The U.S. Army’s Natural Resource Program on O‘ahu

Vince Costello (Vincent.j.costello4.ctr@mail.mil) , Deena Gary (deenagary@gmail.com) and Stephanie Joe (sjoe@hawaii.edu) are invertebrate specialists with the Pacific International Center for High Technology Research, working for the U.S. Army's Natural Resource Program on O‘ahu.*Disclaimer: The authors of this poster do not represent the U.S. Army in any official capacity

• The program has nearly 60 personnel on staff, comprised of management and administrative support staff,an ecosystem restoration crew, an ungulate management crew, three resource management crews, and anursery/seed bank crew. Most of these staff are employed via a Cooperative Agreement funded by theArmy through the Pacific International Center for High Technology Research (PICHTR) and administered bythe Research Corporation of the University of Hawai‘i - Pacific Cooperative Studies Unit (PCSU).

• The program conducts management unit protection and native ecosystem restoration, has rodent andungulate control programs, a rare plant and bird monitoring program and an outreach program andmanages Achatinella mustelina and rare vertebrates.

Author Affiliation

Management of Endangered O‘ahu Tree Snails Using Predator-Proof Enclosures

Prepared By:Vince Costello, Deena Gary, and Stephanie Joe

Literature Cited•Hadfield MG, Mountain BS. 1980. A field study of a vanishing species, Achatinella mustelina (Gastropoda,Pulmonata), in the Waianae Mountains of Oahu. Pacific Science 34(4): 345-358.•Holland, B.S., Montgomery, S.L. & Costello, V. 2010. A reptilian smoking gun: first record of invasive Jackson’schameleon (Chamaeleo jacksonii) predation on native Hawaiian species. Biodiversity & Conservation 19: 1437-1441.•Meyer, W.M., and R.H. Cowie. 2010. Feeding preferences of two predatory snails introduced to Hawaii and theirconservation implications. Malacologia 53 (1): 135-144

Predator-Proof Enclosures

Map showing the locations of four predator-proof enclosures on O‘ahu.

A schematic showing the design and barrier system used to exclude mammal, reptile and rosy wolfsnail threats to tree snails at Hāpapa. A slightly modified design was used at the Palikea and Kahanahāiki enclosures.

•The Army has four predator-proof enclosures on O‘ahu to protect A. mustelina from threats.•The first enclosure was built in 1998 at Kahanahāiki, is 133m² and contains over 200 tree snails.•The next enclosure was built at Palikea in 2012, is 1,097m² and contains ~170 tree snails. A secondenclosure, completed in 2017 is 2,480m². It is undergoing habitat restoration in preparation for snailintroductions planned in late 2018.

•The enclosure at Pu‘u Hāpapa (Hāpapa) also completed in 2012 is 1,564m² and contains 70% of alltree snails protected within enclosures. We highlight Hāpapa in particular because of its role as animportant refuge for tree snails.

Achatinella mustelina (O‘ahu Tree Snail)•Achatinella mustelina is an endemic, endangered species of tree snail found only in the Wai‘anae Mountains of western O‘ahu .•This snail has a slow growth rate, late maturity, low motility, and a low rate of fecundity –between one and fourlive births a year.•The Army’s O‘ahu Natural Resources Program currently workswith eight populations of tree snails as part of its endangeredspecies management requirements. At each, we attempt to maintain at least 300 or more snails and control all threats.•Tree snails have evolved in the absence of many predators. With the introductions of non-native species, A.mustelina have become prey to rosy wolfsnails (Euglandina rosea), rats (Rattus rattus), and Jackson’s chameleons(Trioceros jacksonii xantholophus).

•Other threats to the survival of tree snails include habitat loss, climate change and loss of genetic diversity.

Pictured above, examples of A. mustelina with slight variation in shell markings; each is unique. They are the jewels of the forest.

Control of Rats and Jackson’s Chameleons• Recently the Jackson’s chameleon has been documented as a predator of tree snails (Holland et al. 2010). • Introduced rats, in particular Rattus rattus, are common in the forested areas of tree snail habitat and are

known to prey on tree snails with devastating results (Hadfield & Mountain, 1980). • Smooth galvanized aluminum walls and the rolled hood

prevent rats and chameleons from climbing the wall.• Trees near the perimeter of the enclosure are trimmed

regularly to prevent rats or chameleons from using branchesabove the wall to breach the enclosure.

• Self-resetting rat traps are used both inside (as a precautionary measure because rats are not eradicated here)and outside the enclosure to benefit the habitat overall. These need only be maintained 3x per year to be effective.

• There is no control for chameleons other than manualremoval.

• A total of 639 chameleons have been captured from Hāpapasince 2011. However, as with the rosy wolf snail, this is only effective when done within the bounds of an enclosure or when the predator population is not contiguous so that re-invasion doesn’t outpace removal.

A dead rat beneath a self-resetting A24 trap

Smooth galvanized aluminum walls and the rolled hood

Staff holding a mature male Jackson’s chameleon

Pu‘u Hāpapa Enclosure

Staff and preparing to release A. mustelina from the UH Labinto the Hāpapa enclosure.

Aerial view of Hāpapa enclosure

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Achatinella mustelina counts at Hāpapa

Translocations into enclosure (1835 total) Timed-count Quarterly ground shells

Timed-counts of A. mustellina over time showing snails translocated into the enclosure as well as mortality within plots over time.

•Hāpapa is located in the southern Wai‘anae Mountains and falls within the Honouliuli Forest Reserve.•Since its completion, a total of 1,805 A. mustelina snails have been introduced from the University ofHawaii (UH) at Mānoa Captive Rearing lab and from neighboring areas.

•The snail populations in this area are threatened by all three predators. If not translocated to an enclosure, many satellite populations of tree snails will be extirpated.

Population Monitoring•Ground shell plot monitoring was used to detect mortalityrates of tree snails within the enclosure. These data werecollected from two ground shell plots installed directlybelow the core reintroduction zones.

•Timed-count monitoring (TCM) was used to quantify long-term population trends and assess whether thereintroduced population was self-sustaining over time.TCM data is likely and underestimate of the truepopulation, as not all snails are detectable at any onetime.

Control of Rosy Wolf Snails•Euglandina rosea (the rosy wolfsnail) was introduced to Hawaii in 1955 to control agricultural mollusk pests.•This predatory snail is known to have a catastrophic impact on native tree snail populations (Hadfield & Mountain,1980; Meyer & Cowie, 2010) and has been found to have a distribution that extends across most known tree snailhabitats on O‘ahu.

•There is no effective control for the rosy wolfsnail except for manual removal within the bounds of a definedarea where no re-invasion is possible.

•Since 2009, 2,662 rosy wolfsnails have been removed from Hāpapa. We believe our efforts have caused an overalldecline in this population (see graph below).

Barriers on the outside wall of the enclosure to prevent rosy wolfsnail invasion

•15 degree angle: An overhang traps rosy wolfsnails. Thesnails have difficulty negotiating the tight angle.

•Copper cut-mesh barrier: The cute mesh barrier facesdownward and is attached to the underside of a board.This orientation makes it likely the snail will detach andfall to the ground. The limited surface area makes itdifficult for the snail to attach securely.

•Non-lethal electric wires: A series of four electric wiresprevents rosy wolfsnails from crossing. There are twoindependent sets of wires (+ and -) powered by 12Vbatteries. As the snail crosses the wires, it receives amild shock causing it to either retreat or fall to theground.

Rosy wolfsnail having difficulty crossing electric wires

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Graph showing rosy wolfsnails removed from Hāpapa over 9 years. As search effort and area has been inconsistent from year to year, declines in predator population is based on anecdotal evidence.

Angle barrier with cut mesh and electric system above.Rosy wolfsnail attempting to cross copper mesh

Electrical barrier

Rosy wolfsnail pursuing an Achatinella (left) and consuming a leopard slug (right) (Photos by Brenden Holland)