Spawning pattern, length at maturity, and fecundity of the southern blue whiting (Micromesistius australis) in the south-west Atlantic Ocean

Abstract

Southern blue whiting (Micromesistius australis Norman, 1937) inhabits the waters of the Southern Hemisphere, and in the south-west Atlantic Ocean is distributed over an area next to the Malvinas Islands. At present, this species is suffering over-exploitation and its biomass has decreased drastically. The histological analysis of ovaries and the oocyte size frequency distribution of gravid females indicate that southern blue whiting is a batch spawner with determinate annual fecundity. The spawning season of M. australis in the south-west Atlantic Ocean extends from August to October, with a main peak during September. Spawning females were recorded mainly in the waters south and south-west of the Malvinas Islands, close to the 200 m isobath. Total fecundity of seven M. australis females ranged from 148 300 to 713 900 yolked oocytes (46-55 cm total length (TL)). The mean total fecundity was 477 700 (206 783 SD) oocytes for one 51 cm TL female. Mean relative fecundity was 706 (258 SD) oocytes per g female weight, ranging from 277 to 967. The percentage of sexually mature females for each total length class indicated 50% female maturity was reached at 37.8 cm. This value was similar to those reported for this species between 1980 and 1990.