Blue whale (Balaenoptera musculus) occurrence off the Galapagos Islands, 1978-1995

Abstract

Twenty-three blue whale (Balaenoptera musculus) sightings made in the vicinity of the Galipagos Islands (~00°S, 90°W) between1978-1995 are analysed. Blue whales occurred seasonally in the austral winter/spring months. A significant proportion of the sightings (13co 56.5%) had a tendency to occur on the same day or on consecutive days in a given year. Five (21.7%) of the sightings were of groupsof three or more individuals, Distribution was to the west and southwest of the Galipagos archipelago, where a plume of coo!,Uupwelling-enriched surface water with high planktonic biomass develops during this season. Blue whales were observed feeding on surfaceswarms of the euphuusiid Nyctiphanes simplex in 1993, Defecation was commonly seen, The external appearance of these whales suggeststhey were true blue whales (B.2. interniedia). Much of the evidence from this study suggests a Souther Hemisphere stock feeding westof the Gulipagos during the austral winter/spring months. Alternatively, they may' belong fo a presumed eastern tropical Pacific stack ofblue whales which exploits the productive habitars of the Cost Rica Dome and the Peruvian/Ecuadorian coast.