The Utility of Uncertain Historical Data When Assessing Stock Status

Historical data may provide critical information on marine fish stocks and are frequently available to stock assessment scientists.  Longer time series that include data from the beginning of fisheries are desirable, but not if they mask population patterns because of high levels of measurement error.  A simulation model was constructed using life history parameters and data for four commonly caught species in the Southeast and generated catch-at-age data over two time periods of a simulated fishery.  Two different levels of measurement error were incorporated into the catch time series, including a larger variance for the first half of the time series.  The resulting data were input into a statistical catch-at-age model.  The population benchmarks produced by the model were compared to the “true” benchmarks created by the “true” population without error.  Simulations were run to test a range of variances.  Results indicate that the benefits of incorporating historical data dissipate as measurement error variance increases.  Understanding the implications of error in historical data on a stock’s status will allow assessment scientists to make improved decisions on when to include older, more error-prone data.