Movement of a blue whale (Balaenoptera musculus) between the Costa Rica Dome and the Galapagos: Management implications of the first documented cross-equatorial movement

Citation

Douglas, A, R Sears, J Denkinger, E Dobson, P Olson, T  Gerrodette, and J Calambokidis. 2015. Movement of a blue whale (Balaenoptera musculus) between the Costa Rica Dome and the Galapagos: Management implications of the first documented cross-equatorial movement. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.

Abstract

The Costa Rica Dome (CRD) has been documented as one of the more productive regions in the Eastern Tropical Pacific (ETP) and is recognized as an important area for blue whales year-round, including Eastern North Pacific (ENP) whales in winter. Year-round presence of blue whales on the CRD has lead to speculation that the region may support a local resident population, or that the region is a winter migratory destination used alternately by both northern and southern hemisphere whales. Photographs collected both systematically and opportunistically since the early 1980s by Cascadia Research and collaborators have identified 2,142 individual blue whales in the ENP/ETP with 111 (5.1%) encountered in the ETP, 27 (1.2%) in the Galapagos and 12 (0.56%) along South America starting at 3̊ South. We report on the first confirmed trans-equatorial movement between the Galapagos Islands (February 2009) and the CRD (January 2014), a distance of 1,300 km. Of the individuals identified in the Galapagos and coastal South America this is the first to be re-sighted in the eastern North Pacific, while 26% of CRD whales have been encountered along the US west coast and/or Baja California. The International Whaling Commission considers blue whales in the North Pacific as one stock, separate from blue whales in the southern hemisphere - this study adds to the growing body of evidence that the stock structure of blue whales in the eastern Pacific (north and south) may be more complex. Past genetic studies have shown similarity among some of the coastal blue whales in the eastern Pacific including those in southern and northern hemisphere. The interchange we show here provides evidence that greater exchange is possible among these animals north and south of the equator than had previously been demonstrated.