Mixed-Gas, Closed-Circuit Rebreather Use for Identification of New

Hamilton, Pence and Kesling (Eds.): Technical Diving Forum, MUS, November1999

Mixed-Gas, Closed-Circuit Rebreather Use for Identification of New Reef Fish Speciesfrom 200-500 fsw

Richard L. PyleIchthyology, Bishop Museum, 1525 Bernice St., Honolulu, HI 96817 &

Dept. of Zoology, University of Hawaii, Honolulu, HI 96822Abstract

Pyle RL. 1999. Mixed-Gas, Closed-Circuit Rebreather Use for Identification of New ReefFish Species from 200-500 fsw. In: Hamilton RW, Pence DF, Kesling DE, eds. Assessmentand Feasibility ofTechnical Diving Operationsfor Scientific Exploration. Nahant, MA:American Academy of Underwater Sciences.

Tropical coral-reef habitat extends to a maximum depth of about 500 fsw. Historicallimitations of undersea intervention technology and specimen collection techniques have leftcoral-reef habitat deeper than 200 fsw almost entirely unexplored. The purpose of this project isto utilize mixed-gas, closed-circuit rebreathers to access these depths on coral reefs, in order todocument previously undescribed species (particularly fishes). We have conducted extensivedeep-reef explorations in Papua New Guinea, Belau (Palau), and Hawaii. We use Cis-Lunar MK5P closed-circuit rebreathers as the primary life-support. Decompression schedules are generatedby the on-board, real-time computers on the MK-5P (DCAP TIIa algorithm), modified withadditional deeper stops. The surface-support vessel is usually 'live', with divers towing a surfacefloat and communicating topside via surface-marker buoys. The standard response to symptomsof DCS is immediate in-water recompression (IWR). After more than 800 combined hours ofrebreather dive time (including over 200 deep dives) three incidents of DCS symptoms and onepotentially serious equipment problem have been experienced, all of which were successfullyresolved without serious injury. We have collected at least 43 confirmed new species of reeffishes, and several new invertebrate species, with others awaiting confirmation.

Introduction

Among the most complex and biologically diverse ecosystems on Earth are the tropicalcoral reefs. Although terrestrial rain forests likely contain greater numbers of species, coral reefsharbor a far broader array of plant and animal phyla. Representatives of algae, vascular plants,sponges, corals, ctenophores, flatworms, segmented worms, mollusks, crustaceans, echinoderms,tunicates, and fishes are common constituents of coral reef communities. To explore thisbiological diversity, early marine biologists had to rely on remote sampling gear (such as traps,trawls, dredges, nets, and hook and line equipment) for collecting specimens from all but theshallowest of undersea habitats. Although these collecting methods have provided a wealth ofspecimens from a wide range of depths, they are non-selective and do not allow researchersdirect examination of study subjects. They are especially ineffective in coral reef environments,which are characterized by complex topography and an abundance of cryptic species. The use ofremotely operated vehicles (ROV's--miniature submersibles equipped with lights and a videocamera tethered to a surface-support vessel) for biological research has alleviated many of theproblems associated with other remote sampling methods. Unfortunately, however, they are

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greatly limited in their ability to collect specimens, and thus are inadequate for many scientificstudies.

For more effective and selective collections and in-situ observations, marine researchersmust use diving technology to allow direct access to undersea habitats. For studies of coral reefenvironments in particular, scuba has proven indispensable for the collection of specimens andin-situ ecological and ethological research. Sale (1991) wrote, "While a few individuals hadattempted observational work much earlier, it was the development of scuba and the accesswhich that gave to the reef environment which opened up the possibilities for significantecological study of [coral reefs]." Despite these advantages, however, conventional scuba divingtechniques are limited to a maximum depth of about 50-60 meters. Because coral reef habitatextends to depths well beyond 100 meters (Strasburg et aI., 1968; Hartman, 1973; Porter, 1973;Fricke and Schumacher, 1983; Colin et aI., 1986; Hills-Colinvaus, 1986; Fricke and Knauer,1986), conventional scuba allows access to less than half of the overall coral reef environment.

Over the past three decades, deep-sea submersibles have been used in military operations,offshore mining and rescue, and scientific research. The advantage of submersibles is thatoccupants are not directly exposed to increased ambient pressures. As a result, deep-seasubmersibles have allowed researchers the opportunity to explore great depths and remainunderwater for hours at a time. Unfortunately, however, submersibles have not been utilizedextensively for investigations on the deep coral reefs. Submersibles are extremely expensive toconstruct and operate, and they require extensive logistical support. Enonnous operational costsof submersibles (typically $10,000 to $25,000 per day) greatly limit the availability of thesedevices for research. Consequently, the majority of undersea biological research projectsutilizing submersibles have concentrated on examining mid-water environments and habitatsdeeper than 150 meters.

Because of these historical limitations in underwater biological exploration technology,coral reefs at depths between about 50-150 meters remain poorly elucidated. What little is knownabout this deep-reef ecosystem (also referred to as the coral reef 'Twilight Zone'), however,suggests a wealth of undocumented species of marine organisms (Hartman, 1973; Porter, 1973;Colin, 1974; 1976; Thresher and Colin, 1986; Pyle, 1992b; 1996a; 1996b). In an effort toovercome the limitations of conventional scuba, I began investigating the use of mixed-gasdiving techniques in 1989. Using an open-circuit mixed-gas scuba rig (Pyle, 1992; Sharkey andPyle, 1992a; Pyle, 1996c), Charles J. Boyle and I conducted a series of exploratory dives inRarotonga to depths of 90-125 meters, with highly successful results (Pyle, 1991). Nevertheless,this open-circuit rig limited effective bottom times to no more than 12-15 minutes.

To extend bottom-time duration, reduce total gas requirements, and increase overallsafety, I (along with John L. Earle) began using prototype MK-4P mixed-gas, closed-circuitrebreathers developed by Cis-Lunar Development Laboratories, in 1994. The rebreathers provedhighly effective during an exploratory expedition to Papua New Guinea in 1995, and onnumerous dive operations in the Hawaiian Islands. In 1997, we began using Cis-Lunar'sproduction-model MK-5P rebreathers, which we used successfully during an expedition to Belau(Palau) that same year, and have been using ever since. Our project, which is intended to beperpetual, endeavors to continue the exploration of biological communities on deep coral reefs inall tropical seas.

Project personnel

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Hamilton, Pence and Kesling (Eds.): Technical Diving Forum, AAUS~ November1999

At present, project exploration divers include primarily me (R.L. Pyle) and John L. Earle.Recently, Lt. Joseph Dituri (USN, MDSU-l) has also begun participating as an explorationdiver. During the 1997 expedition to Belau, two additional exploration divers participated on theproject: Dr. Patrick L. Colin (using his horne-built mixed-gas rebreather), and Ken Corben(professional videographer, who used a Cis-Lunar MK-5P). Additional personnel on this projectinclude surface-support divers and boat operators.

There are no fonnal screening requirements for project participants. Prospectiveexploration divers and surface-support personnel must meet only one criterion for participationon the project: I must be willing to entrust my life to them. Personal experience hasdemonstrated that objective screening techniques such as medical examinations, divecertifications, and other like qualification documentation have failed to serve as reliableindicators of meeting the singularly important criterion for project participation. While the lackof such fonnal screening techniques might seem inadequate, in fact the single criterion methodhas proven extremely successful, because it involves scrutiny of a wide array of diverqualifications that, considered together, ultimately determine the success of project dives.Unfortunately, this method of diver selection is limited in application outside this project only tothose projects with project leaders suitably experienced in subjectively detennining who should,and should not, participate on project dives.

Equipment configuration and dive protocol

Equipment

The primary piece of underwater life-support equipment used during this project is theMK-5P mixed-gas, closed-circuit rebreather developed and manufactured by Cis-LunarDevelopment Laboratories (Figure 1). This rebreather unit is capable of at least 6 hours of divetime (or longer, depending on diver metabolic rate) to a maximum depth of 500 fsw, and wasdesigned specifically with reliability as top priority. It has many innovative features thatminimize the probability of system failure. The breathing loop inch~des a mouthpiece with anintegrated open-circuit bailout system, dual over-the-shoulder counterlungs for reduced breathingresistance, ballistic breathing hoses, and perhaps most significantly, a fully waterproof C02absorbent canister. Gas supplies include one 20 cubic-foot (c.f.) capacity "onboard" diluentcylinder, one 13.5 c.f. "onboard" oxygen cylinder, routed to a manual-control gas manifold withcapability to connect to "offboard" diluent and oxygen supplies. A unique feature of the gassupply system allows the diver to simultaneously purge all three oxygen sensors with a blast ofdiluent gas. This serves two important purposes: it removes any condensation that might haveformed on the oxygen sensors, and it simultaneously exposes the all three oxygen sensors to aknown oxygen fraction (the selected diluent gas). The latter of these purposes is especiallyuseful because it allows instantaneous verification of the validity of the three sensor readings.

The integrated electronics system on the MK-5P is also rife with useful features. Itstriple-redundant microprocessors (anyone of which can completely operate the unit) arenetworked so that a faulty processor can be locked out, if necessary. Each processor calculatesreal-time decompression status using a modified DeAP algorithm developed by HamiltonResearch, Ltd. It incorporates three oxygen sensors, four cylinder-pressure sensors, two depthsensors, two temperature sensors, and five separate batteries (at least four of which mustsimultaneously fail to leave the diver without a readings from the oxygen sensors). Displays

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Hamilton, Pence and Kesling (Eds.): Technical Diving Forum, AAUS, November1999

include a LCD screen for detailed data display; an independent analog P02 display of all threeoxygen sensors; a heads-up display for P02, decompression, and system data; "buddy lights";and redundant audio alarms. The electronics also store detailed downloadable dive log data for awide variety of parameters.

Figure 1. Cis-Lunar Development Laboratories MK-5P closed-circuit rebreather.

Front

AdjustableCounterlungs

ABS Case

AutomaticDiluentValve

BuoyancyCompensator

Water Dump Valve

Emergency Buddy

Data Communications

Triple Oxygen Sensors

Onboard Diluent

Condensation Trap

Carbon DioxideAbsorbent Canister

Onboard Oxygen

Ballistic Hoses

Mouthpiece

Integrated BailouRegulator

Multi-PurposeI ------- Gas Manifold

4--- Heads-Up Display

DualRedundantComputers

56 Back (without shell)



The 20-c.f. onboard diluent cylinder is filled with air, which is used for on-the-fly trimixblending and flushing the loop with Enriched-Air Nitrox (EAN) during decompression. Inaddition to the two onboard cylinders, each diver carries minimally (on deep dives) an additionaloxygen cylinder with 13.5-20 c.f. capacity, a 30-40 c.f. capacity cylinder containing heliox, and alarger-capacity cylinder containing 80-100 c.f. of trimix (blended appropriately for the targetdepth). Besides the carried gas cylinders, an additional 100-600 c.f. of oxygen, 80-100 c.f. oftrimix, and 100-200 c.f. of EAN are available for emergency open-circuit bailout purposes. Howthese additional gas supplies are deployed depends on whether the dive is conducted on a verticaldrop-off, or a deep ledge (see below).

All exploration divers carry at least one inflatable surface-marker buoy (SMB) attachedto a reel with at least as much line as the depth of the first anticipated decompression stop. Otherequipment carried by the divers includes nets, buckets, cameras, and/or other items needed tocollect or otherwise document marine life on the deep coral reefs.

The surface support vessel of choice for project dives is a small boat in the range of 2035 feet in length. If larger support vessels are used (e.g., live-aboard vessels), there must besmaller "chase" boats available. In any case, there must be at least two separate motors forsupport vessels; either as dual motors on a single boat, or two separate boats.

Pre-dive preparations

Pre-dive preparation procedures are as important as actual dive procedures. Prior to anydive, all gas cylinder contents are analyzed and verified for their oxygen content. The C02absorbent canister is inspected and/or packed, if necessary. For any dive requiring more thanminimal decompression obligation, fresh CO2 absorbent is used. Additionally, all valve positionson the gas manifold and cylinders are verified for correct position. The breathing loop integrity isverified with both a positive-pressure loop test (loop filled to capacity and monitored for leaks),and a negative-pressure loop test (loop drained to the point of a mild reduced pressure andmonitored for leaks). After all of these pre-dive verifications have been completed, andimmediately prior to starting the dive, the built-in pre-dive checklist on the integrated electronicssystem is completed. This checklist includes both a variety of specific equipment checks, and aminimum 2-minute system pre-breathe to verify overall system function.

General dive procedures

Most of the general dive procedures followed on this project are outlined in Pyle (1996e).The maximum P02 setpoint used during the dive is 1.4 atm. Occasionally this is elevated to 1.5atm during final decompression stages. The maximum nitrogen partial pressure (PN2) allowedduring the dives is 2.6 atm. Trimix is blended in one of two ways: constant nitrogen fraction(FN2), and constant PN2. The constant FN2 method involves using a pre-blended trimix diluentsupply, serving as the active diluent source beginning at the start of the dive. With this method,the nitrogen:helium ratio is held constant regardless of the depth. The constant-PN2 methodinvolves an initial descent to a maximum depth of 100 fsw using air as the active diluent source.Upon reaching 100 fsw, the electronics system has achieved the P02 setpoint in the breathingloop (generally 1.4 atm), with the balance of loop gas being nitrogen (2.6 atm). At that point, theactive diluent source is switched to heliox (no nitrogen at all), and the descent is continued.With a constant loop volume, the effect of this is to maintain an essentially constant PN2, "locked

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in" at the time of diluent gas source switch. This gas mixture tends to drift towards heliox overthe course of a dive if loop gas is periodically vented and replaced by the heliox diluent (e.g.,mask-clearings; frequent small ascents and descents; etc.) On dives without "saw-tooth" bottomprofiles, by well-trained divers who do not waste much loop gas, this drift is negligible.

On all dives involving helium, the breathing loop is flushed with air during theascent/decompression upon reaching a depth of about 100 fsw, fonning a constant-P02 EANbreathing gas. By the time a depth of 20 fsw is reached, the loop contains more than 90%oxygen.

Decompression profiles follow the advice of the integrated computer, with a fewmodifications. Initial ascent rate from depth is maintained at a maximum of 30 fsw/min; even atdepth. Deep "safety" decompression stops are included according to the method outlined in Pyle(1996d) and Pyle (1997). Essentially, this method is to add a 2-3-minute decompression stop athalf the distance between the bottom depth and the first "required" decompression stop; and thenadd additional stops at similar half-depth increments until the remaining gap between the lastdeep safety stop and the first "required" stop is less than 30 feet. Also, the time required for thelO-fsw stop is added to the 20-fsw stop, and the final ascent to the surface is kept very slow(optimally at a rate of 1 fsw/min).

Dive procedures on vertical drop-offs

Many of the dives in remote locations for this project are conducted on vertical reef dropoffs. Typically, these drop-offs start at a shallow depth (10-30fsw), and continue vertically ornear-vertically to depths well in excess of 500 fsw. Under these circwnstances, the support vesselis anchored at the top of the drop-off and remains there throughout the dive. Exploration diversdescend down the drop-off, following either a guideline or a geologic feature on the reef face.Emergency open-circuit bailout cylinders (oxygen, EAN, and/or trimix) are staged at appropriatedepths on the way down, and recovered either at the end of the dive, or at the end of a series ofdives at the same site. The bottom portion of the dive is conducted within a short distance fromthe fixed pathway back to the surface. Decompression is conducted along the drop-off.

Dive procedures on deep ledges

Most dives conducted in Hawaii, and some dives conducted elsewhere, involve a habitatbest described as a "deep ledge". In this circumstance, the horizontal distance between shallowreef habitat and the dive site is large - often on the scale of a mile or more. In this circumstance,divers must descend through several hundred feet of open water to reach the reef habitat.

Dive procedures on deep ledges are somewhat different than they are for vertical dropoffs. These procedures are similar to those described in Pyle (1996e), but have been modifiedsomewhat, as illustrated in Figure 2. The divers tow a float behind them during the dive. Theboat is not anchored, but instead is in constant operation following the diver's tow-float (Figure2-a). This system avoids complications due to unpredictable currents, and allows divers theability to cover relatively long distances without the need to return to the surface via anyparticular pathway.

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Figure 2. Dive Procedures for deep ledges.

a.

c.

b.

d.

When the divers begin their ascent, the lead diver deploys the 5MB attached to the reel ofline. If necessary, a slate with a written message may be attached to the 5MB. The end of thetow-line is also attached directly to the 5MB and sent to the surface, to avoid risk ofentanglement (Figure 2-b). When the 5MB reaches the surface, the support vessel positions itselfat the 8MB while support personnel attach a weighted decompression line with its own surfacefloat and a gas supply to the 5MB line via a clip, and drop it down to the divers (Figure 2-c).This gas supply is normally not needed by the divers, but is deployed just in case the diversrequire it for open-circuit bailout. After deployment of the decompression line and emergencygas supply, the 8MB and tow-float with their respective lines are removed from the water andcollected in the boat.

At this point, a support diver wearing open-circuit scuba gear descends thedecompression line and communicates with the exploration divers. The support diver brings anyadditional equipment (such as a supply of drinking water that can be consumed by the diversduring decompression to maintain hydration), and takes other equipment that is no longer neededby the divers (e.g., nets, buckets, etc.) back to the boat. The support diver re-visits theexploration divers every 30-60 minutes to monitor progress throughout the decompressionperiod.

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Hazard Identification and Mitigation, and Emergency Response

Unpredictable currents

Common to many of the coral reef environments where project dives take place areunpredictable currents. Although these currents are usually ultimately driven by tidalfluctuations, they often do not follow predictable patterns correlated with tides. This may bebecause of gyres and other non-linear current patterns, and because of local reef topology. Insome cases, the currents at the depth of the planned dive may be different, or even opposite, tothe surface currents. Because of the unpredictable nature of the currents, the best way to avoidcomplications is to plan the dives with enough flexibility that they will be successful regardlessof what the currents are like. Logistically, this is usually best accomplished by maintaining a"live" (non-anchored) support vessel, and free-drifting divers; for both the bottom portion of thedive and during decompression.

Decompression sickness

Because of the nature of the dive profiles involved with this project, the risk ofdecompression sickness (DCS) is omnipresent. Steps taken to prevent the onset of DCSsymptoms include using a proven decompression algorithm (DCAP TlIa), slow ascent rates(including at depth), deep "safety" decompression stops, and continuous in-water hydrationthroughout decompression. Additionally, immediately following completion of decompression,exploration divers maintain low levels of exertion, and preferably lie horizontally to avoiddramatic blood volume shifts as much as possible immediately after the dive.

The standard response protocol to onset ofDCS symptoms following a dive is immediateIn-Water Recompression (IWR). Although this procedure is an absolute necessity in many of theremote locations where project dives are conducted, it is also the standard first response evenlocalities where recompression chamber facilities are less than an hour from the dive site. Areview of this controversial procedure is available in Pyle and Youngblood (1995 & 1997), andthe specific protocol followed for this project is described in detail in Pyle (1999). Severalmethods of IWR have been published, and all appear to have virtually equal (and high) successrates. Of critical importance to all methods is the need for immediate response to the onset ofsymptoms, which means that the procedure needs to be well-versed among all personnel, andequipment must be prepared and ready to deploy before the start of each deep dive.

Out of more than 800 hours of dive time, including 200 deep (>190 fsw) dives, conductedover the course of this project, we have experienced three cases of DCS symptoms among twodifferent divers. All three cases shared several common characteristics. In all cases, thesymptoms experienced were consistent with cutis marmorata, an ominous form of "skin" bends(Edmonds et ai., 1991); including purplish bruise-like blotches on the abdomen. All casesoccurred in Hawaii, and involved extended heavy workloads at depths in excess of 380 fsw. Onecase involved a reverse-profile spike where the diver had completed decompression to the 100fsw level, then returned to a depth of 200 fsw momentarily before ascending back to continuedecompression. The first case was misdiagnosed as dry-suit squeeze and was not treated. Thesymptoms in this case resolved after several days, with no apparent residual effects. In the othertwo cases, symptom progression was arrested immediately after commencement of IWR, withcomplete resolution within the first few minutes of treatment. In both cases, IWR was continued

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Hamilton, Pence and Kesling (Eds.): Technical Diving Forum, AA US, November1999

for approximately 60 minutes, with no recurrence of symptoms.. Divers sought follow-upexaminations at a hyperbaric facility, and no subsequent treatment was deemed necessary ineither case.

Except for these three cases, decompression procedures have proven very successful.More than just the absence of DCS symptoms following dives, exploration divers consistentlyfeel very low levels of fatigue; even after multiple repetitive exposures. For example, during the1997 Papua New Guinea expedition, deep (330-420 fsw) dives were conducted nearly every day(sometimes twice per day), and divers felt energetic enough each evening to carry on casualdiscussions past midnight, and then start again the next day at 6 am. This pace was maintainedfor the entire 13 days of the expedition.

Equipment failure

The Cis-Lunar MK-5P system is designed with enough built-in redundancy that singlepoint equipment failures virtually never pose a serious threat. Even in the event of a totalelectronics failure - which would require the simultaneous failure of three processors, or at least4 simultaneous battery failures, or the loss of all three oxygen sensors - the diver can easilycontinue operation in "semi-closed mode" (venting every 4th to 10th breath, replacing withdiluent). The only situation requiring open-circuit bailout would be an unrecoverable totalbreathing loop failure. On the MK-5P system, this means either a failure of the CO2 absorbent(e.g., diver neglects to re-pack the absorbent material after it has expired, or uses bad absorbentmaterial to begin with), or a catastrophic mechanical loop failure, such as a split breathing hoseor badly torn counterlung. Nevertheless, it is core policy within this project that each diver has analternate safe pathway to the surface (including decompression). Thus far, that alternate pathwayhas been in the form of open-circuit bailout.

The most notable equipment failure experienced on this project so far occurred during the1997 expedition to Belau. Details of this event are documented on the web site for thatexpedition, at:

http://www.bishopmuseum.org/bishop/treks/palautz97/14may97 log.html.

In summary, the cause of the problem was that I neglected to close a drain plug on thebottom of the CO2 absorbent canister housing of the rebreather. The plug stayed sealed longenough to allow me to complete the first 20 minutes of bottom time, then suddenly popped openwhen I inverted to a head-down position. Within the span of two breaths, the entire canister filledwith water, physically preventing further breathing from the loop. I commenced an open-circuitbailout without complications. During the decompression phase of that dive, the cause of theloop flood was identified. The plug was replaced, and the water flushed out of the loop,restoring the rebreather to full operational status. I completed the remainder of thedecompression in closed-circuit mode. Upon inspection following the dive, the CO2 absorbentmaterial (Lithium Hydroxide) was found to be completely dry, due to the waterproof design ofthe C02 absorbent canister.

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Hazardous marine life

Sharks have not proven to be a problem on any project dives so far; however, experienceon non-project dives has demonstrated that the potential problem does exist. The potentialproblem does not seem to be important during the bottom portion of the dive; rather, the concernis if sharks were to become agonistic during the decompression portion of the dive. In extremecases, divers may be forced to choose between the risk of shark bite, and the risk of DCS.Preliminary efforts to use bang-sticks and underwater electronic repellant devices have not beenespecially favorable. Although these devices do seem to work as. they are intended to, theproblem they are intended to thwart is rare enough that the benefits do not usually outweigh thecosts of additional bulk and complexity of dive equipment carried by the diver. The potential tostage these devices on the decompression line, or deploy them from the boat only whennecessary, remains a viable option, which may be explored for future use on this project.Currently, however, exploration divers on this project feel that the overall risk presented bysharks is small enough that it can serve as the base-line level of "acceptable risk"; with the goalbeing to reduce the risk ofother hazards to this acceptably low level.

Other forms of hazardous marine life (such as stinging planktonic organisms) haveproven to be, at worst, more of an annoyance than a real hazard.

Project Discoveries

Fishes

A summary of the ichthyological discoveries made so far during this project is includedin Table 1. The data presented in this table are for confirmed (and collected) new fish speciesonly, and the total new species count does not include species overlap (i.e., species are onlycounted once, even if they were taken at more than one locality). Exploration time representstime actually spent on the bottom, collecting specimens; and the "New Species Per Unit Effort"(NSPUE) is calculated accordingly.

Table I. Summary of new fish discoveries.

Locality

Rarotonga (1989-1990)Papua New Guinea (1995)Belau (Palau; 1997)Total

New FishSpecies

11172348

ExplorationTime (hr)

2.83.23.99.9

NSPUE

3.95.35.94.8

As can be seen in Table I, the "NSPUE" values have steadily improved over the course ofthe project. The comparatively low number for Rarotonga may be in part due to the loweroverall diversity of species there as compared to Papua New Guinea and Belau; but more likelydue to the reduced efficiency of open-circuit equipment as compared to closed-circuittechnology. There is also an overall trend in improvement of our basic technique over time, asillustrated by the improved performance in Belau as compared to Papua new Guinea; despite the

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Hamilton, Pence and Kesling (Eds.): Technical Diving Forum, AAUS, Novemberl999

fact that both localities have similar faunal diversity and reef topography, and both expeditionsinvolved the use of closed-circuit rebreathers.

There are several interesting aspects of the new species discoveries over and above whatis illustrated in Table 1. For example, more than half of the new species discovered so far arelarge, colorful, conspicuous species on the reef; which have been conducive to collection withhand-nets. Certainly, with the application of techniques to capture more cryptic species (e.g.,rotenone), rates of new species discovery will improve even further. Another noteworthy patternnot shown in Table 1 is the fact that NSPUE values showed no trend of general decline over thecourse of the expeditions at both Papua New Guinea and Belau, as would be the expected patternif we were collecting a significant portion of the new species to be found at these localities. Thefact that both the total number of species discovered and the NSPUE figures for Belau exceededthose for Papua New Guinea, suggest further that our effort to discover new species at theselocalities is far from complete. Finally, the degree of species overlap between Palau and PapuaNew Guinea for deep reef fishes is considerably less than it is for their shallow-reef counterparts.Whereas the vast majority of shallow water species at these two localities occur at both places,only two of the combined thirty-eight new deep-reef species were collected at both. This patternsuggests higher rates of endemism for deep-reef species than for shallow-reef species, leading topredictions of greater numbers ofundescribed deep-reef species overall.

Invertebrates

Although the emphasis on this project is reef fishes, sessile marine invertebrates are alsoabundant at these depths. In fact, the potential for new species discovery within invertebratedeep-reef fauna vastly exceeds the potential for new fish species discovery, given the greaterdiversity of invertebrate life at those depths. Although we have collected a number of newinvertebrate species during the course of this project, the efforts of Dr. Patrick Colin, acollaborator on this project during the 1997 expedition to Belau, are more focused on the deepreef invertebrate fauna (Colin, 1999).

Recommendations for Scientific Applications of Rebreathers

Not just deep

The use of closed-circuit rebreathers is often associated with increased diving depth.While it is certainly true that the logistics of deep diving operations can be greatly simplified,and the level of risk greatly reduced, with well-trained rebreather divers on deep dives; increasedtime at depth is only one of three important fundamental advantages afforded by closed-circuittechnology. In scientific applications especially, deep diving activities may represent only afringe of underwater research involving divers. Perhaps of more widespread value to thescientific diving community are the other two fundamental advantages of closed-circuitrebreathers: extended bottom times at moderate depths, and quiet operation.

One of the main factors that limit underwater research at moderate depths (60-130 fsw) isreduced allowable bottom time, both in terms of decompression obligations, and breathing gassupply considerations. Closed-circuit rebreather technology functionally eliminates thebreathing gas supply limitation, by allowing upwards of 4-12 hours (depth-independent)underwater at a time. Decompression obligations can be mitigated somewhat at moderate depths

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through the use of EAN with open-circuit technology. Because of the ability of most closedcircuit rebreathers to maintain a constant oxygen partial pressure at all depths, rebreathers takethis one step further by allowing for a dynamic EAN mixture, optimized for each depth of thedive. The decompression advantage of closed-circuit over open-circuit EAN is most pronouncedon dives involving multiple depths.

Hanlon et al. (1982) described the advantages of quiet closed-circuit rebreather forcephalopod observations. Similarly, we have on many occasions witnessed the effectiveness ofclosed-circuit diving for observations of natural fish behavior. In particular, we have observedmore instances of reef fish reproductive behavior during rebreather dives than we have overdecades of open-circuit diving.

In any event, closed-circuit diving technology should not be viewed purely as a tool fordeep diving, as it has tremendous potential within the context of other kinds of underwaterresearch.

The diver makes the difference

Much concern has been focused on singular equipment-related hazards of diving withclosed circuit rebreathers. In particular, emphasis is often placed on the issues of electronicsfailure, oxygen sensor failure, so-called 'caustic cocktail', and improper system maintenance.While these are all certainly points of concern; none of them represent a substantial risk when awell-trained diver is using a well-designed rebreather. The real risk of rebreather diving, whichseems to be borne-out by the pattern of rebreather accidents in the recreational community, is'pilot error'. Rebreathers do require specialized training when compared to open-circuit scuba.They also require a different mind-set on the part of the diver. The emphasis on rebreather divingwithin scientific organizations, therefore, should be placed on confirming the prospective divers'qualifications on the specific rebreather unit to be used.

Literature cited

Colin PL. 1974. Observation and collection of deep-reef fishes off the coasts of Jamaica andBritish Honduras (Belize). Mar. Bioi. 24: 29-38.

Colin PL. 1976. Observations of deep-reef fishes in the Tongue-of-the-Ocean, Bahamas. Bull.Mar. Sci. 26(4): 603-605.

Colin PL. 1999. Palau at depth. Ocean Realm, Summer, 1999: 77-87.Colin PL., Devaney DM, Hills-Colinvaux L, Suchanek TH, Harrison, JT III. 1986. Geology and

biological zonation of the reef slope, 50-360 m depth at Enewetak Atoll, MarshallIslands. Bull Mar. Sci. 38(1):111-128.

Earle SA. 1991. Sharks, squids, and horseshoe crabs-the significance of marine biodiversity.BioScience 41(7): 506-509.

Edmonds C, Lowry, Pennefather 1. 1991. Diving and Subaquatic Medicine. 3rd Editon,Stoneham, MA; Butterworth Heinemann.

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Mixed-Gas, Closed-Circuit Rebreather Use for Identification of New