Detection and survival rates for the eastern hellbender ( Cryptobranchus alleganiensis alleganiensis) in the Blue River, Indiana

Bart T Kraus, Purdue University

Abstract

The Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis ) is a large, fully aquatic salamander that inhabits clean, cool, well-oxygenated rivers and streams of the Eastern and Midwestern United States. Eastern Hellbenders occupy higher trophic levels within lotic ecosystems and are believed to regulate and maintain aquatic invertebrate communities. However, Eastern Hellbender populations have suffered precipitous declines throughout their range over the last three to four decades. The Midwestern United States, in particular, have experienced severe Eastern Hellbender population declines. In Indiana, recent empirical data indicate Eastern Hellbender densities are much lower than historical estimates and that the population consists of older adults with little to no spatial overlap. State and federal agencies are now focusing on captive-rearing and translocation efforts for juvenile and adult Eastern Hellbenders to supplement existing populations. To track the success of these efforts, individuals are often marked with passive integrated transponder (PIT) tags. This ensures that individuals can be identified during surveys to monitor populations. However, traditional survey methods can damage habitat, especially nesting habitat, which can cause abandonment. I sought to: 1) determine the efficacy of using a PIT tag scanner to detect marked Eastern Hellbenders under limestone boulders, 2) compare the effectiveness of PIT tag surveys to radio-telemetry and rock-lifting and snorkeling surveys, and 3) estimate survival rates using a known-fates model to evaluate the efficacy of translocating captive-reared juvenile and wild adult Eastern Hellbenders. Specifically, I wanted to estimate survival rates, determine whether survival rates were significantly different between resident adults and translocated adults, and relate potential explanatory variables to the survival rates. Rock thickness detection tests revealed the PIT tag reader and antenna could detect a 23.0 mm PIT tag under rocks nearly twice as thick (i.e., 35.6 cm versus 19.2cm) compared to a 12.5 mm PIT tag. Detectability surveys conducted by naïve surveyors exhibited considerable variation in detection and CPUE. The duration of radio-telemetry was 1.9 person-hours and resulted in 100.0% detection and a catch per unit effort (CPUE) of 9.6 Eastern Hellbenders/person-hour. The duration of PIT tag scanning was 5.3 person-hours and resulted in 33.3% detection and a CPUE of 1.1 Eastern Hellbenders/person-hour. The duration of rock-lifting and snorkel sampling was 51.5 person-hours and resulted in 38.9% detection and a CPUE of 0.1 Eastern Hellbenders/person-hour. Radio-telemetry detection was higher than both PIT tag scanning and rock-lifting and snorkel surveys. PIT tag scanning detection was comparable to rock-lifting and snorkel sampling, but was an order of magnitude more efficient in CPUE. Cox proportional hazard models indicated differential survival rates when all 42 individuals were included in the analysis, age class was the only significant explanatory variable (i.e., adults had higher survival). Survival rates did not vary depending on resident status or site location. The overall survival rate was 0.60 and ranged from 0.23 (juveniles) to 0.82 (adult males). Adult male Eastern Hellbenders had higher annual survival than adult females (0.82 vs. 0.65), although the difference in survival rates was not statistically significant. There were no significant differences in survival rates between resident adults and translocated adults at either study site. This study: 1) demonstrates the effectiveness and potential utility of PIT tag technology for surveying and monitoring marked Eastern Hellbenders in a less invasive manner than traditional survey methods, 2) provides baseline survival data for captive-reared juvenile Eastern Hellbenders released in Indiana, and 3) emphasizes the importance of translocations in herpetofauna conservation and management.

Degree

M.S.

Advisors

Williams, Purdue University.

Subject Area

Wildlife Conservation|Wildlife Management

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