Yellow-eyed penguin diet and indirect effects affecting prey composition

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Summary

Information about yellow-eyed penguin prey composition is scarce, with the bulk of the work being conducted in the mid-1980s and early 1990s and more recent dietary information being very limited. However, data at hand suggests a significant shift in the major prey species has occurred in the last 30 years where red cod, a dominant prey species in terms of frequency of occurrence and diet biomass, has been largely replaced by blue cod since the 1990s.

There is a considerable difference in size between red cod caught during the larval early juvenile stage (length: 50-80mm), and blue cod, which was consumed at significantly larger sizes (160-220mm). This may affect the survival of penguin chicks which appear to not be able to ingest such large prey.

The shift from red to blue cod coincides with reduced landings in the red cod industry, indicating fishing pressure may have contributed to a depression in red cod stocks. It appeared fisheries-related disturbance of yellow-eyed penguins benthic foraging habitat may have favoured blue cod, due to species relative tolerance to fishing disturbance.

There are regional differences in yellow-eyed penguin diet composition. In regions containing habitats with coarse sand and gravel the diet is dominated by opalfish, while in structured benthos and seafloors exposed to bottom fisheries, blue cod is the more important prey species.

There are clear indications that yellow-eyed penguins are impacted by indirect effects of anthropogenic activities at sea. However, the current knowledge of the penguins' diet composition and marine ecology is limited, making it difficult to assess the extent to which these effects contribute to the populations decline.

Publication information

Mattern, T & Ellenbert U. 2018. Yellow-eyed penguin diet and indirect effects affecting prey composition. Report prepared by Eudyptes EcoConsulting for the Conservation Services Programme, Department of Conservation, Wellington. 39 p.