Finding Nemo 7
Previous Nemo Chronicles: * 1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 * 9 * 10
To explore deep sea habitats and biodiversity in the Tasman Sea, a joint Australian-New Zealand research voyage carried leading Australian, New Zealand and other international scientists to uncover new marine species and habitats. The NORFANZ research voyage explored deep sea habitats around seamounts and abyssal plains around Lord Howe and Norfolk Islands through to northern New Zealand. The voyage collected biodiversity samples, DNA tissue samples, seabed habitat data, photographs and video on seamounts at depths between 200 meters and 1.2 kilometers, and surveyed free-swimming animals that live in the water masses above and around these seamounts. Australia's National Oceans Office - the body responsible for developing and implementing Australia's Oceans Policy - and the New Zealand Ministry of Fisheries supported the four-week voyage between 10 May and 8 June.
With cooperation from the National Oceans Office , the NASA-sponsored Astrobiology Magazine chronicles the scientific notes written by the researchers onboard. As the director of the Hayden Planetarium, Neil Tyson, wrote about the marvels of biodiversity: "I do not know whether biologists walk around every day awestruck by the diversity of life. I certainly do. On this single planet called Earth, there co-exist (among countless other life forms), algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. Imagine these seven living organisms lined up next to each other in size-place. If you didn't know better, you would be hard-pressed to believe that they all came from the same universe, much less the same planet".
The main goal of the summer expedition mirrored that sentiment: to provide baseline information on the, nature and potential vulnerability of these unique habitats and their biodiversity. The results will give scientists interested in biodiversity a much better understanding of the species that live on and around the deep seamounts and ridges throughout the Tasman Sea, many of which were new to science. The information will also enhance and contribute to international collaboration in oceans management.
Day 19, 28 May 2003.
Mark Norman, Museum Victoria
Slightly larger swell (3+ m), 25 knot SE wind, 16 ° C
It's around 3 am and we're groggily doing the changeover of shifts. I'm still not used to the starting time of these 12 hour shifts. Some of us stumble round bumping into each other during the changeovers. The crew seem more used to it.
A ratcatcher has just gone down so we're about an hour off it coming onboard. Last night an orange roughy trawl to around 800 m brought up 10 species of chondricthyans (the scientific name for the group containing sharks and rays, all of which have a skeleton of cartilage): the tally was 9 shark species and one skate species. Yesterday the head of a mako shark was found in one catch. By the clean knife cuts on it, it must have been discarded by a fishing boat. Bernard Seret of IRD in Paris has spent the last day preparing the skull and jaws to be kept as a reference specimen. He has been carefully scraping away the skin and flesh with a scalpel. The soft cartilage skull is then "fixed" in a chemical known as formalin, the same embalming fluid that funeral directors use. It stops muscle and cartilage from decaying. This chemical is used to "fix" many of the reference specimens collected in this voyage. Others are fixed in alcohol so that DNA can be extracted for studies of fish stocks, populations and the evolutionary origins of different groups.
Other fish catches overnight included orange roughy, silver roughy, oreo dories, halosaurs, spineback eels, more rattails, slickheads, lanternfish, viperfish and several deep-water conger eels. The invertebrates included jewel squids, brittle stars, sponges and small urchins.
Each 12 hour shift of researchers has a fish team and an invertebrate team. The catch is quickly sorted into these major groups on deck and then tubs of animals are taken to the different labs for sorting, identification, photography and labelling. The invertebrate team is co-ordinated by Karen Gowlett-Holmes from CSIRO Marine Research in Hobart . Karen has a wide knowledge of marine invertebrates and is joined on the night shift by experts in particular groups: Rick Webber, Te Papa (prawns, shrimps and other crustaceans), Matilde Richer de Forges, Queensland Museum (sponges) and Tim O'Hara, Museum Victoria (brittle stars and other echinoderms). The day shift consists of Penny Berents, Australian Museum, Sydney (amphipods and other crustaceans); Peter Davie, Queensland Museum (crabs and other crustaceans); Don McKnight (seastars, urchins and other echinoderms) and myself, Mark Norman, Museum Victoria (octopuses, squids and other cephalopods).
For each new species found or for species that are captured for the first time on this voyage, digital photographs are taken for placement into photo reference folders. These folders are constantly updated by Karen and Penny for the invertebrates and their data entered into the trip database. These folders are very useful for checking identifications against species already encountered. The fish teams use the same process. Brent Wood and Neil Bagley co-ordinate input of all the data onto the ship's computer systems with input from shift leaders Malcolm Clark (day) and Peter MacMillan (night). At the end of the trip the resulting large databases of information and images, combined with getting the unidentified material to experts around the world, allows the results of the voyage to be quickly worked up and the information rapidly disseminated. At this stage of the voyage, around 1000 species of invertebrates have already been recorded.
I can hear the winches starting up which means it will be half an hour to go before the 3 kilometres of "warp" (the steel cable connected to the trawl) will be brought up. For each kilometre of depth, you need about 1.7-2.0 kilometres of steel cable to tow the net at a low enough angle so that it sits flat on the seafloor but not so low that it digs in. The ideal speed is around 3 to 3.5 knots. The captain, Andrew Leachman, describes it as being like landing a plane, you adjust the speeds and angles according to the conditions. The "Tangaroa" carries 4 km of cable on each of the two major winches, enough to trawl down to 2.7 km deep.
The last trawl from 1500 m deep brought up a lot of ox-eyed dories, some prawns, collapsible sea urchins, basketwork eels, some sharks, more orange roughy, one of the deeper hatchetfishes with eyes on the side of its head, more rattails, a snailfish (probably Psednos sp.) and a blobfish (Psychrolutes sp.).
This afternoon we snagged the orange roughy net on rough ground once and then got tangled doors in the next trawl. The second trawl went to 250 m and did catch some shallower colourful sea perches and some pieces of black coral carrying serpent stars and barnacles. While repairs are made to the orange roughy gear the Sherman sled has been sent down. More tomorrow
Day 20, 29 May 2003
Mark Norman, Museum Victoria
Slightly larger swell (3 m), 18 knot SE wind, 17 ° C
It's now 8 am and we're currently choosing a suitable location to send down the nets on a shallow seamount on the Wanganella Bank. Trawl sites are chosen according to the scan images and information generated onboard by the NIWA seabed mapping team: Richard Garlick, Kevin Mackay and Miles Dunkin.
It is important to remember that very little of the world's seafloor has been mapped. In the past our knowledge of the bottom of the oceans has come from individual depth measurements by ships in their narrow tracks across the sea. In the early days even the ship's location at each depth station was not accurate. This gave a very weak picture of the seafloor and even with the development of echo sounders there were still many errors caused by things such as large fish schools or backscatter layers in the water. This situation is now starting to change with the development of some very fancy technology.
|Topographical map, Lord Howe undersea floor, see full image slide show
The first stage starts with satellites. Exact location information is now provided by "GPS" (Global Positioning Systems), able to separate location a metre apart. Another satellite system provides "satellite altimetry data" which can generate a rough map of the seafloor for all the earth's oceans. It does this by measuring the height of the sea surface. No, the sea is not evenly curved all over the earth (even if you take out the influences of tides, currents and swell). In spots it bulges up, elsewhere it is lower. This corresponds to the depth and type of the seafloor directly underneath. It is all about gravity: the pull of gravity on the seawater depends on the size and composition of underwater features. Large underwater mountain ranges of dense rock have higher gravity pull than trenches full of mud. By measuring the sea surface heights, this system can generate a rough map of the seafloor and can pick up large underwater features like the Lord Howe Rise. Errors can occur where different rock densities can give false readings of shallower or deeper depths. For more detail, like defining individual seamounts, the mapping must be done more directly. This is where our ship comes in.
The Tangaroa is specially fitted for multibeam mapping". It works like the echo sounders used on small boats, but on a much larger scale. The keel of the ship has had a special structure added called the pod" or the gondola" that carries two large arrays of transducers (large plates that send and receive pulses of sound). The transmitter series is 8 metres long in line with the ship's hull while the receiver series is 4 metres wide across the ship. This system, known as the Kongsberg Simrad EM300, sends out a thin fan of 30 kHz sound waves with an angle of up to 150° wide. The receivers receive the bounce-back signal. It is the equivalent of 135 single echo sounders all sending and receiving at once. The width of the seafloor scanned depends on the depth, if the sea is one kilometre wide, then it can scan up to 4 km wide beams across the seafloor. When you get a lot shallower, the beam narrows, so more passes are required.
To make the multibeam system as accurate as possible, the speed of the sound transmissions through the water needs to be considered. Seawater is not just seawater. It varies in temperature, salinity, pressure, particles and marine life. There are layers in the sea of temperature changes (thermoclines), salinity changes, density changes or dense bands of animals (the "scattering layer"). These factors can bend (refract) or change the scanner beam, just like light through prisms. To compensate for these layers, an SV probe" (Sound Velocity probe) is lowered to measure the speed of sound through the water at the different levels in different layers. The results improve the accuracy of the data and images generated. Another factor to be considered is the motion of the ship. How can the signal be held steady by a rocking and rolling ship? The job of taking motion into account is done by a little orange box known as the inertial motion sensor"; it contains spinning wheels and disks that sense ship motion and instantly controls the direction of the scanner beam to keep it steady.
There's one more thing that this system does. It can measure the hardness of the seafloor. It does this by measuring the strength of the returning signal, if it is weak, the sediment is soft, and if it is very strong it is bouncing back from hard rock. This information can be draped over the resulting maps to show the rock types. You can even see the lava flows that ran down the sides of extinct volcanoes millions of years ago.
The result of all this technology is spectacular maps, like moonscapes. The three images shown are: 1) the seafloor at site 7 north of Lord Howe Island, 2) the passes of the ship that allowed this map to be generated, and 3) the overlay of rock density, showing the ridges of hard lava down the sides.
On a side note, Side-scan Sonar" is a different system that the Tangaroa uses in some surveys. It is a towed unit (called a "towfish"), pulled behind the ship that can get closer to the bottom. It sends out the beam to the side so that it is effectively looking for shadows, like shining a torch across a night landscape. It has much higher resolution but is more appropriate for mapping small areas in high detail, i.e. marine farm sites or sewerage outfalls. It can resolve objects down to less than a metre, handy for finding lost wrecks.
Enough technology. Back to the critters. Last night we trawled to around 1400 m deep. This morning, crewmember Barry Fleming made a discovery when preparing the nets for the day: a missed specimen of one of the more dramatic toothy creatures of the deep, a Humpback Anglerfish.
Shallower trawls today (140 m) brought up large numbers of porcupine fish (returned spiky and flapping overboard), slender bellowsfish, a few flying gurnards and leatherjackets.
We are now waiting for the mapping team to tell us the best place to set down the next beam trawl. You know how they do it now.
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the New Zealand National Institute of Water and Atmospheric Research Ltd (NIWA) are providing scientific support for the voyage. The NORFANZ voyage will use NIWA deep-sea research vessel, the R.V. Tangaroa (NORFANZ).
The expedition received considerable interest from scientists worldwide. Twenty four scientists from more than eleven research organisations will be represented onboard, including staff of CSIRO, Hobart; Museum Victoria; the University of Tasmania; Australian Museum; Queensland Museum; Northern Territory Museum; NSW State Fisheries; Te Papa, Wellington; National Institute of Water and Atmospheric Research, New Zealand; Institute de Recherche pour le Développement, Noumea; Natural History Museum, Paris; and California Academy of Sciences, San Francisco.
Related Web Pages
Expedition Slide Show
Ghost Hunters Tasmanian Tiger Expedition
Spying on Biodiversity
Australian Museum Norfanz