Factors determining the number of seabirds impacted by oil spills and the success of their rehabilitation: Lessons learned from Namibia and South Africa

The coastal waters of Namibia and South Africa have an extensive history of oil spills, with 71 recorded up to 2021. Thirty-nine spills reportedly affected 83,224 seabirds, with African penguins (Spheniscus demersus; 91.0 %) and Cape gannets (Morus capensis; 8.5 %) most affected. Spills affecting seabirds were caused by unknown sources (46 %), bulk/cargo carriers (43 %), tankers (38 %) and ship-to-ship transfers (14 %). The number of penguins oiled was predicted by the breeding population size within 25 to 75 km, but not the volume of oiled spilled, the month or the year. Rehabilitation records from penguins oiled in spills since 2001 reveal that the day of admission (relative to the start of the spill) was predictive of packed cell volume, body mass, and plasma total solids, with the latter two being predictive of rehabilitation success. Our results highlight the importance of rapid monitoring at colonies to locate oiled birds in the event of spills.

Automated summary

The coastal waters of Namibia and South Africa have a long history of oil spills, with 71 recorded up to 2021. These spills have had significant impacts on seabirds, particularly African penguins (91.0%) and Cape gannets (8.5%). The main sources of these spills include unknown origins, bulk/cargo carriers, tankers, and ship-to-ship transfers. Monitoring the breeding population size within a specific range has shown to predict the number of oiled penguins, while the admission day of oiled birds is indicative of their rehabilitation success.