Environmental Factors Controlling Juvenile River Herring Productivity and Emigration
Dates
Start Date
2019-05-01
End Date
2022-04-30
Summary
River herring [collectively alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)] have been valued by human societies since pre-colonial times, but populations have undergone a dramatic coast-wide decline over the past five decades (ASMFC 2012, NFWF 2012). Declines in river herring have sparked a series of conservation and restoration measures, including dam removal, extensive moratoria on directed harvest, caps on bycatch (e.g., in the Atlantic herring fishery), designation as a species of concern both at Federal and State levels, and petitions for listing under the Endangered Species Act (ESA). The Northeast Association of Fish & Wildlife Agencies (NEAFWA) identified alewife and blueback herring as Species of Greatest [...]
Summary
River herring [collectively alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)] have been valued by human societies since pre-colonial times, but populations have undergone a dramatic coast-wide decline over the past five decades (ASMFC 2012, NFWF 2012). Declines in river herring have sparked a series of conservation and restoration measures, including dam removal, extensive moratoria on directed harvest, caps on bycatch (e.g., in the Atlantic herring fishery), designation as a species of concern both at Federal and State levels, and petitions for listing under the Endangered Species Act (ESA). The Northeast Association of Fish & Wildlife Agencies (NEAFWA) identified alewife and blueback herring as Species of Greatest Conservation Need (RSGCN) for New Hampshire, Massachusetts, Rhode Island, Connecticut, Maine, New Jersey, New York, Pennsylvania, Delaware Virginia, and the District of Columbia in their 2015 State Wildlife Action Plans (Whitlock et al. 2007; NEFWDTC and RCN program).
Current knowledge of river herring population status and trends is primarily based on monitoring adults in fishways as they migrate upstream to spawn. While these assessments are useful to assess long-term trends and year-to-year variation in populations, they do not necessarily reflect river herring productivity. In fact, our recent research on juvenile productivity in 32 lakes from Connecticut to Maine has revealed that adult run size does not explain much variation in juvenile densities and growth (Devine 2017). There is even less information linking adult run size to productivity for juvenile blueback herring that generally spawn in rivers, or understanding what factors contribute to good growth and survival of young. Adult monitoring in large river systems is particularly challenging, as many fish spawn in rivers below dams, and thus fishways cannot be used to census the population. For example, migrating fish are counted at the Holyoke fish lift in the Connecticut River, yet population estimates based on electrofishing indicate that most adult river herring are currently located in riverine areas downstream of the Holyoke dam. Given the challenges assessing river herring and the weak relationships between numbers of adult and juvenile river herring, information on factors influencing freshwater productivity juvenile river herring, emigration timing and early seawater survival are needed to understand, predict and mitigate population declines.
In the US, river herring spawn in freshwater lakes and rivers between March and July and juveniles reside in freshwater until they emigrate to the ocean throughout the summer or fall. While in freshwater, they feed on zooplankton in pelagic zones during the night and seek refuge from predatory fishes during the day. Recent work in our labs has shown that river herring growth varies widely among lakes, and likely depends on temperature, juvenile river herring densities, zooplankton densities, and water quality (e.g., dissolved organic carbon) (Devine 2017). In large rivers, flow, temperature, and turbidity are hypothesized to be important factors influencing juvenile production, as seen with the congeneric American shad (Alosa sapidissima) in the Connecticut River (Crecco and Savoy 1984), yet no study has directly investigated factors limiting juvenile blueback herring productivity in the Connecticut River. While river herring growth determines emigration timing (sensu Gahagan et al. 2010), abiotic and biotic factors affecting growth may also influence timing of emigration from freshwater. Generally juvenile emigration has been documented between June and November and is likely triggered by water temperature, precipitation, discharge, and prey availability (Kosa and Mather 2001, Gahagan et al. 2010). There is evidence that emigration patterns exhibit interannual and regional variation (Kosa and Mather 2001); however, studies on the topic have been limited by time (often occurring in only one year) and region (often occurring in one site). Studies that cover multiple years and sites will allow a broader understanding of what environmental and biological conditions influence emigration. Knowledge of emigration is also critical to fully understand factors limiting juvenile productivity, since we cannot directly assess juvenile mortality without monitoring emigration. Collectively, information on factors influencing juvenile productivity and emigration is critical for assessing threats to river herring populations, understanding mechanisms for population declines, and ultimately determining effective restoration strategies.
This project expands on recent research on juvenile river herring productivity conducted at the University of Massachusetts Amherst (UMass) by using a combination of lab experiments, field assessments, and analysis of spatial and temporal datasets to assess environmental factors limiting juvenile productivity. The results will provide an understanding the effects of abiotic and biotic factors on juvenile river herring growth, survival, physiology, and emigration rates, which are essential for improving estimates of productivity and developing strategies for conservation and restoration in response to climate change, habitat alterations and other environmental challenges to river herring populations.
Objectives:
The overall goal of this project is to conduct research to fill critical information gaps about juvenile river herring productivity and emigration. We will achieve this through two major objectives: Objective 1. Evaluate limits to juvenile river herring productivity
Conduct lab experiments to test the impact of temperature, food availability, and turbidity on survival, growth, swimming performance, and seawater tolerance of blueback herring
Compare blueback herring growth in field enclosures with different environmental conditions
Assess abiotic and biotic factors associated with river herring productivity (density, growth, mortality) among lakes and rivers in the northeast
Objective 2. Assess factors influencing juvenile river herring emigration rates and timing
Assess timing and rates of juvenile emigration in lake and river systems
Compare biotic characteristics (e.g., size, age, growth rates) of emigrating and non-emigrating juveniles to assess factors influencing emigration timing
Perform analyses to understand how emigration rates influence juvenile densities in lakes, and thus how productivity estimates are affected by emigration events.
