Evaluation and optimization of a long-term fish monitoring program in the Hudson River

Long-term monitoring programs are essential for understanding the dynamics of fish populations in freshwater ecosystems, which are threatened by anthropogenic change. Assessment of monitoring programs helps ensure that they continue to meet stated goals, but published assessments are rare. Here we use a power analysis to assess the three surveys that form the core of the Hudson River Biological Monitoring Program, one of the longest-running fish monitoring programs in the United States. All three surveys had substantial power to detect changes in young-of-year abundance for anadromous species of primary management interest and for a variety of other species with diverse life histories and habitat preferences. In particular, the Beach Seine Survey and Fall Juvenile Survey could reliably detect declines in abundance of 15-30% or more over ten years, while the Long River Ichthyoplankton Survey could reliably detect declines of 40-55% or more over ten years. Simulated reduction of sampling intensity to 75-25% of the historical level of effort in these surveys still yielded good power to detect change for many species, particularly for the Beach Seine and Fall Juvenile surveys. Power to detect change varied in freshwater and brackish portions of the river and across different habitat zones, as well as by survey and species. Our results provide guidance for the re-design of fish monitoring programs in the Hudson River following the recent cessation of the historical funding for those programs, and could serve as a useful model for assessing similar programs in large river and estuarine ecosystems around the world.