How Big Is a Population of Darters?

To be effective at conserving fish, we should assess, protect, and manage fish populations at spatial scales that match those of key demographic and evolutionary processes.  Such efforts are complicated for darters, because we seldom understand the size or structure of darter populations on the landscape.  I use data from my previous and ongoing studies of five species of darters to investigate the spatial scales over which population processes act, essentially asking, "How big is a population of darters?"  Movement, demographic, and genetic data are considered.  Observed movements were mostly localized (<0.5 km), with infrequent extensive movements (>2 km), suggesting that populations are small-grained.  However, strong demographic correlation and genetic similarity over large distances (10-40 km) suggest that populations are larger-grained than typically assumed.  Conservation efforts for many darters may therefore be inappropriately focused at a scale too local to be effective.