Fishermen's News - The Advocate for the Commercial Fisherman

Sensitive Trawling Using New Technology

 


For many years, trawler owners and captains have been criticized for damaging the fishing grounds with heavy fishing gear, such as trawl doors and ground-ropes on bottom trawls. There may be some truth to these criticisms, even though it has not been proven if the practice has a negative effect on the fishing grounds. Some say it is good for the seabed to plow it up, similar to how farmers plow their fields. They point out that in many fishing areas the trawlers have been fishing on the same spot for decades and the fish return every year. For example a very productive fishing ground in Iceland, called “Hali bank,” located approximately 45 nautical miles NW of the Icelandic West fjords, is known for Atlantic cod. This fishing spot was first discovered sometime in the mid 1930s and has been productive ever since, even though the seabed is getting flat like a highway. I believe that many such fishing spots exist in the Bering Sea, where the fishermen can go every year to the same spots and catch the same amount as they did the years before.

Others say trawling on the ground with heavy trawl doors, ground-ropes and bobbins is damaging the seabed and plants that may live there. This is true where vessels have been fishing in areas where Coral can easily be damaged by the heave gear. Coral damaged by trawling takes decades to recover.

Although it is necessary to have bottom contact for catching fish like Cod, Haddock, Flounder and many other fish species, dragging the heavy trawls doors on the bottom is very fuel intensive. Net designers and users should be seeking to improve the gear for less bottom contact, and therefore less fuel consumption, for other fisheries.

What Can Be Improved?

In the past few years it has become popular to use midwater trawl doors for spreading the bottom trawls, instead of the traditional bottom doors. By doing this, it is easier for the captain to have the trawl doors “floating” above the seabed, while the bobbins and part of the sweep-lines (bridles) are sitting on the seabed. This practice results in a fuel savings of 8 to 12 percent per year, as well as reduced maintenance on the fishing gear.

Most manufacturers of sensors are producing sensors to measure the distance between trawl doors, the distance between wing tips, the distance of the headline down to the bottom and the distance from the trawl door down to the sea bed. Sensors are also available to measure the distance from the wing tips to the center of the headline to indicate if the trawl is in full geometry.

All this information is very useful for the captain while fishing, but the information alone is not sufficient, because the captains must carefully be watching the sensors and adjusting the wire length to keep the trawl on the seabed, but still be sensitive to the seabed by holding the trawl doors steady off the bottom. Naust Marine has been watching the trend closely and has developed a winch control program to make this more easy and effective. The soon-to-be launched update for the ATW system for electrical towing winch systems will make it possible to choose various ways for controlling the trawling winches in “Auto trawling” mode. The options are:

  • Normal function. By measuring the tension on each trawl wire and adjusting the wire length accordingly, the same tension can be held on both sides, keeping the trawl in full geometry. The wire length is selected by the captain.
  • Control using signals from the sensors. With this function it is possible to hold the trawl doors at a preselected distance from the seabed, reducing workload for the captain and avoiding a sudden “crash” of the doors into the seabed in case the depth decreases.

    Combination of control using signals from tension read-out on each wire and the sensors on the trawl and trawl doors.

    The new program will be standard in new systems, but also available as an update to older ATW systems from Naust Marine, including a new and improved “ATW picture”, where all necessary information can be displayed at the same time. The system gives a better overview to the captain and makes it easier to keep the trawls as “light” on the sea bed as possible, to fish efficiently while lessening the impact on the seabed.

    Another feature for better control of the fishing gear, especially when the sea is rough, is a new wave-compensation system, to be launched along with the new sensor controls.

    With new advances in technology, fishing trawlers can be outfitted with equipment that is good for the environment and secures sustainable fishing for the future. The discussion on trawling’s effect on the seabed can continue, but we should at least utilize the fishing grounds as gently as possible with minimum ground contact. Improved winch contols can help the captain do just that, while saving fuel at the same time.

     
     

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