About River Herring
Anadromous species spend most of their lives in salt water, but return to freshwater to spawn (reproduce). Due to the predictable timing of spawning runs to freshwater, many anadromous species are commercially or recreationally important. In the Potomac River, four species of anadromous herring have become important to fisheries: alewife (Alosa pseudoharengus), American shad (A. sapidissima), blueback herring (A. aestivalis), and hickory shad (A. mediocris).
American shad, the largest of the four species, have been documented to spawn in the main river channel. Hickory shad spawn somewhere between the main channel and river tributaries depending on conditions, but are not as common in the Potomac River as the other three species. Alewife and blueback herring, referred to collectively as river herring, spawn in the lower reaches of the tributaries, where the water is completely fresh but still tidally influenced.
Over the last few decades, all four species have been reduced in population size, with river herring currently under moratorium in the Chesapeake Bay region due to low population sizes. Low populations are hypothesized to be caused by overharvesting (both on and off shore) and habitat degradation due to dams, river channelization, pollution, increased impervious surfaces around spawning rivers, etc.
The purpose of the PEREC anadromous fish project is to investigate the spawning activities of anadromous or semi-anadromous species (such as gizzard shad Dorosoma cepedianum, threadfin shad D. petenense, white perch Morone americana, and striped bass M. saxatilis) that use the tributaries feeding the Potomac River at any point in their life cycle. Spawning adults are monitored using large hoop-nets to understand annual occurrence and seasonal timing. Also, adults captured can be studied to determine size distribution and sex ratios. Eggs and larvae are sampled with plankton nets to estimate total larval production. Juveniles are collected further downstream to understand habitat use at different life stages. Spawning adults, eggs, and larvae are monitored in three creeks Pohick Creek, Accotink Creek, and Cameron Run. Juveniles are collected in Gunston Cove (fed by Pohick Creek and Accotink Creek) and in Hunting Creek (fed by Cameron Run and Hoof’s Run).
Additional investigations have begun to better understand the life history traits of river herring. Otoliths (ear bones) and scales are collected from adults and juveniles to determine age and spawning frequency. Pairing age with length measurements for each species, allows us to determine growth rates for the local population. Also, we are estimating mortality rates for a particular habitat in the study area. This information will be used to construct a predictive model of river herring productivity in Potomac River tributaries. The model will provide insight about spawning and nursery habitat, as well as to better understand how environmental variables affect each life stage. This study aims to help management determine areas of interest for future restoration and conservation of this species.