Lots of small tags on top of each other. (wagwalking.com)
Elephant seals like to cover themselves with sand when hauled out, and the very small tag was not visible until rescuers got close to him. (marinemammalcenter.org)
An even smaller tag is being developed for juvenile eels and lamprey, and a longer - lasting tag was made for juvenile sturgeon last year. (sciencedaily.com)