Intensive feeding of humpback whales (Megaptera novaeangliae) in the breeding ground of Banderas Bay, Mexico

Abstract

Banderas Bay, located in the Mexican Pacific, is a breeding/calving ground for the North Pacific stock of humpback whales (Megaptera novaeangliae) during the winter.  While sporadic registers of humpback whales feeding on their mating grounds exist, this is the first occasion where feeding activity was observed intensively and extensively on a breeding ground.  Between 19 December 2011 and 6 March 2012, 26 such occurrences were registered in Banderas Bay, along the mainland pacific coast.  On five occasions, groups of 20 or more individuals were recorded feeding. They were feeding over and under the surface using lunging and gulping techniques.  On several occasions humpbacks were observed feeding alongside Bryde´s whales (Balaenoptera edeni), Pantropical spotted dolphins (Stenella attenuata) and Bottlenose dolphins (Tursiops truncatus).  Two different samples of fish at two different feeding sites were taken and the fish identifications showed these were Pacific anchovies (Cetengraulis mysticetus).  Among the 26 sightings, nine different species of birds were registered feeding in the same area as the humpback whales.  The number of whales feeding over an extended period of time in their breeding ground could be an indicator that there was not enough food in their feeding grounds, but the possibility that they might just be taking advantage of good food availability is also possible.