Performance of an Active Stimulating Device Using a Rope Kite or Array in the Cod End to Reduce Juvenile by-catch

Abstract

An active stimulating device (ASD) using a rope apparatus may operated by the flow of turbulence inside a cod end, generating variable stimuli in addition to flow-related effects to minimize the bycatch of juvenile fishes. Preliminary testing involved a hydrodynamic effect inside the cod end with a rotating rope kite or conical rope array to generate variable stimuli (visual stimuli, water flow, or physical contact with fish) to change fish position. The experimental rope kite offered more choice in rotating period and range of sweeping action; adjusting the towing line or flow velocity helped to drive fish toward the net panel and encouraged escape. The conical shape of the rope array in the cod end helped to clear a path for fish by disturbing the rigging and providing more contrast between objects, preventing an optomotor response. This enabled more black porgy to be herded toward the net at an early stage of towing. Therefore, either a conical rope array or a rotating rope kite can be used as an effective ASD to prevent juvenile by-catch.

Effects on the Escapement of Juvenile Bastard Halibut Paralichthys olivaceus of Actively Stimulating Devices Inside a Model Cod End

“…However, the existing square-mesh window and grid methods are static, *Corresponding author: yonghae@gnu.kr passive stimuli that do not change position with short towing periods. An alternative method is the so-called active stimulating device (ASD), which may take the form of a conical rope array, rotating rope kite, or fluttering net panel inside the cod end that generates variable visual stimuli for juvenile fishes in addition to flow-related effects (Kim, 2010). From the first ASD trial, the retention rate of juvenile red seabream was sig-nificantly lower using an ASD cod end, including an attached fluttering net panel and a flaglike rope array, than with conventional cod ends (Kim and Whang, 2010).…”

“…First, although a fluttering net panel was an effective stimulating device for seabream, flatfish could settle on the panel due to their sea floor habitat (Kim and Whang, 2010). Second, the fact that flatfish have been easily herded by sweep lines could be applied in reverse to use ropes to drive fish from the cod end, as shown in a preliminary test for black porgy (Kim, 2010). As a first test, the escape responses of juvenile bastard halibut were observed in a circulating water channel using ASD and conventional cod ends, and retention rates were compared.…”

Fluttering Characteristics of the Ropes and Nets as an Active Stimulating Device inside the Cod End of a Trawl Net

“…The existing square-mesh window and grid methods are static, passive stimuli with short periods that do not change position. An alternative method is the so-called active stimulating device (ASD), which may take the form of a conical rope array, rotating rope kite, or fluttering net panel inside the cod end, that generates variable visual stimuli for juvenile fishes in addition to flow-related effects (Kim, 2010). An ASD consisting of a fluttering net panel and ropes within the turbulence inside the cod end has been suggested as effective in reducing juvenile by-catch of red seabream and bastard halibut (Kim and Whang, 2010;Kim, 2011).…”

Shaking Motion Characteristics of a Cod-end Caused by an Attached Circular Canvas during Tank Experiments and Sea Trials

“…The effects of a shaking cod-end on fish escapement considering fish swimming mechanics in turbulent flow (Liao, 2007;Webb and Cotel, 2010) should be also investigated using both tank experiments and sea trials. Other issues to consider include the possibility that the shaking motion of the rear of a codend (caused by a shaking disk) might also be affected by an imbalance in the lifting force over time, combined with an angle similar to the rotation of a rope kite (Kim, 2010). In future research, we also plan to investigate the shaking motion described by the amplitude and period of an oscillating canvas, as well as the effects of the canvas size and attachment position, to determine the optimum conditions affecting fish escapement.…”