Maryland Biologists Say Older, Larger Female Stripers Produce More Eggs - The Fisherman

Maryland Biologists Say Older, Larger Female Stripers Produce More Eggs

Do larger stripers produce better eggs?  Some who support the BOFFF (big old fat fecund females) theory would say yes, and the latest research out of Maryland could help corroborate that belief.

A new study from biologists in the Maryland Department of Natural Resources (DNR) published in Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science in February, determined that half of females reach sexual maturity between ages 5 and 6, and larger, older females produce more eggs per kilogram body mass than smaller, younger females.

“This research demonstrates the importance of protecting the female breeding stock of striped bass, both throughout their life cycle and particularly when they are at large, productive sizes,” said Lynn Fegley, director of the department’s Fishing and Boating Services. “By protecting large female striped bass, we can help make sure they produce a lot of eggs that will survive better when the environmental conditions are right for successful spawning.”

Through collaboration with multiple state and federal agencies, surveyors collected a wide range of samples throughout the fall and the entire spring spawning season in the Chesapeake Bay and Atlantic Coast, accounting for all developmental stages.  Scientists at the Oxford Cooperative Laboratory then stained cross sections of striped bass ovaries with special dyes, encased them in paraffin wax, and mounted thin slices on a glass slide. The dye highlights different components of the developing eggs, allowing biologists to determine if a striped bass could produce fully developed eggs by the spawning season, or had just recently spawned.

The authors found that some younger females produced enlarged oocytes (developing eggs) that appeared developed but lacked the critical yolk material. These were determined to be fish that had begun maturing, and go through a “practice” reproductive cycle, but hadn’t yet become fully mature adults capable of reproducing. As water temperatures rise in June, the unspawned, unreleased eggs are reabsorbed in a process called atresia. The resulting analysis showed that just a small percentage of females reach maturity by age 4, but about 90% do by age 7.

The researchers determined fecundity by taking a photo of small samples of mature striped bass eggs, using a computer algorithm to count the eggs in the photos, and conducting further calculations to come up with an estimate of the total numbers of eggs found in a ripe striped bass ovary. The number of eggs produced by a female striped bass ranged up to 4 million in a 13-year-old fish, but eggs also increased disproportionately with body weight. This means, for example, that in one spawning season, a 30-pound striped bass will produce more eggs than two 15-pound striped bass combined.

While the authors noted methodological and interpretive differences between this study and others ranging over the past decades, the resulting calculations of age at 50% maturity and fecundity were consistent with previous findings. Given that environmental and fishing pressure on spawning striped bass has been variable over the last four decades, this study concludes that reproductive-related life history traits of female Atlantic striped bass are robust to long-term changes.

This research contributes to DNR’s continuing effort to understand the spawning challenges striped bass face in the Chesapeake Bay and use the latest science to inform management.

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