Report on a tuna long-lining fishing voyage aboard Southern Venture to observe seabird by-catch problems

Incidental captures of seabirds, and the behaviour of seabirds around the fishing gear as it was deployed, were observed during 8-days' fishing of a New Zealand-owned tuna long-liner. From 11,200 hooks set 6 seabirds were hooked and recovered: 5 Wandering Albatross Diomedea exulans of which 3 were released alive, and one Black-browed Mollymawk D. melanophrys impavida. Relatively more birds survived hooking in this study because of the lighter gear and quicker recovery of the long-line (about 6 hours between beginning the set and beginning hauling-in).
Petrels, particularly Cape Pigeons Daption capense, were mainly responsible for bringing the sinking baits back to the surface where albatrosses/mollymawks subsequently ate most of them. About 1.2% of baits were taken by seabirds, but only 4.5% of bait-takes resulted in a bird being hooked. The mollymawk was hooked at night near full moon, but under thick cloud.
Most bait-takes occurred in daylight, particularly before dusk. The vessel's bird-scaring line seemed to reduce, but not eliminate bait-taking. The mortality rate of seabirds (0.2711000 hooks set) is similar to that in the only other two reported studies.
Seabirds scavenged intensively on the waste baits (41% of those cast) thrown overboard during hauling-in. More birds followed in the wake during hauling than during setting.