Age Determination And Growth Rate Of The Northern Benguela Sardine (Sardinops Sagax)

Abstract

The main objective of this study was to determine sardine age by counting rings on otoliths and to analyse the length, age and growth through regression and Von Bertalanffy Growth models. Otoliths amounting to 826 pairs were collected from the annual sardine research survey of the Ministry of Fisheries and Marine Resources in October 2013. A total of 713 sardine otoliths were mounted on black Perspex plates and aged by means of counting rings using a Zeiss microscope at a magnification of 22x. A micrometer (4 epu = 1 mm) was used to measure the radius and distance of rings from the nucleus on each otolith. In total, six age groups were represented in the sample, including, zero, one year, two years, three years, four years and five year age groups. The one year old age class was the dominant age group. Mean lengths at age were determined for each age group and were as follows: Zero age group had a mean length of 13.8 cm, one year olds were 16.8 cm, two year olds were 19.6 cm, three year olds were 21.4 cm, four year olds 22.4 cm and mean length for the five year age group was 23.4 cm. All these lengths were significantly different from each other, except the four and five year age groups. Fish length and otolith radius relationship was strong (r = 0.75, p < 0.05). The estimated parameters for the Von Bertalanffy Growth model were: = 26.6 cm, K = 0.28, and t0 = 2.69. Growth rate of females (K = 0.2256) was lower than males (K = 0.3188).