growth and mortality of larval and juvenile rough scad Trachurus lathami Nichols, 1920, were studied, based on samples collected during December 1991 in the south-eastern Brazilian Bight. Young rough scad were widespread throughout the region surveyed, but spawning was more intensive in the northern area and tended to be greater in areas of low temperature and high salinity. The length class distribution of the rough scad larvae and juveniles ranged from 2.25 to 32.25 mm body length (BL), and the preflexion larvae of size categories from 2.25 to 3.25 mm BL were the most abundant. Net avoidance was detected for early larvae (2.25 mm length class) and for juveniles larger than 12.25 mm BL length class. Two models were applied to estimate growth and daily growth rate: a linear regression and a Gompertz curve. Both curves showed similar results and a good fit to the data. The mean growth rate estimated by linear regression was 0.44 mm per day (SD=0.008 mm). In small larvae up to 25 mm BL the linear and Gompertz curves showed similar estimated lengths. The hypothetical length at age zero ( L ₀) was estimated as 1.5 mm. The instantaneous daily mortality coefficient estimated from the slope of the regression of log-transformed values of relative production rates ( P _t/ d _t) against age ( t_i ) was Z=0.1888 for larval and juvenile rough scad. This corresponds to a daily mortality rate of 17.2%.