Population dynamics of a threatened pitviper in a geographic stronghold

Estimating long-term variation in population parameters can provide important insights into the mechanisms regulating population dynamics and support at-risk species conservation. Such studies are rare for species with slow life histories owing to the extended time series required to capture key demographic events. We used long-term capture–recapture data (2011–2025) on adult female eastern massasaugas ( Sistrurus catenatus ) in southwest Michigan to estimate apparent survival, recruitment, realized population growth, and abundance using robust design time-symmetric models with the Huggins model incorporated over secondary sampling occasions. Apparent survival varied over time (0.598–0.776) as a positive linear function of snout–vent length. Annual per-capita recruitment rate was estimated as a constant: 0.319 (95% CI 0.270–0.372). Model-averaged estimates of adult female abundance ranged from 42.5–140.7. The model-averaged estimate of realized population growth was 1.013 (95% CI 0.986–1.040), suggesting slight positive growth. Survival accounted for 0.685 of realized population growth (95% CI 0.636–0.733) and was 2.19 (95% CI 1.75–2.74) times more impactful than recruitment on realized population growth. The larger contribution of survival to realized population growth indicates that management efforts focused on reducing adult female mortality, rather than increasing recruitment, may be the most effective strategy to increase the probability of population persistence.