habitat_narrative
Marine
The Humpback Whale migrates seasonally between winter breeding grounds in the tropics and feeding areas predominantly along continental shelves in temperate and high latitude areas (Clapham 2002). In the southern hemisphere summer, Humpbacks feed nearly exclusively on Antarctic krill (Euphausia superba), usually around Antarctica (Skinner and Chimimba 2005). However, some feeding activity takes place in the Benguela upwelling system along the migration route west of Africa by Breeding Stock B (Best et al. 1995), where Humpbacks consume another krill species (E. lucens) and the amphipod (Themisto gaudichaudii) (Barendse et al. 2011). The feeding here appears to be linked to productive upwelling cells at Cape Point, Dassen Island, Cape Columbine, and probably others further north. There is evidence that âknowledgeâ about the use of the feeding opportunities is transferred by mothers to their calves (Barendse et al. 2013), and whales in B2 demonstrate high fidelity to the region (Barendse et al. 2013, Carvalho et al. 2014), with several animals returning to the region between years and for long periods of time. The relationship between whales feeding here and whales migrating along mid-oceanic routes has not been established. Recent work looking at scarring by cookie-cutter Sharks (Isistius spp.) suggests that whales found off west South Africa have spent extended periods in nearshore or cooler waters where wounds (acquired in warmer tropical waters) have had time to heal (Elwen et al. 2014). Feeding at Saldanha Bay and St Helena Bay occurs mainly from October to February, although whales may be present in low numbers throughout the year.For the broad population, the bulk of their feeding takes place in summer around Antarctica, where the major food source is krill. This resulting energy is converted to reserves in the form of blubber. In some areas outside of their summer feeding zones, Humpback Whales may feed on schooling fish, but they usually only consume limited amounts of food while migrating northwards, and on return to the south. In Durban, Bannister and Baker (1967) examined the stomach contents of 25 Humpback Whales; only three of the whales were found to have food in their stomachs, all of which consisted of Euphasiid remnants.
The inshore area associated with the Benguela upwelling (from the coast to about 70 m depth) is used regularly as a feeding area in the spring and summer months by a sub-group of Humpback Whales (B2 Breeding Stock). Feeding aggregations form of up to 20 whales at a time, with more recent evidence of âsuper-groupsâ (J. Barendse unpubl. data). Some of the whales may remain in the area for over a month. They are associated with upwelling plumes at Cape Columbine, Dassen Island, Cape Point, Lamberts Bay, Elands Bay and possibly also Lüderitz, but are known to be absent from Saldanha Bay and St Helena Bay. Findlay and Best (1996) reported that individuals of the B2 Breeding Stock may feed opportunistically off the west coast of South Africa during the summer, where one individual was found to have been feeding on stomatopods.
In the southern hemisphere, Humpback Whales will reproduce during the winter months in tropical, coastal waters. With a gestation period of approximately 11.5 months, females usually give birth every two years, but may produce calves annually. Calves grow very quickly and usually reach lengths of 8.8 m by the time of weaning. Mehta et al. (2007) reported that Humpback Whale calves may be subject to predation by Killer Whales (Orcinus orca). Males and females become sexually mature once they reach lengths of 11.5 m and 12 m respectively (Skinner and Chimimba 2005). Humpback Whales have a generation time of 22 years (Taylor et al. 2007). This species is known to be extremely vocal at breeding grounds, where they produce a sequence of diverse sounds for durations of between 8 and 30 minutes. Sequences are consistent between individuals at particular breeding grounds, and most commonly come from breeding adult males, announcing their presence (Skinner and Chimimba 2005).
Ecosystem and cultural services: As indicator species, marine mammals integrate and reflect ecological variation across large spatial and long temporal scales, and therefore they are prime sentinels of marine ecosystem change; migratory mysticete whales may be used to investigate broadscale shifts in ecosystems (Moore 2008).
The B subpopulation is considered a flagship subpopulation of the west coast of South Africa. The location of a Humpback feeding ground so near the shore and so far north in the southern hemisphere is unique (Barendse et al. 2013). The only other comparable situation is at the Antarctic Peninsula. It offers unique research and tourism opportunities.
