Effect of blue dyed bait on incidental seabird mortalities and fish catch rates on a commercial longliner fishing off East Cape, New Zealand

A pilot experiment was undertaken to test the potential effect of blue dyed bait on incidental seabird mortalities and on fish catch rates in the New Zealand domestic tuna longline fishery. The East Cape region on the east coast of the North Island of New Zealand was chosen as the area to conduct the experiment because fisheries in this area are known to have a relatively high rate of interactions with seabirds and this high rate potentially would maximise the probability of observing encounters between fishing gear and seabird species. Seven longline sets were observed over an eleven day trip. A total of 10,040 hooks were set, 4,999 of which held control baits (undyed squid) and the other 5,041 hooks held blue dyed squid. Two juvenile male Antipodean wandering albatross (Diomedea antipodensis) were caught in the first set on the control bait section of the longline, but no bird strikes were observed for the remainder of the experiment. Observations on how dyed bait affects seabird interactions with the longline are reported and recommendations are made for future research. An aversion response by seabirds, rather than a camouflage effect of bait, is put forward as a possible mechanism for how the use of blue dyed bait might reduce the attractiveness of longline baited hooks.