Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus

Abstract

Population trends of African penguins Spheniscus demersus in the Western Cape, South Africa, and their breeding success have been linked to the abundance of their main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. During the late 1990s and early 2000s, both fish species increased markedly in abundance, but after 2004, sardine biomass decreased to below average levels. In addition, adults of both stocks were principally located to the east of Cape Agulhas from 2001 to 2009 and were thus distant from seabird colonies on South Africa's West Coast. The number of African penguin pairs counted at Robben Island from 2001 to 2009 and the fledging period of chicks from successful nests increased and decreased in apparent response to the biomass of sardine prior to each breeding season, possibly linked through adult condition at the onset of breeding. Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony. In addition, chick-fledging rates were depressed in 2-chick broods during years when anchovy contributed < 75% by mass to the diet of breeding birds. Previously reported relationships between the overall abundance of forage fish in South Africa and penguin breeding success were not supported. Taken together, these results highlight the combined importance of ensuring adequate local food availability for seabirds during the reproductive cycle and safeguarding regional prey abundance during the non-breeding season.

The initial journey of an Endangered penguin: implications for seabird conservation

“…Crawford et al 2011, Sherley et al 2013. Neither of the foraging areas identified here had any formal protection at the time of writing: the area offshore of Hondeklip Bay was utilized by the South African fishery (Pecquerie et al 2004) and the Namibian Islands' MPA was defined by the range of breeding birds, thus only extended to 20 km north of Hollamsbird Island in 2012 (Ludynia et al 2012a).…”

“…Blood samples and weights of several candidate birds were taken ca. every 7 d, and 5 individuals were selected that satisfied SANCCOB's conditions for release and exceeded the mean fledging mass at Robben Island in 2004 (2830 g), a year of aboveaverage chick growth (Sherley 2010; Table 1). Two birds originally hatched at Robben Island (33°48' S, 18°22'E; Fig.…”

“…Grémillet et al 2008). African penguins Spheniscus demersus feed predominantly on anchovy and sardine and rely on the prey available close to their colonies to breed successfully (Sherley et al 2013). These 2 factors make the population vulnerable to changes in the distribution or availability of their prey, and the species is currently Endangered following a decline in South Africa of > 60% between 2001(Crawford et al 2011.…”

Influence of environmental variables on the larval stages of anchovy, Engraulis encrasicolus, and sardine, Sardinops sagax, in Algoa Bay, South Africa

“…Moreover, the high relevance of small pelagic fish in the marine ecosystem and in the economy of the region and the urgent requirement of scientific information to help assess the risks and/or benefits of Marine Protected Areas (Pichegru et al 2012;Sherley et al 2013) or of fish farming activities (Bloom 2012(Bloom , 2013Hutchings et al 2013) in Algoa Bay make the present study particularly necessary.…”

Bottom-up effects of a no-take zone on endangered penguin demographics

“…for each year independently using parametric survival models in R v. 3.0.2. We used nest identity as a shared frailty term, an exponential error distribution [13] and an exponential distribution to transform the failure rates to annual estimates of chick survival [8]. An island-wide census in May each year estimated the annual breeding population [14].…”