The choice of appropriate tools (technologies), procedures and strategies can make the difference between the success and failure of a research expedition.
Advances in technology provided the impetus for the famous expedition to the North Atlantic on the RV Michael Sars in 1910. The vessel was new. It was equipped with an advanced winch system that enabled the scientists to collect samples at depths that had previously been almost inaccessible. Researchers continue today to study the many of the specimens collected.
Norway has recently built a new research vessel, the RV G.O.Sars. She is equipped with latest generation of modern technology for marine studies, including multifrequency echo sounders for density estimation and species identification (grouping) of plankton and fish, advanced sonar systems, and bottom-penetrating/-mapping sounders etc.
The new vessel can tow large, commercial-sized pelagic and bottom trawls to 3000m depth. It will also carry towed observation and recording systems that facilitate standard echo sounding and density estimation at depths close to 2000m. In addition, it supports standard oceanographic monitoring instruments such as CTDs and ADCPs as well as having a variety of winches capable of supporting the operation of most of the possible towed or lowered observation and sampling systems currently in use or under development. MAR-ECO will use the new G.O.Sars for a two-month cruise during the summer of 2004.
The diversity of marine life in deep water often goes beyond our imagination and many life forms have probably still not been discovered and described. Rigorous documentation of new observations is thus critical, and this requires capability to carry out visual inspection and systematic studies, for example along transects.
Being able to collect simple samples is also of utmost importance for the success of the expedition. This work requires the use of Remotely Operated Vehicles (ROV) and Autonomous Underwater Vehicles (AUV) capable of operating at depth.
Olav Rune Godø, a researcher at the Norwegian Institute of Marine Research, has been responsible for organising many of the technology elements for the G.O.Sars cruise. Godø describes three different data collecting situations: on station, where the boat remains at a particular location while researchers collect data; continuous, where researchers collect data while the boat is in transit; and, stationary, involving the use of buoys and independently anchored data collecting systems to give dial and seasonal changes.
All three systems are necessary, says Godø, to get a 4D picture (latitude, longitude, depth and time) of the deep-sea eco-system.
Trawls are one of the primary “on station” tools. Not only is the G.O.Sars capable of towing commercially-sized trawls as deep as 3000m, but today’s trawls can be outfitted with many other instruments to help scientists gather a more complete picture of the under-water world.
Some trawls involve different nets mounted in series that can be opened and closed at different depths to ensure discrete sampling. In addition, video and photographic equipment can be mounted on the trawl as well as acoustic instrumentation and even CTD instrumentation to monitor water quality data.
Trawls are one of the primary “on station” tools. Not only is the G.O.Sars capable of towing commercially-sized trawls as deep as 3000m, but today’s trawls can be outfitted with many other instruments to help scientists gather a more complete picture of the under-water world. Some trawls involve different nets mounted in series that can be opened and closed at different depths to ensure discrete sampling. In addition, video and photographic equipment can be mounted on the trawl as well as acoustic instrumentation and even CTD instrumentation to monitor water quality data.
The only problem with trawling as a research technique, says Godø, is that it provides only a small, “snapshot” picture of the under-sea world, and, more importantly, each individual trawl takes such a long time to perform – especially deep trawls. In addition, it is not unheard of to lose a trawl, due to the tangling of ropes, or, more commonly, snagging on some kind of obstruction on the bottom. For this reason, it is critical to have experienced technical personnel and high-resolution bathymetric data of the trawl zones.
Towed instrument platforms are another kind of “on station” equipment. These involve arrays of acoustic sensors that can provide “pictures” of biological presences from near the surface to near the sea floor. Work is underway to develop more highly equipped, combination platforms carrying both acoustic and optical instrumentation. MAR-ECO is also investigating a number of optical sensor systems that are currently under development. Two of these were tested last November. Use of these different systems will provide data giving a complete optical profile of any given station.
During station work, researchers will try to optimise effectiveness by “piggy-backing” as many different technologies as possible. For example, an AUV could be deployed to operate simultaneously with a number of the other technologies.
AUVs and ROVs can be equipped with a variety of instruments and sensors (scanning sonar, scientific sounder, visual sensors (camera, video), ADCP, CTD etc.). They facilitates vessel-independent observations in deep water, which is critical for many fragile organisms.
They will be used:
• to extend the water depth of acoustic observation by providing visual confirmation of recordings
• to obtain detailed study of interesting acoustic scatters of fish and plankton through close-up recording of acoustic properties and visual appearance
• to engage in autonomous operations while the research vessel is conducting other studies
The new G.O.Sars is particularly well equipped to collect acoustic data. A new multi-frequency sensor can record data at six different frequencies. This is important, explains Godø, because within the marine eco-system, different species of fish respond differently to different frequencies. Experienced researchers are able to analyse the complex acoustic data and come up with a fairly good picture of what kind of fish are present, how large they are and how many are present. The researchers at the Norwegian Institute of Marine Research have accumulated many years of experience collecting and analysing acoustic data, as well as collaborating with industry to develop better sensors. Much of the data is collected in areas where trawls are also conducted, giving concrete samples to back up the data results.
In addition to the hull-mounted sensors, the new G.O.Sars is equipped with two independent drop keels equipped with a number of acoustic sensors, and double sonar. The drop keels can be drawn up into the ship for servicing or modification. Drop keel-based sensors will significantly extend to G.O. Sars’ ability to collect data.
Hull-mounted transducers function perfectly adequately in calm waters. However, in bad weather (high winds, storms), turbulence along the hull surface produces a layer of bubbles which interferes with sound propagation. These bubbles confuse the transducer recording system and the data recorded under such conditions will imply that fewer fish are present.
The G.O.Sars is also equipped to tow acoustic arrays that will provide complementary acoustic information gathered up to 1500m deep.
In addition to conducting acoustic studies to “count” organisms, the G.O.Sars is well equipped to conduct bottom mapping studies using a variety of echo-sounders. As mentioned before, the detailed picture of the sea-floor gained from this data is critical to some of the other research work, such as trawling.
The G.O.Sars has another special feature that will enhance its data collecting capacity. It has diesel-electric propulsion to optimise noise reduction. Fish have different hearing thresholds, but most fish are adversely affected by conventional engine noise. They respond to engine noise by diving and swimming away.
Echo sounders cannot take into account body angle, and so schools of diving fish will give off fewer signals, which also will show smaller fish. In addition, the diving fish may move out of the field of measurement and thus miss being counted.
A combination engine, such as the one used on the G.O.Sars, using both diesel and electric power, produces less noise and is less disruptive to normal fish behaviour less giving more accurate data on deep-sea fish behaviour and numbers.
Another “continuous” activity will be that of traditional counting. Mammal and seabird researchers have put together a project to take advantage of the unique opportunity afforded them by the MAR-ECO Project to observe mammal and seabird behaviour in the waters around such a major topographical feature as the mid-Atlantic Ridge. Are they particularly concentrated in the mid-Atlantic Ridge area?
A critical element of the MAR-ECO Project is the development and deployment of stationary instrument packages. In this regard, Godø is pleased to report that the Norwegian international corporation KONGSBERG SIMRAD has decided to become a MAR-ECO Industry Partner.
KONGSBERG SIMRAD is a major contributor to the wide range of acoustic instruments onboard the new Norwegian Research Vessel, the G.O. Sars, and has now granted the MAR-ECO project three transceiver units with split-beam transducers for use in seabed-mounted observation platforms. The plan is to place these three units at selected locations in the MAR-ECO area, at about 1000m depth, where they will monitor and log vertical distribution and abundance of sound-scattering animals for an extensive time period.
This long-term data is vitally important to complement the data gathered during cruises, says Godø. How do patterns of animal movement change during daily 24-hour cycles, and over longer seasonal cycles?
The MAR-ECO Project has also put together acoustic instrumentation (standard echo sounders and ADCP) with other physical sensors (CTD) in instrument packages that can be installed on merchant vessels that regularly traverse the mid-Atlantic Ridge.
The two-month G.O.Sars cruise is only one of the planned MAR-ECO cruises. Relatively few MAR-ECO scientists will actually go to sea, but all will have access to the enormous volume of data that will be collected. Some of the data will be used to try to identify and characterise new species. Some will be used to further understanding of life-history patterns. Some will be used to build up eco-system pictures: who is there? how many organisms are there? where are they going? who is eating whom?
While MAR-ECO researchers thus far have largely been focusing on research questions to be answered in the field, they are now beginning to consider the many questions that can be addressed in the data analysis period that will follow the field phase. Much of the information collected can be used in many different contexts. If researchers are still analysing data and specimens collected in 1910, with the equipment available at that time, imagine how long they will be able to analyse the data collected during the MAR-ECO cruises!
Another important follow-up task for MAR-ECO researchers is to collate the data into an overall picture of the biodiversity of this deep-sea ecosystem in order to be able to advise governments and regulation bodies about its sustainable development.