Translocation and Conservation of Hellbenders (Cryptobranchus alleganiensis) in Missouri

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Populations of eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) and Ozark hellbenders (C. a. bishopi) in Missouri have declined precipitously in recent decades for unclear reasons. As a result, both subspecies are endangered in Missouri and the Ozark hellbender is a candidate for listing under the Endangered Species Act. In addition to working towards identifying the ultimate drivers of declines in Missouri, state agencies are considering release of captive-reared hellbenders as a strategy to bolster wild populations. However, few herpetofauna translocations have been successful, commonly due to long distance movements of animals away from selected release sites or the persistence of factors involved in original declines. To determine whether one suspected driver of hellbender declines, the pathogenic fungus Batrachochytrium dendrobatidis, was present when declines occurred and may have caused declines, we used histological techniques and an immunoperoxidase stain to detect the fungus in hellbenders archived in museum collections. As an immediate attempt to improve wild populations we also released 36 captive-reared Ozark hellbenders at 2 sites on the North Fork of the White River, Missouri, and used radiotelemetry to monitor movements, resource selection and survival post release. We detected B. dendrobatidis prior to or during declines in 4 of 7 rivers including the North Fork of the White (1969, 1973, 1975), Meramec (1975, 1986), Big Piney (1986) and Current (1988) rivers, which suggests the pathogen may have contributed to hellbender declines. However, the fungus occurred in the North Fork of the White River for over a decade while hellbenders were intensively studied and populations appeared to remain stable. Therefore, if B. dendrobatidis were responsible for declines in the North Fork, effects of the fungus there were likely indirect as opposed to the mass mortality of adult amphibians other studies have observed. We collected 3635 locations of 36 captive-reared hellbenders translocated to the North Fork of the White River between May 2008 and August 2009. At the end of our study 16 hellbenders were alive, 13 were dead and we could not confirm status of 7 animals. We observed 3 distinct types of hellbender dispersal including non-dispersal (n = 11), slow-and-steady dispersal (n = 9), and abrupt long-distance dispersal (n = 16). Most hellbenders (26 of 36) dispersed downstream and mean dispersal distance at the upper site ( mean = 318.28 m, SE = 115.39 m) was over 2 times larger than at the lower site ( mean = 121.95 m, SE = 34.13 m). At both sites, daily movements of hellbenders were fewer and covered shorted distances, and home range sizes were reduced in the second season of monitoring, suggesting most hellbenders had settled at least semi-permanently in the wild. At the home range and reach scale, hellbender resource selection was positively associated with presence of coarse substrate relative to fine substrates; and with decreasing distance to nearest rock in all meso-habitats (i.e., pool, run, riffle). In 3 of 4 models, the negative association between increasing distance to rock and selection was intensified as benthic water velocity increased. Annual survivorship of captive-reared hellbenders was 0.7467 (lower site) and 0.4816 (upper site). Release site was the most strongly supported factor associated with the nearly two-fold difference in annual survival rates, though site specific factors driving the difference were not obvious. Annual survival rates of captive-reared hellbenders at the lower site were similar to estimated annual survival rates (0.81) of wild hellbenders from the same river in 1978-1979; but annual survival rates observed in our study were 30-100 % lower than indicated annual survival (0.975) in a wild population from the same river consisting primarily of 12 to 20 year old hellbenders. In addition to having lower survival rates, upper site hellbenders tended to gain less weight post release, and a greater proportion carried B. dendrobatidis, leech parasites and accrued injuries and open sores. Our study is the first to intensively monitor captive-reared or juvenile hellbenders via radiotelemetry for over 1 year. The site differences we observed in dispersal, survival and body condition of captive-reared hellbenders following translocation emphasizes the importance of release site selection and the usefulness of pilot studies to determine suitability of release sites. Regardless of site differences, our study demonstrates that captive-reared hellbenders were capable of remaining and settling in release sites while maturing in a wild environment for over 1 year.