The relative safety of weighted branchlines during simulated fly-backs (cut-offs and tear- outs)

Rawlinson N, Haddy J, Williams M, et al (2019) The relative safety of weighted branchlines during simulated fly-backs (cut-offs and tear- outs). In: ACAP - Ninth Meeting of the Advisory Committee. ACAP SBWG9 Doc 15, Florianópolis, Brazil

The use of weighted branchlines is considered as one of the most effective methods to reduce the incidental capture of seabirds in pelagic longline fisheries. However, weights on branchlines have resulted in fly-backs during hauling that have caused serious injuries and deaths to fishers. During commercial fishing conditions, fly-backs can occur under a range of different circumstances. Cut-offs occur when the hook is bitten off the end of the branchline and the branchline recoils without the hook. Tear-outs occur when the hook is released from a fish/shark and remains attached to the branchline as it recoils. We assessed the relative safety of two different sizes (38 g and 60 g) of fixed weight swivels, two different sizes of two brands of sliding leads, GloLeads (40 g and 60 g) and Lumo Leads (45 g and 60 g) and a Hook Pod (50 g), by simulating fly-backs as both cut-offs and tear-outs. The weights were positioned at different distances from the end of the branchline in accordance with ACAP minimum standards. Twelve metre monofilament branchlines with different weight configurations were placed under 80 kg of tension without hooks to simulate cut-offs and with hooks to simulate tear-outs with the end of the branchline at the surface of the water. Ten replicates of seven different branchline configurations were tested during both cut-offs and tear-outs. High-speed videography was used to track the movement and velocity of the weights prior to impact with a gridded backboard or at the point of release of the end of the branchline. For the different branchline configurations and fly-back types, we predicted the impact injury to the head and chest using the Blunt Trauma Criterion (BTC). All potentially dangerous fly-backs are predicted to result in more than a 50% chance of a skull fracture or a thoracic skeletal injury if the head or chest is impacted by a weight or a hook. The safety risk of a fly-back was influenced by the type of weights