May 8th, 2010 
molitva leyli 
”Fishing gear and technology on board tuna purse seine vessels” by David G. Itano. 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.
Detile Purse Seine Fishing Gear
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
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.
Knotless nylon purse seine
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.
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. 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.
Old style steel purse seine rings with chain
Securing purse seine rings to the ring stripper
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.
modern stainless steel roller snap purse seine rings
Snap roller ring hold many advantages to the fishing operation and have been widely adopted by most fleets . 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.
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. 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.
Tuna purse seine winch circa 2003
A huge purse seine davit and blocks
Purse seine winch davit and blocks on a 1970s era tuna seiner.
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.
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.
MARCO B56F Puretic power block
AUXILIARY VESSELS
Tuna purse seine vessels use a variety of auxiliary vessels to enhance fishing and searching operations. Bellow 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.
Japanese net skiff and towboat
Purse seine light boat for use on FADs
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).
FISH LOADING SYSTEMS
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, 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.
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. Bellow figure shows the corkline suspended by the brailing boom and a load of tuna being brailed using hydraulic power alone.
Spanish style brailing system (Fonteneau).
Diagram of Spanish style brailing system (Casamar)
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’, equiring each fish to be pried out by hand and crowbar.
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).
ELECTRONICS
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.
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.
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, suc h 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.
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.
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.
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.
Recent developments in radio buoy technology
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.
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.
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SkySails System - Kite Sail Technology - Wind Power Vessel
Effective Longline Fishing Operation - Vessel and Gear
Effective Tuna Trap - Floating Sea Trap Structure