Effect of line shooter and mainline tension on the sink rates of pelagic longlines and implications for seabird interactions

Differences in sink rates of baited hooks attached to mainelines and set under varying degrees of tension, were tested aboard pelagic longlines off eastern Australia.  Three mainline configurations were tested 1. surface set tight with no slackness astern, 2. surface set loose with two seconds of slack astern and 3. deep set loose with seven seconds of slack astern.  Baited hooks on tight mainlines reached depth almost twice as quickly (5.8 s) compared to those on the two loose mainline configurations (9.9 s and 11 s).  The loose configurations therefore allows increased availability of baited hooks to seabirds.  It was hypothesized that the propeller turbulance slowed the sink rates. The authors suggest that unless the mainline can be set to avoid propeller turbulence, mainline deployed with a line shooter (to reduce sea bird interactions) for deep setting should not be accepted as an effective detterent to seabirds.