An actively stimulating net panel and rope array inside a model cod-end to increase juvenile red seabream escapement

One method of increasing juvenile fish escapement from net cod-ends is to encourage fish to approach the netting by placing an active stimulating device (ASD) in the cod-end. Two types of ASD were tested inside model cod-ends to generate variable visual stimuli. One was a free-end flag-like net panel and the other consisted of an array of free-ended ropes. Escape responses of juvenile red seabream were observed in a circulating water channel using a cod-end fitted with the ASD, and they were compared with responses to conventional polyethylene multi-ply, high-contrast cod-ends with and without ASD made from either 28- or 43-mm mesh under three light conditions. With the ASD attached, the retention rate was significantly lower, 20%, than for conventional cod-ends except in dim light with 28-mm mesh. The effect of the ASD was independent of mesh size or light level. Thus, the use of active fluttering devices in the cod-end could help to reduce juvenile bycatch due to disturbance of the orderly optomotor response.