SREL Reprint #3365

Using PIT tags to evaluate non-individual-specific marks under field conditions: a case study with Greater Siren (Siren lacertina)

Thomas M. Luhring

Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, South Carolina, 29802, USA
Biological Sciences, 105 Tucker Hall, University of Missouri, Columbia, Missouri, 65211, USA

Abstract: Mark-recapture models used in estimating population size require the capture, marking, and recapturing of marked animals (Donnelly and Guyer 1994). Although several methods are available for marking amphibians (see Ferner 1979), sirenids and Greater Siren (Siren lacertina), in particular, present several problems for marking schemes. Sirenids have fewer total toes (6 or 8) than most salamanders and this limits the applicability of toe clipping schemes. Additionally, the dark skin of Greater Sirens prevents marks made by tattooing and injectable dyes from being easily read (Sorensen 2003). The only known test of multiple marking techniques on S. lacertina was conducted on two captive animals (Sorensen 2003). The marking techniques used on the two captive animals included cyano-acrylic, tail-notching, heat-branding and Passive Integrated Transponders (PIT tags). Of these, only PIT tags were successful in creating a lasting mark and were later used in field studies. While it was not deemed applicable for Greater Siren, previous studies on Lesser Siren (Siren intermedia) used heat branding to create marks that lasted for up to 96 months (Frese 2000; Gehlbach and Kennedy 1978; Raymond 1991).
The required level of identity (e.g., individual, cohort) and persistence (e.g., permanent, month, day) for a mark is dependent on the specific goals of a mark-recapture study. I tested two types of non-individual-specific marks on S. lacertina in an isolated herbaceous bay wetland to determine their permanence and readability. Passive integrated transponder (PIT) tags are effective at providing a permanent individual mark in S. lacertina (Crabill 2007; Sorensen 2003). Their proven persistence as a mark for S. lacertina allowed me to use them as a redundant mark to test other marking techniques used in this study.
There are several individual marking schemes for toe clipping amphibians (see Donnelly et al. 1994). However the utility of toe clipping for individually marking Siren is fairly limited as they only have eight total toes (most toe-clipping schemes are designed for amphibians with 18 total toes). For this reason, toe-clipping in this study was considered to be a cohort mark (i.e., different toe-clip combinations can be used in order to separate animals into smaller groups by a pre-defined criterion such as period of capture). Tail notching has been successfully used as a marking technique for larval anurans (Turner 1960). Sirens often have minor damage to their tailfins that can resemble a tail notch (personal observation). To avoid confusion with naturally occurring tailfin damage, I used an elongate arc or “tail scoop” (see Luhring 2008) as a tailfin mark on each marked animal. Because there is not an effective way to vary the appearance of a tail scoop, this method was considered to be a non-specific capture mark.

SREL Reprint #3365

Luhring, T. M. 2009. Using PIT tags to evaluate non-individual-specific marks under field conditions: a case study with Greater Siren (Siren lacertina). Herpetological Review 40(2): 170-173.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).