Characterization of Cordell Bank and Continental Shelf and Slope: 2021 ROV Surveys, 2010-2021

Greater Farallones and Cordell Bank National Marine Sanctuaries coordinated a joint cruise to survey Cordell Bank National Marine Sanctuary, Greater Farallones National Marine Sanctuary, and northern Monterey Bay National Marine Sanctuary using a remotely operated vehicle in August 2021. This report summarizes the four remotely operated vehicle dives completed in Cordell Bank National Marine Sanctuary. The objectives of these dives were to survey soft sediment habitat on the shelf in areas expected to have varying trawl intensity, to explore a new area of the slope to characterize habitat, and to return to a previously surveyed area on Cordell Bank to monitor for changes. Data collected included visual imagery (stills and 6 hours of video); oceanographic metrics from a conductivity, temperature, and depth sensor; and navigational information. On the area of the slope that was explored, the majority of low-relief rock and mixed substrates were mud-draped, and few corals and sponges were observed. The flat rock with overhanging shelfs and bands of jagged rocks the size of cobbles provided excellent habitat for fish, particularly high abundances of blackgill rockfish (Sebastes melanostomus). On the shelf, all substrate was characterized as mud, and sea pens and flatfish were present in typical densities in both the trawled and non-trawled areas. Throughout the surveys on the shelf and slope, there were abundant dead pyrosomes on the seafloor that were predated on by brittle stars, sea stars, and urchins. At the North Point monitoring site on Cordell Bank, densities of indicator species such as hydrocoral (Stylaster californicus), strawberry anemone (Corynactis californica), and various sponges were similar to previous surveys (2017 and 2018). The extent of encrusting tunicates and size of rockfish at Cordell Bank were also assessed. Conducting remotely operated vehicle surveys helps expand understanding of the patterns in habitats and species diversity and richness to inform effective sanctuary research and management.

Key Words

California continental shelf and slope, Cordell Bank, deep-water benthic habitats, corals, sponges, rockfishes, national marine sanctuaries, remotely operated vehicle