Tuesday, February 13, 2024

MDDNR Finds Excuses for Striper Dearth

MDDNR, Two Studies by DNR Scientists Highlight Spawning Challenges for Striped Bass

Two recent studies by Maryland Department of Natural Resources scientists highlight spawning challenges that striped bass, also known locally as rockfish, 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.

Jim Uphoff, a DNR fisheries biologist, authored a paper that 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. Angela Giuliano, also a DNR fisheries biologist, published a study that looks at the effects of warming water temperatures in the Chesapeake Bay on the timing and length of the striped bass spawning season.

“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.”

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

The Atlantic States Marine Fisheries Commission, of which Maryland is a member, also approved an amendment that modifies recreational regulations and commercial quotas in the ocean and the 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, and DNR is trying to understand how habitat changes may affect management.

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 Bay. 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.

Beginning in the early 1970s, the striped bass population suffered from an extended series of poor class years. By the early 1980s, excessive fishing pressure combined with poor recruitment continued to critically deplete spawning stock. States along the Atlantic coast imposed fishing moratoriums or much 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 declared the stock recovered in 1995. Uphoff’s analysis filled in missing larval survival information from prior to the collapse.

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 this 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.”

So fisheries science, it's way more complicated. No single cause of failure is likely to be found because many factors are involved, and most of them have year to year fluctuations, for reasons that are highly correlated.

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 research in the North American Journal of Fisheries Management 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.

So, there's no shift in temperatures seems to be involved in the start of the spawning season.

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 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.

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

It's carefully written around but it sounds like what they're saying is that for some unknown reason, spawning seems shut off earlier than it used too. Is that because their are fewer larger stripers to sample? 

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