He conducted the first census of California gray whales and is credited with creating public interest in their conservation by leading the earliest whale-watching excursions for the San Diego Natural History Museum.

[7] From 1935 to 1938, Gilmore worked for the International Health Division of the Rockefeller Foundation as the zoologist on a 65-member team researching jungle yellow fever in the Amazon Basin.

Fish and Wildlife Service, first in the San Francisco Bay area, and from 1952, on the Scripps Institution of Oceanography campus in La Jolla.

In 1954, participating in Carl L. Hubbs's seven-year gray whale breeding survey, Gilmore (with Gifford C. Ewing) discovered the species's mainland calving sites in the Gulf of California.

Retiring from the Fish and Wildlife Service in 1972, Gilmore expanded his involvement in cetology at the museum, opening the Office of Marine Mammal Information in 1977.