The Paradox of Invasive Endangered Species Conservation

By Dr. Tag Engstrom

Invasive species are a major threat to natural ecosystems. Conservation strategies for invasive species usually involve elimination of the invasive. 

Chris Radford with turtle

Figure 1.  Chris Radford with juvenile Wattle-necked Turtle found in Kealia Stream, Kauai. This is one of three turtles captured at this site in 2010, and is the first juvenile turtle to be captured by the project.

But, what if the introduced species wreaking havoc on a natural ecosystem is also endangered in its native habitat and this introduced population may represent the last of its kind anywhere else on the planet? Center for Ecosystem Research (CER) biologists Dr. Tag Engstrom and Dr. Michael Marchetti have been chipping away at this interesting conservation conundrum through their research on the Chinese Wattle-necked Softshell Turtles introduced to Hawaii.

The Chinese Wattle-necked Softshell Turtle, Palea steindachneri, is a large, secretive-turtle that is native to China and to Viet Nam. Most of the turtles native to China and Viet Nam are now listed on the IUCN Redlist for endangered species because of the long-standing cultural traditions, that call for the consumption of turtle meat, combined with the human population explosions in the region, which have made turtle products, previously luxury items only, affordable and available to the growing population; this is especially true for large softshell turtles, such as the Wattle-necked Turtles whose meat is a highly valued delicacy and whose shell cartilage is coveted for traditional Chinese medicine. This high commercial value has lead to the near extinction of the turtles in the wild and the inclusion of Palea steindachneri to the IUCN "endangered" list. 

Ironically, the Wattle-necked Turtles’ food and medicinal value may have accidentally planted the seeds for its survival. Beginning in the 1850s these turtles were transported and introduced to Hawaii by Chinese immigrants who provided much of the labor-force for Hawaii’s sugar cane industry. Since arriving in Hawaii, the turtles' populations on the islands of Kauai and Oahu have apparently flourished and may represent the only viable option for the long-term survival of the species. Drs. Engstrom and Marchetti are studying whether the turtles’ are damaging the unique Hawaiian aquatic-ecosystems, which host their own suite of endemic and endangered species.

The research initially began in 2007, as a series of week-long visits to Kauai with CSU, Chico field classes. Dr. Engstrom was studying the turtle conservation biology and Dr. Marchetti was studying the effects of this invasive species on the aquatic community food-web. During these trips, the distribution and abundance of the turtles was studied by trapping and studying the turtles, as well as interviewing local biologists and fishermen. Once a turtle was captured, tissue and fecal samples were collected to determine what it was eating and to study what effect the turtles have on the local-ecological food-web using a stable isotope analysis.

These initial exploratory trips were very informative: the turtles are apparently widespread and reproducing generously. They live in habitats that have a lot of other, non-native species (Large Mouth Bass, Asian Catfish, Tahitian Prawns, etc.), but not in areas with predominantly native fauna.  As a result, their diet is primarily those other non-native species even though the stable isotope analysis indicates that they are "top predators" and could feed on native fish as well.


Figure 2. Juvenile Wattle-necked Turtle captured in Kealia Stream 2010.

In 2010, CER awarded this research project a seed grant. The grant partially supported Chris Radford, a CSU, Chico graduate student, to work on the project during the summer of 2010. Chris conducted extensive interviews with locals and also sampled aquatic habitats at over 100 sites in Kauai, Oahu, Maui, and Lanai (Figure 1. Trap locations and Palea steindachneri capture localities on Kauai. See Map) and caught three new turtles on Kauai (Figures 1&2).  He has continued to refine the research methods that will be used in more detailed studies in the future, and most importantly, has built relationships with local biologists and landowners. To date, twelve Wattle-necked Turtles have been captured and tagged from three different watersheds on Kauai. This ongoing project has established that this species is not extinct and has provided much of the, limited, natural history data available for this species.

The next step is to expand research of the Waddle-necked Turtle, and further examine the invasive, endangered-species conservation-paradox. During spring and summer of 2011, Dr. Engstrom will be spending his sabbatical in Hawaii conducting additional field work: including more mark-recapture studies, extending trap efforts into Oahu; radio tracking individuals on both islands; and beginning experiments on the effect of incubation temperature on sex determination. He is also creatively working to secure long-term funding for this project through: the American Zoological Association and the Chelonian Research Foundation, in collaboration with the Honolulu Zoo, to fund work on captive rearing and sex determination; The Castle Foundation to fund involvement of local high school students in the long-term monitoring of populations on Oahu; and National Geographic Society to continue the work in Hawaii and expand research to the turtle’s native range in China.