Population dynamics and demography of the stream-associated coastal giant salamander at the northern extent of their range

Management of at-risk species requires estimates of demographic rates and population dynamics, and also details about how those rates vary with and without human influence.  For stream-associated amphibians the estimates of numbers are largely based on larval stages.  We sampled the larval stages of coastal giant salamanders (Dicamptodon tenebrosus) in streams of the Chilliwack River valley east of Vancouver, Canada.  Giant salamanders were trapped over 8 years in 10 streams using mark-recapture methods (PIT tags or elastomer marks).  Variation in numbers and survival rates between years and sites were large, and of roughly the same magnitude across sites and years.  In these populations larvae take about 3 years to reach metamorphosis, so overwinter survival rates may be critical to species’ persistence.  No data exist for adult survival rates, so sets of assumptions were tested in simple demographic models.  These models indicated that the species hovers just below or at the level of replacement based on estimates of finite rate of increase.  These estimates differ from those for species’ populations further south which have shorter in-stream life stages. The mechanisms by which land use affects populations, and the magnitude of those effects, vary spatially and with life stage.