Lisa Etherington, Research Coordinator
Cordell Bank National Marine Sanctuary
R/V Fulmar heading out the Golden Gate of San Francisco, CA. (Photo: Dale Roberts, Cordell Bank National Marine Sanctuary)
We finally made it out to Cordell Bank today! After two days of working out the kinks in our equipment and operations, it was great to be out on the water and conducting work. We passed under the Golden Gate Bridge in San Francisco around 730am and headed out to meet the open ocean.
We were hoping that calm seas would greet us ‘outside the Gate,’ but instead we were met with some moderate swell and some wind-chop. But, we had to test the offshore waters and motored for almost 2 hours to reach Cordell Bank. Upon reaching the Bank, we were greeted by swooping Black-footed Albatrosses, which skimmed the tops of the 4-5 foot swells.
ROV dragging gear up that was cut below. (Photo: Michael Carver, Cordell Bank National Marine Sanctuary)
The objective of our project was to test various methods of removing derelict fishing gear using an ROV from deep water environments like Cordell Bank. Therefore, we picked out several locations where we knew there was gear (from past submersible dive observations), and chose locations that represented different gear types (including long lines and gill nets), different degrees of entanglement on the bottom, and different types of habitats (flat sand and cobble versus higher relief rock). Today we decided to start with the easiest scenario (long line on flat sand/cobble bottom) and then work our way towards the most challenging.
Derelict gear in bucket on deck of R/V Fulmar. (Photo: Lisa Etherington, Cordell Bank National Marine Sanctuary)
We were happy to discover that we were able to re-locate previously sighted long line gear using the tracking equipment that integrates the ROV’s position underwater (using a beacon attached to the ROV and a hydrophone attached to the boat that listens for the beacon’s signal) with the ship’s position (using GPS-global positioning system). Once on the bottom and near the gear, we went to work at pulling up and cutting the line. The manipulator arm and cutters made it difficult to get close to the bottom and grab the line. Nevertheless, we were able to find some loose sections above the seabed where we were able to make some cuts, and after 25 minutes we freed a section of line about 10m (33 ft) long. The ROV arm grasped the section of line and brought it to the surface our first success!
Crinoids attached to fishing gear. (Photo: Jennifer Stock, Cordell Bank National Marine Sanctuary)
We also were excited to see that there were some animals attached to the line, including soft bodied invertebrates such as crinoids, tunicates, brittle stars, and amphipods. This is the first time that we have ever been able to directly sample and examine any animals on Cordell Bank.
After our first success at long line removal, we decided to move on to a more challenging gear type. We conducted two ROV dives at two other known gear locations to try and recover gill nets. What we encountered were snarled masses of net and lines that were twisted together.
Salmon shark approaches ROV before ROV descends to Cordell Bank. Click here to watch the video. (Movie: Craig Bussel, Cordell Bank National Marine Sanctuary)
Despite multiple attempts, it was obvious that the cutting device on the manipulator arm was not going to be able to penetrate the twisted masses of tangled lines. The ROV returned to the surface without gear on both dives disappointing, but all part of the experimental process.
The highlight of the day appeared in an unexpected place within the water column, not on the seafloor. As the ROV was heading down on the last dive of the day, we caught a glimpse of a dark silhouette lurking up above. We stopped the ROV’s descent to the seafloor at 20m below the surface of the water so that we could investigate further. As we tilted the video camera up and focused on the dark shape, it became clear that we were looking at a large shark.
Sixgill shark approaches ROV. (Photo: Craig Bussel, Cordell Bank National Marine Sanctuary)
But then we were surprised once again there were two sharks! We were treated to some close up shots of the sharks as they made passes by the ROV. Could these be salmon sharks? Or maybe white sharks? We will have to take the videos back to some shark experts in the area to have our identifications verified. But, our shark experience did not end here. Soon after arriving on the seafloor while we were searching for a lost piece of net, a sixgill shark swam straight at the ROV and bumped the lens of the video camera.
Sixgill shark swims up to camera of ROV. Click here to watch the video. (Movie: Craig Bussel, Cordell Bank National Marine Sanctuary)
Once we were back at the dock, the work was not over. We had a small piece of long line that had organisms on it that we needed to store in a saltwater tank before identification and display in an aquarium. So, we made a trip to University of California-Davis, Bodega Marine Laboratory where we placed the line and organisms in an outdoor tank.
New arm on ROV. (Photo: Jennifer Renzullo, Cordell Bank National Marine Sanctuary)
Meanwhile, our operations coordinator had the idea that we could modify the current manipulator arm by adding a different cutting tool to improve its cutting power and efficiency. So, it was off to the hardware store to walk the aisles in search of the perfect tool for attaching to the ROV. Hours later, $14.99 lighter, and several power tools later, the ROV looked spiffy with a new arm configuration
Can’t wait to see how it performs tomorrow let’s clean up the sanctuary!