In the Delaware River, climate change and invasive species threaten shad, ‘America’s founding fish’

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American shad were a major food source for early European settlers and Native Americans who lived along the Delaware River.

Known as “America’s founding fish,” the species were so abundant that it was said people could “walk across their backs.” In 1896, more than 4 million shad were caught in a single year. But by the 1900s, overfishing caused a steep decline.

A new study published this month indicates that American shad, as well as river herring, have failed to recover in the Delaware River, which could threaten the aquatic ecosystem.

Today, the migratory fish face threats such as dams that impact their ability to travel and reproduce, as well as low oxygen levels caused by ammonia discharges from wastewater facilities into the river. As a result, populations of the fish are close to record lows in eastern North America.

“Shad and river herring are iconic species in the Delaware estuary, and seeing them in such low numbers, as an ecologist, is concerning,” said LeeAnn Haaf, estuary science director at the Partnership for the Delaware Estuary.

The study was a collaboration between the Partnership for the Delaware Estuary, the U.S. Fish and Wildlife Service, the Philadelphia Water Department, the Pennsylvania Fish and Boat Commission and PSEG Nuclear, which operates the Salem and Hope Creek nuclear power plants along the river in Alloway Township, New Jersey.

“These populations will still exist in some capacity, but in terms of people being able to recreate or enjoy these species, there’s going to be so many regulations on their populations to keep them functional that people aren’t going to be able to be allowed to fish for them,” said co-author Ella Rothermel, urban resilience assistant manager at the Partnership for the Delaware Estuary.

“People used to be able to witness these migrations, but that’s not really feasible to do at this point, either because of dams or low population numbers,” she added.

American shad, along with alewife and blueback herring, collectively termed “river herring”, migrate to the Delaware River’s tributaries to spawn. They are a critical food source for larger fish like striped bass, as well as bears, raptors, cormorants and gulls. They help with nutrient cycling and act as a host fish for freshwater mussels.

Climate change threatens shad, ‘America’s founding fish’

The new study finds that American shad and river herring continue to be threatened by predation from invasive species and changing water conditions, such as warming temperatures and ocean circulation patterns.

As climate change poses the risk of heavy rainfall events, it could also impact the migration and spawning of fish.

“Things are changing faster than the fish can adapt to,” Rothermel said.

More research is needed to determine how shifting environmental conditions impact fish species, the study suggests.

The researchers said there are some positive developments for the species. For instance, water quality in the Delaware River Basin has improved since the passage of the Clean Water Act in 1972, and dam removal initiatives have helped improve fish passage. However, additional collaboration is needed to ensure American shad and river herring can thrive in their environment.

“They’re migrating along the Atlantic Coast. So it really takes a group effort across the Atlantic Coast if we really want to make a meaningful difference in these populations and restore them,” Rothermel said.

Haaf said working to insure flourishing populations of American shad and river herring would create a healthy estuary, which benefits aquatic life and people alike.

“Even if folks aren’t fishermen, or aren’t looking to eat shad under any circumstances, I think that it’s still representative of the clean water and resources that are available in our estuary,” she said.