Giant Salamander Research


Amphibian populations are declining worldwide. Approximately 41 % of the world’s amphibian species are estimated to be threatened, making amphibians as the most threatened group of vertebrates. Family Cryptobranchidae, known as the giant salamander family, is not an exception. This family consists of three fully aquatic giant salamanders - the hellbender (Cryptobranchus alleganiensis), the Japanese giant salamander (Andrias japonicus), and the Chinese giant salamander (A. davidianus) - and represents one of the oldest salamander lineages. Populations of all giant salamander species have declined for the past decades and these declining trends are not sufficiently countered by conservation efforts. As top predators, these giant salamanders play vital ecological roles in river ecosystems. In addition, their unique life history, such as prolonged parental care by males, makes them scholarly important species as well. Unfortunately, many aspects of their life history remain unexplored, and their declining populations making studying these secretive amphibian harder. Below I introduce the giant salamander research projects being undertaken in my lab at Bucknell University. 

Hellbender (Cryptobranchus alleganiensis)

The hellbender consists of two subspecies, the Ozark hellbender (Cryptobranchus a. bishopi) and the eastern hellbender (Cryptobranchus a. alleganiensis). The distribution range of the Ozark hellbender is limited to the Ozark streams of northern Arkansas and southern Missouri. In response to their recent rapid decline, U.S. Fish and Wildlife Service listed Ozark hellbender as an endangered Species in 2011. The distribution of the eastern hellbender stretches from northern Alabama/Mississippi to New York along Appalachian Mountains. Despite their wide distribution range, eastern hellbenders are also in a state of decline due to factors such as pollution, illegal harvesting, habitat destruction, and possibly wildlife diseases such as chytrid fungus and ranavirus. As a result, there are a limited number of regions known to harbor healthy populations of eastern hellbenders. Though few locals are aware of it, the tributaries of the West Branch Susquehanna River represent one of the best known regions for the hellbender. One of the conservation challenges we are facing is to grasp their distribution range at a stream level and establish an effective and sustainable monitoring program. This task is challenging because of their secretive nature, confusion with mudpuppies (another fully aquatic salamander), and the insufficient number of researchers available for covering the wide distribution range. In addition, the traditional survey techniques, which involve physically finding them by snorkeling and rock turning, require specialized skill, time, and effort since large rocks may need several people to lift and diving gear is needed to reach them. Such traditional methods also risk disturbing their habitats and reproduction, as well as accidentally causing physical harm to the animals.

An environmental DNA or eDNA technique offers an exciting alternative to the traditional survey method. This relatively new technique does not require invasive sampling and assesses target populations through detection of their genetic materials contained in the water. Our research lab initiated the hellbender eDNA project in 2014, using the protocol developed by Spear et al. (2015). Using quantitative PCR, we analyzed 150 water samples (including negative controls) collected from 13 sites across eight tributaries of the Western Branch from June through October 2014. Exciting results came out of this project (Takahashi et al. in prep); 1) we repeatedly found hellbender eDNA from the streams known to have hellbenders, 2) the concentrations of eDNA tend to sharply increase in September, their breeding season, possibly reflecting the signatures of the breeding events (this trend was also found in Spear et al. 2015), and 3) we found hellbender eDNA from the streams which do not have current records of hellbenders. Overall, eDNA technique worked well. Our future plan is to both expand our sampling area and pinpoint more specific locations of the newly found hellbender populations by conducting finer water samplings along the streams.      

Japanese Giant Salamander (Andrias japonicus)

I have also been involved in a few Japanese giant salamander projects, and spent fall 2015 working with my collaborators in Japan. The Japanese giant salamander can grows up to 5 ft and is widely (though not commonly) distributed throughout the southwestern Japan. Since 1952 the species has been federally protected as a special natural monument designated by the Japanese Agency for Cultural Affairs; this designation is based on its cultural and educational significance. However, the Ministry of Environment, which accesses the conservation status of organisms in Japan, recently raised the status of the Japanese giant salamanderfrom NT (Near Threatened) to VU (Vulnerable). Major conservation issues include damming, concrete banking, habitat destruction, water pollution, and hybridization with introduced Chinese giant salamander. Despite their declining status, the government shows no initiative in conserving this culturally, ecologically and academically important species. This situation is further exacerbated by a lack of researchers and funding. As a result, not only do we fully understand the population status of many sites throughout the distribution range, but we also lack the basic knowledge of its biology and ecology.  

Dr. Okada (Vice Chief Director at Japanese Giant Salamander Research Institute) and I have studied their reproductive ecology for the past years and conducted the first quantitative analyses of male parental care behaviors in the family of giant salamanders (Okada et al. 2015). Parental care by females is commonly observed among salamanders and is generally associated with terrestrial reproduction and internal fertilization. On the other hand, parental care provided by male salamanders is rare and associated with aquatic reproduction and external fertilization. We found that male Japanese giant salamanders exhibit a diverse array of care behaviors such as 1) tail fanning to provide oxygenated water for the eggs, 2) agitation of the eggs likely to prevent yolk adhesions and promote healthy embryo development, and 3) removal of unfertilized, dead, or water-mold infected eggs likely to prevent the infection from spreading over the entire clutch. Our lab is currently collaborating with Asa Zoo in Japan on the analyses of the nesting behaviors recorded by a video camera.

Our next step is to test the effects of dams on their migration patterns and population health. Since the end of World War II, the construction of dams and concrete banking has been promoted as public-works projects throughout Japan. As a result, it is no exaggeration to say that there are no Japanese rivers without dams. Because Japanese giant salamanders are fully aquatic, dams have likely prevented their migrations and caused population fragmentations. Fragmented populations are susceptible to extirpation (regional extinctions) because of small population size, potential inbreeding, and the lack of breeding sites. Giant salamanders often conduct long-distance up-stream migrations in search of suitable breeding/nesting sites. My Japanese collaborator observed that a gravid female released eggs at the downstream portion of a low-head dam while attempting to climb up the dam. These eggs were not fertilized and thus wasted. There are also numerous observations that repeated attempts to climb over dams caused serious scrapes on their limbs, which in turn may lead to secondary infections. Despite these detrimental effects of dams, there is no published study exploring these issues. By using video camera recording and population genetics, the ultimate goal of this project is to provide data for the installation of salamander ladders that enable migration of giant salamanders across dams. 

The conservation status of the Chinese giant salamander is worst among the giant salamanders. IUCN (International Union for Conservation of Nature) lists it as “critically endangered”.  While farming of Chinese giant salamanders has grown to be a large food industry in China, the information gathered from my colleagues and published literature suggest that the future of the wild populations in China is not bright. In contrast, there is a growing group of university researchers, zoo keepers, and state/federal researchers who strive to conserve hellbenders in the U.S. The current status of Japanese giant salamanders is also much better than that of its Chinese counterpart, and its conservation is largely propelled by civilians with nonprofit Japanese Hanzaki (giant salamander) Research Institute and Japanese Giant Salamander Association being the axis. Our lab hopes to be part of such conservation efforts and to promote collaborative conservation by providing a bridge between the two countries.