The awe-inspiring images here are of a pregnant female bluntnose sixgill shark (Hexanchu griseus) that was found dead on a beach in Alberni Inlet on low tide. She was necropsied by Department of Fisheries and Oceans staff on February 11th 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 (click images to see at larger size).
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 -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 and reaching sexual maturity only between age 18 and 35. It is believed that they may reach 80 years in 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 six gill. It relates that the number of pups carried by females is known from only three previous credible accounts (ranging from 47 to 70 pups of size 61 to 73 cm).
The bluntnose six gill 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 six gill 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 by-catch in longline fisheries. There is no information on the survival rates from by-catch nor is population size and reproductive rate known for this species.
Please read more about the biology and conservation of bluntnose sixgill sharks in the Species at Risk Public Registry. Click here.
See the Alberni Valley News for coverage on this sixgill.
See the Draft Management Plan for the bluntnose six gill shark and tope shark in Canada for natural history information and a summary of threats.