Title: The effect of twine stiffness on codend size selectivity, a full scale experiment

Author(s): Justy Moses
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Knowledge of fishing gear selectivity is of fundamental importance when recommendations for harvest strategies are being made. The objective of this experiment was to estimate and compare the selectivity of two types of trawl codends with different stiffness; 135 mm codends of soft and stiff materials. Data were collected using the covered codend method in the Westfjords of Iceland. The results showed that codend stiffness affects selectivity significantly. For haddock L50 was reduced by 17.4 cm on average, from 57.4 cm for the soft codend to 40 cm for the stiff codend. For cod L50 was decreased by 13.6 cm on average from 57.7 cm for the soft codend to 44.1 cm for the stiff codend. Difference in SR due to stiffness for haddock showed an increase by 3.1 cm on average from 10.2 cm for the soft codend to 13.3 cm for the stiff codend. Similarly, SR for cod increased by 9.4 cm, from 10.2 for soft codend to 19.6 cm for the stiff codend. This study showed that in fisheries where factors other than mesh sizes are not controlled by regulations, fishermen can easily manipulate codend selectivity legally to increase catches of small fish if they want to do so.

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