Spatio-temporal occurrence patterns of cetaceans near Ross Island, Antarctica, 2002-2015: implications for food web dynamics

The Ross Sea pelagic food web is closely coupled, with the foraging among abundant upper level species affecting the foraging of one another. To investigate the roles cetaceans may have in such interspecific interactions in this system, we studied within-season and interannual occurrence patterns of Antarctic minke whales (Balaenoptera bonaerensis) and type-B and type-C killer whales (Orcinus orca) within the southwestern Ross Sea, 2002-2015. Time series analysis summarized daily observations made from 3 shore localities: Capes Crozier, Bird, and Royds distributed around the similar to 120 km periphery of Ross Island. In early mid-November, both species arrived at Crozier, the easternmost point and westward edge of the Ross Sea Polynya marginal ice zone. Subsequently, coinciding with decreased sea ice cover and numbers off Crozier, both species appeared off Bird, then Royds, 80 and 117 km to the west/southwest, respectively. Arrival in either area coincided with SIC decreasing to < 80%, consistent with observations elsewhere. Within-season off Crozier, both species occurred in cycles of multi-day presence followed by absence, perhaps reflecting the spatio-temporal patchiness of prey indicated also by penguin foraging patterns. Within-season off Royds, especially for killer whales, occurrence was even more episodic; type-Bs arrived before type-Cs, and results support previously described resident and transient portions of the type-C population. Combined with results showing that whale arrival leads to food stress among penguins, we suggest that relatively few cetaceans can alter food availability to alter the foraging behavior of other mesopredators, despite primary productivity being the richest in the Southern Ocean.