Simultaneous estimation of dispersal and survival of the gulf killifish Fundulus grandis from a batch-tagging experiment

The gulf killifish Fundulus grandis has been widely used as an indicator species for studying impacts of disturbance. However, such use requires an understanding of the spatial and temporal scales over which an individual may have been exposed to a disturbance, i.e. its dispersal range and survival. Here, we present a novel spatial capture-recapture (SCR) model for simultaneous estimation of dispersal and survival from batch-tagging data. The model is applied to simulated data and data from a mark-recapture experiment on gulf killifish in 4 saltmarsh creeks near Cocodrie, Louisiana, USA. The model is relatively robust to misspecification of the functional form of dispersal and outperforms a non-spatial model when dispersal beyond the study area occurs. However, in 2 of the study creeks, the expected decline in recaptures with distance and time from release was not observed. In the other 2 study creeks, model predictions generally matched observations, and the average estimated mortality rate was 3.44 yr-1, equivalent to a maximum age of 1.3 yr. The long-term cumulative 50% dispersal distance averaged 29 m. These results suggest that observed responses of gulf killifish to disturbance generally reflect extremely local conditions (<100 m). Thus, this species can serve as a site-specific indicator of disturbance, though only individuals collected within the same year as the disturbance event are likely to have been directly exposed. Our SCR model is widely applicable to batch-tagging experiments where release and recapture locations are recorded.