Catch Rates and Biological Characteristics of Bluntnose Sixgill Sharks in Puget Sound

The bluntnose sixgill shark Hexanchus griseus is a wide-ranging marine predator and the largest predatory shark in Puget Sound. Biological characteristics of the Puget Sound bluntnose sixgill shark population remain largely undocumented, despite a recent escalation in recreational angling for the species. Standardized longline sampling, supplemented with other opportunistic collections, was used to collect size, sex ratio, and relative catch rate data at three locations during 2006-2008. Fishing trials were also used to examine the effect of soak time, fishing depth, and time of day on catch rates. Captured bluntnose sixgill sharks were exclusively subadults (175-315 cm total length) found in approximately equal sex ratios in all seasons. Catch rates were highest in Elliott Bay, the urbanized port of Seattle, Washington, and were not affected by sampling season. Catch information derived from hook timers implies that the sharks locate and encounter baited hooks relatively rapidly (<2 h); diel fishing trials suggest some trend toward lower catch rates at shallower sites during the day. Data collected in this study provide some basic context for informing management decisions associated with a large marine predator in the Puget Sound-Georgia Basin ecosystem and improve our basic understanding of bluntnose sixgill shark biology in the region.