Browsing by Subject "Apollo Sea"

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    Breeding success of African penguins Spheniscus demersus at Dassen Island, especially after oiling following the Apollo Sea spill
    (2008) Wolfaardt, A C; Underhill, L G; Nel, D C; Williams, A J; Visagie, J
    The reproductive success of African penguins Spheniscus demersus at Dassen Island from 1994 to 2000 was variable, but much higher than previously reported figures for the species. Breeding success was positively related to the abundance of anchovy Engraulis encrasicolus and sardine Sardinops sagax, and the high reproductive output during the study was attributed to the large biomass and high availability of these two species for much of the study period. De-oiled penguins from the Apollo Sea spill had a slightly lower hatching success but a significantly lower overall breeding success than that of un-oiled birds, driven mainly by the reduced number of chicks which fledged. Nests with two de-oiled Apollo Sea parents were less successful than nests with one de-oiled bird. There was increased mortality of chicks 40 days and older in nests with de-oiled birds. Chicks from nests with one de-oiled Apollo Sea parent grew at a similar rate to chicks from nests with no de-oiled parents. However, chicks from nests that comprised two de-oiled Apollo Sea birds had significantly slower growth rates than these other two groups. Breeding success and chick growth at nests with de-oiled birds were more negatively impacted when feeding conditions were less favourable. These results suggest that one of the main reasons for lower breeding success in de-oiled birds was their reduced ability to provision chicks, especially during the period in which the energy demands of the chicks is greatest. The rate of mate fidelity was lower in de-oiled birds than un-oiled birds, and there was a positive association between mate fidelity and breeding success.
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    Restoration of oiled African penguins Spheniscus demersus a decade after the Apollo Sea spill
    (2008) Wolfaardt, A C; Underhill, L G; Altwegg, R; Visagie, J
    The bulk ore carrier Apollo Sea sank south-west of Dassen Island off western South Africa in June 1994, oiling approximately 10 000 African penguins Spheniscus demersus, most of which were collected from Dassen Island. A total of 4 076 de-oiled penguins was released with flipper bands. From 1994 to 2005, follow-up research using re-sighting and capture-mark-recapture methods indicated that about 73% of the de-oiled penguins observed back at Dassen Island attempted to breed, and were thus successfully restored into the breeding population. For de-oiled breeders, the median interval between their first recorded sighting and first recorded breeding attempt was 11 months, indicating a short-term delay in restoration. At least 45% of the de-oiled breeders were still being re-sighted five years after their release, and a minimum of 4% survived into their ninth year. These results represent the most successful restoration estimates anywhere in the world. The proportion of de-oiled juvenile penguins re-sighted back at Dassen Island and recorded breeding was lower than that of birds in adult plumage. De-oiled non-breeders spent significantly more time along the shore and less time within breeding colonies than de-oiled breeders. The mean proportion of de-oiled breeders that abstained from breeding each year during the study period was greater than expected. There was a negative relationship between breeding and subsequent survival and breeding, suggesting a cost of reproduction for de-oiled birds.