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Marine Ecology Progress Series

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MEPS 537:277-288 (2015)  -  DOI:

Foraging distribution of Cape gannets in relation to oceanographic features, prey availability and marine protected areas

David B. Green1,*, Janet C. Coetzee2, Gavin M. Rishworth1, Pierre A. Pistorius

1DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology, Nelson Mandela Metropolitan University, Summerstrand 6031, South Africa
2Fisheries Branch, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South Africa
*Corresponding author:

ABSTRACT: Seabirds forage in a dynamic environment of heterogeneously distributed prey resources. Many seabird species use oceanographic features that promote prey aggregation, as a means of locating prey patches. The combination of tracking data, remote-sensing data and estimates of prey availability is useful in determining how seabirds locate prey. GPS tracks of foraging Cape gannets Morus capensis were collected across 3 breeding seasons and tested for inter-annual changes in home range size and foraging effort, and compared against the availability of their predominant prey (sardine Sardinops sagax and anchovy Engraulis encrasicolus) as determined from acoustic surveys. Biophysical features associated with foraging were compared to a random point dataset using a binomial general linear mixed model, while foraging distributions of Cape gannets were compared against the placement of marine protected areas (MPAs). The total home range of foraging Cape gannets, breeding at Bird Island, South Africa, propagated westwards over the 3 breeding seasons, which coincided with a concurrent westward contraction in the distribution of sardine and anchovy. Foraging effort showed an apparent increase in response to low prey densities and occurred mostly outside MPAs. Although gannets seemed to forage in relatively cold waters, biophysical features were generally unreliable predictors of gannet foraging distribution. The relationship between home range and prey distribution, coupled with recent declines in local prey availability, demonstrates the ability of gannets to track the distribution of their prey resources. However, the ephemeral and dynamic nature of these prey resources places a major constraint on conservation-based spatial planning involving Cape gannets.

KEY WORDS: Morus capensis · Agulhas Bank · Home range · Predator-prey relationships · Productivity · Marine protected areas

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Cite this article as: Green DB, Coetzee JC, Rishworth GM, Pistorius PA (2015) Foraging distribution of Cape gannets in relation to oceanographic features, prey availability and marine protected areas. Mar Ecol Prog Ser 537:277-288.

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