Abstract
Translocations are stressful, especially when captive animals are naïve to natural stimuli. Captive eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) identify predatory fish as threats, but may be more vulnerable to predation and stress because of inexperience with them. We investigated the use of predator conditioning to prepare hellbenders, behaviorally and physiologically, for the presence of a common predator, largemouth bass (Micropterus salmoides). We reared hellbenders for 30 d with and without continuous exposure to largemouth bass kairomones and heterospecific alarm cues and found conditioned hellbenders became less active compared to unconditioned individuals (p = 0.017). After conditioning, we exposed hellbenders to water, a low concentration of kairomones, or a high concentration of kairomones in a closed respirometer system. We measured activity within respirometer chambers and routine metabolic rate. We found unconditioned hellbenders exposed to low and high concentrations of kairomones were 41% and 119% more active than conditioned animals (p = 0.002 and p < 0.001). Moreover, conditioned individuals had on average 6.5% lower metabolic rates across all three kairomone concentrations compared to unconditioned individuals (p = 0.017). Our data suggest that predator conditioning induces behavioral avoidance tactics and physiological changes that could improve future translocation efforts for hellbenders and other imperiled species.
Highlights
Translocations are inherently stressful for animals [1,2,3]
We investigated the ability of juvenile hellbenders to detect predators, and their foraging and behavioral responses over acute periods of exposure, and their physiological response to low and high levels of risk after being conditioned to largemouth bass kairomones
Hellbenders are a slow-growing species, yet within 30 d the conditioned hellbenders gained weight. This suggests that conditioned hellbenders were better able to direct resources toward growth and that this technique can effectively increase size prior to release. We found that both conditioned and unconditioned individuals reduced their level of activity when they were exposed to largemouth bass kairomones in respirometer chambers
Summary
Is transportation and release into a novel environment challenging, but stress is further exacerbated by exposure to additional threats that are typically absent from the captive environment. Stimuli such as stochastic weather conditions, contaminants, pathogens, and predators are novel to captive-reared animals and can magnify the stress of translocations [1,4,5,6]. Stress (in a variety of forms) is a leading cause of translocation mortality [1,2,3,9,10]. Captive-reared animals have higher mortality rates than wild or predator-conditioned conspecifics [12].
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