Humpback whale “super-groups” – A novel low-latitude feeding behaviour of Southern Hemisphere humpback whales (Megaptera novaeangliae) in the Benguela Upwelling System

Abstract

Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migrations from polar summer feeding grounds to winter calving and nursery grounds in subtropical and tropical coastal waters. Evidence for such migrations arises from seasonality of historic whaling catches by latitude, Discovery and natural mark returns, and results of satellite tagging studies. Feeding is generally believed to be limited to the southern polar region, where Antarctic krill (Euphausia superba) has been identified as the primary prey item. Non-migrations and / or suspended migrations to the polar feeding grounds have previously been reported from a summer presence of whales in the Benguela System, where feeding on euphausiids (E. lucens), hyperiid amphipods (Themisto gaudichaudii), mantis shrimp (Pterygosquilla armata capensis) and clupeid fish has been described. Three recent research cruises (in October/November 2011, October/November 2014 and October/November 2015) identified large tightly-spaced groups (20 to 200 individuals) of feeding humpback whales aggregated over at least a one-month period across a 220 nautical mile region of the southern Benguela System. Feeding behaviour was identified by lunges, strong milling and repetitive and consecutive diving behaviours, associated bird and seal feeding, defecations and the pungent “fishy” smell of whale blows. Although no dedicated prey sampling could be carried out within the tightly spaced feeding aggregations, observations of E. lucens in the region of groups and the full stomach contents of mantis shrimp from both a co-occurring predatory fish species (Thyrsites atun) and one entangled humpback whale mortality suggest these may be the primary prey items of at least some of the feeding aggregations. Reasons for this recent novel behaviour pattern remain speculative, but may relate to increasing summer humpback whale abundance in the region. These novel, predictable, inter-annual, low latitude feeding events provide considerable potential for further investigation of Southern Hemisphere humpback feeding behaviours in these relatively accessible low-latitude waters.

Song recorded near a super-group of humpback whales on a mid-latitude feeding ground off South Africa

“…In general, the production of song in humpback whales is strongly linked to breeding behavior, with structured song most ubiquitous at low-latitude, warm water breeding grounds (reviewed in Helweg et al, 1992). However, we recorded song in late spring, after the completion of the breeding season in Angola and Gabon, and in an area where breeding is not thought to occur (Barendse, 2011;Findlay et al, 2017). Although singing during migration toward feeding grounds (e.g., Norris et al, 1999) and on feeding grounds (e.g., Stimpert et al, 2012) is well documented, this is the first time it has been documented in western South Africa.…”

“…The Benguela upwelling ecosystem is an extremely nutrient rich environment (Fr eon et al, 2009). Recently (2011 onwards) large numbers of whales have been observed forming aggregations exceeding 20 animals per group, termed "super groups" (Findlay et al, 2017). These whales are abundant from October to February and are feeding on euphausiid shrimp (Euphausia lucens) (Barendse et al, 2010;Findlay et al, 2017).…”

“…Recently (2011 onwards) large numbers of whales have been observed forming aggregations exceeding 20 animals per group, termed "super groups" (Findlay et al, 2017). These whales are abundant from October to February and are feeding on euphausiid shrimp (Euphausia lucens) (Barendse et al, 2010;Findlay et al, 2017). The number of humpback whales feeding in super-groups is highly unusual in mid-to low-latitudes, with estimated group sizes of up to 200 individuals reported from western South Africa (Findlay et al, 2017).…”

“…These whales are abundant from October to February and are feeding on euphausiid shrimp (Euphausia lucens) (Barendse et al, 2010;Findlay et al, 2017). The number of humpback whales feeding in super-groups is highly unusual in mid-to low-latitudes, with estimated group sizes of up to 200 individuals reported from western South Africa (Findlay et al, 2017). It may be that some BSB humpback whales suspend their southward migration to feed in South African waters in the spring and summer months (Best et al, 1995).…”

“…It may be that some BSB humpback whales suspend their southward migration to feed in South African waters in the spring and summer months (Best et al, 1995). Alternatively, feeding aggregations may comprise a non-breeding migration of young, physically immature animals or represent the immigration of young non-breeding animals from IWC Breeding Stock C (BSC) during their southward migration (Findlay et al, 2017, Fig. 1).…”