Spatial ecology, population size and health status of Eastern hellbenders
by Nick Burgmeier, FNR Graduate Research Assistant
While unbeknownst to many traversing the tributaries of the Ohio River in southern Indiana, whether floating lazily down the river by canoe or wading among the rocks, they may be very near an ancient creature few people see, but many “old timers” once feared. This reclusive creature goes by many names with varying origins, including: snot otter, devil dog, grampus, and Allegheny alligator. More commonly, it is referred to as the eastern hellbender (Cryptobranchus alleganiensis alleganiensis), a name which itself is of uncertain origin. Take one look at this two-foot-long, brown and slimy salamander, and the name “snot otter” will seem the perfect description.
The face of a not so cuddly Eastern hellbender.
photo by Shem Unger
Hellbenders are found throughout the eastern United States. They are long-lived, fully aquatic salamanders requiring cool, rocky, swift flowing streams and rivers with abundant large, flat shelter rocks for cover and a high dissolved oxygen content allowing for them to breathe through their skin. Unfortunately, these traits make the species particularly vulnerable to decimation by common land practices throughout its range. In the past several decades, much of its habitat has been degraded or destroyed as rivers became silted and contaminated due to agricultural run-off and channelization, while dams have reduced available habitat through decreased flows and the reduction of dissolved oxygen. Additionally, many negative myths surround the hellbender. It was once thought to be poisonous by local residents, and fishermen believed they would steal fish off of their line or eat all of the fish in an area. In reality they feed almost exclusively on crayfish. These beliefs led to widespread persecution in areas where hellbenders were commonly captured by fishermen. The direct killing of hellbenders resulted in local extinctions, because the species is slow to mature and has low reproductive output. In Indiana, hellbender populations have been reduced to one tributary of the Ohio River in southern Indiana. Biologists with the Indiana Department of Natural Resources (IDNR) were becoming increasingly aware that this remaining population had been declining and that reproductive output was seemingly small, if occurring at all. This prompted the IDNR to implement a comprehensive research strategy aimed at gathering as much ecological information about the population as possible in order to implement a management plan based on the best, most complete science possible.
In order to accomplish this goal, our research has focused on several different aspects of hellbender biology. My research ranges from spatial ecology and molecular biology to overall physical health. Thus, the objectives of my work are to:
- Estimate current population size and density in Indiana;
- Compare demographic and genetic techniques of population estimation;
- Determine home-range size, and habitat use and preference;
- Establish baseline blood chemistry parameters, evaluate health and disease status, and enumerate blood-borne parasites;
- Investigate the potential use of molecular techniques to check for a biomarker (vitellogenin) linked with endocrine disruption and as a possible means of gender determination; and
- Evaluate physicochemical water quality parameters.
Sometimes the search for hellbenders requires the use of a little muscle.
photo by Nick Burgmeier
During the summer and fall of 2008 and 2009, we implemented an intensive mark-recapture survey (~1,500 person hours) across 35 sites (~11km). Individuals were captured, marked, and biological samples were taken before they were released back to their site of capture. The results of this study confirmed the IDNR’s initial suspicions that the population size had decreased far below that which was reported in the mid-1980’s. During a total six months of actual surveys, we only captured 78 individuals, all of which were adults. To put this in perspective, we captured 70 individuals across all age classes from a healthy population in Georgia in only three days. The density has also dropped to a level much less than that reported from most other “healthy” hellbender populations throughout its range. This paints a grim picture for the continued survival of the population, but provides managers with a solid number to work with when designing the goals of future projects. Using the results from the demographic data derived from this study, we’re also looking to compare classic mark-recapture population estimators with various genetically determined estimates of effective population size. This will allow fine-scale tuning of our estimates and provide a more realistic view of the status of the population.
During the same period as the previous study, we implanted 21 radio transmitters in hellbenders across eight sites. These individuals were monitored from June 2008 to October 2009 and the movements and habitat use of each were recorded. Using 1,193 locations, I estimated home-range size and habitat use for each individual. Though highly variable, our home-range estimates were considerably larger than those developed for other populations. However, habitat use was relatively similar, as individuals tended to prefer large flat rocks and gravel substrate. Due to the low densities at the sites, the home ranges may be larger as hellbenders expend less energy defending shelter rocks and may need to range further to encounter a mate.
In order to evaluate the health of the remaining population, a series of biological samples (i.e., blood, skin swabs, sperm, and tissue) were taken from each captured individual.
Many types of biological samples are taken from each captured individual including blood, skin swabs, sperm and tissue.
photo by Cody Marks
Blood samples were used to determine baseline blood chemistry parameters and to check for parasites. Knowledge of baseline blood chemistry will allow for the evaluation of individual health of captured hellbenders and give some idea of the overall physical well-being of the population. Although parasites are common in many wild species, none were found in any captured hellbenders. Plasma collected from the blood was also used to check for potential endocrine disruption and as a means of gender determination for unknown individuals. Vitellogenin (VTG) is an egg-yolk precursor protein found in most egg-laying species and is typically only expressed in females. Thus far, positive readings in individuals of known gender have only been found in females, indicating the utility of VTG as a means of sex determination. A positive VTG result in a male individual would indicate endocrine disruption.
Skin swabs have also been taken from all individual to check for the presence of the infectious and often lethal chytrid fungus (Batrachochytrium dendrobatidis). This fungus has caused the decline of amphibian populations in central and South America. Unfortunately, we had a positive result in one individual within the Blue River. This was not entirely unexpected as the fungus has been found in many hellbender populations without producing noticeable affliction. Sperm was taken when available to ensure reproductive viability. Despite small sample sizes, all indications show that hellbender sperm were healthy and similar to other populations. Finally, tissue samples were taken as part of another study to develop genetic markers in order to determine genetic variability within and between populations, but also to develop the genetic population estimates for comparison to the mark-recapture method.
As a final measure, to determine potential stressors to the population, water quality at all radio-telemetry sites was evaluated to determine whether water quality might be a factor in continued hellbender population decline. Physical properties (e.g., dissolved oxygen, pH, temperature, specific conductivity), nutrients (e.g., nitrogen, phosphorus, ammonia), and 27 pesticides were tested for from November 2008 through July 2009. All physical properties indicated a high quality system with high dissolved oxygen levels and low specific conductivity. Nitrogen and ammonia levels were low, though phosphorus levels were slightly higher than recommended by the USGS. Atrazine, simazine, and metolachlor were three pesticides found in the system from late April through early July. Atrazine is one of the most widely used pesticides in the world and some reports implicate it as a potential endocrine disruptor. This is especially worrisome for hellbenders, as their long life spans and fully aquatic nature would allow continual exposure over long periods of time.
Radio-telemetry is used to track hellbenders to study home range size and habitat use.
photo by Marci Skelton
The steep decline of hellbenders over the past few decades is especially concerning given their potential as a bioindicator. Their decline suggests a potential problem with the overall system. Moreover, their extinction would mean the loss of an ancient creature which has persisted in this region for millions of years. Our findings provide a considerable amount of information of value for both basic ecology and practical management. It will serve to drive management recommendations and will be instrumental in the development of a successful translocation plan if this step is deemed necessary. This research represents an important first step towards developing a comprehensive management plan aimed at not only preventing the extirpation of the species from Indiana’s waterways, but to the eventual restoration of the species’ previous range.
Dr. Rod Williams is heading up this important research using his expertise in wildlife and genetics. He is broadly interested in the ecology and conservation of amphibians and reptiles. His research interests focus on using a combination of field and laboratory methods to: investigate habitat selection and use in both aquatic and terrestrial systems; characterize amphibian and reptile mating systems; examine the factors influencing amphibian malformations; and measure population structure and inbreeding in threatened or endangered herpetofaunal species. To find more information about hellbenders see The Education Store, Salamanders of Indiana.