Australasian Science: Australia's authority on science since 1938

Penguins Feed in Straight Lines

A research team at the University of Otago has discovered that the endangered and endemic yellow-eyed penguin forages in straight lines for several kilometres by following furrows in the seafloor scoured out by fishing trawlers.

“This research is unique as it shows for the first time that not only do flying seabirds follow fishing vessels, but also penguins, with the latter foraging after a trawler has gone through a particular area,” said lead research Professor Philip Seddon.

Blue cod and other bottom feeders are likely to forage around the seafloor lines because they are attracted to the marine life stirred up and exposed by the nets being dragged behind fishing trawlers. The lines made by the otter boards, which keep the mouth of the trawl net open, can remain on the sea floor for a year or more and are clearly visible.

GPS dive loggers attached to the backs of the penguins revealed that the penguins swim to a depth of 60–70 metres to feed during up to 80 dives over several hours before returning to shore. The penguins can travel up to 120 km in one trip while foraging in the mid-shelf fishing grounds 20 km off the Otago Peninsula. The penguins also revisit the lines on subsequent occasions and might develop a visual memory of the area.

“It appears that using the lines for foraging is particularly related to bad breeding years when penguins are more likely to go further out to sea to find blue cod and other bottom feeders. This might also be due to the individual preference of some birds though,” says Dr Thomas Mattern, the first author of a research paper published in PLOS ONE.

However, the researchers say that one of the downsides of foraging around the trawl lines might be that an exclusive diet of blue cod, which tends to be low in nutritional value, could affect breeding.

As yet there is no confirmation of this hypothesis, further research is needed to determine if there is any relationship between the foraging patterns, diet quality and breeding success of the 500 yellow-eyed penguin pairs that still exist around the New Zealand mainland.