Analyzing trends in the Hawaiian humpback whale (Megaptera novaeangliae) population using citizen science

Abstract

Every year since 1996, the Hawaiian Islands Humpback Whale National Marine Sanctuary has hosted its signature Sanctuary Ocean Count during the peak season of humpback whale (Megaptera novaeangliae) activity in Hawai'i. The Sanctuary Ocean Count brings together citizen scientists three times a year - in January, February, and March - to count whales from almost 70 sites across O'ahu, Hawai'i Island, and Kaua'i. This analysis uses data collected from 2002 through 2023 at 30 of the most consistently studied site locations. Kruskal-Wallis tests were used to determine if there are significant differences in the number of adult and calf sighting rates by site locations and year. Additionally, general population trends seen in the Sanctuary Ocean Count data were compared to recent findings from other studies, to see how well the Sanctuary Ocean Count data track what was seen by other humpback whale monitoring efforts. The results from the Kruskal-Wallis tests reveal a statistically significant difference in adult and calf sighting rates when compared among site locations, as well as individual years. We see a rise in whale sightings across O'ahu, Hawai'i Island, and Kaua'i from 2005 to 2015, when the population hit its peak, followed by a decrease in the subsequent years. The Sanctuary Ocean Count findings are generally consistent with data collected through more traditional research methods, such as mark-recapture photo-identification studies and acoustic monitoring observations. Despite concerns regarding data quality and observer bias, results suggest that citizen science data can provide valuable insights into humpback whale distribution, abundance, and habitat use. Future research should include a more sophisticated modeling approach to examine variations between months, as well as factor environmental data into analyses. Moving forward, it will be important to evaluate the long-term impacts of citizen science on volunteer attitudes and behaviors, as well as to explore strategies for maximizing citizen science efforts to improve the data's scientific integrity and strengthen their potential to inform policy and wildlife management decisions.