MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12475

Oceanographic drivers of near-colony foraging site use in tropical marine systems

Fiona McDuie*, Scarla J. Weeks, Bradley C. Congdon

*Email: fiona.mcduie@gmail.com

ABSTRACT: Wedge-tailed shearwaters of Australia’s southern Great Barrier Reef (GBR), obtain food for their chicks on short-trips adjacent to the breeding colony. GPS tracking (Feb-Apr 2013-14) indicated that most trips were of one-day duration (70-85%) and that all were within 300km of the colony. Oceanographic characteristics of foraging and non-foraging areas were compared to identify mechanisms linked to prey availability. Foraging generally occurred adjacent to the Capricorn shelf, where the largest oceanographic feature in the region, the Capricorn Eddy, creates increased frontal activity and upwellings. Shearwaters consistently revisited four bathymetrically and topographically distinct foraging zones influenced by this mesoscale eddy. In 2013, strong sea-surface temperature (SST) fronts associated with relatively intense eddy activity influenced foraging activity in all foraging zones. In 2014 the dominant oceanographic factors influencing foraging were SST and [Chlorophyll a] or their anomalies, with these influences varying among zones; thus suggesting a weakened effect of the eddy and elevated importance of fine-scale phenomena such as localised upwellings. Foraging in the coastal foraging zone was also significantly influenced by terrestrial inputs. At these times birds foraged in association with freshwater flood plumes and higher [chlorophyll a]. The oceanographic mechanisms underlying prey availability to shearwaters in this system are tightly linked to variations in climatic conditions. Consequently, predictions associated with climate change such as increased ENSO frequency or severity, are likely to seriously diminish the profitability of identified foraging locations and the reproductive output from impacted colonies. Currently, most identified foraging areas are without specific management or protection status.