TUNA purse seining is a sector on which Norwegian catch control Specialist Scanmar is currently focusing, having delivered gear monitoring systems to several fishing vessels operated by French, Spanish and United States companies.

They include: Avel Vor, Avel Vad and Torre Giulia (CMB of France); Via Gwalarn and Via Libeccio (Saupiquet, France); Gueotec (Cobrecaf, France); Txorri Berri (Impesca, Spain); Elai Elay (Echebastard, Spain); and Alexandre (Sokimonar Fishing, USA).

"We believe there's a large potential for our products in tuna seining. It's a segment which we wish to develop further in the future, perhaps with additional sensors," says Scanmar's Roger Ward.

Hundreds of purse seiners targeting large and small pelagic species are already using Scanmar, according to the Norwegian catch control specialist.

Scanmar depth sensors provide information about the net's ascending or descending speed in addition to its actual depth. They show if the net stops sinking due to underwater currents or other factors.

By interfacing the echo sounder to Scanmar it is easy to see where the net is in relation to the bottom or the school of fish.

How many sensors should be used on a purse seine? You need at least one sensor on the purse line, according to Scanmar. With a large net the use of two or three sensors may be considered. One sensor on the cork line will help you avoid pursing too fast and enable dolphins to escape over the net.

Fishing close to the bottom is dangerous, so you can set the depth alarm to avoid snagging the bottom.

The Scanmar hull-mounted hydrophone H4B30X90-3 is used for purse seining and detects signals from all the company's sensors. It covers three 90 degree sectors in the horizontal plane; fore, starboard and aft. A ten degree overlap provides a total coverage of 250 degrees.

A three-position switch is used to select the individual sectors, and Scanmar can supply the trunk and cable gland for installation.

Scanmar says that its depth sensor for purse seines is a robust, battery- powered, unit which measures depth and the ascending and descending speeds. The sensor is activated by a sea water detector.

According to the manufacturer, this sensor has become an essential part of the net for most purse-seiners. The information these devices provide makes it possible for the skipper to follow the net throughout the set.

A temperature sensor for purse seines is also available from Scanmar. Water temperature is an important parameter for fishing. Most species are comfortable in a given temperature, both regarding feeding and spawning.

Experienced fishermen have learned to use this kind of knowledge. It is particularly important in tuna seining that the net sinks below the thermocline before pursing starts.

Temperature layers are constantly changing. As a consequence, says Scanmar, the temperature sensor should be used all the time.

Scanmar offers a variety of bridge units including its top of the range CGM monitor with PC.

The CGM is ideal for use by combined purse seiner/trawlers as it can be configured for trawling or purse seining. All Scanmar sensors, up to nine, can be displayed simultaneously.

The skipper can select between three pictures. Screen One is split between instrument panel and a graphic presentation. The instrument panel has a window for each configured sensor and graphic presentation may be split in two - trawl data on one side and echo sounder data on the other. Screen Two shows historic data where important parameters can be logged.

Screen Three presents a geometric picture of the trawl. The CGM is operated by menu entries and controlled by a keypad. Help menus explaining each function are included in a user friendly format.

Another popular bridge unit is Scanmar's RX 400, which can also be configured for purse seining or trawling. The main picture on this unit also consists of three parts, and it can be interfaced with the vessel's echo sounder to provide trigger pulse.

It can also be interfaced with a GPS for presentation of the vessel's position and speed, and can be connected to a PC for logging of data.

Scanmar points out that it also has sensor systems for smaller purse seiners.

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Scanmar moves into monitors for purse seines