Thanks to Ryan Schloesser for allowing Virginia Sea Grant to repost “The Health of Juvenile Fishes in Virginia Estuaries.”
Fisheries scientists generally accept that the health, or condition, of juvenile fishes reflects the quality of their nursery areas. Estuaries are often used as nursery areas, and a large number of fish using an estuary is often thought of as a sign of quality habitat. But what if all those fish were in poor condition and not likely to survive? Perhaps an estuary with lower fish abundance, but with much healthier fish, would be more important in contributing to the adult population.
For the last four years, my dissertation has been looking at how different estuarine habitats may prepare juvenile fish for surviving the difficult journey of life ahead of them. Specifically, I have been looking at whether different areas of estuaries in Virginia produce juvenile summer flounder, striped bass, or Atlantic croaker that are more likely to survive migrations to the continental shelf or winter residence in Chesapeake Bay. What’s more, I wanted to investigate non-lethal ways of measuring condition of juveniles to determine which estuarine areas produced the healthiest fish. Fortunately, I found that length-weight ratios were suitable for measuring condition of summer flounder and striped bass (Fulton’s condition factor and relative condition, respectively). Atlantic croaker condition was easily measured with the Distell fish fatmeter, which uses microwaves to measure lipids stored under the skin.
Juvenile fishes were using a variety of habitats, but these habitats were not equally suited to produce healthy fish. In fact, some of the areas most commonly used by these species produced fish in the lowest condition. For example, although the abundance of juvenile Atlantic croaker is high in the lower James River, a tributary of Chesapeake Bay, these fish were in much lower condition than the fewer juveniles that used the main stem of the Bay. But that doesn’t mean the James River is poor habitat for all juvenile fishes. In fact, juvenile summer flounder from the James were among the healthiest. Interestingly, regardless of where juvenile striped bass were found, they were usually in similar condition.
Even though all three species had suitable habitat in Chesapeake Bay estuaries, producing healthy juveniles prepared for coastal migrations or enduring the cold winters in Chesapeake Bay is another issue. The majority of Atlantic croaker was in high condition and well prepared for migration, and striped bass condition was steady throughout the year and didn’t decline due to winter temperatures, but summer flounder told a different story. Throughout the summer, juvenile flounder continuously declined in condition and were actually the least healthy nearing the time to migrate to the continental shelf.
Ultimately, identifying nursery areas that produce healthy juveniles with a better chance at surviving will help focus conservation efforts to protect vital nursery estuaries. Alternatively, areas with large numbers of fish that are in poor condition could benefit from remediation to help increase production and maintain sustainable fisheries.
This article was originally posted in July 2014 in the American Fisheries Society Estuaries Section newsletter.
