April 5, 2021 — The following was released by NOAA Fisheries:
Even without a pandemic, figuring out the number of eggs a fish will lay during its spawning season is a difficult task. While this information is important to fishery biologists, long-term data are scarce. That hampers researchers ability to answer a fundamental question important for fishery managers: What affects the ability of marine fish, and fish populations, to replace themselves in an open ocean? The pandemic made answering this question even more difficult—but our researchers persevered.
“Many marine fish produce hundreds of thousands to millions of eggs per female per year, the survival of which determines the future abundance of a population,” said Mark Wuenschel, a fish biologist at the Northeast Fisheries Science Center. Wuenschel is leading a long-term study on “fecundity”—a term for reproductive potential—in two commercial flatfish species, winter flounder and yellowtail flounder. “We had to have enough samples, and we had to work out the methodology to do it.”
Annual fecundity — in this case, measured by the number of eggs — varies and depends on the size, age, and condition of the female fish. Environmental variables, such as temperature and available prey, also affect the growth, condition, and reproduction of the females. Like many things in life, timing is everything. To study fecundity, female fish have to be collected at just the right time from the right locations, and in large numbers. Then, lots of eggs need to be counted.
Enter Emilee Tholke and Yvonna Press, both center biologists who work with Wuenschel. They were granted access to their lab one day a week under specific safety protocols. They prepared egg samples and captured images of the eggs using a high-resolution camera with a macro lens and a microscope. Images were stored on a flash drive or transferred to a shared network file.
Then, working from home, each analyzed the images and entered the results into a shared database. Working from home not only kept the egg counts going, but ensured that critical sampling would continue, and prevented a back-log of sample processing work. This year’s effort completes a 10-year time-series of sampling, image analysis, and fecundity estimates for winter and yellowtail flounders.