September 29, 2026 — Bluntnose sixgill sharks are something of an enigma, even to scientists who study them. Using data collected over more than 20 years, scientists have learned that the Salish Sea, including Puget Sound, comprises one of the world’s few known pupping grounds for the species. Typically researchers see and catch only younger animals in relatively shallow, nearshore habitats. Only through unusual events, such as the stranding of female sixgills in 2007 and 2019, have researchers accessed adults for study.
Northwest Fisheries Science Center research fisheries biologist Kelly Andrews works with other scientists from the Seattle Aquarium and Washington Department of Fish and Wildlife studying sixgills in the Salish Sea. The team recently reported on the genetic analysis of 274 sixgill tissue samples collected over 16 years. It revealed that litters of pups such as those collected from the stranded females had multiple fathers. That shows that females mate with multiple males during breeding seasons, a strategy that increases genetic diversity.
They also found that sixgills collected over more than a decade were closely related. This indicates that relatives such as half-siblings, grandparents and grandchildren, and aunts and uncles return to the Salish Sea over successive years and decades. These repetitive movement patterns increase the connectivity between offshore and estuarine habitats and food webs. As top predators and their offspring migrate across ecosystems, they potentially prey on species we manage and species we are responsible for conserving. They also bring with them and transfer nutrients and contaminants across the systems. Understanding the interconnectedness of ecosystems is a key tenet of NOAA’s Ecosystem-Based Fisheries Management policy that helps maintain resilient and productive ecosystems across the U.S. West Coast.
We asked Kelly Andrews what the new findings tell us about this mysterious species.