Migratory destinations of North Pacific humpback whales from Guerrero state in Southwest Mexico reveal extension of Central American breeding grounds

Humpback whales in the North Pacific are known to winter in low latitude areas off Asia, Hawaii, Mexico, and Central America. Most of the research off Mexico has focused on the offshore Revillagigedos and mainland Mexico from Mazatlán to Puerto Vallarta, with little work conducted off the coast of central or southern Mexico. Here we look at the migratory destinations of humpback whales identified at a new area of research around the state of Guerrero (about 550 km SE of Puerto Vallarta) and examine whether resighting patterns of these whales more closely resemble the other Mexico wintering areas or those in more distant areas off Central America (more than 1110 km away). Of 70 non-calf whales identified off Guerrero in January to March 2014-15, 42 (60%) had been seen previously off the US west coast from southern California to northern Washington from 1986 to 2013. This high proportion suggests that the vast majority of whales seen off Guerrero migrate to these mid-latitude feeding areas similar to whales that winter off Central America. This is in contrast to mainland Mexico whales that are known to migrate to multiple feeding areas including the US west coast, British Columbia, and Alaskan waters. The Guerrero whales in this study were primarily resighted in the more southern part of the US west coast feeding area, again similar to what has been seen for whales from Central America compared to those from mainland Mexico. Although a full comparison between Guerrero, Central American and Mainland Mexico has not yet been achieved, we are able to confirm that 13 of the whales from Guerrero have previously been seen in Central America and 6 in mainland Mexico. These finding indicate that despite their closer proximity to the primary wintering areas for humpbacks in mainland Mexico, those from Guerrero are more similar in their migratory destinations to humpbacks from much more distant areas in Central America. These findings are important given the recently proposed recognition of Distinct Population Segments for humpback whales that would delist those off mainland Mexico but keep as threatened those off Central America under the US Endangered Species Act.