Refining tickler chains for penaeid trawls

Abstract

Tickler chains are simple additions to the ground gears of benthic trawls that can improve the catches of some target species, albeit with considerable variability. The purpose of this study was to decipher some of the technical variability associated with tickler chains used with generic, paired trawls targeting school prawns, Metapenaeus macleayi. In the first of two experiments, single tickler chains were either attached between the trawl otter boards or the wing ends and compared against each other and a control trawl (no tickler chain). Attaching the tickler chain to the otter boards significantly reduced wing-end spread and the trawled area without significantly affecting catches of school prawns. By comparison, attaching the tickler chain to the wing ends maintained spread and resulted in significantly more school prawns being caught (by 1.11 ×) than in the control trawl, and also fewer numbers of one teleost species, pink-breasted siphonfish, Siphamia roseigaster. In experiment two, a single tickler chain was compared against one with multiple chains and one with a double chain; all attached at the wing ends. Trawls with the multiple- and double-tickler chains had the same wing-end spread as those with the single tickler chain, while retaining up to 1.17 × more school prawns, and for the double-chain tickler, 45% fewer southern herring, Herklotsichthys castelnaui. The results are attributed to mechanical and visual stimuli affecting school prawns and some fish, respectively, and support maximising the surface area of tickler chains within the wing ends as a means for improving penaeid-trawl species selectivity without affecting swept area.