Influences of twine diameter and mesh area on the efficiency and durability of baited hoop nets targeting portunids
The utility of varying twine diameter (0.5-0.8 mm Ø) and/or mesh area (0.5:1) in south-eastern Australian recreational hoop nets was assessed in response to concerns over (1) impacts to discarded, undersize Scylla serrata L. and Portunus pelagicus Forskål and (2) marine debris (lost meshes). There was a negative relationship between Ø and breakage, with more in the narrowest (16.16-18.42 meshes deployment-1) than thickest (8.79-4.68) twines. Mesh damage was also affected by interactions between netting area and (1) soak time (only S. serrata) and (2) catches, with all nets similarly damaged during <3.5-h soaks, or when only one crab was caught, beyond which the large-area nets incurred more. Irrespective of net, there were consistent positive relationships between mesh damage and water temperature, and more damage overnight. Large crabs took longer to remove, but more so from thicker-twined and large-area nets, and some also sustained the most damage. Twine diameter did not affect S. serrata catches, but was negatively associated with catches of P. pelagicus, while the small-area nets caught proportionally (to area) fewer portunids. The results reflect species- and size-specific behavioural variability, but support using thick twine and limiting deployment durations for hoop nets. Alternatively, other less controversial traps might offer a more holistic solution to the stated concerns.