Effect of Line Sink Rate on Albatross Mortality in the Patagonian Toothfish Longline Fishery
An experiment was conducted on autoline and Spanish-system longline vessels to derive a sink rate and line-weighting regime that would minimise the capture of albatrosses based on knowledge of line sink rates and albatross diving abilities. Sink rates of lines deployed into propeller turbulence, which tended to keep lines aloft, varied as a function of distance between line weights. Asymptotic sink rates (0.1-0.15 m/s) were achieved with 70 m intervals between 6.5 kg weights. Sink rates to 4 m depth were greatest with 35 m (0.44 m/s) and 50 m (0.33 m/s) between weights. For vessels using bird-scaring lines and setting lines in propeller turbulence, longline sink rates >0.3 m/s should greatly reduce the incidental take of albatrosses. For autoline vessels with gear and line-setting characteristics similar to the experimental vessel, this sink rate should be achievable with 4 kg weights distributed every 40 m on longlines.