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Accurate forecasting of population trends is one of ecology’s great challenges. Current population models simulate birth and death rates well, but generally underestimate the rate of immigration in and out of the population, simply because immigration events are difficult to observe directly. Bradley’s project introduces a novel approach to estimate immigration rates that avoids the underestimation bias present in other methods of assessing individual movements.

Bradley is testing this approach on the mottled sculpin, a small non-game fish, to facilitate its use as a bioindicator species for North Carolina’s coldwater streams. The bioindicator approach uses a species known to be sensitive to the threats facing a habitat like the “canary in a coal mine” to indicate damage to the habitat.

From 2000 to 2002, Bradley conducted mark-and-recapture surveys of fish populations in headwater tributaries of the Nantahala River. Among the 1,400-plus fish recaptures, Bradley found individuals moved up to 180 meters, about six times farther than the longest move seen in previous work. Bradley also plans to assess individual movements over 200 meters by using microsatellite DNA markers.

Adding long-distance movement data to the data from Bradley’s direct captures will yield a complete picture of sculpin movement from the individual to the population scale. Such a view would improve existing models of sculpin population dynamics and therefore facilitate the species’ use as a bioindicator. In addition, this project will be among the first to integrate genetic data with direct observations to produce realistic immigration predictions.

This approach could be useful with many species that feature difficult-to-observe, long-range movements. This project will aid conservation and management efforts and potentially enhance understanding of population dynamics as well.