Assessment of River Herring and Striped Bass in the Connecticut River: Abundance, Population Structure, and Predator/Prey Interactions

Populations of anadromous alewife Alosa pseudoharengus and blueback herring A. aestivalis, collectively referred to as river herring, have declined in the Connecticut River. An explanatory hypothesis for these declines is that predation pressures have increased as a result of recent increases in abundance of sympatric striped bass Morone saxatilis. We sampled river herring and striped bass from the stretch of the Connecticut River between Wethersfield, CT and Holyoke, MA during the vernal migration seasons of 2005-2008. The objectives of the sampling program were to assess abundance, temporal/spatial distribution, and population structure of both river herring and striped bass, as well as striped bass food habits. Blueback herring population structure has changed over recent decades. Contemporary runs feature younger, smaller fish that are less likely to complete multiple spawning runs over their lifetime. These temporal shifts are indicative of elevated mortality rates operating on older, larger herring. Striped bass predation is a significant source of mortality for adult blueback herring in the Connecticut River. River herring comprise a significant portion of striped bass diets in the Connecticut River during May-June, and striped bass congregate in locations where they are successful in capturing herring. The estimated seasonal consumption of blueback herring by striped bass in our study stretch is comparable to the numbers of herring passed annually at the Holyoke fish lift prior to the onset of recent declines. Future studies will incoporate estimates of predation mortality described here into structured population models that can be used to hindcast the impact of striped bass predation on river herring run size in recent decades, and examine the potential for amelioration of river herring mortality via changes to management of striped bass fisheries