Use of Pup Counts in Indexing Population Changes in Pinnipeds

A series of population simulations were used to test the accuracy of estimating the discrete rates of population change (RPC) f rom annual pup counts. The simulations indicate that pup counts can give a biased estimate of RPC, and that t h e magnitude and direction of bias depends on which life history parameters are density dependent and on the maximum rate of population change. In general, if precensus pup survival is density dependent the estimated RPC using pup counts is too low. If post-census pup survival is density dependent, the estimated RPC is too high. If adult survival is density dependent, there is very little bias in the estimate. The results indicate that pup counts can be reliable indicators of population growth, but caution should be used in interpreting the results unless density feedback mechanisms have been identified.