Citation: Yoklavich M, Clarke ME, Laidig T, Fruh E, Krigsman L, Anderson J, Taylor J, Romsos C. (2016) A Characterization of Deep-Sea Coral and Sponge Communities in Areas of High Bycatch in Bottom Trawls off Northern California. NOAA Tech Memo NOAA-TM-NMFS-SWFSC-556.

At a glance: 

Using an autonomous underwater vehicle (AUV) and towed camera system (TCS), deep-sea corals, sponges, and seafloor habitats were visually surveyed for the first time in areas of longtime trawl fishing off northern California. During an 11-day cruise aboard the R/V Point Sur 8-18 September 2014, researchers completed 6 dives with the AUV and 9 deployments of the TCS, and spent over 42 hours underwater at depths of 586-1169 meters from the Oregon-California border to the Mendocino Ridge. 

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 over 60,000 images of corals, sponges, fishes and other marine life with digital, paired still cameras during daytime operations. Nearly 48,000 corals from at least 23 taxa were observed, including black corals, bamboo corals, and gorgonians, some of which may be hundreds if not thousands of years old. Sponges occurred on most of the dives, with a total of 5,200 individuals represented by 13 taxa. Relatively few fishes (mostly thornyheads) and marine debris were observed. The ship's echosounder was used to map the seafloor and sub-bottom geologic features each night; water conductivity, temperature, dissolved oxygen, and depth were measured at each station. These data will help us characterize seafloor habitat types associated with the corals and sponges.

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 have begun to 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, as well as continuing these surveys, 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.

  • Technical Report
Type: DSCRTP Supported Date: 2016

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  • Pacific Council
  •  None Defined.