At least 17 sevengill sharks were killed by two notorious killer whales, Port & Starboard, this week in South Africa. The killer whales only ate the livers of the sharks, with the leftover carcasses washing ashore.
Marine biologist Dr. Alison Kock, from the Cape Research Centre, said that she first observed the pair hunting sevengill sharks in False Bay, Cape Town, in 2015.
Sevengill sharks are named for having seven gill slits on either side of their bodies, they can reach lengths of at least 3 meters with an average length of 1.5 meters and can weigh up to 107 kg. They are known to live as long as 49 years and reach sexual maturity when they reach 1.5 to 2.2 meters in length.
This shark species can be seen in Cape Town in the shallows and in the stunning protected reefs in the Kelp forests along the Cape Peninsula marine reserve. Last year, researchers noted a decline in sharks in the Gansbaai coast area since 2017, as two orcas have killed at least eight great white sharks.
According to a study published in the African Journal of Marine Science, the shark carcasses washed up without their livers and hearts or with other injuries distinctive to the orca pair. Shark experts at the Dyer Island Conservation Trust suggested that the orcas trigger the ‘flight’ response to the fear of sharks when nearby.
The report states that this, in turn, results in their rapid, long-term emigration from the area, creating an opportunity for an influx of new predators to deplete other species. Senior White Shark biologist Alison Towner reported that she has tracked 14 sharks fleeing the areas where orcas are present over five-and-a-half years in a study published today in the African Journal of Marine Science.
Towner also said that “the research is particularly important, as by determining how large marine predators respond to risk, we can understand the dynamics of coexistence with other predator communities. These dynamics may also dictate the interactions between competitors or intra-guild predator-prey relationship.”
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