African penguin (Spheniscus demersus) distribution during the non-breeding season : preparation for, and recovery from, a moulting fast

Little is currently known about the spatial ecology of the endangered African penguin during the non-breeding season. As foraging success during this period is critical to adult survival, this project explores their dispersal patterns, as well as the degree of overlap with commercial purse-seine fisheries which target the same prey. African penguins from two colonies (Bird Island, Algoa Bay, south coast and Dassen Island, west coast) were tracked over 3 non-breeding seasons using Platform Terminal Transmitters and Global Positioning System devices to explore their pre- and post-moult dispersal patterns. Dispersal trips varied greatly between individuals, but there were still significant differences in the dispersal patterns found between islands and between life history-stages at Dassen Island. Bird Island penguins tended to make frequent, short trips, returning to their breeding colony in between, whereas Dassen Island penguins followed one of two strategies: either making few (up to 3) very long trips (up to 4000km), or adopting a central-place foraging pattern based at a point along the coast, distant from their breeding colony. At Dassen Island a clear spatial divide is evident with most pre-moulters dispersing south whereas most post-moult birds dispersed north, off the west coast. Bird Island penguins all moulted at their breeding colony and seldom visited either the adjacent coastline or other islands. During pre-moult, Dassen Island birds often spent nights close to shore along the coast or at other colonies and about a quarter of them moulted at another colony, most often at Stony Point, on the mainland east of Cape Point. Five dispersal patterns (defined in terms of the direction and distance of the furthest point reached) were identified for birds from Dassen Island and there is some indication that different dispersal patterns have distinct survival implications. Over 60% of PTT loss (a proxy for penguin mortality) occurred in a small area in the northern part of St Helena Bay, offshore from Lambert's Bay and Strandfontein and could be due to high levels of seal predation, which has been previously documented in the area. Commercial small pelagic fishing data were analysed over three years (2012-2014). Average fishing effort decreased each month from September to December (when hardly any fishing occurred in any of the three years) and there was much greater fishing effort along the west coast than on the south coast. Commercial fishing effort was compared to penguin track data to assess the degree of potential overlap between these two pelagic predators. Firstly, the spatial overlap between core penguin non-breeding dispersal areas and core fishing areas was assessed on a broad temporal scale (three years). Bird Island penguins were found to be more spatially removed from fishing activity with no overlap in core fishing and dispersal areas on the south coast. Compared to the size of their dispersal area, Dassen Island penguins which stayed along the lower west coast showed the highest overlap with core fishing areas. The two most common dispersal patterns exhibited by Dassen Island penguins both involve journeying to areas outside the range of purse-seine fishing, indicating the possibility of avoidance behaviour once the pressures of breeding are lifted. Direct (daily) overlap between commercial fishing effort and penguin tracks was studied although the low frequency of the penguin position data restricted the analysis to a 20 km scale. The results were similar to those described above, with most direct overlap occurring between Dassen Island and Gansbaai.

Grantor dc:publisher.institution

Percy FitzPatrick Institute of African Ornithology

Year dc:date.issued

2016

Author dc:creator

• Roberts, Jennifer

Advisors dc:contributor.advisor

• Ryan, Peter G
• Pichegru, Lorien
• Wanless, Ross M
• Hagen, Christina

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/20525

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/20525