Assessing population trends, evaluating management actions, and identifying community responses to anthropogenic impacts all require an accurate time-series of populations. In practice, such data are often scarce or of poor quality due to the limited resources of managing agencies.  In such situations, analyses that integrating multiple data sources (e.g. agency monitoring programs, citizen science observations, fisheries catch records) can yield dramatic improvements in the estimation of population trajectories. To do so effectively, however, such integrative models must account for differences in observation errors across data sources.  We used multivariate state space models (MSSMs) to assess the population trajectories of 10 reef fish species from the Monterey Bay National Marine Sanctuary based on data from 1) transect surveys conducted through academic institutions and 2) citizen-science monitoring surveys conducted by volunteer Scuba divers.  
Results/Conclusions

By developing competing models and applying information theory, we demonstrate how MSSMs can be used to compare and integrate multiple monitoring time series, and ultimately improve estimates of the true states of populations though time.  Additionally, we demonstrate that by combining multiple time series, it is possible to recover method-specific observation error estimates even for very short time series of data (~10 sampling periods).