BULLETIN OF MARINE SCIENCE, 55(2-3): 651-666, 1994
TEN YEARS OF FISH AGGREGATING DEVICE (FAD) DESIGN DEVELOPMENT IN HAWAII
Glenn R. Higashi
ABSTRACT Fish Aggregating Devices (FADs) were introduced in Hawaii in an attempt to increase sportfishing opportunities and revitalize the fishing industry by taking advantage of the "ag- gregating" behavior of pelagic fishes around floating objects. In 1980, the State of Hawaii's Department of Land and Natural Resources established a FAD system of 26 buoys around the main Hawaiian Islands. Since their introduction, FAD buoy and mooring system designs have undergone considerable technological changes. The Hawaii FAD System evolved from the use of foam-filled tire buoys, using one type of synthetic line to the present sphere buoy design with two types of line, The design changes were developed to create a buoy and mooring line system that would remain on station for a long time and enhance sportfishing opportunities. Today, Hawaii's 78 FADs make up a system, including 56 surface and 22 midwater buoys. The FADs have proven to be very popular among Hawaii's fishermen. Catch statistics show that the FADs have contributed to increased catches and historical data on FAD survival in the field show that design improvements have produced longer lasting FADs. Future developments in FAD systems point to a combination of surface and midwater FADs around the main Hawaiian Islands.
Fishermen in Hawaii and other parts of the world have long known that tunas and other pelagic fishes are attracted to floating objects, Fishermen have benefited from this behavior by fishing around floating logs, nets, debris, and other flotsam (Matsumoto et aI., 1981; Shomura and Matsumoto, 1982). Scientists in the state have capitalized on this phenomenon by placing fish aggregating devices (FADs) in waters surrounding the Hawaiian Islands. In these waters, schools of tunas and other important pelagic fishes such as dolphin fish (mahimahi), wahoo (ono) and billfishes are induced by the presence of FADs to congregate and remain for periods of time in an area so that fishermen can easily locate them. In 1977, the Honolulu Laboratory (Southwest Fisheries Center) of the National Marine Fisheries Service, with funds from the Pacific Tuna Development Foun- dation (now Pacific Fisheries Development Foundation), installed a few experi- mentally anchored rafts off Oahu, Lanai and West Hawaii. Large skipjack tuna (Katsuwonus pelamis or "aku") catches of 4.5 to 13.6 MT per boat were reported by pole-and-Iine fishing vessels around these rafts as opposed to previous catches averaging 3 MT per boat during the peak summer season (Division of Fish and Game, 1978; Division of Fish and Game, 1979). The aku boats also found they were using less than the usual amount of live bait, enabling them to make more fishing trips per week since the live bait resources are limited. Sport fishermen also reported catches averaging 136-318 kg of skipjack tuna and 91 kg of ma- himahi per boat-weekend (Matsumoto et aI., 1981; Brock, 1985). Encouraged by the successful results in Hawaiian waters, the Department of Land and Natural Resources, Division of Aquatic Resources, proposed establish- ing a system of FADs in 1979 to revitalize the fishing industry and increase sportfishing opportunities, The State Legislature has continued to appropriate funds to the Department for developing, establishing and maintaining such a sys- tem. Matching funds were obtained from the Federal Aid in Sport Fish Restoration Program (Dingell-Johnson). In April 1980, the Division designed, built and deployed 26 FADs in waters
651 652 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994
PentasphEH"e Buoy
Single-Sphere Buoy nre Buoy
tire filed with polyurethane loam
chain wilh streamers
chain wi1h cable streamers
Not Drawn to Scale polypropylene line
chain \ chain
'.'. '.
Figure I. Tire, pentasphere and sphere FAD designs.
around the main Hawaiian Islands. The FADs were placed 3.9-40 km offshore, in depths from 146-2,76] m, as recommended by Hawaii's fishermen through statewide public meetings. The following study describes the original FAD design as well as a series of modifications that were made in the FAD system as a result of the State's findings regarding FAD longevity, structural stability and effective- ness as demonstrated by the experience of Hawaii's fishermen.
MATERIALS AND METHODS
Development, Deployment and Modification.-The State's experience has led to the development of three different FAD designs: the initial foam-filled tire design, a pentasphere design and a single sphere design (Fig. I). A concomitant development of mooring system designs has been necessary to suit each FAD type from a single type of rope initially used to moor the tire design, to the current more complex mooring system, fabricated with two types of ropes and three concrete anchors. The first generation FAD consisted of "tire" design of discarded rubber truck tires (1.8 m diameter, 56 cm wide) enclosed on both ends by steel plates and filled with polyurethane foam. The buoy weighed 680 kg and had a 2.4-m steel-ballast counterweight-pipe attached to the bottom steel plate and a 1.5-m steel mast on top with a navigational aid light. The navigational aid lights were made of polyvinyl chloride (PVC) pipe with a radar reflector made up of angular plates at the base of the mast. The mooring system consisted of a chain bridle and 30.5 m of 13-mm galvanized chain, attached directly to the buoy then connected to 19 mm diameter 3-strand polypropylene line and another 9.1 m of chain terminating at a 1,361 kg Danforth anchor. The mooring line had a 2: I scope with a short section of 13-mm galvanized chain, linked into the middle of the polypropylene line as a weight to prevent the mooring line from floating on the surface during periods of no or changing current (Fig. 2). The cost of building a tire buoy is $1,200. To improve the fish aggregating system, consultant marine engineers designed a new FAD buoy HIGASHI: FISH AGGREGATING; HAWAII 653
1.8 m Tire Buoy
1~~~~~~eye 19 mm RPL
3 m -16 mm Chain Bridle
16mm RPL 16 mmSWV 16 mmSAS o SAS - Safety Anchor Shackle o SWV - Swivel 30.5 m - 13 mm Chain o RPL - Replacement Unk
16 mm RPL 16 mmSWV 13mm SAS 19 mm Newco Thimble
19 mm 3-strand polypropylene rope 19 mm Newco Thimble 13mmSAS
13 mm Chain weight SCOPE = 2:1 16 mm RPL 16 mm SWV 13 mm SAS 19 mm Newco 19 mm Nawco Thimble Thimble 13mm SAS 16 mm SWV 16mm RPL
9 m - 13 mm anchor chain
Figure 2. Tire FAD mooring system.
called a "pentasphere" in 1981. Weighing 363 kg, it consisted of five 71-cm diameter steel spheres welded into a rosette configuration. The pentasphere FAD had a 1.5-m aluminum mast bolted in the center of the 5 spheres and topped with a PVC navigational light, a radar reflector of 4 angular aluminum plates and a two-tone pennant on a fiberglass pole. The aluminum mast was isolated from the steel buoy, using a plastic sleeve, thereby reducing corrosion. The mooring system of the pentas- phere FAD consisted of 9-15 m of 13-mm galvanized chain, 183 m of 9.5-mm (6 X 7) galvanized wire rope (16-mm diameter 12-strand single-braid polyester rope spliced into a 19-mm diameter 12- strand single-braid polypropylene rope), and another 9 m of 13-mm galvanized chain terminating at a 1,361 kg surplus Danforth anchor. (Fig. 3). The scope for the mooring line was 1.3:1. The cost of 654 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994
Pentasphere Buoy 5- 71 cm diameter steel spheres
19 mmJE-SWV 16 mm SAS
9-15 m - 13 mm Chain r::J JE-SWV - Jaw - End Q Swivel o SAS - Safety Anchor Shackle 16 mmSAS 71 cm diameter steet sphere o SWV - Swivel 16 mmSAS 16 mmSWV o RPL - Replacement Unk 16mm SAS 9.5 mm wire thimble
183 m -9.5 mm (6x7) wire cable 16 mm 12-strand single-braid polyester line (non buoyant) Length (It) = depth (It) x 0.267 9.5 mm wire thimble 16mmSAS (spliced to) 16 mm RPL 16mmSWV 19 mm 12-strand single-braid polypropylene rope (buoyant) 16mmSAS Length (It) = 1.067 x depth (It) - 75Z 16mm RPL 19mm SAS SCOPE = 1.3:1 16 mm Newco Thimble 16 mm Newco Thimble 19mmSAS 16mm RPL 16mmSAS 16mmSWV 16 mm SAS 16mm RPL
9 m - 13 mm Chain
Figure 3. Pentasphere FAD mooring system.
building and deploying a pentasphere buoy is approximately $3,700, of which $700 are construction costs alone. By October 1981, the 26 tire FADs were all replaced by FADs of the pentasphere design. In replacing the existing tire buoys with the pentasphere design, only the buoy was changed; however, modifications were made to the original tire mooring. The 30.5 m 13-mm chain was removed and a 9-15 m 13 mm chain and single 71-cm steel sphere below the buoy were attached to the 183 m of galvanized wire rope. In 1981, an experimental midwater FAD, the "U" buoy (Kaneohe, Oahu) was deployed off wind- ward Oahu (Fig, 4), at a depth of 18.3 m below the water surface, allowing for the unrestricted passage of surface vessels. The midwater buoy consisted of a 147 cm diameter steel sphere with a 71 cm steel sphere surface marker buoy attached. The subsurface FAD was expected to have a longer, more maintenance-free operating life, since it would no longer be exposed to rough ocean surface conditions. HIGASHI: FISH AGGREGATING; HAWAII 655
". '60' 159' lSS' 157" ,,. 155"
".
>IT
".
161' 159' '60' 1511' '57" 1S6' '5"
Figure 4. Statewide FAD system and commercial statistical catch area map.
In 1982, loca] marine engineering consultants analyzed the pentasphere design to determine possible causes of losses and recommend ways to correct FAD failure. The study resulted in a third generation FAD consisting of a 147 cm diameter surplus steel sphere with a I.I-m detachable mast bolted to the top, and a 2.] -m pipe counterweight (116 kg) welded to the bottom. The FAD weighs 399 kg and has a total positive displacement of 1,361 kg. The mooring system consists of 15 m of 13-mm galvanized chain attached to the buoy (the same type of mooring line used in the pentasphere design), 16 mm-diameter 12-strand single-braid polyester rope spliced into] 9-mm diameter 12-strand single- braid polypropylene rope and 9 m of 13-mm galvanized chain, terminating at a ],361 kg surplus Baldt or Danforth anchor. Other modifications included the use of nylon thimbles in the pad eye of the pipe counterweight to isolate the chain from the buoy and the addition of zinc anodes on the buoy and chain to reduce corrosion. Concrete anchor blocks were also built and used when the surplus supply of anchors was depleted. The cost of building and deploying a single sphere buoy is approximately $7,]00, of which $1,000 are buoy construction costs and $3,600 for deployment costs. Three single sphere FADs were installed experimentally around Maui and Hawaii to determine their cost and effectiveness. The new design proved to be less costly to build and had less drag and greater buoyancy than the previous designs. In 1983, single sphere FADs replaced all existing and missing pentasphere FADs in waters around the main Hawaiian Islands, excluding the OTEC (Ocean Thermal Energy Conversion) "OT" buoy (Fig. 4). In May 1985, the Division built and deployed 24 new single sphere FADs with State Capital Improvement Funds in waters around the main Hawaiian Islands. This increased the total number of FADs statewide to 48 (16 Hawaii, 14 Oahu, 7 Kauai, 5 Maui, 3 Molokai, 2 Lanai, 1 Kahoolawe) (Fig. 4). Modifications were made to the mooring system of the single sphere FADs in 1985 (Fig. 5). The 15 m of 13-mm chain below the buoy was increased to 30 m when fishing hooks were observed embedded in the mooring line at a depth of 30 m. The 12-strand single-braid mooring line was replaced with ]9-mm diameter 3-strand "Steel Line"@ (polypropylene/polyethylene) rope spliced into 19-mm diameter 3-strand Poly-Plus (polyester/polyethylene) rope. The "Steel Line"@ is 40% stronger, stretch- es less, and is more resistant to abrasion than the polypropylene line and both these lines cost sub- stantially less than a 12-strand single-braid rope. The "Steel Line"@ line is buoyant and the Po]y-Plus line is nonbuoyant. The combined buoyant/nonbuoyant lines form an inverse catenary mooring, the 656 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3. 1994
147 an Sphere Buoy
19 mmJE-SWV o 16mmSAS • 70mmZNC 30 m - 13 mm Chain Q JE-SWV - Jav. - End o Swivel 70 mm ZNC ~ o SAS - Safety Anchor 70 mm ZNC Shackle • 16 mm SAS 16mmSWV o SWV - Swivel 16mm SAS 16mmSWV tJ SL - Sling Unk 19 mmSAS 11l 19 mm Nylite o RPL - Replacement Unk Connector • ZNC - Zinc Anode
19 mm 3-strand polyesterlpolypropylene rope Length (ft) = 0.267 x depth (0.43 X depth for W. Hawaii)
(spliced to)
19 mm 3-strand poIypropyiene/polyethyiene rope Length (ft) = 1.067 x depth - 752'
19 mm Nylite11l Connector 19mmSAS 16mmSWV 16mm SAS SCOPE = 1.3:1 70 mmZNC 70 mmZNC I •I I• 26 m - 13 mm Chain I I I ' 70mmZNC 16 mmSAS 16mm S'NV 16mm SAS
~ 19mm SL poq 16mmSAS 8 8 'B 1.5~-~~~:~Chain DOD 3 - 771.1 kg Concrete Anchors (71.1 em X 71.1 em X 61 em)
Figure 5. Sphere FAD mooring system. line below the buoy sinking and the line above the anchor floating off the bottom. The inverse catenary synthetic rope design allows for a wider depth variation and a relatively small buoy (Boy and Smith, 1984). Concrete block anchors 71 X 71 X 61 em (length X width X height) were added to the system at this time. Three of these concrete blocks (a total of 771 kg dry weight) are used to anchor each FAD. In May 1986, the Division established an experimental fish trolling alley off Waianae, Oahu, as part of the Statewide FAD system. The "alley" consists of 10 midwater FADs, separated by about 0.8 lan, placed in a straight line that extends over 8 km parallel to the shoreline in nearshore waters. The "trolling alley" is located 1.6 to 3.2 km off the west coast of Oahu, between "Y" and "R" FADs off Makua and Makaha, at depths of 366 to 549 m (Fig. 4). The mid water FADs are located HIGASHI: FISH AGGREGATING; HAWAII 657
18 to 21 m below the surface. Each midwater buoy is made of four, 71-cm spheres, welded together in a pyramid configuration and attached by a chain. Each buoy system is moored as a unit to three concrete block anchors moored as a unit via 25-mm diameter polyester/polyethylene line. In 1989, the existing U.S. Army Corps of Engineers' FAD permit was modified to include 13 additional FAD sites: eight surface sites (2-Hawaii, 5-Maui County, l-Kauai) and 5 midwater FAD areas around Molokai. Three existing FAD sites ("1'\', "D", "P") were relocated at that time and one FAD site ("WW", off the island of Hawaii), was terminated. Sixty-three authorized FAD sites are currently in use (Fig. 4). In December 1989, the Division chartered the Naval Ocean Systems Center (NOSC) vessel, SSP Kaimalino, to deploy 12 midwater buoys in four areas off southern Molokai. The Kaimalino was used as the deployment vessel, because its small waterplane area twin hull (SWATH) design provided the stability and maneuverability critical to deploying mid water buoy mooring systems at the proper depths below the surface. A marine consultant was contracted to assist in the deployment of the midwater FADs, whose technicians set up transmitting and receiving stations on the vessel and shore to triangulate the vessel's position in relation to the land and the midwater buoy's position with respect to each other. This positioning system will be used to help relocate the midwater buoys for future monitoring. The four Molokai mid water areas are located 1.6-3.2 km off Kolo Harbor, Palaau, Kamal 0, and Pukoo in depths between 73-110 m. Each area consists of 3 midwater buoys, deployed approximately 0.8 km apart in a straight line and submerged 12.2-18.3 m below the surface. Each midwater buoy has a temporary surface light marker buoy to enable fishermen to locate the midwater buoy and triangulate its position for future reference. The midwater buoys are of the same design as used in the experimental fish trolling alley deployed off Waianae, Oahu in May 1986, consisting of four 71-cm spheres welded together in a pyramid configuration. The buoys are attached to a 9.5-mm diameter plastic-impregnated-and-coated galvanized steel cable and anchored to the bottom with three concrete blocks of an aggregate weight of 2,449 kg. The only difference in the mooring system from the Oahu trolling alley design is the use of wire cable instead of synthetic line. This cable design improvement alleviates line stretch, normally caused by taut moored conditions and prevents the midwater buoy from surfacing and becoming a hazard to navigation. Monitoring.-Since its initiation in 1980, the success of the Hawaii Statewide Fish Aggregating Device System can be measured by its continued support and popularity among Hawaii's fishermen. The increased number of FADs and the indignation aroused when they are lost is indicative of their popularity with the local fishers. This has presented many on-going problems associated with FAD development and maintenance especially in dealing with an environment as harsh and unpredictable as the ocean. In 1980, concurrently with the development of the FAD system, the Division initiated a reporting system to gather data on fish catches around the fish aggregating devices since the program is partially supported and funded under the Federal Aid in Sport Fish Restoration (Dingell-Johnson) Program along with the State's Land and Natural Resources Commercial Fisheries Program. Buoy fish catch data are also obtained from the Department's commercial fish catch reporting system which is man- datory under Hawaii Revised Statutes HRS 189-3 for commercial fishers to include in their monthly commercial report fish landed in the State. The voluntary reporting system consisted of a postage paid, business reply "Fish Buoy Card" that was distributed to the recreational sport fishers who fish around the FADs. A total of 8,000 fish buoy cards were distributed to the public through fishing supply stores, DAR offices, and State boat harbors. A cut-out facsimile of the buoy reply card was also printed in the local fishing newspaper for fishermen to send in.
RESULTS AND DISCUSSION Development, Deployment and Modifications.-In the first generation of Ha- waii's FADs, problems encountered with the "tire" FAD design were its low net buoyancy, bulkiness, and water absorption by the polyurethane foam. Over a period of time, tire FADs were observed sitting low in the water with the upper surfaces awash from the waves. Tire FADs recovered during the pentasphere replacements had their inner flotation foam saturated with water. The tire FAD's bulkiness also presented a removal problem when they washed ashore, requiring that they be cut up with a torch and removed in pieces. The "pentasphere" FAD design had some advantages over the tire design: its increased buoyancy, light weight, and economical and easy construction, place- ment and retrieval. However, this design still had some serious disadvantages. The 658 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994 increased surface area of the buoy structure generated considerable drag on the mooring system causing increased friction and additional wave and current stress, On some occasions, the buoys were observed being pulled underwater during strong current conditions. Strain on the mooring system and corrosion of hardware produced areas of weakness in the mooring line. The pentasphere buoy was not very stable during navigational light pack maintenance and was easily capsized in high waves, This characteristic may have been a cause of the high loss rate for pentaspheres, The single sphere FADs have proved to be the most successful design to date. The sphere design has increased buoyancy, stability and visibility in rough sea conditions, decreased drag, and improved economical feasibility, ease of construc- tion, and deployment. The synthetic line used in the mooring system of the current FAD design utilized a 3-strand line based on its low cost. Previous experience with pentasphere FADs showed losses attributed to fish bites in mooring lines weren't prevented by 8 or 12 strand lines, which have a decreased tendency to twist, "hockle" and link. The incorporation of several swivels in the mooring system alleviated problems of hockling and kinking when using 3-strand line (Boy and Smith, 1984) and these mooring systems still cost considerably less than those made with 8 or 12 strand lines, Of all the 70 spherical FADs recovered recently, only two FADs have shown signs of line hockling and kinking; and these were both due to the swivels below the buoy being fouled and bound up (one with monofilament line from trollers and the other with chafing twine used as a fish attractant), The spherical FAD design has proven its success in accomplishing the pro- gram's goal of maintaining a FAD on station for as long as possible, attaining an average of 659 days on station with a maximum life span of 5,5 years (1,988 days). The construction and use of concrete anchors are contributing factors in the increased longevity of the present FAD design. Divers observed that extensive corrosion occurred on the mooring chain of midwater FADs deployed in the Waianae Artificial Reef with steel anchors. Other midwater FADs deployed with concrete anchors about the same time did not exhibit extensive corrosion (Ka- nenaka, 1991),
Catches.-The monitoring of fish catches around the FADs was based on the State's commercial catch reports. The poor response and low returns (3%) of the fish buoy card program provided insufficient data for analysis and invalidated their usefulness as a means of obtaining fish catch data. The important pelagic commercial fish species reported caught around the FADs consisted of: ahi or tuna (mostly yellowfin tuna, Thunnus albacares; along with bigeye tuna, Thunnus obesus); aku or skipjack tuna, Katsuwonus pelamis; ka- wakawa or bonito, Euthynnus affinis; au or marlin (includes blue marlin, Makaira nigricans; striped marlin, Tetrapterus audax; shortbill spearfish, T. angustirostris; black marlin, Istiompax marlina; sailfish, Istiophorus orientalis; and swordfish, Xiphius gladius); mahimahi or dolphin, Coryphaena hippurus; ono or wahoo, Acanthocybium solandri; opelu or mackerel scad, Decapterus pinnulatus; and sharks. The FADs contributed an average of 9% (25% is more representative due to underreporting and total deficiency of reporting from the recreational fisher- men) to the statewide pelagic catch of these commercially important species, Aku, ahi, billfish, mahimahi and ono account for 99% of the total weight caught around the FADs (Table I), The fishing methods most widely used around the FADs include trolling, rod and reel (drift fishing), live bait pole-and-line (aku boats) and handline. In the 10 HIGASHI: FISH AGGREGATING; HAWAII 659
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Table 3. Means comparisons (Student-Newman-Keuls Means Rank Test) for FAD design versus re- gion/windfactor. Underlined means are not significantly different. Only means comparisons for which significant differences in mean values were found (ex = 0.05) are noted.
Regionlwindfactor Variable FAD design All over Days on station T P S x 203.09 329.52 645.45 (N) (44) (23) (143) All over Total FAD catch (kg) P T S x 4,444 8,457 29,108 (N) (19) (43) (137) Leeward Days on station P T S x 215.6 341.3 708.6 (N) (27) (15) (84) Windward Days on station P T S x 183.3 307.4 555.6 (N) (17) (8) (59) Big Islandlleeward FAD daily calch T S P (kg/day) x 0.258 1.291 2.149 (N) (4) (23) (11) Big Islandlleeward NONFAD daily catch P S T (kg/day) x 0.199 0.223 0.577 (N) (11) (23) (4) Maui, Molokai, Lanai NONFAD daily catch S P T Kahoolawelleeward (kg/day) x: 0.0484 0.0880 0.1185 (N) (40) (8) (5) years that the FADs have been in existence commercial aku boats visited the FADs over 1,554 times and caught 1,083.2 MT of fish with an average catch of 697 kg/trip (Table 2). The different FAD designs all aggregated fish, but sphere designs were signif- icantly more durable and produced higher long-term catches than the tire or pen- tasphere FADs because they were able to remain on station longer. A cursory examination of the data shows a number of overlapping trends, on the basis of FAD design (Table 3). Table 3 shows the results of a two-dimensional comparison of FAD type versus mean days on station, total catch and catch per day, both on the FADs and in their immediate proximity. The Student-Newman-Keuls (Sakal and Rohlf, 1969) means rank test showed that both the number of days on station and the total catch were significantly higher for the spheres. The test showed that the spheres stayed significantly more days on station for either windward versus leeward areas or for all areas. In the case of tires and pentaspheres, neither was significantly longer lived because of the high variability in the duration of these FADs. Although means comparisons were conducted by region (on a leeward versus windward and island-specific basis) for the number of days on station, total catch, depth, FAD catch, total catch per unit area, FAD catch per unit area, FAD catch per day, and total catch per day, there were no significant differences be- cause of the large variance in these parameters and the relatively small sample size for some regions. The only significant regional difference was seen for the Big Island leeward side, which had higher daily catch rates on either the sphere or pentasphere than on the tire FADs in the immediate vicinity of the FAD (FAD daily catch). The sphere FADs had significantly lower catches in areas close to, but not immediately adjacent to the FAD (NONFAD daily catch) than the tire HIGASHI: FISH AGGREGATING; HAWAII 661
Table 4. Number and proportion for FAD type versus depth
FAD lype
Penlasphere Sphere Tire TolDl Feet ==>700 Frequency ]6 42 8 % 7.48 19.63 3.74 66 Row % 24.24 63.64 12.]2 30.84 Column % 34.04 29.37 33.33 Feet ==>1,000 Frequency 16 2] 10 47 % 7.48 9.8] 4.67 21.96 Row % 34.04 44.68 21.28 Column % 34.04 ]4.69 41.67 Feet ==>1,500 Frequency 7 41 3 51 % 3.27 19.16 1.40 23.83 Row % 13.73 80.39 5.88 Column % ]4.89 28.67 12.50 Feet ==>2,000 Frequency 8 39 3 50 % 3.74 ]8.22 ].4 23.36 Row % 16.00 78.00 6.00 Column % 17.02 27.27 12.50 Total Frequency 47 143 24 214 % 21.96 66.82 ] 1.21 100.00
FAD on MauiIMolokai leeward. However, these comparisons are confounded by regional and temporal variation in the numbers and types of FADs deployed. Tables 4, 5, and 6 show the numbers and proportion of each FAD type as a function of depth, windward versus leeward orientation with respect to the islands and geographic region. While at shallow depths the experimental design is bal- anced, only the spherical FADs were placed in large numbers within deep areas.
Table 5. Number and proportion for FAD type versus windfactor
FAD lype
Windfnctor Pentasphere Sphere Tire Total Leeward Frequency 30 84 15 129 % 14.02 39.25 7.01 60.28 Row % 23.26 65.12 11.63 Column % 63.83 58.74 62.50 Windward Frequency 17 59 9 85 % 7.94 27.57 4.21 39.72 Row % 20.00 69.41 10.59 Column % 36.17 41.26 37.50 Total Frequency 47 143 24 214 % 21.96 66.82 11.21 100.00 662 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994
Table 6. Number and proportion for FAD type versus region
FAD type
Region Pentasphere Sphere Tire Total Big Island-leeward Frequency II 25 4 40 % 5.14 11.68 1.87 18.69 Row % 27.50 62.50 10,00 Column % 23.40 17.48 16,67 Big Island-windward Frequency 6 17 3 26 % 2.80 7.94 1.40 12.15 Row % .23.08 65.38 11.54 Column % 12.77 11.89 12.50 Kauai-Ieeward Frequency 2 6 1 9 % 0.93 2.80 0.47 4.21 Row % 22.22 66.67 11.11 Column % 4.26 4.20 4.17 Kauai-windward Frequency 4 17 2 23 % 1.87 7.94 0.93 10.75 Row % 17.39 73.91 8.70 Column % 8.51 11.89 8.33 MauilMolokai-leeward Frequency 10 40 5 55 % 4.67 18.69 2.34 25.70 Row % 18.18 72.73 9.09 Column % 21.28 27.97 20,83 Oahu-leeward Frequency 7 13 5 25 % 3.27 6,07 2,34 11.68 Row % 28.00 52.00 20.00 Column % 14.89 9.09 20.83 Oahu-windward Frequency 7 25 4 36 % 3.27 11.68 1.87 16.82 Row % 19.44 69.44 11.11 Column % 14.89 17.48 16.67 Total Frequency 47 143 24 214 % 21.96 66.82 11.21 100.00
This probably affects the species and size of fish caught, and thus the weight of the catch. Spherical FADs lasted considerably longer, and thus their catches can be expected to be greater if aggregations of fish persist in the area, There were more spherical FADs so their numbers were higher, but the proportion of wind- ward to leeward FADs of all three types was roughly equivalent (-60% leeward to 40% windward). Furthermore, although there were more spherical FADs the proportion of FADs in each region was roughly equivalent for all three FAD types. Thus windward-leeward, within- and between-region comparisons can be made and regional differences should balance out in overall comparisons for all islands, Fish catches on the experimental midwater FAD ("U" buoy), weren't as high HIGASHI: ASH AGGREGATING; HAWAII 663
Table 7. Chronology of "u" FAD catches and life span for different buoy designs
Life span Catch Chronological order FAD design (days) (kg) I tire 190 86 2 midwater 401 182 3 pentasphere 168 76 4 sphere 902 409 5 sphere 75 34 6 sphere 1,154 523 7 sphere 14 6 compared to the previous and post "u" surface FADs relative to the number of days on station (Table 7). Fish catches around the midwater trolling area off Waianae were small as very few catch reports were turned in. One of the main problems was that the fishermen had trouble locating the midwater FADs and if they did, didn't credit the catches to the trolling area to keep others away. It was reported by one fisher that a fisherman caught between 454-1,351 kg of opelu (mackerel scad) around the midwater FADs. Fish caught around the midwater FADs were mostly opelu and small tunas. The trolling alley's effectiveness in aggregating fish may have been affected by the close proximity of a 73-m natural drop-off, with which the fish associated during daylight hours and the presence of three surface FADs ("V", "R", and "S") in the nearby offshore area (Holland et aI., 1990). Molokai midwater FAD areas produced small catches for the year they were on station, probably due to limited reporting. In 1990, fishermen reported making 124 trips to the midwater FAD catching 2,112 kg consisting mostly of mahi and ono which make up 75% of the total catch. FAD Life Span, Recoveries and Losses.-Longevity of Hawaii's tire and penta- sphere FAD designs was relatively short compared to the sphere design, ranging from 55 to 667 days (mean = 329.5 days; N = 23) and 32 to 776 days (mean = 203.1 days; N = 44), respectively. The life span of the single sphere design FAD was significantly longer ranging from 33 to 1,988 days (mean = 645. 5 days; N = 143), based on the Student-Newman-Keuls (SNK) test for days on station (Table 3). The exact causes of FAD losses are difficult to determine without recovering the FAD and examining the mooring line. Even if the FAD and mooring is re- covered it is still difficult (or sometimes impossible) to determine the exact cause of loss, because of differences in the length of time the FAD was adrift, whether fishermen cut off or removed part or all of the mooring, whether or not the mooring was entangled on the bottom, etc. As an example: the Commonwealth of the Northern Marianas recovered Hawaii's "DD" FAD off the east coast of Saipan 3 years after it was reported lost. The FAD was deployed in May 1985 and reported lost in December 1987. The buoy and light pack were in good condition and only 0.3 m of chain were found attached to it in a terribly eroded condition. Determination of the cause of loss was not possible because excessive time had expired since its loss. The State was able to recover 76 FADs (16 of which were intentional remov- als), with a full range of FAD designs. Recovered FADs and onsite observations provided possible causes for some of the FAD losses, which are summarized in Table 8. Mooring line failure accounted for most of the losses in all 3 FAD designs, but 664 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994
Table 8, Known or probable cause of loss of the different FAD designs
Known or probable cause Total Percent Mooring line failure-hardware corrosion. capsizing 32 42,] Mooring line break by vessels 12 15,8 Buoy breakage/failure I 1.3 Fish bite (shark) 10 13,2 Deployment error-upside down mooring line 1 1.3 Storm-hurricanes 1 1.3 Intentional removal-replacement. hazard 16 21.9 Vandalism-shooting and sinking 3 3.9 Total 76+ was responsible for a lower percentage of the sphere design compared to the tire and pentasphere designs. Intentional removal made necessary the replacement of 15 tire buoys with pentasphere buoys and one pentasphere FAD removed by the U.S. Coast Guard and became a hazard to navigation after it capsized. In addition, 162 losses were of unknown cause. The experimental midwater FAD "U" that was deployed off windward Oahu was on station for only 401 days (Table 7). It didn't last very long compared to some of the surface sphere FAD designs. The State's experience with the deployment and monitoring of midwater FADs has included many problems. Many of these problems have been resolved, but some of the solutions created new problems. The triangulation of exact position of the deployment vessel during FAD placement and feasibility of their relocation for future monitoring has been improved by setting up transponder stations. How- ever, fishermen don't have this capability. With the increased use of GPS by fishers these stations aren't necessary. The problem of calculating line stretch and elasticity for synthetic mooring lines has been resolved by using plastic coated wire cable, although this is not completely impregnable to sea water and corro- sion. The strumming of the mooring line (characteristic of taut line mooring) which is considered an acoustic attraction factor for sharks and possible fish bite can be resolved by using fairings on the mooring line, but this adds to the cost (Boy and Smith, 1984). Fairings are plastic ribbons or streamers attached to the mooring line to reduce strumming or vibrations caused by current moving past the rope. The most critical period for a taut moored system is during the deploy- ment of midwater FAD. This process requires extreme accuracy, since an error of ± I % of the total deployment site depth could result with the buoy either resting on the surface or situated deeper than the intended depth. This is a problem if the buoy is pul1ed deeper, under strong current conditions as the increased pressure can cause the buoy to col1apse or implode. Overall, the midwater FADs deployed haven't lasted any longer or as long as the longest lasting surface FAD. Even though they are more maintenance-free, they are more difficult and costly to deploy. Also, fishermen don't know where they are or if they are on station and so don't credit any catches to them. User Conjlict.-The State's FADs effective "aggregating" capacity was not only limited to fish, but also attracted and aggregated a wide mixture of fishermen: trollers, aku boats, handliners and even longliners. This mixture of users resulted in user conflicts with trol1ers and handliners both complaining about the large aku boats taking all the fish around the FAD and conversely, the larger ~ll(Uboats complaining about the trollers and handliners cluttering up the area and running over the fish school. In early 1989, the gear conflicts became more evident with HIGASHI: FISH AGGREGATING; HAWAII 665
longliners creating a problem for the other user groups with their longline gear paid out over large areas entangling fishing lines as well as the FAD mooring lines. As a result of user conflicts, area closures were established around the main Hawaiian Islands in early 1992 prohibiting longline fishing from 92.6 km and 138.9 kIn offshore of Maui County and Hawaii; and Kauai and Oahu, respectively. Allocation of different FADs to the different user groups is one alternative to user conflict, but it creates another problem of monitoring and policing of that allo- cation.
CONCLUSION The development of Hawaii's Fish Aggregating Devices has improved to a point where the State is comfortable with the present sphere buoy and mooring system designs, maintaining an average life span of 659 days and a maximum life span of 1988 days. The FADs continue to enhance sportfishing opportunities as demonstrated by their capacity to increase fish catches, decrease time and baitfish use, and reduce costly fuel consumption. With the continued study of the FAD mooring system losses, further improvement can be made on increasing their longevity with minor modifications. The use of midwater FADs as a tool to aggregate fish requires further devel- opment and modifications in design and deployment techniques. The resolution of a whole new set of problems from those of surface FADs will be necessary to ensure their continued use as fish aggregators. The design, construction and de- ployment of midwater buoys is more critical in nature than surface FADs and may be more costly. Midwater buoys must be designed and built to withstand increased pressures associated with depth, have a smaller surface area to produce minimum drag and enough buoyancy to support the mooring system. The life span of midwater FADs needs to be triple that of surface FADs to make their use economically feasible since their cost is three times that of the surface FADs. New advances in ocean engineering technology may make that a possibility some- day.
ACKNOWLEDGMENTS
I would like to thank the Division of Aquatic Resources staff for their assistance and particularly the neighbor islands staff for their logistical support, the Statistical Unit for the compilation of the Commercial Catch data, and all the fisheries aides who provided the manpower for FAD dcployment cruise preparations and assisted in all other aspects of the program. Special thanks to the University of Hawaii Marine Center for FAD construction, deployment and logistical support and NOSC SSP Kaimalino crew for their assistance in the deployment of subsurface FADs off Molokai.
LITERATURE CITED
Boy, R. L. and B. R. Smith. 1984. Design improvements to fish aggregating device (FAD) mooring systems in general use in Pacific island countries. South Pacific Commission Handbook No. 24. 77 pp. Brock, R. E. 1985. Preliminary study of the feeding habits of pelagic fish around Hawaiian fish aggregation devices: or can fish aggregation devices enhance local fisheries productivity? Bull. Mar. Sci. 37: 40-49. Division of Fish and Game. 1978. A Statewide Fish Aggregating System. Division of Fish and Game, Department of Land and Natural Resources, State of Hawaii. 18 pp. ---. 1979. Hawaii Fisheries Development Plan. Division of Fish and Game, Department of Land and Natural Resources, State of Hawaii. 297 pp. Holland, K. N., R. W., Brill and R. K. C. Chang. 1990. Horizontal and vertical movements of yellowfin and bigeye tuna associated with fish aggregating devices. Fish. Bull. U.S. 88: 493-507. Kanenaka, B. K. 1994. Hawaii's artificial reef program: past, present and future. Bull. Mar. Sci. 55(2-3): 1341. 666 BULLETINOFMARINESCIENCE,VOL.55,NO.2-3, 1994
Matsumoto, W. M., T. K. Kazama and D. C. Aasted. 1981. Anchored fish aggregating devices in Hawaiian waters. Mar. Fish. Rev. 43(9): 1-13. Shomura, R. S. and W. M. Matsumoto. ]982. Structured flotsam as fish aggregating devices. NOAA- TM-NMFS-SWFC-22. 9 pp. Sokal, R. R. and F. J. Rohlf. 1969. Biometry. W. H, Freeman, Co., San Francisco, California. 776 pp.
DATEACCEPTED: July 29, ]993.
ADDRESS: State of Hawaii, Department of Land and Natural Resources, Division of Aquatic Re- sources, 1151 Punchbowl Street, Honolulu, Hawaii 96813.