The bluntnose sixgill shark proliferates in tropical and temperate seas throughout the world but are identified within the Species at Risk Act (SARA) as a species of Special Concern in Canada (DFO, 2011). On February 5, 2019, the carcass of a four-metre-long bluntnose sixgill shark (Hexanchus griseus) was discovered on the shore of Coles Bay, North Saanich (Lawrence, 2019). While the deepwater shark is considered common in the waters of British Columbia, it is typically found in depths of 200 metres with the capability of diving to depths of 2000 metres. Sixgill sharks habitually remain close to the seafloor but have been observed in higher water columns in the Strait of Georgia region during summer months, likely facilitating the reproductive cycle or a thermocline response (Comfort and Weng, 2015). A separate study conducted by Dunbrack and Zielinski (2002) did not observe any sixgill sharks in the Georgia Strait between October and May. The shallow waters of Coles Bay holds potential as important nursing grounds for the sixgill sharks, but breeding data is notably limited on this species (Ebert, 2002).
I had heard on Chek News of a rare shark observation at Coles Bay, approximately 3km from my childhood home in Sidney. I had the opportunity to visit the site on 6 Feb, 2019 with a school friend and her daughter, which happily coincided with the booming popularity of a song called “baby shark. What we witnessed was nothing short of both tragic and spectacular; dozens of baby sharks released from its mother upon the beach. As I later learned, this was a rare, but no completely unexpected occurrence.”Observation of a deceased pregnant shark in February is uncharacteristic given what has been recorded regarding diel vertical movement and thermo response patterns. With no evidence of trauma, it is assumed that trouble was experienced while attempting birth. While it is likely that the death is related to environmental changes, questions remain concerning a pregnant shark appearing in such shallow waters during the winter period. Ebert (2002) observed that the typical pupping period occurs in the late spring to summer period and while male sharks consistently maintain depths in excess of 300 metres, females may venture slightly shallower. While there are currently no reliable indicators to estimate bluntnose sixgill shark abundance in Canadian Pacific waters, an index from a single sampling site approximates a decline of 90% in abundance of immature sixgill sharks over 5 years (DFO, 2011). I assert that this knowledge gap has led to an underestimation of the impact of climatic events upon this species population, both here on Vancouver Island and globally. The uncertainty linked to this specific occurrence represents a lack of information surrounding sixgill shark patterns, which renders research scientists on Vancouver Island uniquely postured to examine social and biological patterns in accessible waters.
Dr Jackie King, University of British Columbia and Department of Fisheries and Oceans Research Scientist, is the lead for the Canadian Pacific Shark Research Program. Dr King was consulted on this observation, stating that sixgill sharks are typically found in extremely deep water off the BC coast. The Strait of Georgia is one of the only locations in the world where juvenile sixgills can appear in shallow waters, likely as a nursery grounds for birthing. It is not frequent for a sixgill to wash ashore, but can occur.
References
Dunbrack, R., & Zielinski, R. (2003). Seasonal and diurnal activity of sixgill sharks (Hexanchus griseus) on a shallow water reef in the Strait of Georgia, British Columbia. Canadian journal of zoology, 81(6), 1107-1111.
Ebert, D. A. (2002). Some observations on the reproductive biology of the sixgill shark Hexanchus griseus (Bonnaterre, 1788) from South African waters. African Journal of Marine Science, 24, 359-363.
Fisheries and Oceans Canada (DFO). (2011). Management Plan for the Bluntnose Sixgill Shark (Hexanchus griseus) and Tope Shark (Galeorhinus galeus) in Canada. Species at Risk Act Management Plan Series. Fisheries and Oceans Canada, Ottawa. Retrieved from https://www.sararegistry.gc.ca/virtual_sara/files/plans/mp_griset_milandre_bluntnose_tope_0112_eng.pdf.
Bluntnose sixgill shark
