Long-term Retention, Readability, and Health Effects of Visible Implant Elastomer (VIE) and Visible Implant Alpha (VI Alpha) Tags in Larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis)
The ability to identify individuals is essential for determining population demographics of a species, but traditional marking techniques, such as passive integrated transponder tags, are often limited to individuals that meet minimum size thresholds. Visible implant elastomer (VIE) and visible implant alpha (VI Alpha) tags are promising methods for marking small-bodied individuals. However, the efficacy and health effects of VIE and VI Alpha tags are not established for many, increasingly imperiled, herpetofauna. Over a 12-mo period, we examined tag retention, tag readability, VIE tag color readability, and effects on growth and body condition of VIE and VI Alpha tags in larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis), a species of conservation concern. We observed 100% retention of VIE tags and 80% retention of VI Alpha tags over 1 yr. Readability degraded over time for both tag types but was consistently higher for VIE relative to VI Alpha tags. Degradation in readability over time increased our reliance on a 450-nm-wavelength VI light to read VIE tags but had more severe implications for VI Alpha codes, which were illegible after 4 mo. Pink- and green-colored VIE tags performed similarly well and we found that neither VIE nor VI Alpha tags negatively affected growth or body condition of larval hellbenders. Our findings collectively suggest that VI Alpha tags are an unviable tagging method, but VIE tags were safe and effective for identifying unique larval hellbenders up to 1 yr.Abstract
Examples of larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) implanted with (A) pink and green visible implant elastomer (VIE) tags and (B) a yellow visible implant alpha (VI Alpha) tag after 12 mo. Inset in panel B is a close-up of the VI Alpha tag demonstrating the low readability of the alpha-numeric code. Images were taken under a VI light and yellow lens filter.
Retention (A) and probability of tag legibility (B) of visible implant elastomer (VIE) and visible implant alpha (VI Alpha) tags implanted in larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) over a 12-mo period. “×”s mark time points at which we assessed detection and readability of tags. Tag legibility was scored as a binomial response (0 = nonlegible; 1 = legible).
Changes in estimated total length of larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) across three tagging treatments over a 12-mo period. Points represent mean estimates and error bars represent standard error. Points at each time point are staggered slightly (left-to-right) to better illustrate standard error. The vertical solid line represents the time point when hellbender diet was switched from live blackworms (Lumbriculus variegatus) to thawed mysis shrimp (order Mysida) and vertical dashed line represents the time point when hellbenders were consolidated from three hellbenders to five hellbenders per 38-L or 76-L aquaria.
Mean body condition, calculated as scaled mass index (SMI), of larval Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) over a 12-mo period. Scaled mass represents an estimate of an individual's body mass if it were of a reference structural size (defined here as 90 mm total length). Average larval hellbender SMI did not differ across treatments at any sampling occasion. Points represent mean estimates, averaged across treatments, and error bars represent standard error. The vertical solid line represents the time point when hellbender diet was switched from live blackworms (Lumbriculus variegatus) to thawed mysis shrimp (order Mysida) and vertical dashed line represents the time point when hellbenders were consolidated from three hellbenders to five hellbenders per 38-L or 76-L aquaria.
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