Hawksbill Nesting in Hawai‘i: 30-Year Dataset Reveals Recent Positive Trend for a Small, Yet Vital Population

Abstract

Evaluating wildlife population trends is necessary for the development of effective management strategies, which are particularly relevant for highly threatened species. Hawksbill marine turtles (Eretmochelys imbricata) are considered endangered globally and are rare in Hawai‘i. Remnant hawksbill nesting beaches were identified in Hawai‘i in the late 1980s and the primary sites have been monitored since that time. In this study we summarize all available hawksbill nesting activity around the Hawaiian Islands between 1988 and 2018, highlighting relevant demographic and geographic data for the species. Because monitoring effort varied substantially across space and time, we implemented a predictive modeling approach that accounted for varying effort to explore potential trends in annual number of nesting females and nests over time. Field monitoring efforts documented an annual average of 14 ± 4.3 (range: 5–26) nesting females and 48 ± 19.0 (range: 12–93) nests, with a cumulative total of 178 individual nesting females and 1,280 nests recorded across all years. Nesting has been documented on four Hawaiian Islands, with the overwhelming majority of nesting females (78.4%) and nests (86.5%) recorded at four beaches along the southern coast of Hawai‘i Island. Recent monitoring (2018) at a beach on Moloka‘i Island revealed numbers similar to the most important beaches on Hawai‘i Island. Despite difficulty discerning obvious trends when looking solely at the raw tabulated numbers from field monitoring, our analysis suggests both the number of nesting females and nests have been positively trending since 2006, and this is supported by a higher percentage (57.1% of annual cohorts) of neophyte (vs. remigrant) nesters over the second half of the monitoring timeframe. The masking of obvious trends in the tabulated numbers is likely due to decreased overall monitoring effort as a result of reduced funding in recent years, coupled with a shift in focal monitoring effort from the historical primary nesting site of Kamehame, to the more recently established nesting site of Pōhue. Although the positive trend is encouraging, our findings highlight the precarious state of hawksbills in Hawai‘i and the need to enhance monitoring across all sites to support more robust population assessments and management decision making.

Three decades of stranding data reveal insights into endangered hawksbill sea turtles in Hawai‘i

“…ju-veniles and adults) in Ha wai'i. However, the number of individuals docu mented nesting on the MHI is extremely low (Sno ver et al 2013), with an annual average of approximately 14 nesting fe males and a cumulative total of 178 nesting females (and 1280 nests) documented between 1988 and 2018 (Gaos et al 2021). In comparison, the central North Pacific green turtle population has been estimated to have 3846 nesting females (Seminoff et al 2015).…”

“…Both hawksbill and green Chelonia mydas sea turtles are the primary nearshore residents around the Hawaiian Islands, yet population estimates for these 2 species in the region contrast marked ly, with those for green being several orders of magnitude grea ter than the hawksbill (Balazs & Chaloupka 2004, Seitz et al 2012, Gaos et al 2020). An average (± SD) of only 14 ± 4.3 hawksbills have been documented nesting annually on the Hawaiian Islands (Seitz et al 2012, Gaos et al 2021 for green turtles (Balazs & Chaloupka 2004, Pacific Islands Fisheries Science Center (PIFSC) unpubl. ), highlighting the precarious state of hawksbills in the region.…”

Non-random mating between nesting sites of Hawaiian hawksbill turtles: demographic discontinuity within a small isolated population

“…2), and there are other nesting areas in the main Hawaiian islands that could be genetically and demographically unique. Most nesting sites not on the island of Hawaii are extremely low-density, having less than two nests laid annually, but one rookery on the island of Molokai has at least as many nesting females as any of the Hawaii Island nesting complexes (Gaos et al 2021). Samples from multiple breeding seasons are also needed to better understand mating systems and female nesting behavior within and between complexes.…”

“…Ten females from the 2018 nesting season were included in this study to act as control samples for assigning mothers to nests. Female Hawaiian hawksbills are not known to nest in consecutive years (Gaos et al 2021), so it is presumed that these off-year individuals could not have been the unidentified mothers and thus serve as negative controls. Inconel flipper tags (National Band & Tag, Newport, KY, USA) and Passive Integrated Transponder (PIT; Avid, Norco, CA, USA) tags were applied to all female turtles encountered to confirm and track identity during the nesting seasons.…”

“…The population may also be predominantly female, as only 1 in 5 strandings in Hawaii are male (Brunson et al 2022). Field surveys of nesting activity have been conducted since the 1980s with varying levels of effort, and predictive modeling based on these data suggests a recent uptick in the number of nesting females (Gaos et al 2021). Nevertheless, the population remains extremely small, even though hawksbills have had endangered species status in the United States since 1970 (https://www.federalregister.gov/citation/35-FR-8491).…”