These predation events resulted in the prolonged absence of sevengill sharks from what is the largest known aggregation site for this species globally, which remained abandoned for up to a month. Although selective feeding on shark liver by killer whales is established, this is the first record of killer whale predations on sevengill sharks in False Bay, and the first documentation of a novel feeding technique, in which killer whales used force applied to the pectoral fins of each shark to rupture the pectoral girdle and thereby access the liver. However, in 20 we documented two events in which killer whales preyed upon broadnose sevengill sharks, using a specialized feeding method in which only the liver of each shark was consumed. These super predators are known to specialize on certain prey species, and up until 2015 were only documented preying on marine mammals within False Bay. However, since 2009, their position at the top of the food chain has been subverted by the increased presence of killer whales (Orcinus orca) in False Bay. False Bay, South Africa, is an aggregation site for both white (Carcharodon carcharias) and broadnose sevengill sharks (Notorynchus cepedianus) which together fulfill the role of coastal apex predators.
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While the loss of apex predators has been shown to disrupt ecosystems and trigger trophic cascades, the introduction of novel apex predators to functionally intact systems is less well understood. However, in this report I provide a description of the issueĪt hand, research methods used, preliminary results and recommendations for bothĪpex predators play an important role in structuring food webs and are thus key components of healthy, stable ecosystems. Genetic and tagĭata have yet to be analyzed. Several sperm whales and groups of killer whales were resightedĭepredating in different locations up to 268 nautical miles apart. Three socially cohesive groups and at least 44 unique individual sperm whales were Photo-identification data indicate that at least 58 unique individual killer whales from Whale encountered, I collected genetic samples from eight killer and six sperm whalesĪnd applied a satellite tag to one individual of each species. In addition to undertaking effort to photo-identify every killer and sperm June 15 I spent 40 days aboard the fishing vessel, San Aspiring, conducting research
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Patagonian toothfish longliners operating around South Georgia regularlyĮxperience high levels of depredation by killer and sperm whales. This morphotype, referred to here as ‘flat-toothed’ and which in several respects resembles the offshore form in the North Pacific and the Type 1 form in the North Atlantic, does not seem to have been recorded previously from the Southern Hemisphere.
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Although dietary information is scant, one stomach contained the remains of several elasmobranchs, identified from a DNA subsample as blue sharks Prionace glauca, a dietary item that, if habitual, might account for the tooth wear. Adult length is some 1–1.5 m smaller, appendages such as dorsal fin and flippers tend to be relatively larger, and tooth wear is excessive. Until recently, all killer whales in South African waters were referred to a single morphotype, Type A, but three individuals (two males and one female) that have stranded since 1969 differ in several respects from other killer whales examined from the region. Killer whales Orcinus orca occur worldwide in a number of morphotypes that differ in size, pigmentation, acoustic behaviour, food type and genetics – some may indeed warrant subspecific or even specific status.