Sharks Among Us #2 – The Bluntnose Sixgill Shark
[Update February 2019 – Another pregnant female Bluntnose Sixgill Shark has been found – February 5th, in Coles Bay, North Saanich, southern Vancouver Island, British Columbia. Original blog about a pregnant female found in 2011 follows after the first two photos.]
The awe-inspiring images below are of a pregnant female Bluntnose Sixgill Shark (Hexanchu griseus) that was found dead on a beach in Alberni Inlet on low tide in February of 2011. She was necropsied by Department of Fisheries and Oceans staff and there were no obvious indications of how or why she died.
The information has been generously shared by federal shark biologist with the Pacific Biological Station, Romney McPhie.
This female Sixgill was 4.2 metres and was estimated to weigh 569 kg (1254 lbs). As a viviparous shark species, she carried her embryos through the entire 12 to 24 month gestation period (species does not lay eggs / egg cases). She may have given birth to some prior to her death and still had 28 pups inside her. If she did indeed give birth, these pups would likely survive.
Sixgill Sharks have been reported to be up to 4.8 metres in length with females being larger than males (females to 4.8 m and males to 3.5 m).Age fo sexual maturity is estimated to be between age 11 to 14 for males and between 18 to 35 years for females. It is believed that life expectancy may be up to 80 years of age.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) 2007 assessment report on the Bluntnose Sixgill puts into perspective how rare an opportunity it is to learn about a pregnant Sixgill. It relates that the number of pups carried by females is known from only three previous credible accounts (ranging from 47 to 108 pups which are 61 to 73 cm in size).
The Bluntnose Sixgill Shark is an extremely cryptic species that can dwell at depts up to 2,500 m. So little is known about them and (sigh) they are “near threatened” globally and are a species of “special concern” in Canada.
I have had the incredible privilege of seeing a Bluntnose Sixgill Shark while diving and felt like I was in the presence of greatness. They are living fossils, perfected by 200 million years of adaptation. They are amazingly graceful with large, luminous and intensely green eyes.
They are of absolutely no threat to humans and, like all sharks, have an essential role in marine ecosystems. As top-level predators, sharks strongly shape food webs and the loss of such predators has proven to have profound effects on the number and diversity of other species.
We however are a threat to them. It is reported that in just three years (2006 to 2009), 1,341 Sixgills were bycatch in longline fisheries. There is no information on the survival rates from bycatch nor is population size and reproductive rate known for this species.
Please read more about the biology, threats and conservation of Bluntnose Sixgill Sharks:
- Government of Canada Management Plan for the Bluntnose sixgill shark (Hexanchus griseus) and tope shark (Galeorhinus galeus) at this link.
- Species at Risk Public Registry at this link.