Sink rate of baited hooks on New Zealand pelagic tuna vessels

Time depth recorders (TDRs) were used to determine the rate at which baited hooks sunk on four pelagic tuna longline vessels in New Zealand waters. TDRs were successfully deployed 21 times. Using no extra weight and no line shooter, at a vessel speed of approximately 7 knots (3.6 m/s), baits were recorded at a mean (± SD) depth of 1.83 ± 1.67 m (range 0-6 m) at a point 50 m astern of the vessel. Possible causes of the variation and the implications for effective incidental seabird catch mitigation measures, such as tori line deployment, are discussed.