COBA 2’s marine drones on the hunt for marine litter in the Azores Archipelago
Having tackled the north to south crossing of the Atlantic from Greenland to the Azores, we arrived on Ile de Flores Island in August 2017 with our two Autonomous Surface Vehicles (ASVs), Hektor and Igor. The aim of the second part of the expedition was to investigate the problem of plastic pollution in the Azores Archipelago, and our ASVs ability to detect and collect marine litter.
The Azores archipelago is located in the northeastern Atlantic Ocean about 1,500 km from the Portuguese mainland and about 3,900 km from the east coast of North America. A small paradise with great natural landscapes, its economy is mainly based on agriculture, fisheries and tourism to support its 250,000 inhabitants. Sadly, the entire archipelago is prone to marine litter accumulation, particularly lightweight plastic[1], due to its close proximity to the North Atlantic Gyre and the shape of the nine islands, which forms a natural net for marine litter.
Plastic is the most predominant type of litter found in the Azores, on both a micro and macro scale, along with glass, metal, paper, rubber and derelict fishing gear[2]. The majority of the litter in the Azores Archipelago is thought to originate from sea and land based sources from other regions[3], having been carried along by the gulf stream and then swept into the north Atlantic subtropical gyre, before finally ending up on the beautiful Azorean beaches.
The nine islands of the Azores (google maps)
Illustration of the World's ocean currents
(seachangeproject.eu)
Close up view of the North Atlantic subtropical gyre [4]
Investigating the extent of marine litter: Ile de Flores, lle de Faial & the Faial-Pico passage
The first test for our ASVS was at the beach next to Lajes harbour, Flores Island.
The bay remained shallow (1.2 to 6 metres) until 1.5 km from shore, the maximum working distance for our ASV.
Bathymetry of Lajes taken by Hector, one of our ASVs
To see if there was any litter on the seafloor, the objective was to command the ASV to take underwater imagery and transmit this back to the control station, while autonomously following a set of waypoints. The images taken by our ASV were very clear; at this point the depth was 6 metres:
Underwater images taken by a 5 MPX camera, Lajes bay
Although we didn’t spot any marine litter during this particular sample of Lajes beach, we conducted the same test in the marina of Horta (Ile de Faial) and found a surprising amount of waste on the seabed:
We can compare our findings of litter on the seafloor in the Azores to that of a recent study by Rodriguez and Pham[8]. Using a Remotely Operated Vehicle (ROV) and a manned submersible, they took images at depths ranging between 40 and 525m in the Faial-Pico passage, collecting 45.2 km of video footage. They found the most litter between 151 and 250 metres, with derelict fishing gear, mostly made of plastic, representing 64% of all items found.
Here is a example of the images they took:
Their results highlight that more research needs to be done to investigate the amount of litter on the seafloor and the effect this has on benthic organisms (creatures that live on the seabed) and other marine fauna.
The imaging technology used in this study is a non-intrusive method for the detection of marine litter, that does not remove benthic organisms or cause damage the environment. However, it is expensive to purchase, deploy and run manned submersibles and Remotely Operated Vehicles (ROVs), and both devices have their limitations. Manned submersibles are large and require a human crew, while ROVs are tethered vehicles, resulting in a lack of freedom due to the ROV’s cabled connection to the control ship. Also, the effectiveness of an ROV can be limited by water turbidity, and the ROV motors themselves may disturb the sea bottom sediments.
We believe that with further developments, our open source, low cost ASV could be a viable alternative to manned submersibles and ROVs. Costing 10 times less than a basic ROV to build - our ASV retails at 2,500 euros - our ASV proved to be reliable and robust, producing steady images which were streamed back to the control station in real time without any delay.
We are currently developing a drop-down system for our camera, with the aim that our ASV will be able to take images at a maximum depth of 100 metres, while streaming the live data back to the control station.
Here is an example of the underwater video footage taken by Hektor at a depth of 7 metres in Horta Marina, Ile de Faial:
Surface and shore based marine litter
Considering the 2017 findings of Rodriguez and Pham[8] in the Faial-Pico passage, we sailed in the same area and came across many bands of marine debris floating like a 'mini gyre' one mile offshore. Deploying Hecktor, our ASV, we were able to collect various plastic filaments using the collection tray, while larger plastic items had to be fished out of the sea by hand from onboard our sailing boat.
Along with finding marine litter on the seabed of Ile de Faial, and floating waste in the Faial-Pico passage, we also collected plastic waste from the beach Praia de Porto Pim, on Ile de Faial.
Praia de Porto-Pim is a semi-enclosed bay facing the south west, at 292 metres long. Dunes, vegetation, cliffs and low sea exposure provide shelter that traps and retains marine waste, making it an ideal beach for debris accumulation. Strong south westerly winds bury marine litter in the sand and vegetation, which is only released in favorable conditions such an opposite wind direction, high tide and strong rain.
Praia de Porto-Pim is therefore an ideal net for plastic waste, as shown by our findings during a 30 minute beach clean:
Plastic waste collected from Praia de Porto Pim, Ile de Faial
In 2015 Pieper[10] conducted a study on Praia de Porto Pim, performing 10 random transects on the beach over a seven month peroid. She collected waste between 2-30 cm long, categorising her finds as either plastics, cloth/fabric, glass, metal, rubber, processed lumber or other material. Plastic accounted for 96% of the waste she found at Praia de Porto Pim, while glass accounted for 3%. 71% of all the waste found was recognized as land based debris that originated far away from the Azores and Portuguese mainland, highlighting just how much plastic is floating within the North Atlantic Gyre.
We were therefore not surprised when we collected another bucketful of plastic waste within 30 minutes of visiting Lajes beach on Ile de Flores, following a night of strong winds (25 knots) and heavy rain:
Findings from a 30 minute beach clean at Lajes beach
It appears that wind and tide are the greatest energy forces which impact the arrival of marine debris on beaches, while physical features of the beach - typography, orientation & sediment - and meteorological factors - wind, storms & oceanic swell - influence the variability of debris found on beaches.
Like Pieper's 2015 study, both our beach cleans at Praia de Porto Pim (Ile de Faial) and Lajes (Ile de Flores) consisted mainly of plastic waste, followed by glass. We found the majority of plastic fragments along the tidal line or further up the beach in the vegetation, while heavier items such as glass and macro debris tended to be closer to the water, buried under sand and pebbles.
While we were staying on Ile de Flores, we also noticed a significant amount of wood and plastic debris floating on the surface of the marina after a particularly windy night. We were able to successfully collect this waste using our ASV’s collection tray, thanks to its small size and manoueverability:
Cleaning up the marina at Lajes with Hektor, our ASV
The tests we carried out confirm that a large amount of plastic waste can be found floating around the Azores Islands, on the beaches, and also within their marinas. Our ASVs proved capable of collecting debris from closed waterways and open water (when deployed from another vessel), both autonomously and under remote control. If deployed in large numbers in conjunction with local cleanup efforts, our ASVs could have a positive impact on reducing the amount of plastic waste present on the beautiful beaches and surrounding waters of the Azores.
Hector working autonomously to collect marine debris in the Faial-Pico passage
Conclusion
Our expedition in the Azores proved that our Autonomous Surface Vehicles are robust, reliable and energy efficient. We were able to deploy our ASVs in small waves, with our control station emitting instructions to the ASV from both on-land and from a sailing vessel. When fitted with a collection tray, our ASVs were capable of collecting floating waste, successfully 'cleaning' the marina in Ile de Flores and collecting plastic fragments floating one mile offshore in the Faial-Pico passage. If deployed in large numbers in conjunction with local clean up efforts, our ASVs could help reduce the amount of marine debris in the Azores.
When fitted with a waterproof camera, our ASVs could be useful to researchers and marine biologists, as imaging is a non-intrusive research method that does not remove benthic organisms or damage the environment [11]. Our 5 MPX cameras proved reliable in taking imagery of the seabed up to a tested depth of 7 metres, when the ASVs were deployed either from land or from a floating vessel. Our ASVs were able to record video and follow a route autonomously up to a distance of 1.5 km from the control station. Using our ASVS, we detected plastic waste on the seabed of the marina in Horta, and viewed clearly the fauna on the seabed in Lajes, Flores Island.
We are currently developing a 'drop-down system' which we hope will allow us to submerge a camera to a depth of 100 metres, making our ASV an invaluable tool to researchers investigating litter on the seafloor, studying delicate strcutre-building organisms such as cold-water corals, algae, or researching topographically complex areas.
Finally, our ASV also proved capable of taking bathymetric readings in smooth to slightly rough sea states, up to a maximum of 15 knots of windspeed, proving to function in water temperatures ranging from 2.8°C / 37°F (Greenland, August 2017) to 25°C / 75.5°F (Azores, September 2017).
Since finishing our expedition, we have been busy producing our ASVs as a kit version, which will be available as of January 2017.
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References
[1] Seachangeproject.eu
[2] Monitoring marine debris in two sandy beaches at Faial Island – Azores: Pieper, 2013
[3] Marine litter Accumulation in the Azorean Archipelago: Azorlit Preliminary Data: Frias et al, 2016
[4] Tracking the long-distance dispersal of marine organisms; sensitivity to ocean model resolution: Putman &
He, 2013
[5] Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins: Pham et al, 2014
[6] Increase of litter at the Arctic deep-sea observatory HAUSGARTEN: Bergmann and Klages, 2012
[7] Increase of litter at the Arctic deep-sea observatory HAUSGARTEN: Bergmann and Klages, 2012
[8] Marine litter on the sea-floor of the faial-Pico passage, Azores Archipelago: Rodriguez et Pham, 2017
[9] Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins: Pham et al, 2014
[10] Monitoring marine debris in two sandy beaches at Faial Island – Azores: Pieper, 2013
[11] Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins: Pham et al, 2014
[12] Methods applied in studies of benthic marine debris: Spengler & Costa, 2008
