Year-round presence of Northern and Southern Hemisphere blue whales (Balaenoptera musculus) at the Galapagos Archipelago

Abstract

Information about blue whales (Balaenoptera musculus) in the Eastern Tropical Pacific is scarce with only few whales sighted within the last decades. Molecular, photo ID and acoustic studies suggest a connectivity of Chilean and Antarctic blue whales to potential breeding areas off the coast of Peru and in the Galapagos, whereas blue whales of the Costa Rica Dome relate to the Northern Hemisphere population feeding off the coast of California and breeding areas are yet unknown.

With opportunistic sighting records in the Galapagos, we document group size and distribution throughout the year during a 17-year period from 2001 to 2018. Sightings slightly increased during the study period with 50% of the whales seen as singletons. Whales were seen year-round but mostly during the Austral winter (82%) and calf sightings occurred from June to September. With 18% of the sightings occurring during the Austral summer, we propose there is geographical overlap between equatorial Galapagos and Northern hemisphere blue whales. One blue whale was identified in the Galapagos in February 2009, resighted in the Costa Rica Dome in January 2014, and sighted again in the Galapagos in May 2016, when whales from the Southern Hemisphere could already be present. The fact that blue whale sightings were recorded throughout the year and the identified individual strongly suggest a non-migratory blue whale population and that in the Galapagos overlapping of both North and South East Pacific blue whale populations can occur.