SCTB16 Working Paper
FTWG–3
Documentation and classification of fishing gear and technology on board tuna purse seine vessels
David G. Itano 1
July 2003
1 University of Hawaii, Pelagic Fisheries Research Program, Honolulu, Hawaii, USA SCTB 16 – FTWG 3 1
Documentation and classification of fishing gear and technology on board tuna purse seine vessels
David G. Itano2
1. BACKGROUND
It is widely recognized that the efficiency or harvesting capacity3 of individual fishing vessels can increase over time due to a complex mix of technological and social factors. Rapid advances in effective effort are particularly evident in tuna purse seine fleets. The influence of new and more powerful deck machinery, sophisticated electronics, subscription to satellite image services and the like will be modified by accumulated experience, expertise and, most importantly, the willingness of vessel operators to utilize new technology. Other factors, such as information networks, sharing of FADs, utilization of auxiliary vessels and global tuna market factors will have a strong influence on catch rates, fishing strategies and species targeting.
Teasing apart the relative contribution of these factors to increasing efficiency is clearly a difficult task. The most empirical and definable means to monitor increasing fishing power may be through the documentation of new gear and technology on board vessels. However, there is a clear danger of basing assumptions of fishing power on a simple gear list as it makes no qualification as to how often or how effectively the new gear is utilized.
This argument may have had greater credibility in the past when the purse seine industry was in a stronger financial position. However, given the current economic situation facing world tuna purse seine fisheries, it is doubtful that vessel owners and operators will be installing expensive gear unless they planned to fully develop its potential. Still, some indication of the gear and the USE of the gear is necessary.
A common problem in examining vessel registries containing technical data to examine effort increase is that registry information is usually not kept up to date. New pieces of electronic equipment are seldom noted in a timely fashion, and even major changes like the installation of a new purse winch or refrigeration system may go undocumented. It has often been left to regional observer programs to attempt to document advances in gear technology and fishing methods. The problem encountered in all observer programs is that most observers do not remain in their program for more than a few trips, limiting their ability to notice and record “new” technology. Their baseline begins on their first trip on a purse seiner, and any innovative gear or fishing method will become their norm.
This paper is an initial attempt at compiling information and illustrated examples of the development and current status of tuna purse seine technology. Documents such as this should be useful for the training of observers and port samplers to assist their ability to categorize vessels and discern changes in gear and fishing methods. It is anticipated that regional observer programs will incorporate this information and illustrations into materials for training and information dissemination.
2 University of Hawaii, Pelagic Fisheries Research Program, Honolulu, Hawaii, USA 3 defined here as the maximum amount of fish that a vessel can produce over a set period if operating at maximum efficiency
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2. FISHING GEAR 2.1 Seine net – knotted
Most modern purse seine fleets utilize the U.S. style tuna purse seines first developed in southern California for the eastern tropical Pacific fishery. These seines are made up of several horizontal strips of pre-fabricated, knotted nylon webbing that lie in parallel and between a nylon corkline and galvanized steel chainline. The strips are laced together with nylon twine and are approximately 4.25 fathoms deep. This style of seine can be accurately classified to depth by simply counting the number of strips between corkline and chainline at the half-net mark, or where the net is deepest. Within the WCPO, this style of purse seine is commonly used by purse seiners from Australia, Indonesia, Korea, New Zealand, Philippines, Russia (or former), Solomon Islands, Taiwan, USA, Vanuatu, and the Pacific Islands. European Union (EU) seiners of France and Spain also use this style of net.
A selvedge strip of heavy webbing secures the corkline and chainline to the rest of the net to handle the massive weight and pull generated by the pursing operation, power block and tuna. Most of the seine is constructed of relatively light webbing with large mesh size which facilitates fast sinking and pursing. It is only the bow end of the net (sack, or bunt) that is very heavily constructed where the catch is concentrated and held for brailing. Due to the warm, clear waters of the WCPO, tuna purse seines in this region are some of the deepest in use anywhere. Typical purse seines of this style may be constructed with 28 to 30 or more strips.
2.2 Seine net – knotless
Japanese purse seines are completely different, constructed of large, vertical panels of lightweight, knotless nylon webbing in contrast to the knotted, horizontal strips described above. For example, Itano (1991) reported on a Japanese group seiner equipped with a tuna purse seine constructed of 31 vertical panels of knotless webbing with mesh sizes ranging between 240 mm (stretched mesh measurement) in the bow and center sections of the net to heavy 75 mm meshes in the sack. The Japanese knotless nets can be stored in a much smaller area for length of net, thus allowing a typical 499 GRT Japanese purse seine vessel to use a net as large as a 1500 GRT vessel equipped with a knotted net. However, the knotless webbing is not as strong and must be set with care with greater attention given to current and wind conditions. Figures 1 and 2 show typical knotted and knotless webbing from regional purse seine vessels.
Figure 1. Knotted nylon purse seine4 Figure 2. Knotless nylon purse seine.
2.3 Purse seine – new materials and styles Materials other than nylon, such as the Kevlar family of “super” synthetics have been successfully adapted to trawl designs and their application to tuna purse seining is being investigated. New styles of knotless webbing that lock the mesh at the crosses are also being developed and utilized. These newer “cross-lock” designs offer greater security as a ripped mesh will not continue, or “run” along a seam. However, the high cost of these materials has slowed their adoption by purse seine vessels.
4 All photographs are by the author unless otherwise indicated
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2.4 Purse rings
Two basic styles of purse rings are used WCPO purse seine vessels. The old style, continuous round steel rings were the norm when Gillett (1986) described a typical U.S. vessel in 1984 (Figure 3). These rings have the disadvantage of creating a great deal of friction during pursing. Also, the process to secure the rings to the vessel prior to net rolling is very time consuming and dangerous, (Figure 4). This process can be speeded up by making the ring bridles detachable from the chainline with nylon rope bridles, but this requires that the vessel be equipped with two entire sets of rings for continuous setting operations.
Snap roller ring hold many advantages to the fishing operation and have been widely adopted by most fleets (Figure 5). The roller action on the purse cable reduces friction significantly, reducing wear on purse cables and allow faster pursing speeds. It has been reported that the purse seine operates more efficiently with roller rings, allowing the net to purse deeper as the rings do not ride up on the cable as is common with continuous rings.
Figure 4. Securing rings to the ring stripper prior to net retrieval.
Figure 3. Old style steel rings with chain bridles
Figure 5. Stainless steel roller snap rings.
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2.5 Purse winch and davit
The basic form of the tuna purse winch has not changed substantially in thirty years, consisting of a hydraulically driven towline drum, sern drum and bow drum (Figure 6). The sole purpose of the uppermost towline drum is to secure the vessel to the stern oertza, or stern end of the seine during the setting process after which it is hauled to the vessel during pursing. The bow drum connects to the bow end of the purse cable during ring pursing. The stern drum holds all of the purse cable during the beginning of the set, paying out cable through the purse rings as the net is set in a circle. At the completion of the encirclement phase, the cable is connected to the bow drum and pursing begins on both bow and stern drums simultaneously.
Modern purse winches consist of the same three drums but are significantly larger in size to accommodate thicker diameter purse cables necessary for larger and heavier seines (Figure 7). Of greater importance is the increase in power of the newer winches which have been engineered to achieve fast pursing speeds with much deeper and longer (heavier pull) nets. The necessary power has been achieved by installing dedicated auxiliary diesel engines to power the purse winch.
Figure 6. Tuna purse winch, circa 1973.
Figure 7. Tuna purse winch circa 2003
A graphic illustration of the increase in purse winch sizes over this time period can be seen in a comparison to purse davits and sheaves. A typical purse davit to accommodate the pull and stresses of a 1970s era tuna purse seine may have measured about 2 m in height (Figure 8). In comparison, Figure 9 shows a huge purse davit and purse blocks on a 100 meter tuna purse seiner vessel currently in operation.
Figure 8. Purse winch, davit and blocks on a 1970s era tuna seiner. Figure 9. A huge purse davit and blocks on a modern tuna purse seiner (c 2003)
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2.6 Power blocks
There are several types and makes of power blocks that have been used in the WCPO purse seine fishery. Most of the fleets use some form of the boom suspended “Puretic” type hydraulic power block first introduced to the region by US flag vessels. The entire seine from chainline to corkline passes through the power block, descending to deck level for manual stacking by the crew. Correct positioning of the net is assisted by vertical and lateral movements of the main boom to which the block is attached. Figure 10. Hauling net on a Taiwanese seiner.
The concept is simple, but requires a great deal of hydraulic power to haul the net high in the air prior to stacking. However, the process allows ample time to clean the net of debris and gilled fish and inspect the net for holes and damage. The main disadvantage of this type of net hauling gear is that it is restricted to calm areas of the world. Net hauling and stacking with this type of gear is extremely difficult or impossible in moderate to strong winds. Figure 10 shows a typical Puretic type power blocks in operation.
Power blocks have increased in size and rated net pulling power in step with the increased depth and bulk of new seine nets. As vessels increase their ability to load and freeze very large sets, the fishermen have been able to fabricate nets capable of handling catches in excess of 400 mt per set. This means very deep, long nets with thicker diameter corklines, doubled or bunched corks in critical areas, heavier chainlines and very heavy or doubled net bunts (sack end). Figure 11 shows a modern Puretic style power block with greatly flared and expanded sides to accommodate the larger net volumes. Modern power blocks are also equipped with cleats and hydraulic net press to reduce net slippage, two-speed operation for high speed net stacking, and low speed high torque piston drive systems to pull extremely heavy loads prior to sacking up. All of these features combine to reduce the time it takes to complete a haul, sack up and begin brailing.
Figure 11. MARCO B56F Puretic power block.
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There are several other types and styles of power block besides the Puretic style single boom mounted block. These systems are more popular in regions of the world subject to much rougher seas compared to the WCPO as the net is hauled from deck level. A good example is the Petrel system (Figure 12), that hauls net from deck level and stacks the seine inside an enclosed net bin with the assistance of an articulated crane mounted block. An unusual “duplex” system was noted on a New Zealand tuna and mackerel seiner (Figure 13). Figure 12. Petrel net hauling system.
The Triplex system is commonly used in many temperate water fisheries and is recognized as a strong net hauling equipment capable of operation in very rough and windy conditions. The three vertical sheaves provide a very strong net pull with minimal slippage (Figure 14). A Japanese single purse seiner was experimentally equipped with a Triplex system for operation in the WCPO during the 1980s. (Gillett, 1986). Figure 15 shows the vessel hauling and stacking net using the Triplex system.
Figure 13. “Duplex” style double sheave power block.
Figure 14. Triplex power block (Gillett)
Figure 15. Triplex system hauling net on Japanese tuna purse seiner Takuryo Maru (Gillett)
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The Japanese use several classes of pelagic purse seiner, many of which normally operate within their coastal or east coast temperate water fisheries. However some of these vessels have or still do operate seasonally within the WCPO. Figure 16 is an example of a double block group seiner that formerly operated in Micronesian waters for the Caroline Fishing Company. Most of the net was hauled and stacked on the stern with some netting pulled on the bow block during the sacking up stage which was greatly assisted by a long rail roller. A large carrier vessel then tied up to the corkline with all fish brailed directly to the carrier. At the completion of the operation, all netting was released from the bow and hauled through the stern block and re-stacked for the next set.
Figure 16. Japanese style double block group seiner.
Figure 17 is a typical Japanese group seine vessel, similar to the vessel described in detail by Gillett (1986b) and Farman (1987). Note that the vessel is designed to set in a clockwise direction in contrast to most single tuna purse seiners. Being a group seiner, the vessel has no fish holds and works in conjunction with refrigerated carrier vessels that load and transport the catch. Note that this vessel is equipped with a deck mounted power block on the stern, a boom mounted block to haul the net up for stacking and a travelling block on the boom that aids in net stacking.
Figure 17. Japanese group seiner with travelling boom block for net stacking.
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Figures 18 shows a more modern style Japanese group seiner as described by Itano (1991) during the final stages of sacking up alongside her refrigerated carrier. This vessel was also equipped with a retractable, swiveling deck mounted power block that was stored below deck during the setting process (Figures 19 – 20). The net bundle passed over the deck block, under an idling sheave to create pulling tension, up to a crane mounted power block that could be moved in any direction to assist net stacking (Figure 21).
Figure 18. Modern Japanese tuna group Figure 19. Retractable deck mounted seiner. power block.
Figure 20. Deck mounted power block in action.
Figure 21. Net hauling and stacking machinery on Japanese group seiner.
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2.7 Rail rollers
Hydraulically driven, rubberized rail rollers have been used on Japanese group seiners for decades. The entire side of some vessels are equipped with these rollers which greatly speed the process of drying the net (sacking up) prior to brailing (Figure 22). On some vessels, swivelling pinch haulers assist the process by hauling sections of webbing to keep the net even during the drying process (Figure 23). On group seiners, the catch does not have to be completely dried up before brailing so the rail rollers can handle most of the process very quickly and efficiently.
Figure 22. Long rail roller on Japanese Figure 23. Sacking up with rail roller and group seiner. pinch hauler on Japanese group seiner
European Union single seiners have been using rail rollers for several years to speed up the sacking up process. Currently, almost all modern seiners of the French and Spanish fleets are so equipped (Figure 24). Rail rollers are an essential component to ‘Spanish style’ brailing, described in section 4.2.
Figure 24. Note rail roller on port side of working deck below the gangway.
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3. AUXILIARY VESSELS
Tuna purse seine vessels use a variety of auxiliary vessels to enhance fishing and searching operations. Figure 25 shows a highly specialized net skiff from a Japanese group purse seiner, complete with mounted tow line winch, deck mounted pelican hooks to release messenger cables and a full suite of electronics for communication and school assessment. Japanese auxiliary vessels and towboats are often equipped with telesounder units that transmit depth sounder images to the mothership for direct evaluation by the fishing master.
Heavy duty, diesel powered towboats are a standard item on WCPO purse seiners as they are needed to tow large logs out of the net and are used to investigate and mark floating objects. Figure 26 shows a towboat that has been modified to a light boat used to attract fish to anchored or drifting FADs. Such auxiliary craft are equipped with a generator and above and/or underwater lights and are deployed on a FAD the evening before a set is planned to attract baitfish and tuna. This is a common feature of the Philippine purse seine fishery but is practiced by several fleets.
Figure 25. Japanese net skiff and towboat from group seiner.
Figure 26. Purse seine light boat for use on FADs.
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The following figures show large vessels that assist purse seine operations. Figure 27 is actually a Japanese pole and line boat but has been converted to serve as a refrigerated carrier within a group seine fleet. Carriers can take any form or size, but most are large purpose built vessels that accept and transport the catch of several vessels.
Figure 27. Former Japanese pole and line vessel converted to carry frozen catch for a group seiner.
Figure 28. Search boat as part of a Japanese group seine operation.
Figure 28 is of a search vessel that is a key component of a Japanese group seine operation. These vessels are used to expand the range of searching for the group. This particular vessel was also used as a large light boat on floating object sets and was equipped with a telesounder that send readings to the catcher vessel of the group. A saltwater spray system was also installed on the vessel and she was used in attempts to stabilize unassociated tuna schools prior to setting operations (Itano, 1991).
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Figures 29 and 30 are examples of Spanish supply vessels that work in conjunction with one or more single purse seine vessel of the same company. The main activity of these boats is to search for, assess, maintain, retrieve, monitor and deploy drifting FADs for the benefit of their purse seiner(s). Arrizabalaga et al. (2001) provides detailed information on the activities of anchored and seagoing supply vessels in the Indian Ocean. A similar analysis has been conducted for Spanish purse seiners operating in the Atlantic (Pallares, et al. 2001). In the Indian Ocean, Spanish purse seiners first began utilizing supply vessels in 1999, with five to eight supply vessels in operation between 1999 – 2002 (Molina, et al. 2003).
Seagoing supply vessels appear to engage mostly in searching operations for their own FADs, other vessels FADs and natural objects (Arrizabalaga 2001). Communication between the fishing and supply vessel is constant, with the captain relaying instructions to the supply vessel, who in turn sends email providing all details of FADs visited that day (i.e. location, amount of tuna, species, estimated sizes). When a productive floating object is located, the supply vessel may stand guard over it or use stealth in attempting to disguise its purpose to other purse seiners in the vicinity. On the other hand, the supply vessels monitor closely the activities of other purse seiners in an attempt to locate their more productive FADs. Deploying or “seeding” of drifting FADs is another important activity of supply vessels which provides more time for their purse seiner to engage in searching and actual fishing activities.
Figure 29. Purse seine supply vessel and FAD tender.
Figure 30. Purse seine supply vessel in Victoria, Seychelles.
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Anchored supply vessels primarily hold position on productive seamounts and light the area at night to enhance the tuna aggregation effect. These boats are primarily “place holders”, preventing other purse seiners from capitalizing on the tuna aggregations over the shallow area of a seamount. In particular, there are two anchored supply vessels that maintain a near constant presence on the Coco de Mer Seamount north of the Seychelles, Indian Ocean (Figures 31, 32). These vessels clearly benefit from their anchored supply vessels that act like huge FADs on the seamount summit. The setting operation is made early in the morning with the buoyed mooring line released after the ship is encircled but before pursing is well advanced (Itano, 2002a). The mooring line passes beneath the chainline as the vessel drifts to deeper water where the set is completed and the supply vessel exits the net.
Figure 31. Supply vessel Explorer III anchored on the Coco de Mer Seamount.
Figure 32. Supply vessel Ocean Scout I anchored on the Coco de Mer Seamount for the exclusive benefit of a single purse seine vessel. Note the large array of lights that are illuminated every night to attract bait and tuna.
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4. FISH LOADING SYSTEMS 4.1 Traditional brailing
Rapid loading of the catch is critical in the WCPO where sea surface temperatures (SST) are normally at or above 28°C. The older US style of brailing, as pictured in Figures 33 - 36 use a relatively lightweight brailer fitted with a long handle that was manually pushed down into the sacked up tuna. This system was developed and introduced from the Eastern Pacific purse seine fishery where SSTs are much lower and set sizes were typically not as large. Brailing in this style loads approximately two mt per brailer, is relatively slow, therefore suitable for sets of less than ~ 100 - 125 mt.
Figure 33. Positioning brailer for drop. Figure 35. Hydraulics on brailing boom take over.
Figure 34. Pushing brailer handle into sack. Figure 36. Weight transfers to main boom hydraulics to direct catch to loading hatch.
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Figures 37 – 40 show a brailing operation on a Taiwanese seiner using the same principal with a much heavier brailer without a handle. The heavier mass of the brailer rim allows the entire process to proceed without the need to manually push the brailer into the sack. Heavier rim construction also allowed brailers to expand in size to load more tonnage per operation.
Figure 37. Positioning brailer with Figure 39. Winch on brailing boom lifts hydraulics. fish.
Figure 38. Weight of brailer sinks it into Figure 40. Winches direct brailer to sack. loading hatch.
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4.2 Spanish style brailing
EU tuna purse seine vessels utilize a completely different system of sacking up and brailing, first commonly used by Spanish vessels in the Atlantic. French purse seiners have adopted the technique that is commonly referred to “Spanish style” brailing. The unique feature of the method is that the net skiff is not used at all during the entire sacking up and brailing process. The entire weight of the corkline that was suspended by a large, low net skiff is held aloft by a heavily reinforced brailing boom. Figure 41 shows the corkline suspended by the brailing boom and a load of tuna being brailed using hydraulic power alone. The entire process is shown in Figure 42.
Some variations of this system use a pole mounted brailer that slides through a guide on top of the davit to control the swing and movement of the brailer. Large brailers (approximately 5 mt) can load catch at a very high rate compared to the old style of brailing, and the sacking up process is also much faster.
Figure 41. Spanish style brailing system (Fonteneau).
Figure 42. Diagram of Spanish style brailing system (Casamar).
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Group seiners sack up against a large refrigerated carrier vessel and the catch is loaded directly to the carrier. The sack is not dried up so the fish are generally brailed to the holds in alive or very fresh condition. Brailing is conducted with a large panel of net forming a “flap” type net brailer that is drug through the large sack with hydraulic winches (Figures 43 – 44).
Figure 43. Net brailer on group seine operation in position for drop.
Figure 44. Net brailer hauling fish directly into carrier holds
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5. CATCH UNLOADING
High catch rates will not equate to high annual production if vessels experience long delays in port for unloading and provisioning. Old style unloading of purse seiners involved manually removing every fish from fish wells and transferring the catch through inter-connecting chutes to stern and bow unloading wells. The brine wells were pumped dry and stevedores had to enter each well to throw frozen tuna into the chutes and unloading bins. Sometimes, loads of fish were heavily frozen together or ‘sticky’, requiring each fish to be pried out by hand and crowbar.
Figure 45. Floating the catch during unloading assisted by a raised combing bolted to the well.
The unloading process on modern purse seiners has been revolutionized by “floating” the wells. This unloading process involves pumping brine into the wells to float tuna up to the surface. Raised stainless steel combings are bolted to the well being unloaded allowing the tuna to rise up approximately one meter above the existing well tops (Figure 45).
The raised height of the combing allows the catch to flow by gravity to an electric conveyor belt that runs the length of the wet deck (Figure 46). Brine is recirculated to facilitate the unloading process and conserve refrigerated brine. The conveyor belts can run forward or aft and are split to allow species and size sorting during the unloading process. There is little manual labor involved in this system aside from sorting by species and size. For example, unloaders may pull large yellowfin aside if most of the well is filled with small skipjack, sending pure skipjack loads to the conveyor (Figure 47). When enough yellowfin have accumulated on deck or the top of the well, they are loaded to the conveyor for transport to the unloading hatches. Fish can be directed to the bow or stern unloading hatches where they fall directly into unloading bins or cargo nets for hoisting to the dock or carrier scales.
Figure 46. Frozen tuna flowing out of a Figure 47. The wet deck conveyor belt floated well to the conveyor. loaded with skipjack and heading aft for offloading.
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6. DRIFTING FISH AGGREGATION DEVICES (FADs)
Effective, year around tuna purse seining in the equatorial Western Pacific was first demonstrated by Japanese purse seiner vessels fishing on natural drifting logs (Watanabe, 1983). Japanese purse seiners operating in the WCPO soon adopted the use of free drifting FADs in conjunction with natural floating objects and free school sets (Gillett 1986b). Some U.S. seiners experimented with drifting FADs as 1980, but their use was sporadic and secondary to sets on natural drifting objects or unassociated schools (pers. obs.). However, reliance on artificial drifting FADs increased significantly with the U.S. fleet in the late 1990s. Reliance on drifting FADs went from 0% in 1991 to 89% in 1999 (Coan and Itano 2002).
Itano (1998) describes the general construction and some features of drifting FADs used in the WCPO and related considerations to FAD definitions, searching and fishing time:
“The construction of these FADs
This generalized design varies from vessel to vessel, but there is a consensus among fishermen that a significant amount of subsurface area is important to a successful FAD. It is common pknowledgeo in the fleet that the most successful natural drifting object besides a dead whale is a large log that has become waterlogged and floats vertically with only a small portion above the surface (Hampton and Bailey, 1993). Several theories have been put forth to explain the importance of sub-surface structure to drifting and anchored FADs, including:
‚ vertical logs are vertical because they have become waterlogged with time and have been in the water longer and have had more time to aggregate tuna;
‚ sub-surface mass pholdso or tracks better in the water column, positioning the FAD in productive current gyres or current boundaries, rather than drifting with surface winds;
‚ sub-surface structure offers greater surface area for shelter and habitat for baitfish and associated drift communities, including juvenile tuna;
‚ tuna
The reason for the apparent success of FADs with large sub-surface structure is not clear but the fishermen believe this to be true and fashion their drifting FADs accordingly. The predictable drift of FADs that hold well in the prevailing current is an additional benefit as one vessel may be tracking and monitoring more than 10 FADs at the same time.
Another point that becomes clear when examining observer data is that the distinction between plogso and pdrifting FADso is seldom clear as the fishermen usually enhance natural logs with netting or straps or tie several logs together. Natural logs are also lifted on board and deployed at new locations with select-call radio buoys making them essentially a drifting FAD. The heavy reliance on drifting FADs has also clouded the definition of
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psearchingo as many days are spent simply steaming from one radio buoy marked log or FAD to another that are assessed with sonar and depth sounder with minimal visual searching conducted between FADs in the conventional sense.”
Figure 48 shows an example of a combination between a natural and man-made floating object. In this example, a small, waterlogged piece of wood was found to be aggregating a sizable tuna school. Rather than risk losing the log if it sank, the purse seiner attached bamboo flotation and enhanced the lo g with at surplus net webbing that hangs vertically beneath the log. In this case, it would be more correctly classified as a drifting FAD.
Figure 48. Natural log enhanced with bamboo and netting to create a drifting FAD.
The Spanish purse seine fleet first entered the western Indian Ocean in 1984, when the majority of their effort focused on unassociated schools. The use of artificial drifting FADs increased in the early 1990s, and by 1992 rafts of bamboo and netting were in common use (Morón, et al. 2001). It is interesting to note that these rafts were patterned after those already in use by Japanese purse seiners that have now left the region of the western Indian Ocean. Spanish purse seiners now rely heavily on drifting FADs and the French Atlantic and Indian Ocean fleets have followed suit. Figure 49 shows the working deck of an EU purse seine vessel with several bamboo raft style drifting FADs.
Delgado de Molina et al. (2003) compiled catch and performance statistics for the Indian Ocean Spanish purse seine fleet for years 1984 – 2002. In 1984, floating object sets accounted for only 13.5% of the number of sets but 30% of the catch. The proportion of associated sets rose slowly but steadily until they represented 54.5% of all sets in 1995 and 70% of the total annual catch. Since then, associated sets have been as high as 65.4% of effort, representing up to 79% of the total annual catch. The presented statistics do not differentiate between natural drifting objects or purpose built drifting FADs. However it is recognized that the increase in associated sets since 1995 is largely a result of the use of FADs.
Figure 49 Bamboo and net drifting FADs on an EU purse seiner (Fonteneau).
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7. ELECTRONICS 7.1 Communications and navigation
Advances in ship to ship and ship to shore communications have been rapidly incorporated into fishing operations, improving basic efficiency and information sharing. Inmarsat systems, email and satellite phones have eliminated the need to code transmissions and provide economical, secure links between vessels and their management. Observers should be aware of the range of possible communication systems now available aside from radios.
GPS chart plotters have also greatly simplified navigation, documenting waypoints, fishing events and keeping track of FADs and other vessels. GPS technology has been integrated into radar and sonar systems to allow real time, relative positioning and movement data to the fishing captain.
7.2 Navigational and Bird RADAR
The presence of seabirds in the open ocean areas of the WCPO is a sure sign of baitfish and tuna, with dense seabird concentrations often indicating surface concentrations of tuna or the proximity of floating objects. S-Band, or Bird Radar is capable of detecting birds and bird flocks at considerable distances, even through rain and clouds that visually obscure the birds from a vessel. Most modern tuna purse seine vessels have adopted bird radar as a basic component of their searching/fishing strategy and in many cases have eliminated the searching helicopter and some visual searching in favor of radar monitoring. Observers should be aware of the basic difference between S-Band bird radar and X-Band navigational radar.
As an example, Figure 50 shows a high end bird radar, the Furuno5 FR-1760DS. The unit has a rated range of 120 nautical miles, 60 kW output on a bright 17” color CRT display. Integration with the vessel GPS allows head up or relative tracking of targets, which greatly assists when pursuing and setting on unassociated schools of tuna. In addition to birds, this unit has been optimized for detection of small ships, buoys and net floats. This is likely in response to the desires of purse seine fishermen to actively search for and utilize drifting FADs belonging to other vessels. Observers should be aware that radar units may resemble a computer more than the traditional CRT radar display. Figure 51 shows the Furuno FR 2165DSBB, 60 kW, 120 nmi range S-Band bird radar. These fully computerized units can utilize sophisticated chart plotting software to monitor multiple targets and the display can easily be distributed over onboard televisions or multiple LCD displays.
Figure 50. CRT display S-Band bird radar Figure 51. Modern S-Band bird radar with unit (Furuno). LCD display (Furuno).
5 The examples of Furuno brand hardware in no way constitutes a preferential endorsement of these products. Comparable units are available from a variety of manufacturers.
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Navigational radars have also continued to develop and are no longer used only for vessel navigation. Purse seine and supply vessels now utilize highly tuned X-Band navigational radar to actively search and locate drifting FADs belonging to other vessels, which may be set upon and marked with their own radio buoys. The loading coils on the antennae of older style radio direction finding (RDF) buoys can be detected by high-end navigational radars. Many purse seine vessels actively scan for foreign buoys and associated FADs as they transit to their own FADs or during normal searching activities.
Also, the new generation of navigational radars are equipped with sophisticated target acquisition and tracking software. Purse seine vessels now use their navigational radars as a fishing tool, to simultaneously track the position and course of multiple vessels. This is particularly useful when maneuvering in an area of school fish with many seiners engaged in searching and fishing operations. Foreign vessels can also be monitored to detect FAD associated behavior. Figure 52 shows a state of the art navigational radar with 28” color CRT display, 120 nmi range capable of acquiring and tracking 40 targets.
Figure 52. Modern X-Band navigational radar with 28” CRT display (Furuno).
7.3 Water column monitoring
Most modern tuna purse seine vessels are equipped with Doppler current meters to monitor surface and sub-surface currents prior to and during fishing operations. A typical unit, such as the one pictured in Figure 53 will provide a constant readout of the speed and direction of the water column at three programmable depths. There are a number of sounding units that monitor the actual depth of the net, such as the one pictured in Figure 54. Net depth is displayed from up to three sensors in large digits or simple graphics on the display screen. Transponders are usually attached to the chainline at different areas of the net which allow the vessel to monitor actual net depth during the pursing operation. Pursing depth can be increased if necessary by slowing the purse winch, which is not uncommon on early morning FAD and log sets.
Vertical temperature profiles have not been considered useful for purse seining in the WCPO, hence the lack of bathythermograph recording instruments. Much of this data is now available via remote sensing, monitoring buoys and websites.
Fig 54. Purse seine net depth monitor ing Fig 53. Doppler current meter (Furuno). system (Furuno)
SCTB 16 – FTWG 3 23 7.4 Depth sounders
Purse seine vessels and their auxiliary craft utilize depth sounders to enhance their ability to discern the school size, species and depth distribution of tuna schools found in association with drifting objects. Small tow boats or work boats may be equipped with a simple depth sounder and radio to relay information on the location and depth of the school to the main vessel during a set or when investigating a FAD. More sophisticated telesounders transmit the sounding image from an auxiliary craft to the mothership, and are common on Japanese vessels.
New generation scientific sounders, such as the Simrad ES60 pictured in Figure 55 add new dimensions to echo location and are being increasingly used on modern purse seine vessels. These fully configurable units operate in the Windows NT environment and allow storage and
Figure 55. Simrad ES 60 scientific echo sounder (Simrad). playback of data. Up to four frequencies can be displayed simultaneously with separate gain controls for fish, schools and bottom. With experience, the school size, species and size of fish in a school can be assessed with a high degree of accuracy.
7.5 Sonar
Modern tuna purse seiners often have two or three sonar units operating at low and high frequency and at different range settings for short and long range detection and school assessment. Bridge personnel often monitor sonar displays when on watch 24 hours a day for the presence of subsurface tuna concentrations. Of course, they are essential for school assessment and setting operations on logs and FADs when sets are made in pre-dawn darkness.
New generation low frequency, long range sonar units like the Simrad SP90 (Figure 56) are appearing on state of the art purse seiners that recognize their value to fishing success. This unit operates at 26 kHz with a maximum rated range of 8000 m and a rated detection range of 3000 m. It is advertised specifically as a low frequency, long range tuna sonar. EU purse seine captains claim that these sonar units have been responsible for estimated increases in vessel productivity of 10% to 20% and note high success in species discrimination with sonar (Fonteneau, pers. comm..).
Figure 56. Simrad SP 90 low frequency long range tuna sonar (Simrad).
SCTB 16 – FTWG 3 24
7.6 Radio buoys
The importance of radio buoy technology to modern purse seining can not be overemphasized. Developments of new types and features on transmitting buoy have allowed the fishery to develop hand in hand with technology, particularly in regard to fishing on drifting FADs.
7.6.1 Historical development
Early model radio buoys, that are still used in many fisheries, are always activated, transmitting an undisguised signal every few minutes detectable by an onboard radio detection finder (RDF). These devices were commonly used in the development phase of the WCPO purse seine fishery to mark logs and natural drifting objects. The range of detection is limited to less than 100 nmi, and generally less than 75 nmi with limited battery duration. These devices provide the vessel with only a crude bearing and their distance can only be estimated by signal strength. As the fishery developed, vessels began to capitalize on the open nature of the transmissions and actively scanned common RDF frequencies to locate and set upon logs belonging to other vessels. The transmitting frequency of these buoys could be easily changed, so theft of radio buoys was also a problem. However, it was the loss of logs and associated schools that drove the industry to demand more sophisticated technology. Constant transmit radio buoys were commonly used by WCPO purse seine fleets from the beginning of the fishery to around the mid 1980s 6
Select call radio buoys were quickly adopted in the 80s to reduce theft of gear and productive logs and FADs. A single drifting object can (over some time) fill up a purse seine vessel, so this is no small consideration. Select call, or ‘sel call’ buoys remain in a low power ‘sleep’ mode until a coded signal from the vessel activates the buoy for a short series of transmissions. The vessel can lock in on the direction of the buoy during the brief ‘wake up’ period and obtain a general range and bearing. Further developments raised the transmit frequency to improve detection of bearing to approximately 200 nmi (Morón, et al. 2001). Figure 57 depicts the general characteristics and gear involved with constant transmit, select call and GPS positioning radio buoys.
Drifting FAD fishing increased significantly for the EU Indian Ocean fleets, and radar detection of radio buoys was becoming problematic. As noted in the previous section on navigational radar, the loading coils of RDF buoys can be detected by high grade radar units, thus allowing vessels to actively scan for the logs and FADs belonging to other vessels. In 1995, EU vessels began to incline their radio buoy antennas to reduce the detection range by other vessels (Morón, et al. 2001). Figure 58 shows radio buoys with inclined antennae that are a standard feature of Indian Ocean purse seiners. However, it is not believed that this development has been widely adopted in the WCPO fishery.
In the late 1990s, GPS technology was incorporated into drifting radio buoys. GPS positioning buoys have revolutionized purse seine fishing and were quickly adopted by all modern fleets. These buoys combine a sel call feature with the ability to transmit the exact GPS position, allowing vessels to carefully plan their fishing campaigns. Interestingly, Morón (2001) notes that GPS buoys contributed to an expansion of the Indian Ocean fishing grounds as vessels ventured further a field to retrieve lost radio buoys that had drifted out of traditional areas.
6 All dates of gear adoption are general estimates and need to be better defined by systematic interviews and research.
SCTB 16 – FTWG 3 25
constant emitting system and buoy
select call system sel call transmitter
GPS transciever and buoy GPS transmitting sel call system
Figure 57. Early evolution of radio buoy technology (Ryokuseisha Corp.)
Figure 58. Inclined antennae on RDF buoys.
SCTB 16 – FTWG 3 26 7.6.2 Recent developments in radio buoy technology
In the late 1990s, more sophisticated radio buoys became available, again revolutionizing modern purse seining. These GPS tracking buoys transmit continuous position data to a computer interface at ranges close to 1000 nmi. A continuous “worm trail” of the buoy is represented on the computer screen at all times. These buoys also transmit sst and battery condition with slim antennae without loading coil making them very difficult to detect by radar (Figure 59).
Figure 59. Serpe type GPS tracking radio buoys and computer interface (Martec).
The next development in transmitting buoys utilized Inmarsat technology to link the vessel to a low profile sonar buoy with no visible antennae (Figure 60). These buoys transmit GPS position, SST, battery life and sonar readings directly to computer displays on the vessel via satellite. With no antennae, the units are extremely difficult to detect by other vessels and have unlimited range. Also, a bright light can be triggered to flash and signal the vessel when it approaches the unit for FAD detection and retrieval.
Figure 60. Satellite linked sonar transmitting GPS buoy (Zunibal).
SCTB 16 – FTWG 3 27 The latest generation radio buoys (2003) continue to improve in response to the needs and concerns of industry. GPS transmitting buoys have eliminated the need for antennae and taken a low profile shape, making them extremely difficult to detect visually or by radar. Computer transceivers and display units are now marketed in laptop computers to conserve space (Figure 61). Another significant improvement to sonar buoys has been the addition of solar panels, providing them with virtually unlimited autonomy and eliminating the battery concerns of earlier models. The solar powered unit pictured in Figure 61 transmits via satellite a GPS position, battery state, as well as current speed and direction. Current velocity threshold alarms can be set that can notify the owner of unusual conditions. Excessively high speeds may indicate to the owner that his buoy is no longer in use but travelling at high speed onboard another vessel !
low profile solar powered GPS buoy sonar buoy
Figure 61. New generation GPS and sonar transmitting buoys (Martec, Zunibal).
The use of sonar transmitting buoys by purse seiners is a significant development for the industry. Earlier models often represented false hopes to the fishermen and were limited in scope of coverage below the buoy. However, with better technology and experience, sonar transmitting buoys have become very beneficial in maximizing “search” time, or the time spent traveling to and assessing FADs. Aretxe and Mosqueira (2003) examined catch composition and catch parameters for FADs marked by different types of radio buoys. While noting no difference in species compositions, the success rate and percent of larger sets appeared to be significantly higher on FADs equipped with sonar transmitting satellite buoys. This may indicate simply that these devices are efficient in predicting when good concentrations of tuna are present, thus avoiding unnecessary visits that unnecessarily occupy a vessels schedule. The primary manufacturer of satellite linked sonar buoys concluded a business arrangement in 2001 that permitted worldwide, and Pacific -wide coverage for these devices, thus opening up their full use to the WCPO.
SCTB 16 – FTWG 3 28 8. REMOTE SENSING AND COMPUTERIZATION
There are a number of commercial services that provide satellite imagery to commercial fisheries. Purse seine fleets have made ample use of this technology to incorporate information in near real time of SST, currents, chlorophyll and other useful parameters to their fishing operations. Integration of satellite derived environmental data is particularly beneficial in conjunction with FAD based purse seining, i.e. planning optimal areas for seeding FAD arrays, monitoring potential FAD movements and locating FADs in areas of beneficial currents and high productivity.
The integration of remote sensing, buoy data and shipboard electronics (sounder, sonar, GPS, etc.) highlights the importance of computers on modern purse seine vessels. Vessels are being equipped or retro-fittted with fully integrated computer networks. The bridge and chartroom of modern purse seiners bear little resemblance to those of twenty or even ten years ago Figure 62).
Figure 62. Fully integrated and computerized bridge and chart room of tuna purse seine vessel.
9. SUMMARY
Tuna purse seine vessels operating today may superficially resemble boats operating twenty years ago, or may have been continuously operating for the past twenty years, but their fishing power has increased significantly (see Itano 2002a). Improvements in the mechanics of making very large sets, sacking up and brailiing the catch quickly and freezing these large sets have been addressed. Modern purse seine vessels can now set, load and freeze sets in excess of 400 mt with no loss to spoilage in warm tropical conditions. Time spent searching for schools or productive areas to fish have been minimized through the use of drifting FADs, sophisticated radio and satellite buoys, supply vessels, improved communication networks and the use of satellite imagery. Advances in radar and sonar technology have greatly improved the searching and assessment abilities of fishermen along with years of accumulated experience in their fisheries. When confronted with a concentration of tuna schools with several competing vessels in the area, computerized and integrated bridge systems provide the modern vessels with a distinct advantage in selecting the most vulnerable and high value schools to target. Many of these advances have occurred during the past few years, and new technology will appear all the time. Documentation such as this should be carried out periodically to keep track of new developments. Fishery observers and port samplers should consult these documents to assist their ability to recognize and record advances in fishing technology or changes in fishing strategy that may increase fishing power and fleet harvesting capacity.
SCTB 16 – FTWG 3 29 References
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Artetxe, I. and I. Mosqueira. 2003. Preliminary data on FAD deployment, recovery and associated catch by Spanish purse-seiners in the Western Indian Ocean. Indian Ocean Tuna Commission, 5th Session of the Working Party on Tropical Tunas, 2 – 13 June 2003. Victoria, Seychelles. WPTT/03/24. 6 pp.
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SCTB 16 – FTWG 3 30 Morón, J., J. Areso, and P. Pallarés. Statistics and Technical Information about the Spanish Purse- Seine Fleet in the Pacific. 14th Standing Committee on Tuna and Billfish, 9-16 August 2001. Noumea, New Caledonia. FTWG-11. 7 pp.
Pallares P., Mina, X. , Delgado de Molina, A., Artetxe, I., Ariz J., Arrizabalaga, H. (2001). Analysis of the activities of purse seine supply vessels in the Atlantic ocean and their influence on the catch per unit of effort of the purse seiners. Doc. ICCAT SCRS/01/122, 21p.
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