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At-Sea Detection: Reflections on Our Progress

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We’re coming down to the final days of the guts of this cruise – after tomorrow or early Monday, we’ll be getting south of where the UAS is authorized to fly, and we’re already south of where we expect to find debris accumulations. After that, we’ll keep the Big Eyes crew going (just in case, and because we love it so), but otherwise we’ll just be steaming back to Oahu, which is going to take a few days.

I’m going to start with the good news. The marine debris folks even got on this cruise. That was huge! This cruise “belonged” to the Ecosystems and Oceanography Division of the NOAA Pacific Islands Fisheries Science Center, and they let the marine debris component piggyback on their cruise. Thank you! Evan and Hide were the oceanographers out here, and their part of the cruise went great. The CTD casts were a success, and with the convergence zone farther north than expected, we were even able to go back and cover another degree of latitude yesterday. The small boat crew helped out and the CTD operations were able to go 24 hours a day. That’s a big success, and that’s where this cruise, OES-08-02 started. (If you want to read a comprehensive and funny summary of the CTD operations, you can find it on the NOAA Sanctuaries mission page.)

So, where are we with the piggyback part—the marine debris component? What have we learned? How have we done on accomplishing our objectives? I could go cheat and look at the official cruise objectives, but since I’m not the chief scientist, that’s not what I’m held to. I think of myself as an observer, an interested but not yet invested partner, and someone who’s paying attention to the vibes of the scientific party.

If you Google in search of quotations about expectations, you’ll find a lot of cheerleadery stuff from sports figures and Mary Kay about self-fulfilling expectations, but I’d like to think Benjamin Disraeli got closer to this cruise’s outcomes: “What we anticipate seldom occurs, what we least expected generally happens.” I’ve talked to some of the other warm bodies, as we lovingly refer to ourselves, and to some of the Big Cheeses. Over all, a lot of us expected to find—and remove—more debris. The Big Eyes crew had a contingency for when the debris sightings came in so fast and furious we’d get behind on entering them into the computer. We even had a drill planned to train us—we never needed it. We never got to the part of the cruise that was going to bring back tons of debris and save the corals and monk seals. You better believe that’s a disappointment.

We thought going up to the convergence zone was a dead cert at this time of year. Apparently it wasn’t. I can think of a number of reasons. 1) It only apparently wasn’t. There’s plenty of debris, but we didn’t find it—for any number of reasons. The debris is patchy or the fog and high seas impeded our ability to spot it, or both. Our observing methods were in a testing, not operational mode, and the tests were not completed in time to move into operations. 2) It’s a La Niña year, and the convergence was weaker, so the amount of debris concentration was low this year. 3) Our understanding of how debris moves is incomplete. The Pichel et al (2007) paper gives a good idea of correlation between debris sightings and oceanographic parameters (sea surface temperature and chlorophyll content and gradient), but perhaps the year they flew, 2005, was an atypical year, or maybe 2008 was. (You can find the reference to that paper at the NOAA Marine Debris Program website.) 4) We need to work on our observing methods. Whether there was or wasn’t a lot of debris up there, we weren’t prepared to find it.

My mood? I’m a little let down, perhaps because my own expectations were too high. We all hoped that everything would work out just ideally, and maybe it could have. It’s dispiriting that not one component did, other than the CTDs that were the core of the cruise. We’ve tagged just 2 smallish pieces of debris, with 13 more satellite buoys on board. We’ve picked up less than 10 pounds of debris. The Big Eyes have been plagued by poor visibility, high seas, and lack of debris. The UAS flights have been few and not productive in terms of spotting debris.

In spite of the lack of resounding success, should we try this again? In the words of the Magic Eight Ball, my sources say yes. Not only that, but I say yes. Research is a funny thing. You don’t often get to publish the negative findings, but they’re data too. We’ve found at least one area of expected debris concentration that really didn’t live up to its reputation. When we’re getting giddy on the Big Eyes, we joke about that Texas-sized garbage patch, where it is, whether it exists, if we should plant a Texas flag on a buoy and call it good… Is it good news that we didn’t find debris? Well, it’s not bad news, but we do know that derelict fishing gear is making its way into the Northwestern Hawaiian Islands at a rate of over 50 metric tons per year. No one has estimated how much debris lands on the main islands, but we’ve all seen it and quite a few of us have hauled our share of it. We also identified a number of gaps in our understanding and places we need to hone our techniques.

What preparations should we make for the next try? Here’s my wish list.

I’d like to have aircraft support; maybe have a NOAA, Coast Guard, or military airplane run up to the area of interest just before the ship arrives. They could observe quickly over a large area and point us to areas they see the most debris. That would save us a lot of time steaming back and forth.

Additional ground-truthing of the satellite data the DELI (debris estimated likelihood index) maps rely on, like the shipboard measurements and CTD casts from this cruise, would be valuable. I’d also like a few more tests of the DELI maps with overflights.

It would be ideal to go in an El Niño year, when convergence is strong and the zone is closer to Hawaii. Or at least not during another La Niña.

If we continue to use shipboard observers, we should use the data from this cruise to develop some protocols, and then test them in a variety of sea and light conditions with abundant debris to sight. We’ve discussed doing a blind test comparing the sighting efficiency and distance covered by Big Eyes, hand-held binoculars, and the naked eye.

The UAS testing did not always proceed smoothly. More work needs to be done on making the wing tougher, to take on the wind and sea conditions that are inherent in the convergence zone. The wing has not yet flown autonomously on this cruise, but in order to survey greater distances, it needs to be able to do so. Creating an algorithm to detect anomalies (like debris) in the video feed is a big challenge, particularly if there are a lot of whitecaps. We haven’t seen yet how that will work.

So I close this entry with hopes that we’ll come away from this cruise a lot better prepared to tackle this goal of at-sea detection and removal of marine debris. We’ve learned a lot, figured out some places we still need to learn more, and have gained a huge amount of on-the-water experience, even if it doesn’t feel so much like it tonight. And hey, there are still a few days left before we pull into Pearl Harbor on Wednesday. We could spot Texas after all!


Author: NOAA Marine Debris Program

The NOAA Marine Debris Program envisions the global ocean and its coasts, users, and inhabitants free from the impacts of marine debris. Our mission is to investigate and solve the problems that stem from marine debris, in order to protect and conserve our nation's marine environment, natural resources, industries, economy, and people.

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