Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey
| Autor: | Deon Geldenhuys, J Huisamen, Lauren Waller, Azwianewi B. Makhado, Peter G. Ryan, PA Whittington, MK Smith, RM Randall, L Upfold, Rjm Crawford, J Visagie, R Fox, Bruce M. Dyer, Timothée R. Cook, CG Wilke, C McGeorge |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: |
0106 biological sciences
geography geography.geographical_feature_category biology 010604 marine biology & hydrobiology Sardine Foraging Estuary Aquatic Science biology.organism_classification 010603 evolutionary biology 01 natural sciences colony size distribution change food availability foraging behaviour Phalacrocorax capensis population decrease Predation Fishery Engraulis Anchovy Cape Cape cormorant Ecology Evolution Behavior and Systematics |
| Zdroj: | African Journal of Marine Science; Vol 38, No 3 (2016); 373-383 |
| ISSN: | 1814-232X 1814-2338 |
| Popis: | Numbers of Cape cormorants Phalacrocorax capensis breeding in South Africa decreased by nearly 50% from approximately 107 000 pairs in 1977–1981 to 57 000 pairs in 2010–2014. Although four colonies had >10 000 pairs in 1977–1981, there was just one such colony in 2010–2014. Almost all the decrease occurred after the early 1990s off north-west South Africa, between the Orange River estuary and Dassen Island. South of this, the number breeding in the two periods was stable, with some colonies being formed or growing rapidly in the 2000s. The proportion of South Africa’s Cape cormorants that bred south of Dassen Island increased from 35% in 1977–1981 to 66% in 2010–2014, with the opposite situation observed in the north-west. This matched a shift to the south and east in the distributions of two of the Cape cormorant’s main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax. In 2014, an apparent scarcity of prey in the north-west resulted in Cape cormorants attempting to take bait from hooks of fishing lines over an extended period, a behaviour not previously recorded. The number of Cape cormorants breeding in the south may be constrained by the absence of large islands between Dyer Island in the west and Algoa Bay in the east. If so, it may be possible to bolster the southern population through the provision of appropriate breeding habitat, such as platforms, or restricting human disturbance at suitable mainland cliff breeding sites.Keywords: colony size, distribution change, food availability, foraging behaviour, Phalacrocorax capensis, population decrease |
| Databáze: | OpenAIRE |
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