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Results of the examination of 1 062 sei whales Balaenoptera borealis landed at the whaling station at Donkergat, Saldanha Bay, South Africa, in the 1962 and 1963 whaling seasons are presented. Sei whales were usually encountered off the edge of the continental shelf, with males being caught closer inshore than females and mature females furthest of all from the station. Females reached puberty at an average length of 46.1 ft (14.1 m) and an age of 8.2 (95% CI = 7.3, 9.0) years (assuming one growth layer group is formed in the ear plug per year). Males reached sexual maturity at an average length of 45.3 ft (13.8 m) and an age of 8.6 (95% CI = 7.8, 9.4) years. Mean lengths at which growth ceased were 52 ft (15.8 m) in females and 48.6 ft (14.8 m) in males. Most (~90%) conceptions occurred over a 70-day period with a peak in June, and primigravid females conceived six days later than multigravid females. Observed pregnancy rates were as high as 86.1%, but with ovulation rates averaging only 0.47 a year, the catch could not have been fully representative of the population. There was no significant decline in the observed pregnancy rate with age. During the northward migration (May–July), fewer whales were taken in water shallower than 2 000 m than in the southern migration, and the catch was largely composed of immatures. The few adult males taken at that time of year had significantly heavier testes than males of an equivalent size on the southern migration. The southward migration (August–October) was markedly structured, such that pregnant females and immatures of both sexes were in the vanguard, followed by mature males and lastly lactating females and calves. The availability of sei whales off Donkergat declined rapidly from 1965 to 1967, following an episode of massive catching by pelagic whalers in higher latitudes. Keywords: growth, migration, reproduction, sei whales, South Africa African Journal of Marine Science 2002, 24: 111–133

Tissues from fin (Balaenoptera physalus) and sei (Balaenoptera borealis) whales taken off the coast of Southwest Iceland in July–August in 1978 and 1981 were analysed for percent lipid, protein, and ash contents. The tail region of the whales, especially the dorsal area, constituted the main area of lipid storage in both blubber and muscle. No significant differences (p > 0.05, ANOVA) were evident between reproductive classes, except that adult females appear to store more lipid in the tail muscles than other classes. Most sei whale tissues contained more lipid than those of fin whales, but the differences may be explained by variations in seasonal feeding and fattening. Seasonal variations and differences between reproductive classes were evident from girth and blubber thickness. Juvenile males were thinnest and adult females were thickest.