![]() Off the west coast of South Africa, current knowledge on humpback whale occurrence is based on whaling data (Olsen, 1914 Mackintosh, 1942 Best, 2007 Best and Allison, 2010), sighting data (e.g., Best et al., 1995 Findlay and Best, 1995 Barendse et al., 2010 Barendse et al., 2011 Barendse et al., 2013 Purdon et al., 2020), and one coastal (i.e., adjacent to the coast and shallower than 100 m water depth) acoustic study (Ross-Marsh et al., 2021). The distribution and migration of humpback whales are believed to be driven by food availability, suitable environmental conditions, and reproductive status (Matthews, 1938 Lockyer, 1984 Best et al., 1995 Brown et al., 1995 Pomilla and Rosenbaum, 2005 Purdon et al., 2020 Dey et al., 2021 El-Gabbas et al., 2021 Reisinger et al., 2021 Schall et al., 2021a Schall et al., 2021b). Southern Hemisphere humpback whales (Megaptera novaeangliae) perform impressive seasonal migrations between their austral summer feeding grounds in Antarctica and their winter breeding and calving grounds in low latitudes. Inter-correlation between history of exploitation, pregnancy rates and individual growth rate and the attainment of sexual maturity is discussed in relation to possible changes in food supply. The success of factors such as fertility, pregnancy, lactation, developmental growth and sexual maturity, and net recruitment are dependent on efficient storage of energy for body maintenance, foetal growth and milk production. Weaning in most species occurs during or after the summer feeding season. Even Eschrichtius robustus, a bottom-feeder, undertakes such migrations. Baleen whales thus need to leave the home breeding grounds for the high latitude seas each spring in order to feed and store energy in the form of fat as reserves for the months of poor feeding. ![]() Baleen whales feed mainly by filtering small swarming planktonic Crustacea, the production of which is greatest in cold high latitude waters. ![]() The reproductive cycle appears to be geared to this annual cycle of migration and feeding. Most baleen whales undertake extensive migrations for feeding, an exception being Balaena mysticetus. Normally just 1 calf is born in warm temperate or sub-tropical waters. The female reproductive cycle is generally 2 yr, with a gestation period of c1 yr. ![]() In small and greatly reduced stocks such catches can seriously alter the population structure. Geographical segregation of sexes, sexual classes and age classes sometimes occurs, eg in Balaenoptera acutorostrata this can seriously bias the sex ratio and age distribution of catches. Formation of loose aggregations occurs during migration and seasonally. The mating pattern is usually monogamous, with less social schooling of the type common to many Odontoceti. ![]()
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