NMFS Scientists Take a First Look at Deep-sea Corals Near the California-Oregon Border

Using an autonomous underwater vehicle (AUV) and cameras, the SWFSC Habitat Ecology Team and colleagues from the Northwest Fisheries Science Center, Pacific Islands Fisheries Science Center, and Oregon State University surveyed deep-sea corals and habitats for the first time in areas of longtime trawl fishing off northern California. During an 11-day cruise aboard Moss Landing Marine Labs R/V Point Sur, the team completed 9 dives with the AUV and 13 deployments of a tethered camera system and spent nearly 45 hours underwater visiting 8 study sites from the Oregon-California border to the Mendocino Ridge at depths of 550-1200 meters.

With perfect sea conditions and fair skies in an area of the coast that is otherwise notorious for foul weather and high swells, the researchers recorded close to 100,000 images of corals, sponges, fishes and other marine life with digital, paired still cameras during daytime operations. At least 20 taxa of corals were observed, including black corals, bamboo corals, and gorgonians, some of which may be hundreds if not thousands of years old. A high diversity of sponges occurred on most of the dives. Relatively few fishes and marine debris were recorded. The ship’s echosounder was used to map the seafloor and sub-bottom geologic structure each night, and water conductivity, temperature and density were measured at each station. These data will help us characterize seafloor habitat types associated with the corals.

Fishermen have long known that corals occur in this area off northern California, having retrieved parts of corals in their fishing nets along with the harvested fishes. Areas of relatively high numbers of corals also have been recorded in NMFS West Coast groundfish bottom trawl surveys. From the exploration of these sites with cameras, we can now determine the extent of these coral colonies for the first time.

The highlight of the cruise was discovering forests of corals on rocky ridges adjacent to the trawl grounds. These areas of rough terrain likely have received less fishing pressure in recent years, with the elimination of large roller gear on the trawl nets.

Further analyses of the images and resultant data from this cruise will improve our knowledge about deep-sea corals off northern California, increase our understanding of the influence of fishing on coral communities, and will inform decisions to protect and conserve these sensitive habitats.

Learn more:

Deep-sea coral survey images

Yoklavich, Mary, M. Elizabeth Clarke, Tom Laidig, Erica Fruh, Lisa Krigsman, Jeff Anderson, Jeremy Taylor, and Chris Romsos. 2016. A characterization of deep-sea coral and sponge communities in areas of high bycatch in bottom trawls off northern California. NOAA Technical Memorandum NMFS-SWFSC-556 (39 p.).
( View report)

Contact: SWFSC Fisheries Ecology Division, Habitat Ecology Team

(October 21, 2014)

Corals and sponges

At least 4 species of deep-sea corals and 2 species of sponges on the seafloor at 780 m depth off northern California.

AUV retrieval

AUV being retrieved onto the back deck of the R/V Point Sur following a 5-hour mission to the seafloor off northern California.