The Norwegian HI reports that openings in the bottom of trawls can prevent the blasting of large hauls of blue whiting
Marine scientists may have found a good solution in the blue whiting fishery.
When several hundred tonnes of blue whiting are caught per trawl hall, there can be too much fish.
An opening in the bottom can solve the problem.
The Institute of Marine Research has researched solutions and has now made a review, as well as an animation of the proposed solution.
Blue whiting is a small cod fish that is fished largely west of the British Isles. But we who fish this species sometimes have a problem with the schooling fish, since large quantities are often caught in the same hall. The trawl sacks can simply explode because there is too much fish in them.
“In addition, the swim bladder of the blue whiting expands when the fish is lifted towards the surface from several hundred metres deep. This causes the trawl sacks to rise to the surface like a torpedo,” says marine scientist Olafur Ingolfsson in His discussion of the case.
HI researchers themselves began by animating the ascent of a trawl sack after it had caught fish. Using 10-15 depth gauges in the trawls of five fishing vessels, they were given information on how the trawl sacks with blue whiting move underwater.
-“We wanted to see the shape of the trawl below the surface. We were most interested in the last phase, ie the ascent,” says Ingolfsson.
He and his colleagues saw that as the trawl sack approached the surface, the speed increased and it came up almost vertically.
Must release excess fish
With that knowledge, the researchers began to test different solutions.
“We had to find a way to be more accurate on the catch, so that we avoid blasting,” says Ingolfsson.
During a cruise in 2021, they tried different solutions to release excess fish. Three to four different solutions with large openings at the front of the bag were tested.
The challenge is to find a solution where the fishermen do not lose fish until the bag is full.
“Now I think we have found a decent solution. Blue whiting largely seeks out the trawl, so openings in the bottom panel in front of the trawl sack mean that we lose little fish before the sack is full,” says the researcher.
In March, the researchers will embark on a new journey for further testing of various solutions.