Theses and Dissertations

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Defense Date

12-2007

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Curtis M. Burney

Second Advisor

Edward O. Keith

Third Advisor

William Gilmartin

Abstract

e sea turtle population utilizing habitats within the Kaho‘olawe Island Reserve (KIR) has gone practically unstudied. This baseline assessment (2002-2005) used a combination of aerial and in-water research methodologies designed in conjunction with recording all incidental sightings and opportunistic reports. In addition, cultural insight, previous studies, literature, and other references were reviewed totaling 708 sightings that provided the subsequent information on the occurrence of turtles within the reserve.

Overall, the different research assessment techniques produced similar results, suggesting the validity of the observations. All techniques had their separate merits and played significant roles due to the restrictions imposed on operations within a former military bombing range and the ongoing research activities of the Kaho‘olawe Island Reserve Commission (KIRC) Ocean Resources Management Program. The most superior methodology was the aerial survey for island-wide relative abundances and distributions, but in-water surveys were valuable in assessing turtle population characteristics, especially the fibropapilloma rate and site fidelity. Coastal surveys were done to search for signs of nesting or basking, but none were documented.

This study found turtles most commonly swimming individually in clear, shallow water (1-6m depth) coral reef habitats 5-20m from shore. Besides one female hawksbill (Eretmochelys imbricata), all were greens (Chelonia mydas) with no evidence of fibropapillomatosis. Immature turtles predominated and were fairly evenly distributed with some areas of higher density around Kaho‘olawe, namely in the Kākā, Hakioawa and Kealaikahiki regions. Using photo-identification techniques, the strongest example of site fidelity was one particular turtle being resighted three times in the same location, with an 815-day interval between the first and last sighting. It was most common to find the turtles swimming as opposed to resting or foraging. The twenty foraging observations that were made occurred primarily in the Hakioawa and Kākā regions (depth mean=6m, SD=3.8m, range 1-11m). All were seen foraging on turf algae, as the abundance of macroalgae within the KIR was limited.

General turtle reactions to our presence were quantified roughly. With humans in the water the majority of the turtles kept a safe distance while exhibiting a slow departure from humans; unless approached closer (by free-diving) which typically caused them to flee. Near equal percentages exhibited flight responses versus toleration of our presence. Only one turtle displayed flipper swiping. During aerial surveys, our helicopter flew at ~31m which did not appear to alter turtle behavior as much as expected. As was the case of turtle reactions to our vessel Hākilo, disturbance was difficult to quantify unambiguously. Some turtles dove abruptly and others appeared to be unaffected by our presence, likely due to other variables unknown to us.

Abundance estimates were negatively biased due to availability biases (submerged turtles) and our detection limitations of naturally camouflaged, highly alert animals. Twenty-nine standardized aerial surveys averaged 7.2 turtles (SD=3.4, range 1-14, n=209) per ~60-minute circumnavigation survey yielding a mean density of 0.153 turtles per km (0.248/mile). Nineteen north coast surveys averaged 2.3 turtles (SD=1.76, range 0-6, n=43) per ~20 minute survey, resulting in a mean density of 0.131 turtles per km (0.209/mile). Sixty-seven nearly island-wide snorkel transects yielded a 1.31 turtles/hr mean (transect SD=1.8, range 0-8, n=82). Although effort varied widely, it was most common to incidentally witness one turtle at the surface per (~5-hour) day while different research activities within the reserve were conducted (1.29/day mean, SD=1.26, range 0-6, n=76 field days, n=98 turtles).

Exploratory analyses of correction factors for submerged turtles during aerial surveys and the collation of all sightings and references roughly estimate that fewer than 500 turtles inhabit the KIR (although these results should be used cautiously). KIR-specific turtle diving behaviors must be determined to enable reliable correction factors to be applied to density abundance estimates. Although these research results are not directly comparable to other studies within the rest of the Main Hawaiian Islands because this is the first island-wide study, these low numbers suggest a rather insignificant contribution to the extant population of Hawaiian sea turtles.

This baseline estimate allows for a) future comparisons using these standardized monitoring protocols, and b) the prioritization of restrictions to important KIR habitats, with implications for management on other islands. As the restoration and management of the KIR continues successfully, this reserve has great potential to host a healthy population of sea turtles that would be able to thrive in a non-anthropogenically stressed environment. Therefore this population and nearshore habitat should continue to be monitored and protected.

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