Eua zebrina Species Report May 2020 U.S. Fish and Wildlife Service Pacific Islands Fish and Wildlife Office Honolulu, HI Cover Photo Credits Eua zebrina photographs courtesy of D. Clarke and R.J. Rundell. Suggested Citation USFWS. 2020. Species Report for Eua zebrina. Version 1.1. May 2020 (Version 1.1). U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, Honolulu, HI. 33 pp. Primary Authors Version 1.1 of this document was prepared by Adam E. Vorsino, Fred Amidon and James Kwon of the Pacific Islands Fish and Wildlife Office, Honolulu, Hawaii. Preparation and review was conducted by Gregory Koob, Megan Laut, and Stephen E. Miller of the Pacific Islands Fish and Wildlife Office. ii Executive Summary This Species Report summarizes the status of Eua zebrina, a tropical tree snail in the family Partulidae, based on the most recent information. For E. zebrina, this is information from Cowie and Cook, 1999. To assess the viability of E. zebrina, we used three conservation biology principles: resiliency, redundancy, and representation, or the “3Rs”. The viability of E. zebrina is evaluated with reference to the resiliency of its populations, its redundant occurrence across its native range, and its representation in its known habitat types. Eua zebrina is known only from the islands of Tutuila and Ofu in American Samoa. Many of the 120+ partulid species are restricted to single islands or isolated groups of islands. The Samoan partulid tree snails in the genera Eua and Samoana are representative of this endemism and isolation. Historically, Eua zebrina was abundant on the island of Tutuila, and later reduced to its current rare level by the introduction of non-native snail predators. Systematic surveys conducted in and prior to 1998 suggest an overall decline in distribution and abundance of Eua zebrina, with central areas of the National Park of American Samoa representing a large proportion of the known extant populations of the species. Though we are unaware of any systematic surveys conducted for E. zebrina since 1998, E. zebrina is still periodically observed by field biologists. Threats to Eua zebrina include predation by non-native rats, non-native predatory snails and flatworms, as well as habitat destruction due to agriculture, urban expansion, or incursion by non-native invasive plants. Stochastic events such as cyclones (hurricanes), are an important contributing factor in the expansion of non-native invasive plants. The combined effects of these threats is expected to influence the viability of E. zebrina more than any one of the threats alone. Conservation efforts that may benefit E. zebrina are focused solely on the control and removal of invasive plants from native ecosystems. Efforts to control rats on outlying islets do not affect known populations of E. zebrina. Due to these threats and limited conservation actions, current viability of the species is expected to be low, due to low resilience of its populations, low representation in known habitat types, and low redundancy across its geographic range. iii Table of Contents Cover Photo Credits ........................................................................................................................ ii Suggested Citation .......................................................................................................................... ii Primary Authors .............................................................................................................................. ii Executive Summary ....................................................................................................................... iii List of Tables .................................................................................................................................. v List of Figures ................................................................................................................................. v Introduction ..................................................................................................................................... 1 Regulatory History .......................................................................................................................... 1 Methodology ................................................................................................................................... 1 Part 1. Life History and Historical Species Status .......................................................................... 4 Geography ................................................................................................................................... 4 Physical Environment .............................................................................................................. 5 Land-Use ................................................................................................................................. 5 Biological Environment ......................................................................................................... 10 Species Description ................................................................................................................... 11 Breeding Biology and Lifespan ............................................................................................. 13 Habitat ................................................................................................................................... 13 Historical Range ........................................................................................................................ 14 Part 2. Current Conditions and Species Status.............................................................................. 14 Current Range and Distribution ................................................................................................ 14 Factors Affecting Viability........................................................................................................ 16 Habitat Loss and Degradation ............................................................................................... 16 Other Factors Affecting Viability .................................................................................... 21 Conservation Efforts that Affect Viability ............................................................................ 23 Resiliency, Redundancy and Representation of Current Populations and the Species. ............ 24 Tutuila .................................................................................................................................... 24 Ofu ......................................................................................................................................... 24 References ..................................................................................................................................... 26 iv List of Tables TABLE 1. CENSUS ESTIMATES OF THE AMERICAN SAMOA POPULATION ON THE ISLANDS OF TUTUILA, TA’Ū, OFU, OLOSEGA, AND SWAINS. ....................................................................................................................................... 6 TABLE 2. CENSUS ESTIMATES OF THE SAMOA POPULATION BY ISLAND AND FOR THE ENTIRE COUNTRY. .................. 6 TABLE 3. ESTIMATED ACREAGES OF MAJOR LAND COVER TYPES FOR THE SAMOAN ARCHIPELAGO. ACREAGES ARE IN ACRES WITH HECTARES IN PARENTHESIS. ........................................................................................................ 9 TABLE 4. ESTIMATED ACREAGES OF VEGETATION TYPES FOR THE MAIN ISLANDS OF AMERICAN SAMOA. ACREAGES ARE IN ACRES WITH HECTARES IN PARENTHESIS. .............................................................................................. 12 TABLE 5. CURRENT SPECIES STATUS OF EUA ZEBRINA IN RELATION TO THE 3 R’S. .................................................. 25 List of Figures FIGURE 1. THE THREE CONSERVATION BIOLOGY PRINCIPLES OF RESILIENCY, REDUNDANCY, AND REPRESENTATION, OR THE “3RS”. ............................................................................................................................................................ 2 FIGURE 2. THE ISLANDS OF THE SAMOA ARCHIPELAGO. ................................................................................................. 5 FIGURE 3. MONTHLY MEAN PRECIPITATION FOR SELECTED AREAS OF THE SAMOAN ARCHIPELAGO. PACIFIC CLIMATE CHANGE SCIENCE PROGRAM (PCCSP; 2019). ....................................................................................................... 7 FIGURE 4. MONTHLY MEAN TEMPERATURES FOR SELECTED AREAS OF THE SAMOAN ARCHIPELAGO. PACIFIC CLIMATE CHANGE SCIENCE PROGRAM (PCCSP; 2019). ....................................................................................................... 8 FIGURE 5. CYCLONE (HURRICANE) TRACKS FOR THE CENTRAL SOUTH PACIFIC FROM 1898 TO 2019. KNAPP ET AL. (2010) AND NOAA IBTRACS (2019). .................................................................................................................. 9 FIGURE 6. LOCATIONS OF ROADS IN THE SAMOAN ARCHIPELAGO. ................................................................................. 9 FIGURE 7. MAP OF VEGETATION ON AMERICAN SAMOA. DATA FROM MEYER ET AL. (2017). ...................................... 11 FIGURE 8. EUA ZEBRINA COLOR AND SHELL MORPHOLOGY. PHOTOS COURTESY OF D. CLARKE AND R. J. RUNDELL. .. 13 FIGURE 9. MAP OF EUA ZEBRINA OBSERVATIONS AND VEGETATION ON AMERICAN SAMOA. DATA BY MEYER ET AL. (2017). ................................................................................................................................................................