Along with the more common Hawaiian green sea turtles (Chelonia mydas, known as “honu”), endangered hawksbills (Eretmochelys imbricata, known as “honu`ea” or just “‘ea”) inhabit many nearshore habitats within the Main Hawaiian Islands (MHI). Sea turtles are highly revered culturally and are considered one of the most sought after animals for visitors to Hawai`i to view. Certain species-specific characteristics are used to tell them apart.
What's the Hawaiian hawksbill's ecological role? The historical population level of the hawksbill, an indigenous species, is unknown, but it’s likely that they have never populated Hawai`i in great abundance. The answer to why this is seems to be as mysterious as they are. Due to their present day rarity, studying these animals in their marine and nesting habitats is a challenging endeavor. Managing human impacts that threaten the survival of this species is even more daunting.
Gathering information about their in-water distribution, relative abundance plus behaviors yields a much more comprehensive understanding of the population than exclusively monitoring the nesters. An educational website was launched in January 2016 to increase awareness plus encourage citizen science involvement: www.HIhawksbills.org.
This small population makes this rare species an ideal candidate for a photo-identification (photo-ID) research project, which C.King started in the year 2000. Each sea turtle has their own unique arrangement of scales on their head and flippers (like a fingerprint), so they can be monitored over time simply by photographing them and comparing the photographs to the online catalog. This is a very non-invasive way to learn a lot about them.
“Every scale tells a tale!”
Targeted in-water sea turtle research surveys were conducted to assess hawksbill habitats beyond popular snorkeling destinations. Requesting hawksbill photographs from ocean users, who are more regularly equipped with underwater cameras, plus finding incidental sightings on various websites and social media platforms has significantly increased records.
Over 250 photographers have contributed a total of 1,134 sightings of 133 unique MHI individuals (1998-2017). Various metadata accompany each sighting: date, time, location, depth, habitat, behavior, foraging habits, injuries, carapace load, hookings/entanglements, and reactions to human presence.
Since C.King resides on Maui, the majority of individuals have been reported and discovered there (Maui= 64, Hawai‘i Island= 21, O‘ahu= 30, Kaua‘i= 8, Lana‘i= 7, Moloka‘i= 2, and Kaho‘olawe= 1). All individuals were given island-specific numbers, plus each photographer who submitted a unique individual to the catalog was given the opportunity to name it.
The number of times individual hawksbills have been reported varied widely from 1 to >223 times. The longest span of sightings (1999-2017) was an adult female: #MUI2 “83-M=Ake”. Besides when she swam to Hawai`i Island to nest, all in-water 38 location records were within an ~8 kilometer range. The farthest non-nester range (~46 kilometers) was by an adult male: #MUI44 “Psycho”. Mating was photographed once off of Moloka`i, and the female was identified as #MUI6 “Kiniana”, who we have known to be a Maui resident since 2000. The male has not been documented since.
Through the course of our research activities in collaboration with the National Oceanic and Atmospheric Administration (NOAA Fisheries), 7 individuals have flipper and/or passive integrated transponder (PIT) tags, and 3 have also been tracked with satellite transmitters. The nesters that were tagged by the Hawai`i Island (n=3) and Maui (n=1) Hawksbill Recovery Projects and that were photographed in their in-water habitats have been included in this catalog, but other nesters have not been added yet.
Size approximations from photos/videos or direct observations were estimated based on:
*juvenile: <45cm curved carapace length; often with sharp serrated carapace scutes (n=68)
*subadult: between ~46-70cm curved carapace length; worn but still present carapace serrations (n=28)
*adult female: >70cm curved carapace length with a short tail (n=22)
*adult male: presence of a long, thick tail (n=11)
*unknown: photographs didn’t provide enough information (n=4)
Five individuals in the catalog were found stranded (deceased) but remain in the catalog with hopes of matching them to old sightings that will help understand their distribution: 1 juvenile on O`ahu due to a fishing gear interaction (which was not retrieved for necropsy so the gender was unknown), 3 juvenile females due to fishing gear interactions on Maui and 1 juvenile female on Hawai`i Island with no obvious cause of death. Seven other fishery gear interactions were reported, but most individuals were seen again without the gear being externally visible. Two hawksbills were missing front flippers, likely caused by self-amputation from tight fishing line. Watercraft strikes (n=2), injuries likely from predators (n=7) and carapace growth deformities (n=3) were also documented. Barnacle loads existed on 8 hawksbills, representing all size classes.
Three juvenile hawksbills in the catalog were documented in pelagic waters, but have not been matched to any hawksbills to date. The majority of hawksbills have been documented in nearshore, predominantly coral reef habitats in locations frequented by ocean users. Five adults have been seen foraging in deeper, halimeda habitats, and six offshore sightings indicate that utilization of areas that are not within the range of recreational snorkel/SCUBA diving survey operations could be more prevalent.
Hawksbills have been documented foraging on sponges, algae, urchins, coral polyps, live and dead fish, fireworms, and unidentified gelatinous materials. Gaining access to these food items often necessitate the destruction of corals by ripping pieces off with their bills and front flippers. Then, hawksbills consistently use their front flippers to hold the pieces in place while using their bills to bite items of interest. These actions commonly attract capitalizing fish, most commonly the saddleback wrasse (Thalassoma duperrey).
Surveys were limited, but no nocturnal foraging has been recorded. Night surveys have elucidated some consistent sleeping areas amongst nearshore coral reef shelves (<15 feet depth) for four Maui individuals. Possibly due to algae, sediment and epibiont coatings on most Hawaiian hawksbill carapaces, the few attempts made to document biofluorescence have not been as successful as other locations.
Similarly to greens, most appear rather tolerant around human presence, but some have displayed flight behavior. No extraordinary interactions have been noted between greens and hawksbills, but hawksbill-hawksbill exchanges are noteworthy. Regardless of size, they consistently display a face-to-face “sniffing” and circling behavior with their front flippers extended, often after crawling towards each other.
Despite being under the same Federal and State protections as the Hawaiian green sea turtle that is making an impressive comeback, the Hawaiian hawksbill population remains one of the most endangered globally. Only 11 males have been photographed compared to 22 adult females, so the sex ratio seems to be skewed (which is also in accordance with NOAA necropsy results from statewide strandings). Hawksbills are long-living reptiles that may not reach breeding age until ~20 years. No more than 25 hawksbills have been known to nest statewide annually, compared to ~400-800 greens. Since Hawaiian hawksbills are only known to nest in the Main Hawaiian Islands, the close monitoring and protection of all nesting and hatching activities are needed to ensure their survival.
More research and continued conservation actions by government agencies and non-government agencies, fueled by community involvement, are needed for this population to sustain itself into the uncertain future. Survival threats include the destruction and degradation of coral reef and nesting habitats, human behavior impacts such as harassment and poaching, marine debris entanglement and ingestion, fishing gear interactions, watercraft strikes, and the many effects of climate change.
You can help! Please report all hawksbill sightings! Our "Hawaiian Hawksbill Hui" is a statewide network of dedicated community members. Join us!
HIhawksbills.org is a hub for all Hawaiian hawksbill information, including a list and links to all of the Hawaiian hawksbill publications to date. This insightful 20-year photo-ID collection showcases the largest amount of population information known about Hawaiian hawksbills in their marine environment, but there is still much to be learned.
Due to the launch of HIhawksbills.org in January 2016, the popularity of social media, outreach to individuals and businesses, in-water turtle transects, and collaborations with partners, the sighting numbers have significantly increased from 82 individuals from 1998-2015 to150 through July 2018.
This information provides a strong foundation that will be built upon with the utilization of innovative computer-assisted photo-ID matching software (through WildBook.org) and a smartphone application, both of which will be launched this year. Online citizen science platforms such as iNaturalist, SciStarter and WildBook will continue to help diversify hawksbill information gathering.
Future additions to the photo-ID catalog include more strandings when appropriate, sightings in the Papahanaumokuakea Marine National Monument, nesters, and potentially hatchlings. These insights into this population should help guide management decisions, as stated in the “Action Plan for Research and Management of Hawksbill Sea Turtles (Eretmochelys imbricata) in Hawai`i: 2018-2022”.