Maryland Study: Food Supply Not Behind Poor Striped Bass Spawning

New research from Maryland's Department of Natural Resources shows that young striped bass had plenty of food to eat in recent years, ruling out a lack of zooplankton as the cause of poor spawning success. The study suggests climate change and rising water temperatures may be the real culprit behind declining striped bass numbers in the Chesapeake Bay.

A new research study from Maryland’s Department of Natural Resources has eliminated one potential cause for the recent decline in striped bass spawning success in Chesapeake Bay waters.

Scientists found that baby striped bass had sufficient food sources available during 2023 and 2024, despite both years showing poor reproduction rates for the popular game fish. The research, published in December in Marine and Coastal Fisheries journal, examined what tiny striped bass larvae were eating in the Choptank River.

Researchers had theorized that young striped bass might be missing critical feeding opportunities when zooplankton blooms didn’t coincide with their hatching periods. However, this new study shows that theory doesn’t hold water.

“When we got done, basically a strong year class like the one in the Choptank River in 1989 didn’t really look different from 2023 or 2024 in terms of feeding,” said DNR fisheries biologist Jim Uphoff, who led the research team.

The investigation compared stomach contents of weeks-old striped bass from recent years to historical data from the 1980s, when spawning success varied widely. Scientists discovered that larval fish had adequate amounts of copepods and water fleas – their primary food sources – even during years with disappointing reproduction results.

To gather this data, biologists used large plankton nets at multiple Choptank River locations following known spawning periods. Back in the laboratory, they painstakingly searched through preserved water samples to locate larval striped bass and white perch, each measuring just 5 to 10 millimeters in length. Using microscopes and dissecting tools, they analyzed what the tiny fish had consumed.

The study revealed that successful spawning years from decades past had similar zooplankton availability compared to recent unsuccessful years. This finding suggests that food supply alone doesn’t determine whether striped bass reproduction will succeed or fail.

Researchers also discovered that striped bass populations are essentially determined within their first three weeks of life, when the fish are smaller than rice grains. The number of larvae measuring 8-10 millimeters closely matched the juvenile counts found in later surveys.

Uphoff compared striped bass spawning behavior to gambling, explaining that the fish commit fully when temperatures rise slightly. “In enough cases, the timing is bad, and that doesn’t work,” he explained. “But every once in a while, they have a big year class.”

With this feeding theory ruled out, researchers are focusing on water temperature and flow as the primary factors affecting spawning success. Climate change appears to be shortening the spawning season as early spring water temperatures increase in the Bay.

“The amount of eggs is okay and the feeding larvae are okay, so now you’re looking at something in between,” Uphoff noted. “The big drivers are water flow and temperature. More and more, it’s looking like a temperature issue here, related to climate change.”

Previous DNR studies have shown that striped bass are producing sufficient eggs for good reproduction, but another study found that warming waters are compressing their spawning window. This latest research suggests the shortened breeding period is when striped bass face their greatest challenges.

“This study is another important contribution to striped bass research by our fisheries biologists at the Maryland Department of Natural Resources,” commented DNR Assistant Secretary of Aquatic Resources Kate Charbonneau. “Our scientists have brought us another step closer to understanding the ongoing low juvenile recruitment of striped bass.”

DNR officials continue emphasizing the importance of protecting adult striped bass through regulations to maintain healthy breeding populations. When environmental conditions align properly, a strong stock of spawning fish could produce a successful year class in the Chesapeake Bay.

The research team included DNR biologists Shannon Moorhead, Alexis Park, Carrie Hoover, Marisa Ponte, and Jeffrey Horne alongside lead author Uphoff.