Foraging by Humboldt penguins (Spheniscus humboldti) during the chick-rearing period: general patterns, sex differences, and recommendations to reduce incidental catches in fishing nets

Abstract

We studied the foraging behaviour of endangered Humboldt penguins (Spheniscus humboldti) to examine general foraging patterns, sex differences in foraging behaviour, and the reasons for incidental catches in fishing nets. Humboldt penguins foraged diurnally and typically made short, shallow dives within 30 m of the surface. Males and females made overnight (lasting 25.8 ± 3.4 h; mean ± SD) and day (10.4 ± 2.0 h) trips when they departed the colony to forage. Overnight trips were more common (68.2% of all trips) and were associated with a significantly greater amount of foraging time. Males dived to greater maximum depths than females but did not differ in other diving parameters, including foraging time, foraging effort, and proportions of day and overnight trips made. Adults may maintain their body condition during chick rearing by making a mixture of overnight and day trips. The two foraging periods observed during overnight trips may function to feed both the adults and the chicks, whereas the single period observed during day trips may function to accommodate the rate of provisioning required by the chicks. We suggest that both males and females would be protected from incidental catches in fishing nets if commercial fisheries avoided setting surface nets at night and setting nets between 0 and 30 m depth during the day in areas where penguins forage and transit.