HURL 2002

ROV Dive (9/17/02)
Posted by Rachel Shackelford

We are at Raita Bank now. The skies were gray both today and yesterday. The seas are a bit uglier than they had been, but they seas aren't too bad. The waves are choppy but not very big. We saw a fishing boat when we first got here late Saturday afternoon. Chris Kelley talked to one of the fishermen on board; he said that they didn't catch anything and said that we should check out a pinnacle just north of Raita. We were going to try to do an ROV dive there, but technical difficulties have ruled that out.

We were particularly interested in checking out the dive site, considering that someone had just been there and wasn't able to catch anything. Sure enough, on the first sub dive they only saw a handful of onaga, some kahala, and some hapu'u. Not nearly as many fish as we had seen at Brooks. The first dive was a just north of the primary dive target, so we made a point to go closer to the target on the second dive, thinking that there might be more fish there. Again, the observers reported a handful of fish, but not very many. Some of us were wondering if this lack of abundant fish counts might point to an overfishing problem in this area. It is not that clear cut, however. The observers did not see much in the way of fishing debris, e.g. fishing line, anchors, etc., that might suggest such a thing. Furthermore, there seemed to be plenty hapu'u (Hawaiian groupers) in the area. If it were overfished you would expect the hapu'u to be depleted as well. This area was also very sandy without many rocks or ledges for fish to hide under, so maybe it just isn't a very good habitat for many fish. Just goes to show, you can't jump to conclusions about anything in science, there are always several factors to consider.

The primary submersible dive site at Raita is on the east bank. The first ROV dive at Raita was also on the east bank. On the second night we conducted two ROV dives on the west side of Raita. The first dive was shallow, only 150 to 200 m, and the second dive was deep, up to 800 m. As soon as we got to the bottom we knew it would be a good dive. There were animals everywhere! We had a hard time deciding what we wanted a close-up of first. Big purple holothurians (sea cucumbers) were scattered in the sand as far as we could see. We got good close up images of at least two macrourids (rat tail fish) that HURL has never seen before. Chris Kelley (HURL's program biologist) was really excited as he pointed out one target after another in rapid succession. Just as we were coming up slope and started seeing some rocks, one of the ROV pilots noticed something wrong with the winch. The ROV cable wasn't lying down properly on the spool. The level winder, a contraption that moves back and forth in conjunction with the winch to ensure that the cable rolls up evenly on the spool, was jammed against one side. If we tried to wind up the cable to bring the ROV in, it would just pile up on itself and run out of room. We had the captain steer the ship out toward deeper water so that the ROV crew could go to work on the winch. Meanwhile the ROV was too deep to reel back into its cage since part of it doesn't work below 400 m. So someone had to stay at the main control console to keep the vehicle under control while others worked on the winch. The ROV crew was eventually able to free the level winder and devise a way to lay the cable down evenly. It took them nearly 3 hours to get the ROV back on board, when it normally takes about 20 minutes.

A spectacular ROV dive ended too early, and the ROV pilots had a lot of work ahead of them... but that's how it goes. At least we didn't have to resort to cutting the cable and leaving the ROV on the bottom!