CCOP/SOPAC Cruise Report 125 February 1989

0FFSHORE SURVEY FOR PRECIOUS CORALS IN THE LAU GROUP OF FIJI,

10 T0 27 MAY 1988

by

John R Harper Techsec

And

Robert Smith

Mineral Resources Department Ministry of Lands and Mineral Resources

Suva, Fiji Prepared for: Committee for Co-ordination of Joint Prospecting for Mineral Resources in South Pacific Offshore Areas (CCOP/SOPAC) Fiji Project: FJ.20 Contributed by: Canada, International Centre for Ocean Development (ICOD)

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TABLE OF CONTENTS

Page

TABLE OF CONTENTS 2 LIST OF TABLES 3

LIST OF FIGURES 3 SUMMARY 4 ACKNOWLEDGEMENTS 5

INTOODUCTION Background 6 Objectives 7 Personnel 7

MEIHODS Approach 9 Equipment 9 Dredging Gear 10 Dredging Technique 14 Dredging Problems 14

RESULTS Sounding 17 Dredging 17

CONCLUSIONS 20 RECOMMENDATION 20 REFERENCES 22

[3] APPENDICES A Trip Log 23 B Navigation Log 30 C Station Log 39 D Target Log 47

LIST OF TABLES Table Description Page 1. Summary of Dredging Results 18

LIST OF FIGURES Figure Description Page 1 Location map of study area and track lines 8 2 Photograph of winch set-up 12 3 Photograph showing bagging of tangle nets 13 4 Location of dredging stations 19

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SUMMARY

This cruise was undertaken to investigate the occurrence of precious corals, specifically intermediate-depth and deepwater Corallium (200-500 m, 1,000-1,500 m water depths respectively) in Fiji waters. Prior to this survey, there was little information about intermediate-depth Corallium and no information about deepwater Corallium within Fiji's EEZ.

The cruise was conducted from 10 to 27 May 1988 using the Fijian Naval Ship (FNB) Babale. Approximately 13,600 kin of soundings were made and 42 dredging stations were occupied.

As a result of weather and equipment problems, representative sampling distribution was not achieved throughout the study area. Most sampling was concentrated to the south of Lakeba and only five deepwater dredging were made.

Although no Corallium was collected (based on tentative sample identifications), no conclusions can be drawn because of the relatively poor sampling distribution. Hard bottom, which is conducive to Corallium growth, was encountered throughout the survey area. Continued Corallium dredging in the Lau Group is recommended, primarily on a ship-of-opportunity basis.

The dredging technique was significantly improved during the cruise and recommendations that will improve future Corallium dredging programmes are provided.

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ACKNOWLEDGMENTS

The authors wish to acknowledge the excellent support provided from the crew of the FNS Babale throughout the survey. In particular we are grateful for the assistance of the Commanding Officer, Lieutenant Commander Timoci Koroi.

Mr Setareki Ratu, CCOP/SOPAC Geological Technician, was the Senior Technician throughout the cruise.

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INTRODUCTION

Background

This survey was undertaken at the request of the Mineral Resources Department as part of work programme "Investigation of deepwater precious corals in Fiji waters" (FJ .20). Task 2 "Reconnaissance tangle-net dredging for Corallium in Fiji waters". The survey followed a review of bathymetric data (Task 1 - "Review of available bathymetry to define potential Corallium targets") and a previous precious coral cruise to Kadavu Island (Gauss. 1981).

Increased precious coral prices, dwindling world-wide supplies and the discovery of commercial grade Corallium at least two sites within the South Pacific have resulted in renewed interest in precious coral prospecting within the region.

There have been 16 tangle-net dredgings for intermediate-depth Corallium in Fiji (Gauss. 1981) but unfortunately most of these dredgings were conducted in areas not particularly conducive to Corallium growth; nevertheless. Corallium was collected at one locality (Grigg, 1981). There have been no dredgings for deepwater Corallium in Fiji even though there is a large area of suitable habitat (estimated to be in excess of 20,000 km2; Harper, 1988).

Given that (a) Corallium has previously been recovered from within Fiji waters. (b) Fiji's EEZ contains a very large area of appropriate Corallium habitat. (c) very little Corallium exploration has been conducted within the Fiji EEZ and (d) there was recently an unconfirmed collection of deepwater precious coral in Tongan waters, close to and at the same latitude as Fiji (1987 Sonne Cruise), the potential for locating commercial quantities of precious coral within the Fiji EEZ is favorable.

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Objectives

The objective of this cruise was to conduct reconnaissance tangle-net dredging surveys in Fiji waters to determine the potential for a precious coral harvesting industry. During the cruise, targets with promising bathymetry were sounded and then dredged for intermediate-depth Corallium. (200-500 m) or deepwater Corallium. (1.000-1.500 m).

The first cruise was planned for the Lau Group as this area had the greatest area of potentially suitable water depths (Figure 1). Personnel

Personnel who took part in the cruise were: John Harper (CCOP/SOPAC) - Co-Chief Scientist Robert Smith (MRD) - Co-Chief Scientist Setareki Ratu (CCOP/SOPAC) - Technician

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METHODS

Approach

Prior to the cruise, targets were identified on the MRD 1:250,000 scale bathymetric maps (Pratap et al 1987a, 1987b, 1987c; Smith and Raicebe 1984). The targets included water depths in the 200-500 m range, 1,000-1,500 m range and 1,500-2,000 m range; these depth ranges reflect depths of (a) commercially harvested intermediate-depth Corallium in the North Pacific, (b) commercially harvested deepwater Corallium in the North Pacific and (c) the depth of the recent Tongan discovery, respectively. Areas of steep slope were excluded. Topographically high areas were marked as preferred targets as these were assumed most likely to be sediment-free.

At each target, soundings were made to (a) confirm depths indicated on the maps and (b) estimate the bottom conditions (e.g. rock or sediment covered). Where possible, the dredge was dropped at the up-current, down slope side of the target to permit an up-slope dredging during the drift. Typical bottom time of the dredge was 30 to 45 minutes.

Navigation fixes were obtained primarily by radar although during the early part of the cruise SatNav was also used. All fixes were logged, converted to UTM and entered into the computer via AutoCAD to create a record of the ship's track. Equipment

Major equipment components included: 1. Sounding System:

DataSonics, Model SBI'-220 Variable Frequency Sub-bottom Profiling/Sounding System; Raytheon, Model 1R73A, 12kHz, hull-mounted transducer; EPC, Model 46038 Graphics Recorder.

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2. Winch and Cable:

HydroProducts, Model HR65 gasoline-engine powered winch; 2,000 m galvanized 4 mm cable; meter wheel and associated blocks

3. Tangle-net Dredges:

cast concrete tangle-net stones wire-wrapped boulders nylon netting (approx. 1 inch mesh)

4. IEM-Compatible Computers:

Toshiba, Model 1000 Portable PC IBM Compatible Computer with 20 megabyte hard drive Texas Instruments, Model 855 J))t-matrix Printer

5. Software:

Multimate Advantage AutoCAD Mercator (converts geographic coordinates to UTM)

A photograph of the winch set-up is provided in Figure 2. Dredging Gear

Considerable experience was obtained in the dredging technique and a short section is included to summaries improvements in technique. Cable

As a result of experience from a previous survey (Harper, 1988b), 4 mm wire cable was selected for dredging; the primary reason for using wire was to reduce drag on the line by (a) using a small diameter wire and (b) using a negatively buoyant wire (as opposed to most synthetic line). In theory, use of wire as opposed to synthetic line allows smaller weights to be used on the dredge. Stones

We used two types of stones during the survey: cast concrete blocks with embedded reinforcement bar and wire-wrapped

[11] boulders. The cast stones performed significantly better than the boulders. At two stations the wire wrapping loosened to such a degree that the boulders were torn out. At another station the boulder actually cracked in half although we were fortunate enough to recover the dredge. The primary reason for the superior performance of the cast stones was the tracking of the nets; we had less problem with tangling of the nets on the cast stones and felt that the nets tracked closer to the bottom. Netting

A woven nylon netting was used on all dredges; netting with a larger mesh size appears to provide a superior tangling capability (e.g., 2.5 cm mesh as opposed to 1.2 cm mesh). Experiments with monofilament net indicate that this type of netting is totally unsuitable for tangle-net dredges.

Entanglement of the nets during lowering of the dredge is a problem; we minimised this problem by packing the nets into a small plastic bag which was torn off when the dredge dragged along the bottom (Figure 3). This technique significantly reduced entanglement of the nets; on only one occasion did the bag fail to release the nets (believed to be on a soft bottom). Weak Link

In that dredging is conducted on hard bottoms, hang-ups of the dredge are common, and a weak link is recommended for all dredges. We had experience with a variety of weak links during the survey, including the experience of not using a weak link.

As a general rule, the strength of the weak link should not exceed by more than 1/2 the breaking strength of the cable and also should not exceed the brake strength of the winch. The weak links we used were 5 mm and 8 mm polypropylene rope with thimbled eye-splices at each end. The breaking strength of the 8 mm line was too strong and at one station we actually had the cable part above the weak link. The 5 mm line had a similar strength to the brake-strength of our winch but on most occasions broke without having to tie the line off.

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On the occasions when the dredge hung-up and either no weak link were

present or a "strong" weak link was present, the cable was tied off to a bollard on the ship until it parted. This was accomplished by letting out considerable slack (30 m), temporarily securing the line over the side, and quickly making a series of wraps around the bollard before the line tightened up.

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Dredging Technique

Previous reports had indicated that a sufficient length or scope of wire for the dredging was 1.1 to 1.15 times the water depth (Grigg, 1977). Our experience was that considerably more wire had to be used, in some cases up to nearly twice the water depth. The procedure used was to payout about 1.2 times the water depth and then wait for the drift of the vessel to take up slack. The bottom can then be "felt" and additional wire was let out in 10 m increments until the stone made continuous contact with the bottom. The wire handler can quite clearly distinguish when the stone is "flying", or, if in contact with the bottom, if the bottom is rocky, gravelly or "soft".

The discrepancy between dredge-line lengths reported for commercial vessels (Grigg, 1977) and our dredging may be due to a greater drift rate for our vessel. Firstly, our vessel was larger than most commercial vessels and therefore would have had greater windage; secondly, we had only one dredge overboard whereas commercial vessels have up to eight, thereby creating greater drag and reducing the drift rate of the vessel. Dredging Problems

We experienced numerous problems during the dredging operation that affected our efficiency. These are described herein so that future investigations can benefit from our experiences.

Two catastrophic failures of the winch occurred. The first was a bearing failure of the clutch drive. Because no spare was available and 1.000 m of cable was over the side, the remaining cable was hauled in on the anchor winch of the ship. This was a very slow procedure and resulted in severe kinking of the cable. The second failure was the shaft key for the magneto; because of difficulty in maneuvering the ship in a narrow channel, the cable was cut and 400 m cable lost. It is

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recommended that future operations bring at least one empty cable reel to facilitate storage of retrieved cable.

We also had to put a splice in our cable following one of the failures. The splice was done by the Ship's Bosun and. it is notable that during a later failure of the cable, the failure occurred above the splice. Also we had no problem with the splice passing through the sieve of the metre wheel. As a minimum it is recommended that a cable rigging or splicing guide be onboard during dredging operations.

During the survey, the dredging technique was continually refined both in terms of rigging of the tangle-net dredge and. the actual dredging procedure. The use of a "tear-away" plastic bag on the nets significantly reduced net tangles during deployment and. is highly recommended for future surveys. Various combinations of weak I inks and. rigging were tested with the best "rig" as follows:

- cable terminated with loop (double Nicropress fitting) ; - weak link (5 mm polypropylene, eyes spliced with thimbles) ; - swivel (optional); - 3 m chain;

- cast-concrete stone (40 kg with reinforcements bar, integral pipe dredge);

- tangle-nets (at least 1.5 m in length and made of nylon; mesh size of at least 2.5 cm; note that monofilament netting is unsuitable) .

The swivel may be considered optional as the use of a tear-away bag on the nets

minimizes net tangles, reducing the need for a swivel; by omitting the swivel the rigging is less susceptible to hang-up (we suspect that on one lost dredge where the cable parted at the vessel, the rig had hung-up on the swivel).

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Towards the end of the survey, we were able to "feel" bottom on all

casts. This was achieved by letting out about 1. 2 times the depth of cable, then paying out additional cable in 10 m increments until bottom was felt. This procedure effectively eliminated the question of "was the dredge on the bottom?".

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RESULTS Sounding

The echosounder was operated at all times while the ship was underway and approximate 1 y 13,600 km of soundings were obtained. A general location map of the ship's track is shown in Figure 1.

The sounder and. hull-mounted transducer worked we 11, even while under full speed (11 knots) and heavy seas (Force 6).

In general, the soundings obtained during this cruise compared favorably with the MHO bathymetric maps. The most common difference was in close proximity to the islands where the maps typically showed a lower gradient reef-front slope than was actually present. Dredging

A total of 42 stations were occupied during the survey (Table 1; Figure 4); however, at some of these stations, the dredge was either lost or did not touch the bottom resulting in a total of 32 "effective dredgings" (Table 1). Samples were recovered from 18 of the dredgings, which is 42 % of the total or 56 % of the effective dredgings (Table 1).

As a result of weather problems, equipment breakage and. equipment losses, the

distribution of sampling is not evenly distributed within the survey area. Figure 4 indicates the distribution of sample sites and associated sampling depths. Deepwater dredging was conducted at only five of the stations, mostly in the southern Lau Group (south of Lakeba). Strong wind conditions and. eventual loss of cable prevented additional sampling in deepwater. In the northern Lau Group (north of Lakeba), samples were recovered at only two stations; the poor

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CONCLUSIONS

The conclusions listed herein are tentative until final results of the sample identifications and analyses have been completed.

1. Based on tentative identification of samples recovered, the potential for finding

commercial-sized beds of Corallium within the Lau Group is not encouraging. The evidence is not conclusive, however, in that only a few dredgings were made in water depths greater than 600 m and only a few dredgings were made within the northern portion of the Lau Group.

2. The MRD bathymetric maps of the Lau Group proved to be generally accurate

and an excellent tool for planning purposes. 3. The dredging technique was refined to such a point that bottom could be "found"

on almost all casts. However, because of the rugged nature of the bottom, particularly in the northern Lau Group, hang-ups and gear loss were common.

4. Rugged bottom conducive to Corallium growth was common in areas north of

Lakeba.

RECOMMENDATION

The recommendations made herein are tentative until results of the sample identification and analyses are completed. 1. Additional survey work is required in the Lau Group before a representative

sampling is achieved. This can probably be conducted on a ship-of-opportunity basis with dredging concentrated in (a) deepwater in the Southern Lau Group and (b) all "Corallium" depths in the northern Lau Group.

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2. Additional cable (>3000 m of 4 mm cable) and a larger winch are required

for deep dredging. 3. Gear loss proved to be heavy on the rocky seabed; 12 to 15 complete sets of

tangle-net dredges and associated hardware are recommended for a cruise of similar duration.

4. Additional reconnaissance Corallium dredging is recommended in all other

areas of the Fiji waters as the present sampling is not considered representative.

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REFERENCES GAUSS, G. 1981: Fiji offshore survey, Cruise FJ-80(1), 16-19 November 1980.

CCOP/SOPAC Cruise Report 46: 4 p. GRIGG, R. W. 1977: status of the precious coral industry in Japan, Taiwan and

Okinawa. University of Hawaii, SeaGrant Technical Report UNIHI-SEAGRANT - TR-77-D2: 12p.

GRIGG, R.W. 1981: Species identification and assessment of CCOP/SOPAC

precious coral collections in 1980 and 1981. CCOP/SOPAC Technical Report 14: 16 p.

HARPER, J .R. 1988: Precious corals prospecting strategies for the South Pacific

Region. CCOP/SOPAC Technical Report 84: 81 p. HARPER, J .R. 1989: Offshore survey for deepwater precious corals in the

Gilbert Island of Kiribati. CCOP/SOPAC Cruise Report 124: 22 p, 3 Appendices.

PRATAP, A.; RAICEBE, T.; SMITH, R.; WOODWARD, P.; WOODHALL, D.

(compilers) 1987a: Cikobia. [Multicolored bathymetric map, scale 1:250,000], Fiji Mineral Resource Department.

PRATAP, A.; RAICEBE, T.; SMITH, R.; WOODWARD, P.; WOODHAIL, D.

(compilers) 1987b (in press): Lau. [Multicolored bathymetric map, scale 1:250,000], Fiji Mineral Resource Department.

PRATAP, A.; RAICEBE, T.; SMITH, R.; WOODWARD, P.; WOODHALL, D. (compilers) 1987c (in press): Ono-I-Lau. [Multicolored bathymetric map, scale 1:250,000], Fiji Mineral Resource Department.

SMITH, R.; RAICEBE, T. (compilers) 1984: Bathymetric map of Fiji.

[Multicolored, scale 1:1,000,000], Fiji Mineral Resources Department.

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APPENDIX A

Trip Log

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APPENDIX A

Trip Log of FJ.20 Cruise 11 May to 27 May 1988

______________________________________________________________________

Scientific Crew: Co-01ief Scientists - J. Harper (JH). R. Smith (RS); Technician - S. Ratu (SR)

9 May 88 Scheduled departure of 1200 hours delayed due to inability of ship to get to fuel dock and delay in MRD getting hydrology drilling equipment on board.

10 May 88 1100 Ship off from dock (w/o fuel).

1130 Suva Harbour entrance 1325 Target A. station 1 1515 Target E, station 2

11 May 88 0100 Target C, Station 3

0300 Target C, station 4 0400 Finished station, enroute to Fulaga to offload Hydrology people. 1100 most day spent offloading gear; testing

sounder, preparing logs. 1700 depart Fulaga for Target D 1830 sounding in area of target D 1950 Target D, Station 5

2045 chain slipping on winch during retrieval; winch bearing shaft

failed; cannot be repaired on ship 2330 commence hauling cable on main winch

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Trip Log Page 2 of 6 12 May 88 0100 cable finally on board; steam to Fulaga area to get shelter from

weather and. await dawn. 0900 contact E. Saphore, Suva re replacement bearing; steam to Ogea

Levu anchorage to await reply 1000 at anchor Ogea Levu; transferring cable from bow bollard to

back deck while awaiting a reply from Suva 1200 radio transmission from Suva garbled; RS to shore to attempt

direct call via P&T 1430 RS talked with E. Saphore; no replacement bearing possible w/o

S.N.; return to Suva to match bearing. EI'A 0800. 1530 Depart Ogea for Suva

13 May 88 0800 Arrive Suva Dock, Walu Bay Naval Base

0900 Replacement bearings purchase and. installation underway; EID

1600 hrs; splice wire and respool 1600 Informed that ship cannot leave port with less than 40 % fuel

capacity (less than 39 % on board now). Must delay departure until Monday after fueling.

16 May 0740 RS, SR and. JH aboard ship; move to fuel dock for refueling;

awaiting replacement of Chief Engineer. 1620 cast off lines from dock. 1640 Suva Harbour Entrance; enroute to Moala Is, Target "C".

17 May 0400 pass over ridge enroute to Target "C".

0500 Target "C" not at previous position, go back to ridge at 0430

position

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Trip Log Page 3 of 6

0610 stone over side but missed crest so retry. 0700 repositioned for station 6; haul after 1 hour; some worm

tubes and some coral recovered. 0835 enroute to Target "D" off Kabara Is. 1200 ran across interesting target; conducted

Station 7. 1340 enroute to location off Kabara Is. 1500 Station 8 1620 Depart for Target "E" to W Fulaga 1700 Station 9 1930 Dredge onboard.; enroute to Target "F", 600 m crest to W

of Fulaga. 2045 Deploying dredge; missed target so abandon for now. 2145 enroute to One- I-Lau; ETA 0500

18 May 88 0500 arrive Target "G"; lost soundings due to sea state

0630 station 10 0730 sounding for ridge crest 0900 Station 11 0945 enroute Target "H" 10nmi SSE Vatoa; ETA 1400 1330 arrive Target "H"; do station 12 1515 station 13 1600 Station 14 1645 enroute to Target "I", 4. 2nmi NE Vatoa 1900 station 15; standby Target "I" for daybreak stations; too

much wind (>20 knts) to continue 19 May 88 0600 awaiting Sat fix, no positions for over 3 hr; weather is same

- SE winds at 15 knts.

0830 station 16; curtailed dredging at Target "H" due to high wind and rough sea - dredges not reaching bottom.

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Trip Log Page 4 of 6

0930 enroute to Ogea to try and. work in shallower water

1215 Station 17 1330 Station 18

1530 Station 19; winch failed, attempt repairs 1710 cable cut, lost 400m wire

1720 Barracuda Passage, Ogea

1800 anchor, Ogea Lagoon

20 May 88 0720 weigh anchor, enroute to Fulaga

0830 Fulaga to pick up MRD people 1030 Station 20 1230 Station 21 1315 enroute to Target "L" 1430 Station 22 1600 Station 23 1745 at anchor Yagasa Lagoon

21 May 88 0800 weigh anchor from Yagasa Lagoon

0845 Station 24 1115 Station 25; cable parted, lost dredge & 660m

cable

1330 Station 26 1500 Station 27

1700 Entrance to Komo Harbour 22 May 88 0800 weigh anchor from Komo Lagoon 1100 anchor down at Lakeba 23 May 88 0800 enroute from Lakeba Anchorage to Target "Q"

0845 Station 28 1030 Station 29 1200 Station 30 1425 station 31

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Trip Log Page 5 of 6

1515 Station 32

1720 Anchor outside Reid Haven 2230 anchor pulled off ledge; steam throughout the night

24 May 88 0600 north of target; steaming to target off Reid

Haven 0620 Station 33

0640 cable hung up on bottom, manoeuvering ship

0730 weak 1ink finally parted; enroute to Target "D"

24 May 88 0915 Station 34

0940 dredge hung up; cable parted above weak link at nicopress

fitting; leave Target "U" for Target "V" 1015 Station 35; dredge hung-up and was lost 1200 Station 36

1400 Station 37; dredge hung-up and was lost 1430 enroute to anchorage at Vanua Balavu 1530 Vanua Balavu

Lagoon entrance 1620 anchor off Susui

25 May 88 0700 weigh anchor

0750 Lagoon Entrance 0850 Station 38

1000 leaving Target "Y" - bottom appears to be mostly soft with

some bottom penetration of profiler

1100 Station 39 - stones lost 1215 Station 40

1240 enroute Target "M" 1430 Station 41

1500 enroute to Cikobia

1730 at anchorage off Cikobia

[29] Trip Log Page 6 of 6 26 May 88 0745 weighing anchor; preparing for black coral diving in

Vanuabalavu lagoon near American Passage

0800 discovered that RS forget to bring regulator; change plan to conduct additional dredging at Yacata enroute home

0830 lagoon Entrance; enroute Yacata

1230 arrived at Yacata Island, Target "BE"; too deep to

dredge; proceed to seamount target 1445 arrived at Target "CC", seamount; dredge deployed,

hung up and cable parted at deck block with loss of 700 m cable; unable to do more dredging so head for Suva - ETA 1330 at harbour entrance

27 May 88 0100 arrived entrance to Suva 0200 dock, Walu Bay

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APPENDIX B

Navigation Log

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APPENDIX C

Station Log

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APPENDIX D

Target Log