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 shown a reduced population size, causing the implementation of a river herring fishing moratorium in the Chesapeake Bay region. Low populations have been attributed to a combination factors, such as overharvesting (both on and offshore), habitat degradation, stream blockage due to dams, river channelization, pollution, increased impervious surfaces around spawning rivers changing flow patterns, 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).
In 2015, populations using these Potomac River tributaries increased for most species of anadromous and semi-anadromous fish. Astonishingly, river herring were 183% more abundant than the yearly average for the last 10 years. 2015 was the third year of the moratorium for river herring species and river herring reach maturity between 3 and 5 years old, most occurring at age 3 or 4. The large increase in abundance could indicate that the moratorium is working and this is the first successful cohort protected by the moratorium. However, year-class success is extremely variable in fish from year to year. This large increase could just be an extremely successful cohort for other reasons. Additional monitoring under the moratorium is needed to determine if the moratorium is effective.
Investigations into the life history traits of river herring are ongoing. Otoliths (ear bones) are collected from all life stages within the Potomac River tributaries to determine age, which paired with length allows growth rates at each life stage to be calculated. Scales from spawning adults can be used to identify spawning marks (areas of erosion from entering freshwater) and determine how many times an individual has spawned over its lifetime. Spawning frequency and the proportion of the population mature at each age is useful to help determine the potential recruitment (young produced) in a given season.
Current results from analyses on adult populations show that females grow faster and larger than males for both alewife and blueback herring, which has been well documented throughout their geographical range. Interestingly, this study was one of the first to indicate females are maturing faster than males for both species. We hypothesize this is occurring due to the females faster growth rates. When populations are at their peak, many resources like prey availability limits an individual’s ability to grow. Now that populations are low, these density-dependent (limiting) resources are now plentiful to individuals in the population. While both sexes are able to take advantage of the plentiful resources, females naturally grow faster. The increased growth rates allow for faster maturity rates, which are more apparent in the females. Continued monitoring of the population dynamics is needed to determine if this hypothesis is true. The information on life history traits is being used to construct a predictive model of river herring recruitment in Potomac River tributaries. The model will examine the recruitment potential of a population based on environmental variables, such as temperature, dissolved oxygen, turbidity, and flow. By determining how growth rates and mortality rates changed based on the given environmental variables, this study will help determine if Potomac River tributaries are successful nursery habitats for river herring species. This study aims to help management determine areas of interest for future restoration and conservation of this species.
Collaborative Efforts and Management Strategies
NOAA listed river herring as species of concern in 2006. In 2009, the Atlantic States Marine Fisheries Commission (ASMFC) established the second amendment to the Fishery Management Plan for Shad and River Herring. Under the amendment, all jurisdictions of commercial and recreational fisheries must develop an approved sustainable fishery management plan or implement moratoriums for alewife and blueback herring species. Moratoriums have been established throughout the entire Chesapeake Bay as of January 2012.
River herring are split into three management areas within the Chesapeake Bay: the upper bay (Maryland and Delaware), the lower bay (Virginia) and the Potomac River. The Potomac River Fisheries Commission manages the Potomac River, which is a joint unit combining Maryland and Virginia appointed members. Collaboration through a Chesapeake Bay River Herring Workshop was initiated between these management units, the ASMFC, NOAA, the Smithsonian Environmental Research Center (SERC), the Department of Energy and Environment (DDOE), National Fish and Wildlife Foundation, The Nature Conservancy, US Geological Service, Virginia Institute of Marine Science, and Potomac Environmental Research and Education Center (through our lab). Hosted by SERC every year, the workshop aims to share information about river herring within the Chesapeake Bay and identify priorities for ongoing research and monitoring. The goals of the workshop align with the ASMFC river herring goals and the Chesapeake Bay Program to increase understanding of the populations and provide a basis for collaborative efforts. Through this workshop, a collaborative effort has begun to study the life history traits of adult river herring returning to the Chesapeake Bay to spawn.
Dr. de Mutsert serves on the Technical Expert Working Group for River Herring (TEWG). The primary objective of the TEWG is to develop and implement a dynamic conservation plan to help restore river herring throughout its Atlantic coastal range. This will include identifying important conservation efforts, identifying critical data gaps, and monitoring and evaluating progress in achieving the goals. This effort will coordinate and build upon the many previous and ongoing efforts to further river herring conservation, including fisheries work by the Mid-Atlantic Fishery Management Council (MAFMC) and the New England Fishery Management Council (NEFMC), and habitat restoration by the Atlantic Coastal Fish Habitat Partnership and The Nature Conservancy.