Technical Diving for Collections of Deep Water Reef Slope
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Technical diving has been in existence for some time and for the majority of that time, it?s acceptance as A valid working dive method has been not universally accepted by the scientific and commercial diving community. Lately though, more institutions, including the USA?s National Oceanic and Atmospheric Administration (NOAA) have been looking at technical diving as a legitimate and relatively safe means For acquisition of biological life forms from the deep reef. The greatest assets of open circuit scuba is that it relies on simple, uncomplicated gear, that has withstood the test of time and can be accomplished using standard ?off the shelf? dive gear with some minor modifications that is easy to make. Further it can be managed in low technology environments in remote areas. Closed circuit gear is complicated, and while it is being improved in quantum leaps recently; the author is seriously considering switching over to its use due to gas efficiencies and optimal gas management from both a physiological and cost perspective, small oversights in operation and diving with closed circuit will kill you very quickly and painlessly. It is possible also to do this with open circuit, but it is inherently safer gear until the technology for closed circuit is more advanced. It is safe to say that both of these diving methods allow extensive explorations of the deep reef slope that are not possible from a submersible. There is a huge difference between the quiet of a diver approaching a school of small, secretive and cryptic reef fishes and a big, noisy, brightly lit, submersible. Further actually being in the environment and having the use of a pair of hands and fingers, and the tactile sense of both allows a more intimate exploration than is currently possible from a submersible. What costs millions in a sub. e.g. manipulators etc., the author, audience and readers were born with. A pair of hands is the key! Imagine the simple task of typing this paper with a manipulator! Technical diving and open circuit gear have some limitations. One is that it costs a lot is terms of gear and supplies. All breathing gasses are expended during the dive and during decompression; for optimal decompression profiles, lots of diving cylinders and regulators are required. All of this equipment must be maintained in optimal conditions. Two, safe technical diving on open circuit requires a lot of heavy gear, many staged scuba bottles for decompression, and heavy double steel cylinders for bottom mix. An average diver carries at least 5 regulators and separate cylinders of various sizes on him during every dive for complete redundancy. Third, due to the constraints of the number of cylinders of expendable gasses that the diver can carry, most open circuit technical diving is done in depths less than 125m or so. While is fully possible by staging additional cylinders, to penetrate far deeper and the current record for this approaches 300m, it is the author?s current opinion that open circuit gear is best utilized between 70m and 125m. This leaves a lot of room for exploration between former limits of 130? (40m) imposed by NOAA and the new the ones that are being considered. Many of the deep reef slope species begin at about 70m or so, and with this simple gear, we have explored quite a bit of the deep with relatively low risks. The greatest risk of any deep diving venture is drowning by running out of breathing gasses. This certainly applies to open circuit technical deep diving. Rules have been developed by the cave diving community (Exely et al) that if adhered to and if applied in all instances, reduce this risk to very low levels. This rule is call the rule of thirds, that is one third of the bottom mix gas for the dive, one third for return to decompression bottles and one third for emergencies. In the unlikely case of a hose blowing or a valve failing, it gives the diver reasonable time to shut down the leaking gas source by use of the independent valves and still have enough gas to get to the staged decompression cylinders. Secondly, since most deep technical diving is done in pairs; one diver carries enough gas to bring the buddy back to the staged decompression cylinders or to the surface in the case of a complete gas loss on the part of the buddy diver. The second greatest risk is decompression sickness (DCS). While there are a number of good, reliable tables and software for creating custom dive tables, decompression incidences do occur even when the tables are followed scrupulously. Since decompression science is still not completely understood, every deep technical dive takes with it a small inherent risk of a DCS incident. It is the author?s standard practice to add additional decompression stops; add additional decompression gasses that optimize decompression beyond those calculated in the table and to add additional decompression time on pure oxygen at 6m (20?) on every dive; but no matter what precautions are taken, the risk is still there. If one is incapable of absorbing that risk, do not dive deep. The third risk to the deep technical diver is that of oxygen exposure. To maximize bottom time and to minimize inert gas loading, it is the typical practice to keep the partial pressure of the gas supplied to the diver at the highest level of oxygen that the body can physiologically handle. This has been determined by the Navy experimentally, to be at about 1.4 PPO2 for diving operations and 1.6 PPO2 for decompression. Since there are individual differences in a diver?s ability to withstand high partial pressures of oxygen and even in the same diver, these vary markedly from day to day ( Navy Experimental Diving unit, pers, com), this response of the body to oxygen cannot be accurately predicted. Therefore it is essential to log and track individual divers exposure to oxygen and keep the gas mixtures used within these established safer levels. The use of this technology has made possible, the collections of deepwater fish and invertebrates that had previously never been collected alive. Most species of deepwater fishes adjust quite readily to ambient surface pressures and other parameters including brighter lighting and slightly warmer temperatures. The author has found that there are several ways to accomplish this gradual acclimation to surface conditions. For most tropical species of fishes, the simplest method is to collect the fishes, put them individually into separated perforated plastic containers and ? stage them? into gradually shallow water over the course of several days. For example off of Curacao, Netherlands Antilles, in a truly tropical regime, it is moderately warm in 100 m, 22 -24 C. and there is not a huge variation in temperature between the deep reef slope and shallower water. In the tropical Indo Pacific, it is warm much deeper (Pyle, pers. comm). In both locales we can bring deep water species from over 100 m and stage them at about 30 m for a day or two. After this time, we can bring them to about 15 m for an additional day and finally complete the decompression in about 7m for one day and finally in 3-4m for one last day. A similar method is used to bring boarfishes and snipefishes to the surface from 150m off of Monaco (Giles, pers. comm). Since the author?s experience indicates only perhaps 4 to 5 degrees C. temperature elevation from the deep reef slope to the surface in many tropical areas, it does not present a considerable thermal challenge to the fishes. Further since the operations are very close to land based support, it is a simple matter to dive in successive days to gradually bring the fishes to the surface. This is not practical in remote areas or in completely pelagic areas like offshore pinnacles or shipwrecks where one does not plan to stay nearby for multiple days to do the gradual decompression method. The second method that is employed, typically in pelagic conditions where there is no continuous bottom contour to the surface, is a bit more complex for the diver teams. The team pauses during the initial decompression stops and relieves the excess gas from the swim bladder with a hypodermic needle. This is quickly accomplished by an experienced practitioner and typically takes about one minute per fish. An alternative method is to deflate the bladder at the bottom as the fish is put into holding (Pyle, pers. comm). The author finds this to be less preferable as the swim bladder is not expanded on the bottom and is more difficult to locate and deflate The third method of bringing deepwater species to the surface is the use of a pressurized chamber. With small fishes, 10 cm and less, a small plastic cartridge water filter that can withstand about 100 psi (6-7BAR) is sufficient to provide 6 ATM of pressure that is sufficient to keep most species out of hydrostatic stress. It is then a simple matter to add pressurized and chilled sea water with a pump that has a pressure activated switch to effect additional fresh sea water containing the oxygen necessary to sustain the life of the fishes contained within. Similar larger containers have been devised and used by both the author and various other (Bok, pers. comm) aquariums and are not complicated to fabricate at any size. It is significant to note the addition of pure oxygen gas under pressure over 1 ATA can lead to serious complications and high mortality in teleosts The collection of deepwater fishes is exactly the same as the collection of shallow water fishes. With smaller teleosts, the use of a hand net or barrier net works very well and for large fishes like giant groupers, sting rays and nurse sharks and heavy duty barrier net can catch just about any benthic dwelling species.
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