Fig 1.
Example of radar detector data along a Cape gannet foraging trip recorded by a XGPS.
Grey shaded areas correspond to night time. Four « encounters » separated from each other by more than 1h without radar detection were identified. Definitions for the different categories of encounters are provided in the Results section.
Fig 2.
Cape gannet adult body condition index (bars: upper graph) and chick growth rates (bars: Middle graph), as well as Cape gannet diet (bars: Lower graph) for the 2012–2015 and 2017 breeding seasons on Malgas Island.
Numbers at the bottom of histogram bars show sample sizes, and different letters above histogram bars denote statistically significant differences among years.
Fig 3.
Foraging tracks of 50 Cape gannets provisioning for small chicks from the Malgas Island breeding colony in the southern Benguela upwelling region in 2017.
Blue shades indicate bathymetry (R package marmap).
Fig 4.
Vessel encounter characteristics.
(Left): Average Cape gannet traveling speed and contact duration of 28 radar “encounters” by gannets (from 13 individuals), used for visual categorization; the seven encounters identified as true attendance (from 5 individuals) are highlighted in red. (Right): Proportions of speeds < 10km.h-1 during trips as a whole (during day time hours: left) or during the seven “true” attendance (right, red, ***: Wilcoxon test, p < 0.001).
Fig 5.
Foraging tracks of 13 Cape gannets during which vessel radar was detected.
The seven detections with true bird-vessel attendance are indicated with yellow dots, whereas another 21 detections (green dots) featured short (<10 min) bird-vessel overlaps. Blue shades indicate bathymetry (R package marmap).
Fig 6.
Overlap between the at-sea home-ranges of 50 GPS-tracked Cape gannets in Oct-Nov 2017 (90% kernel distributions, dotted lines) and average annual sardine catch by purse-seiners reported at a 10x10 nautical mile grid scale (log tonnes+1; orange dots) in 2008–2015.
The size of orange dots increases with catch value from 0.20 to 9.54. White dots represent no catch in the fishing area. Blue shades indicate bathymetry (R package marmap).
Fig 7.
Overlap between the at-sea home-ranges of 50 GPS-tracked Cape gannets in Oct-Nov 2017 (90% kernel distributions, dotted lines) and average annual hake catch by trawlers in 2008–2015 (log tonnes+1; orange dots).
The size of orange dots increases with catch value from 0.17 to 6.53. White dots represent no catch in the fishing area. Blue shades indicate bathymetry (R package marmap).
Fig 8.
October sea surface temperature (°C; average with error bars showing SD) across 2008–2017 within the Malgas Cape gannet at-sea core home-range (90% kernel distribution), as determined via GPS-tracking of birds provisioning small chicks.