Grid sensor

Sorting g rids were first used in the shrimp fleet (Pandalus Borealis) in the late 1980's. The purpose was to fish shrimp in areas where there were a lot of small fish, without getting this as bycatch. Since then the use of grids has become increasingly widespread and are now being tested in various fisheries.

Scanmar developed early on a highly sophisticated sensor, Trawl Speed /Symmetry sensor, which very precisely measured water velocity into and across the trawl opening. To obtain absolute accurate measurements the sensor that was developed had an inclinometer (angle measurer) which was used to correct the measurement if the sensor was not lying horizontally.

It was ther efore easy to create a variation of the sensor, the Grid sensor, which measures the water flow through the sorting grid and the grid’s angle. S hrimp grids (Pandalus Borealis) are most efficient around 45⁰.

• Water flow through the sorting grid is the most important observ ation - It is not rare for the grid to be blocked by the skate, seals, sharks, rocks, etc. - In some seasons there are large numbers of jellyfish that clog the mesh in the bag, so that water doesn’t flow through. When this is the case i t’s time to end the haul.
• With shrimp (and fish that with no swim bladder) the bag sinks as it fills. It is common to start the haul with an angle above 50⁰ and end it when the angle approaches 37 - 38⁰ .
• Changes in the angle give a good indication of the catch at any time, and the log curve also shows where the influx was the greatest.

Trawl Eye and Grid sensor used on a shrimp trawler. The shrimp influx is visible on the left side of the screen which displays the Trawl Eye’s detection. It can also be seen as blue markings in the log image of the Grid sensor to the right. The grid angle has fallen (ascending curve) from about 55⁰ to 44⁰ . Impact in the angle is corresponding to the influx of shrimp.