How do marine closures affect the analysis of catch and effort data?

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Fishery managers increasingly use marine closures as a tool to conserve ecosystems, biodiversity, and fish abundance. Despite the suggested benefits of closed areas, the limited or no data collection within them leads to difficulties assessing the population status. We investigated how spatial closures impacted the reliability of indices of abundance obtained from standardization methods applied to catch per unit effort data. The presence of closed areas generally introduced a bias in the derived index of abundance, and the magnitude of bias increased as the portion of the population in closed areas increased. In general, restricting the data to the areas that have been continuously fished over time performed best when spatial closures protected a small to medium portion of the population. However, as the portion of the population that was protected increased, the time series bias associated with this approach increased, and the use of an imputation approach was needed for adequate performance. Similarly, the collection of ancillary data in the closed area reduced bias in the estimate of final year depletion when area closures protected a large portion of the population.