Mono- vs multifilament baited conical hoop (tangle) nets: Effects on portunid catches and marine debris

Abstract

Small, baited polyamide (PA) hoop (tangle) nets are a popular recreational fishing gear for targeting portunids (Scylla serrata and Portunus armatus) in southeastern Australia and are comparable to other tangle and entrapment gears used more broadly throughout tropic-temperate regions. While their selectivity is appropriate for legal-sized portunids (≥85 and ≥60 mm carapace length; CL, respectively) and bycatches are low, hoop nets can be damaged and lose twine as marine debris. We investigated an applied solution to this problem here by fishing conventional multifilament hoop nets (made from 0.98-mm diameter–Ø white twisted PA twine) against those made from three diameters (0.65–0.86 mm) of clear monofilament PA twine—a material currently prohibited throughout south-eastern Australian net-based gears owing to an historical perception of excessive efficiencies. Compared to the multifilament hoop nets, all three monofilament hoop nets similarly maintained diel catches of S. serrata but retained significantly fewer (by 67–92%) P. armatus, and without affecting non-target catches. Irrespective of the targeted species, there was less hoop-net damage and twine lost (reduced by 69–99% from an average of 114 mm lost 3-h overnight deployment–1 for the conventional hoop nets) among monofilament hoop nets, which was also negatively correlated to their twine diameter. The results were attributed to the greater stiffness and abrasion resistance of monofilament limiting (i) entangling among smaller P. armatus and (ii) breakage when targeting both species, respectively. For this fishing gear, monofilament clearly is not associated with greater efficiency as perceived; rather it might be encouraged as an inexpensive solution for mitigating marine debris among hoop nets when targeting S. serrata.