Two recent studies by Maryland Department of Natural Resources (DNR) scientists highlight spawning challenges that striped bass face in the Chesapeake Bay. The research was published in “Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science” in late 2023 for the journal’s striped bass themed issue and was recently spotlighted in The Fishing Wire on February 12, 2024.
One of the papers authored by DNR biologist Jim Uphoff uses long-term datasets to bring a new perspective to the history of the striped bass stock collapse and rebound in the last decades of the 20th century, while a second study done by DNR fisheries biologist Angela Giuliano looks at the effects of warming water temperatures in the Chesapeake Bay on the timing and length of the striped bass spawning season.
Uphoff created a long-term historical egg index and combined that with the juvenile index, which tracks reproductive success, from 1955 to 2019 for Maryland’s portion of the Chesapeake. He tested three prevailing hypotheses about factors that led to changes in striped bass spawning success: the impact of habitat quality on larval survival, overfishing of the species’ spawning stock, and a combination of these factors.
The research suggested that poor larval survival initiated the collapse of Chesapeake Bay striped bass, and improvement in larval survival contributed to the species’ recovery. Overfishing contributed to poor recruitment in the 1980s, but Uphoff’s study’s findings did not support it as the singular cause of stock collapse or recovery.
“The factors that affect Maryland’s striped bass population are complex, and looking at long-range historical data provides a valuable perspective,” said Uphoff. “When habitat conditions support larval survival and the spawning stock is protected from overfishing, striped bass have the best chance of producing strong class years.”
In the second study, Giuliano examined how the timing of striped bass spawning in the Chesapeake Bay has shifted as water temperatures have risen over time. Adult striped bass migrate annually in early spring to the same spawning grounds where they hatched. Previous cited research has highlighted the significance of water temperature in triggering striped bass spawning and that larger female striped bass move onto the spawning grounds earlier than smaller females.
Using the spawning stock survey, which occurs on the Upper Bay and Potomac River spawning grounds, and water temperature data collected during the survey, Giuliano looked at how the temperature thresholds that play an important role in spawning activities have changed over time. She also considered how continued temperature variability due to climate change may affect future fishery management.
While surveys have indicated that spawning can occur in late March, this study found no statistically significant change in the timing of the temperature threshold triggering the start of striped bass spawning season in the Chesapeake Bay. This is due to the fact that water temperatures have not shifted sufficiently enough to cause a consistently earlier spawn.
However, a significant change was detected in the timing of the end of the spawning season, suggesting that the striped bass spawning period in the Chesapeake Bay has shortened since 1985 when the survey started. The date on which the last pre-spawn female was observed on the spawning grounds has also occurred earlier in the year since the 2000s, indicating that fish are concluding spawning earlier than in the past.
“With rising water temperatures predicted in the Bay under various climate change scenarios, a broad age range of spawning fish, spawning at slightly different times throughout the season due to size, could mitigate the effects of climate change by making it more likely for spawning to occur when environmental conditions and prey availability are good,” said Giuliano.
“These studies are important contributions to our existing body of knowledge about striped bass,” said DNR Fishing and Boating Services Director Lynn Waller Fegley. “With the recent below-average spawns, it’s critical that we have as much information as we can on striped bass reproduction and habitat. DNR biologists are adding to the scientific understanding of striped bass recruitment that will help manage this population.”
The Atlantic States Marine Fisheries Commission (ASMFC) recently approved an amendment that modifies recreational regulations and commercial quotas in the ocean and the Chesapeake Bay to reduce fishing mortality in 2024. However, spawning and larval habitat quality play a major role in how many striped bass will be available; according to the report Maryland’s DNR is trying to understand how habitat changes may affect management.
