The diving behaviour of little penguins in Western Australia predisposes them to risk of injury by watercraft

The most western little penguin colony globally, and the most northern in Western Australia (WA) is found on Penguin Island, WA. The penguins use coastal bays that are also used extensively by recreational watercraft. These penguins have been found to either dive predominantly to shallow depths of 1-5 m or to depths >8 m. It is thus hypothesized that (a) both the shallow and deeper diving penguins can potentially be disturbed or injured by these watercraft but that the risk will differ between the two diving strategies, and (b) that risk of injury for both is greater during the summer and autumn, when people are more likely to use watercraft. This was tested by attaching data loggers to little penguins during chick rearing and by investigating necropsy records. Diving activity was studied for the very shallow and relatively deeper diving penguins separately, and we considered the penguins were vulnerable to interactions with watercraft when they were within the top 2 m of the water column or at the surface. Shallow-diving penguins executed >1,200 dives per day, 64% of dives occurred within the top 2 m, and they were vulnerable for approximately two-thirds of their time at sea. The deeper diving penguins executed fewer dives. Almost half of dives were to >= 10 m, yet they were vulnerable for almost one-third of their time at sea. Their post-dive recovery was also longer. Thus, the risk of interaction from watercraft differs depending on the diving behaviour. This study highlights the potential impact to little penguins throughout Australia and New Zealand.