Comparison of trends in abundance of guano-producing seabirds in Peru and Southern Africa

  • RJM Crawford
  • J Jahncke

Abstract

The abundant guano-producing seabirds in Peru and southern Africa feed mainly on the large populations of anchovy Engraulis spp. and sardine Sardinops sagax supported by the Humboldt and Benguela upwelling
systems. Numbers of guanay cormorants Phalacrocorax bougainvillii in Peru and the breeding population of Cape cormorants P. capensis in South Africa are significantly related to the biomass of anchovy. For both species,
reproductive success decreases in periods of anchovy scarcity, and there may also be substantial adult mortality. There has been long-term stability in numbers of Peruvian boobies Sula variegata, whereas the numbers of
Cape gannets Morus capensis decreased as sardine decreased in southern Africa. Numbers of Peruvian pelicans Pelecanus (occidentalis) thagus are significantly related to the combined biomass of anchovy and sardine in
Peru. They have been stable in the long-term. There have been ongoing severe decreases in populations of the Humboldt penguin Spheniscus humboldti and the African penguin S. demersus, both of which are now
Vulnerable. Common causes for the decreases have been collection of eggs, loss of habitat through exploitation of accumulated deposits of guano and competition with fisheries for food. Short-term decreases in guanay cormorants, Peruvian boobies, Peruvian pelicans and Humboldt penguins have followed El Niño events. Time-series of indices of the abundance of guano-producing seabirds date from 1908 in Peru and 1896 in southern Africa. They are significantly, negatively correlated in the period prior to the development of intensive fisheries on sardine
and anchovy, suggesting that the out-of-phase nature of the anchovy and sardine populations in the Peru and Benguela systems pre-dated commercial exploitation of these fish resources.
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eISSN: 1814-2338
print ISSN: 1814-232X