Using the Asmfc River Herring Stock Assessment to Illustrate the Difficulty of Data Patchiness

River herring (alewife and blueback herring) are important forage fish for marine and anadromous predators, such as striped bass, spiny dogfish, bluefish, Atlantic cod, and pollock.  River herring utilize a variety of habitats throughout their lifecycle.  As adults, river herring reside in marine waters most of the year and move to freshwater rivers to spawn. Nursery areas primarily include freshwater portions of rivers and their associated bays and estuaries.  As anadromous species, ideally river herring should be assessed and managed by individual river systems. However, the majority of the life history of river herring is spent in the marine environment where factors influencing survival likely have impacts upon multiple river stocks when they mix during marine migrations.  The Atlantic States Marine Fisheries Commission (ASFMC) completed a coast-wide stock assessment of river herring in 2012.  Although 37 rivers representing 52 species-specific stocks of river herring were included in the assessment, this represents only a fraction of the extant populations of river herring and very few data sets contained the suite of data necessary for quantitative fisheries models.  The data gaps for river herring can be attributed mostly to the low priority these species receive in some agency monitoring efforts.  Given the limitations of the available data, the assessment relied heavily on simple trend analysis of often conflicting indices.  In this presentation we illustrate how temporal and spatial data patchiness complicated the coast-wide assessment of these ecologically important species and how only very general conclusions of coast-wide status could be made.  The overall stock complex of river herring was considered depleted, as there was evidence for declines in abundance due to a number of factors, but the relative importance of these factors in reducing river herring stocks could not be determined.  Of the 52 species-specific stocks for which data were available, 23 were depleted, 1 stock was increasing, and the status of 28 stocks could not be determined.   In contrast, NOAA Northeast Fisheries Science Center’s spring and fall trawl survey indices, the only coastwide fisheries-independent survey and representing trends across river-specific stocks, showed increasing trends in relative abundance beginning in 2008.