Diel activity patterns of sixgill sharks, Hexanchus griseus: the ups and downs of an apex predator

New record and morphometry of the bluntnose sixgill shark Hexanchus griseus (Chondrichthyes: Hexanchidae) in Baja California Sur, Mexico

“…Such conditions coincide with the known habitat of H. griseus in its area of distribution, i.e., hypoxic environments with low temperature and high hydrostatic pressure (Compagno, 1984;Barnett et al, 2012). Although this species mainly inhabits the continental slope, juveniles have been reported to make incursions into neritic environments (over the continental shelf) during the night, when they undergo vertical migration possibly related to feeding (Compagno, 1984;Andrews et al, 2007Andrews et al, , 2009Andrews et al, , 2010Comfort, 2012). The caught specimen was dark grey without spots on the back and white on the belly, with no clear boundary between the two colours (Fig.…”

Relatedness and polyandry of sixgill sharks, Hexanchus griseus, in an urban estuary

“…It is likely that many of these sharks are at least 5 years old based on observations that pups are born at *70 cm (Fig. 2) and then double in size during their first year of life (Ebert 2002(Ebert , 2003, and growth for a 200 cm shark is thought to be approximately 12-13 cm/year based on one individual recaptured after being at liberty for 29 months (Andrews et al 2009).…”

“…Andrews et al (2007) found that juvenile sharks in Puget Sound remain within relatively small areas at certain times of the year, with the maximum displacement being 8.4-29.2 km. Some half to full sibling sharks have also been acoustically tracked together making simultaneous vertical movements over 24-hour periods (Andrews et al 2009). Thus, it appears that individuals within the same litter, even half siblings, may associate with one another for long periods of time.…”

“…They are thought to be benthic and are generally found in deep water (Castro 1983). However, they have been observed in relatively shallow waters (less than 20 m) in Puget Sound, WA and British Columbia (Castro 1983;Rupp 2001;Dunbrack and Zielinski 2003;Andrews et al 2009), and have been caught in water as shallow as 30 m in the Mediterranean Sea (Capapé et al 2004). Acoustic monitoring data suggest that sixgill sharks inhabit Puget Sound waters for several years as juveniles, making small seasonal migrations between a couple core areas before leaving Puget Sound for the open coast .…”

“…Acoustic monitoring data suggest that sixgill sharks inhabit Puget Sound waters for several years as juveniles, making small seasonal migrations between a couple core areas before leaving Puget Sound for the open coast . Sixgills within Puget Sound display diel vertical movement patterns throughout the year, as they move from deeper to shallower waters at night, most likely following the movement patterns of prey (Andrews et al 2009). Utilization of shallow water habitat observed in Puget Sound may negatively affect sixgill populations over time due to exposure to polluted effluents and the potential for over-harvest by recreational and commercial fishers causing local extirpations (Rupp 2001).…”