The Sixgill Shark Research Project is designed to address gaps in the body of scientific knowledge on bluntnose sixgill sharks (Hexanchus griseus) in Puget Sound. This project utilizes three interwoven techniques: (1) genetics research, (2) visual marker tagging, and (3) video analysis. Seattle Aquarium biologists monitor sixgill shark sightings reported by local divers (since 1999) and study their relative abundance in Elliott Bay under the Aquarium’s pier (since 2003). Here we report on our findings of relative abundance.
Bluntnose sixgills are a species of conservation concern. Sixgills are listed as “near threatened” on the IUCN Red List. Living mainly at abyssal depths but also in the shallow waters of the Salish Sea, sixgills are thought to be long-lived and slow-growing, and appear to have established movement corridors and home ranges that remain relatively fixed over time. As apex predators they are important members of marine communities; and, owing to their life history characteristics such as a slow rate of maturity and low reproductive rates, are thought to be extremely vulnerable to exploitation.
Here we present our findings of relative abundance of sixgill sharks in Elliot Bay during the two time periods that the research was conducted: 2003-2005 and 2008-2015. We present the number of individual sharks seen each night, number of sharks tagged, number of returning tagged sharks, sex ratios, estimated number of sixgills residing in Elliott Bay (using capture-mark-recapture techniques), and seasonal and long-term trends in abundance
