Last updated: April 7, 2021
March 2021 - Glimpsing the drama of the northern elephant seal breeding season at Point Reyes National Seashore, it can be easy to forget that these huge, noisy, and abundant animals were once nearly extinct due to over-hunting. The thousands of seals that crowd the beaches today were completely absent just 50 years ago. Part of how they were able to return has to do with some seals’ inclination to disperse. Were it not for that, the remnant colony discovered on Mexico’s Guadalupe Island in 1892 could still be the world’s only northern elephant seal colony. But how prevalent is dispersal among elephant seals (which also show a strong attachment to the beaches where they were born)? For those that disperse, where do they tend to go?
Researchers from UC Santa Cruz, Point Reyes, and Point Blue Conservation Science recently quantified dispersal rates among elephant seal colonies for the first time. To do so, they looked at tagging data collected at four well-established elephant seal colonies along the central California coast: Piedras Blancas, Año Nuevo, SE Farallon Island, and Point Reyes. More specifically, they focused on female seals tagged on their hind flippers as pups at each of the colonies in 1998, 1999, and 2000, and looked for re-sights of those seals recorded through 2008.
They found that less than 2% of the elephant seals studied switched colonies as breeding adults. Juveniles, on the other hand, were far more likely to settle down and start breeding at a colony different from the one where they were born. This “natal dispersal” was quite high at Piedras Blancas, the southernmost study site, where 61% of young females moved to more northern colonies. The researchers found far less natal dispersal at the more northern sites—an average of just 11% moved to another colony. Of those, migrants from Point Reyes and SE Farallon Island mostly moved south to Año Nuevo, while those from Año Nuevo mostly moved north to Point Reyes.
The researchers speculate that more seals may be dispersing north than south because their feeding grounds are far to the north. If elephant seals’ remnant colony had by chance been further north, it’s possible that their range and population would remain more restricted today. Yet as things stand, with no shortage of migrants from well-established colonies, the researchers deem it likely that elephant seals will continue to colonize remote beaches along the west coast, as some are already doing from Mendocino County to British Columbia. Continuing to track tagged seals can be an important tool to help anticipate how colonies may grow and change in the years ahead.
For more information
Zeno, R., Condit, R., Allen, S. G., Duncan, G. 2021. Natal and adult dispersal among four elephant seal colonies. bioRxiv. https://doi.org/10.1101/2021.03.18.435977 (preprint)
- Contact Marine Ecologist Sarah Allen (scientist profile)