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Escapes of salmon from nets with different mesh sizes

On behalf of the Directorate of Fisheries, the Institute of Marine Research has been studying the relationship between mesh gauge and fish size. The study focused in particular on identifying the smallest size of smolt for responsible fish capture. A diagonal mesh size of 20 mm retains the minimum permitted smolt weight of 100 g.


The fish used in the experiments were weighed and measured both inside the net and after they had swum out of it. The tests showed that the largest individuals that managed to escape from the different nets weighed 20 g (15.5 mm mesh size), 22.8 g (16.5 mm), 35 g (17.5 mm), 37.2 g (18.5 mm) and 80 g (20 mm).

The trials were performed on salmon parr whose condition factor was somewhat higher than that of smolt, which means that smolt would find it easier to escape and that the minimum smolt size needs to be rather larger. We therefore recommend that a 25% safety margin should be incorporated in these figures. The recommended limits would therefore be as shown in the  table below.

The escape studies with 16.5, 17.5 and 18.5 mm mesh sizes were carried out during the winter of 2005 – 2006, and they supplement previous studies using nets with 15.5 and 20 mm mesh sizes.

Table: Lowest smolt weight retained in nets with mesh sizes between 40 and 32 gauge.