Documentation and Classification of Fishing Gear and Technology on Board Tuna Purse Seine Vessels
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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 SCTB 16 – FTWG 3 2 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 SCTB 16 – FTWG 3 3 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. SCTB 16 – FTWG 3 4 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).