Fine-scale recognition and use of mesoscale fronts by foraging Cape gannets in the Benguela upwelling region
|Author(s)||Sabarros Philippe S.1, 2, Gremillet David3, 4, Demarcq Herve2, Moseley Christina4, Pichegru Lorien4, Mullers Ralf H. E.3, Stenseth Nils C.1, 5, Machu Eric1, 6, 7|
|Affiliation(s)||1 : Univ Oslo, Dept Biol, Ctr Ecol & Evolutionary Synth, N-0316 Oslo, Norway.
2 : Inst Rech Dev, Ctr Rech Halieut Mediterraneenne & Trop, UMR EME 212, F-34203 Sete, France.
3 : CNRS, Ctr Ecol Fonct & Evolut, F-34293 Montpellier, France.
4 : Univ Cape Town, DST NRF Ctr Excellence, Percy Fitzpatrick Inst African Ornithol, ZA-7701 Rondebosch, South Africa.
5 : Inst Marine Res, Flodevigen Marine Res Stn, N-4817 His, Norway.
6 : Inst Rech Dev, Lab Phys Oceans, F-29280 Plouzane, France.
7 : Ifremer, France
|Source||Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Pergamon-elsevier Science Ltd), 2014-09 , Vol. 107 , P. 77-84|
|WOS© Times Cited||13|
|Keyword(s)||Seabird, Environmental cue, Behavioral shift, Area-restricted search, Feeding activity, Fractal landscape, Oceanographic fronts, Morus capensis, Southern Benguela, South Africa|
|Abstract||Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll-a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift from transiting to area-restricted search mode (ARS) at a distance from fronts ranging between 2 and 11 km (median is 6.7 km). This suggests that Cape gannets may be able to sense fronts (smell or vision) or other predators, and that such detection triggers an intensified investigation of their surroundings (i.e. ARS). Also we found that diving probability increases near fronts in 11 out of 20 tracks investigated (55%), suggesting that Cape gannets substantially use fronts for feeding; in the remaining cases (45%), birds may have used other cues for feeding including fishing vessels, particularly for gannets breeding on the west coast. We demonstrated in this study that oceanographic structures such as mesoscale fronts are important environmental cues used by a foraging seabird within the rich waters of an upwelling system. There is now need for further investigations on how Cape gannets actually detect these fronts.|