Distribution and population separation of Bryde's whale Balaenoptera edenioff southern Africa

A review of available catch and biological data suggests that there are 3 p opulations of Bryde's whales in the southern African region, An inshore pop ulation (the South African Inshore Stock) occurs over the continental shelf of South Africa, south of about 30 degreesS, and seems to be nonmigratory, although there is a movement up the west coast in winter. A pelagic popula tion (the Southeast Atlantic Stock) occurs on the west coast of southern Af rica, ranging from equatorial regions to about 34 degreesS, and appears to migrate north in autumn and south in spring. Whales from the Southeast Atla ntic Stock differ from the South African Inshore Stock in size, scarring, b aleen shape, seasonality of reproduction, fecundity and prey types. Both oc curred in the west coast whaling ground off Donkergat, but with differing s easonalities and distributions from the coast. Bryde's whales are rare on t he east coast of southern Africa, but are found in summer in some numbers s outh of Madagascar. Whales from this population are clearly smaller than th ose from the Southeast Atlantic Stock, but are similar in size to, or even smaller than, those from the South African Inshore Stock. Their external ap pearance is unknown, but they differ in prey type from the South African In shore Stock, and because of a clear discontinuity in distribution it is bel ieved that they form a third (pelagic) population (the Southwest Indian Oce an Stock). This population may or may not move north as far as the Seychell es in winter, but seems to be separate from Bryde's whales in the Arabian S ea, From their size composition, length at sexual maturity and infrequent c apture, Bryde's whales taken at Durban may have represented strays from eit her the South African Inshore Stock or the Southwest Indian Ocean Stock, an d recorded stomach contents also indicate prey types common to either stock . The unusual degree of population differentiation shown by Bryde's whales may be a consequence of their limited seasonal migrations and apparent reso urce partitioning.