Honu Count: how shell-etchings, participatory science, and a novel online survey are improving assessments of the Hawaiian Green sea turtle (Chelonia mydas) population.

The Hawaiian green sea turtle (Chelonia mydas; honu) subpopulation is listed as a Distinct Population Segment in the Central North Pacific Ocean under the U.S. Endangered Species Act, which mandates monitoring to understand population viability of threatened species. The honu population abundance has largely been determined by a census of nesting females at the main nesting site, Lalo (French Frigate Shoals), an atoll located approximately 1,000 km northwest of the main Hawaiian Islands (MHI) within the Papah[Formula: see text]naumoku[Formula: see text]kea Marine National Monument. Researchers and later the National Marine Fisheries Service within NOAA (NOAA Fisheries) have monitored honu at Lalo since 1973. One monitoring method used includes etching an alpha-numeric identifier temporarily (6-12 months) onto the shell with a rotary tool and sealing it with non-toxic white paint. In 2017, NOAA Fisheries launched the Honu Count Participatory Science Project, facilitating public reporting on sightings of honu with shell etchings around the MHI. Honu Count evolved in the way it collected sightings data from the public, from employing a hotline (2017-2018), to an email address (2018-2022), and most recently, an online survey via ArcGIS Survey123 (2023-present). Within the first year of the new online survey, data collection from the public increased from an average of 435 sightings per year to a total of 1,227. The project's new format has increased the breadth of invaluable honu population data, including a greater understanding of sea turtle behavior, survivorship, habitat use and migration routes, all while improving NOAA Fisheries' engagement with the public.