Application of a Known-fate Model to Evaluate Crayfish Mark Retention

Abstract Nail polish (paint) is a noninvasive, inexpensive external crayfish marking method for shorter-term studies (i.e., 30–90 d); however, retention time is seldom reported. Our objective was to estimate retention time of two nail-polish types (gel and lacquer) in a probabilistic framework using red swamp crayfish Procambarus clarkii. We marked the carapace of 90 crayfish with six different bottles (treatments) of each type in an indoor raceway that mimicked natural habitat. We estimated nail-polish retention probability using a variation of a known-fate survival model. This approach retained information for crayfish that either molted or died prior to losing the mark (a minimum retention time). Both types had a >0.90 30-d and a >0.80 60-d retention probability. On average, 90-d retention was ~0.75 and ~0.65 for gel and lacquer, respectively. There was more variability in retention among treatments for gel. There was no retention relationship with carapace length. Males had ~0.05 higher mean retention than females. We found that both gel and lacquer nail polish were effective a shorter-term crayfish studies, though gel may be preferred for field studies due to its quicker drying time. Our study framework is applicable to any mark-retention study where individuals perish, molt, or otherwise go unseen.