COW SHARK or BROADNOSE SEVENGILL COW SHARK – Notorynchus cepedianus.
Sevengill cow sharks belong to the group of sharks known as Hexanchiformes, which consists of six species with either six or seven pairs of gill holes (most other sharks have five). The absence of a first dorsal fin in all species is the easiest way to identify these creatures. The broadnose sevengill cow shark is the Hexanchiformes species that divers are most likely to encounter in shallow seas above 50 meters. The body’s colouring ranges from dark brown to black and grey, with an underside that is mottled with white and grey. Individual sharks can be recognized by their body’s pattern of dark and light patches. Around one-third of the body length is made up of the caudal fin’s upper lobe.
Biology of the Sevengill Cow Shark
Broadnose sevengill cow sharks, attain at least 3 m in length and weigh more than 100 kg. They have been recorded to live as long as 49 years and are believed to achieve sexual maturity around 1.5 to 2.2 m in length. A versatile predator, sevengill cow sharks eat a diverse range of prey, including fish, cetaceans, rays, and other sharks. Although the species frequently engage in scavenging, it is also believed that it is an active ambush predator that hunts seals.
Behaviour of the Sevengill Cow Shark
In southern Africafrom East London to Namibia, cow sharks are a common sight. For many years, Cape Town has been known as one of the best places to go shark diving. Up to 30 animals have been observed in a small kelp forest at the dive site at Millers Point. Due to the rarity of sightings today, the cause of these gatherings is not well understood and may never be. Sharks have been driven out of the area by recent orca activity. It’s unclear why they haven’t arrived back. Nowadays, Seal Island in False Bay is where cow shark sightings are most prevalent. Since the white sharks have vanished from the Island, it appears that cow sharks are now acting as the top predators in that ecological niche.
Orca predation on sharks
7 Dead sevengill cow sharks were discovered in 2015 at the Millers Point dive site. At first, we suspected human action, but upon closer inspection, orca predation was amply demonstrated. The body’s bruising from teeth was the most visible sign. It was discovered that the livers had been removed after discovering that all of the deceased sharks had been torn open at the gills (the only part eaten). The jaws and the spacing between the teeth marks were likewise consistent with orca measurements. Although no one was present to witness the attacks, Port and Starboard, two male orcas, have been seen multiple times in the region (due to their bent dorsal fins – one bent to the port side and one to the starboard). What was the connection between the absence of white sharks from Seal Island, some 9 km away, and the cage diving companies reporting it the same day? In the years that followed, it became abundantly evident that these two orcas had developed into expert shark hunters who were remarkably attuned to the motions of both great white sharks and sevengill cow sharks. The sharks disappear whenever Port and Starboard are spotted.