SEFI’s Giant Gray Visitors
March 3, 2021
Each winter the waters surrounding the Farallon Islands teem with charcoal-colored, behemoth-sized visitors arriving from the north… the Gray Whale (Eschrichtius robustus). The coastal Gray Whale with its narrow, triangular head, lack of a dorsal fin, and round paddle-shaped tail fluke is a signature sight each winter along the west coast and around the Farallones.
Every year an estimated population of 27,000 make one of the longest migrations of any mammal, a round trip up to 9,000 to 13,000 miles, between their northern summer arctic feeding grounds to the warm waters of the lagoons of Baja California to breed or calve (Allen, Mortenson, & Webb 2011). The lagoons provide safety from predators and warm temperatures required for newborn calves, who are both defenseless and lack blubber (Allen, Mortenson, & Webb 2011).
The migration begins around October and peaks between January and March, as evident from our whale sighting data. Interestingly, the graph reveals that March actually has a greater number of sightings compared to the month of February, possibly due to the island receiving both southbound and northbound whales at the same time (Townsel). Since the whales arriving from Baja in March are without calves, they are presumably males and non-calving females. This is further supported by the fact that mother-calf pairs are the last to leave the lagoons, typically starting their migration north in April and sticking close to the coast (Townsel).
The Gray Whales visiting the Farallones are either seen alone or associating with one another in groups of two to three and have been seen performing a myriad of behaviors, including foraging dives and rubbing against the rocks. Currently it is not known precisely why the whales visit the islands during their migration. It could be for feeding, resting, navigation, socializing or any combination of these reasons. Even more peculiar is after the winter migration period ends, a few whales stick around the island for the rest of the year to feed. This phenomena has been observed throughout California and the Pacific Northwest, and these individuals are referred to as “summer residents”. SEFI’s summer resident numbers have historically fluctuated anywhere between two to seven whales, and so far it is not known if this group is comprised of the same individuals repeatedly staying around the island.
Luckily, the overall number of Gray Whales visiting the Farallones has held steady the past few years, despite the increased frequency of unusual mortality events starting in 2019. While the exact cause of these events is unknown it could be related to poor health, since recently many whales have been observed to be getting thinner. There is some speculation that these events are due to climate change affecting their food sources or possibly that the population has simply reached its peak (Alexander 2021). As is frequently the case, more study is needed to discern a clear answer, but in the meantime the Farallon Islands will continue to be an important stop-over for this charismatic and respected marine mammal.
Alexander, K (Jan 9th, 2021) “Gray whale die-off pushes into second year. Can the giants survive?”. San Francisco Chronicle.
Townsel, A. “The Gray Whale Migration in California and Beyond”. Oceanic Society.
Allen, Mortenson, and Webb (2011). Field Guide to Marine Mammals of the Pacific Coast. University of California Press.
Migration Map: Ocean Outfitters