They intend to provide new information on the density, mortality and resource needs of juvenile life stages and explore the link between spawning adults and the success of their offspring. The project is one of seven sponsored by Woods Hole Sea Grant that will focus on priority issues in the Massachusetts coastal environment, including not only river herring population studies but shark-seal-human interactions, coastal resiliency and the sources and fate of microplastics in marine ecosystems.
The awards represent a total anticipated research investment of $1.47 million over two years from the National Oceanic and Atmospheric Administration and other non-federal matching funds, and are subject to release of federal funds. Woods Hole Sea Grant Director Matt Charette says, “We are excited to be able to support research on topics of critical importance to Massachusetts and beyond.”
As Jordaan, an associate professor of fish population ecology and conservation in the Department of Environmental Conservation and School of Earth and Sustainability, explains these two fish species known collectively as river herring migrate in spring from the ocean to freshwater to spawn. Both also return to the ocean after spawning and will repeat spawning runs into freshwater in future years until death.
They also display complex and varied movements, shaped by interactions with dams and fish passage structures, in coastal systems during the spawning season. Movements appear to be related to daily temperature and flow conditions but only limited research has been conducted on this topic.
They point out that larvae and juvenile life stages of these fish are generally considered to occupy freshwater, while older juveniles migrate to salt water in summer and fall. However, recent studies suggest that some individuals experience early growth in salt water, which means that estuaries might be important for juvenile river herring growth and perhaps for helping to buffer against poor productivity in upstream freshwater habitat.
“To the best of our knowledge,” Jordaan and colleagues write, “no work to date has effectively sampled juveniles across the freshwater-to-marine transition to understand the relative contributions of production from upstream freshwater and downstream estuarine habitats.” The different contribution of these habitats towards producing offspring is critical for understanding the population dynamics of the two species, and effectively guiding monitoring, restoration and adaptation efforts, they add.
Jordaan and colleagues say that new data from their studies would fill a substantial gap in understanding the life history requirements and sources of mortality of juvenile river herring.