Winter 2019 characterized by late arrival, low calf counts and increased numbers of “skinny” gray whales in Baja Lagoons, a cause for concern...
The arrival of the gray whales (Eschrichtius robustus) to Laguna San Ignacio and Bahía Magdalena in Baja California Sur, Mexico was approximately two weeks late in 2019. Our colleagues monitoring the southward winter migration along the west coast of North America also reported a fewer number of southbound whales passing Los Angeles and Monterey early in the season. The numbers of mother-calf pairs arriving at the lagoons in January was very low and remained low all winter in both lagoon areas. This was the second consecutive winter that we documented reduced numbers of mother-calf pairs (low calf counts also occurred in 2018). This year, the number of mother-calf pairs in Laguna San Ignacio observed in weekly abundance surveys hovered around 20-pairs, and never exceeded 8-pairs in Bahía Magdalena when there should have been 75 to 100 pairs in both of the lagoons. In addition, the percent of “skinny” single whales observed in the lagoons in 2019 jumped from 4.9%-7.6% during the years 2008-2011, to 23.6% skinny. Now, we are receiving reports of unexpected numbers of dead gray whales washing ashore along their North American migratory route to the summer feeding areas, that if continuing could lead to another “Unusual Mortality Event” (UME) for this population..
The low calf counts seen in 2019 are similar to the reduction in calves observed during the years 2007-2010, which followed the 1999-2000 range-wide unusual mortality event (UME) when an estimated 1/3 of the North Eastern Pacific gray whale population was lost. These observations suggest that in recent years the gray whales are not obtaining sufficient nutrition during their summer feeding in the Arctic and North Pacific, and/or they may be suffering from the effects of some combination of environmental factors including disease.
So why is this happening? Perhaps the current “carrying capacity” in the gray whales’ feeding areas has been reduced during the past decade, as the result of the warming of the northern seas and the reduction in sea ice slowing the seasonal plankton blooms that support the gray whales’ benthic prey. Gray whales depend on the seasonal abundance of prey (e.g., benthic amphipods) to obtain sufficient energy to survive their winter/spring migrations to and from their winter breeding and calving areas, and the production and growth of their calves. Skinny gray whales and low calf production suggest that finding sufficient food over the summer is becoming a problem for the gray whales. So with climate change and the warming of the polar seas, is this the new “normal” ?
View other findings, reports, and presentations from the 2019 winter gray whale research in Laguna San Ignacio and Bahia Magdalena on our “Publications and Resources” website page.