Two studies conducted by DNR scientists highlight the spawning challenges of striped bass

Two studies conducted by DNR scientists highlight the spawning challenges of striped bass

Two studies conducted by DNR scientists highlight the spawning challenges of striped bass

The research examines historical egg data and changes in the timing and duration of the spawning season

A DNR biologist measures juvenile striped bass as part of its annual juvenile-of-the-year survey.  DNR photo

A Maryland Department of Natural Resources biologist measures juvenile striped bass as part of its annual yearling survey. Maryland DNR photo

Two recent studies by Maryland Department of Natural Resources scientists highlight the spawning challenges faced by striped bass, also known locally as rockfish, in the Chesapeake Bay.

The research was published in “Marine and coastal fisheries“Dynamics, Management and Ecosystem Science” In late 2023 for the striped bass-themed magazine issue.

Jim Uphoff, a DNR fisheries biologist, authored a The paper uses long-term datasets to fetch A new perspective on the history of charted stock crashes and recoveries In the last decades of the twentieth century. Angela Giuliano, also a DNR fisheries biologist, posted a A study examines the effects of rising water temperatures in the Chesapeake Bay On the timing and length of the striped bass spawning season.

“These studies are important contributions to our current body of knowledge about striped bass,” said Lynn Waller Figley, DNR Fishing and Boating Services director. “With recent below-average spawning, it is important that we have as much information as possible about striped bass reproduction and habitat. DNR biologists are adding to the scientific understanding of striped bass recruitment that will help manage this population.”

After five consecutive years of below-average spawning success in Maryland’s four major spawning rivers, the Maryland General Assembly Joint Committee on Administrative, Executive, and Legislative Review approved Emergency work Friday To extend two periods already closed for targeting striped bass To protect the breeding stock in the Gulf.

The Atlantic States Marine Fisheries Commission, of which Maryland is a member, also approved an amendment stating: Amends entertainment and business regulations Ocean and Gulf quotas to reduce fishing mortality in 2024. However, the quality of spawning and larval habitat plays a major role in how many striped bass will be available, and the DNR is trying to understand how habitat changes could impact management.

Uphoff created a long-term historical index for eggs and combined it with an events index, who tracks reproductive success, From 1955 to 2019 for the Maryland portion of the Chesapeake Bay. He tested three prevailing hypotheses about the factors that led to changes in striped bass spawning success: the effect of habitat quality on larval survival, overfishing of the species’ egg stock, and a combination of these factors.

Beginning in the early 1970s, the striped bass population experienced an extended series of poor class years. By the early 1980s, excessive hunting pressure combined with poor recruitment continued to seriously deplete egg stocks. States along the Atlantic coast imposed fishing moratoriums or more conservative size restrictions on striped bass fishing after 1984. The stock improved in the subsequent decade. Maryland lifted its ban on striped bass fishing in 1990 and adopted conservative regulations. The Atlantic States Marine Fisheries Commission announced the stock had recovered in 1995. Uphoff’s analysis filled in missing information on larval survival before the collapse.

Research suggested that poor larval survival led to the collapse of striped bass in the Chesapeake Bay, and improvements in larval survival contributed to the species’ recovery. Overfishing contributed to poor recruitment in the 1980s, but the results of this study do not support it as the sole cause of stock collapse or recovery.

“The factors affecting striped bass populations in Maryland are complex, and looking at long-term historical data provides a valuable perspective,” Uphoff said. “When habitat conditions support larval survival and the spawning stock is protected from overfishing, striped bass have the best chance of producing strong yearlings.”

In the second study, Giuliano studied how the timing of striped bass spawning in the Chesapeake Bay changed as water temperatures rose over time. Adult striped bass migrate annually in early spring to the same spawning areas where they hatched.

Previous search In the North American Journal of Fisheries Management Highlight the importance of water temperature in stimulating striped bass spawning and that larger female striped bass move to spawning areas earlier than smaller females.

Using the spawning stock survey, which is conducted in spawning areas in the upper Bay and Potomac River, and water temperature data collected during the survey, Giuliano looked at how temperature thresholds that play an important role in spawning activities change over time. It also looked at how continued temperature fluctuations due to climate change will impact fisheries management in the future.

While surveys have indicated that spawning can occur as late as March, this study found no statistically significant change in the timing of the temperature threshold that triggers the start of the spawning season for striped bass in the Chesapeake Bay. This is due to the fact that water temperatures have not changed enough to cause a consistently early spawn.

However, a significant change in the timing of the end of the spawning season was detected, indicating that the spawning period for striped bass in the Gulf has shortened since 1985 when the survey began. The date at which the last pre-spawning female was observed in the spawning area has also occurred earlier in the year since the 2000s, suggesting that the fish are finishing spawning earlier than in the past.

“With water temperatures in the Gulf expected to rise under different climate change scenarios, a wide age range of spawning fish, which spawn at slightly different times throughout the season due to size, could mitigate the effects of climate change by increasing the probability of spawning,” he said. Giuliano: “It occurs when environmental conditions and prey availability are good.”

Both Uphoff and Juliano’s studies resulted from an Atlantic Coast Striped Bass Symposium at the 2021 American Fisheries Society meeting in Baltimore organized by DNR staff. The department continues to actively study striped bass and expects to publish at least one peer-reviewed paper in 2024.

Written by Sinclair Boggs, Marketing Strategist for the Maryland Department of Natural Resources, Fishing and Boating Services

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