Like old-growth trees in a forest, old fish in the ocean play important roles in the diversity and stability of marine ecosystems.
(From Science Daily) — Critically, the longer a fish is allowed to live, the more likely it is to successfully reproduce over the course of its lifetime, which is particularly important in variable environmental conditions.
A new study by University of Washington scientists has found that, for dozens of fish populations around the globe, old fish are greatly depleted — mainly because of fishing pressure. The paper, published online Sept. 14 in Current Biology, is the first to report that old fish are missing in many populations around the world.
“From our perspective, having a broad age structure provides more chances at getting that right combination of when and where to reproduce,” said lead author Lewis Barnett, a UW postdoctoral researcher at the School of Aquatic and Fishery Sciences and the Joint Institute for the Study of the Atmosphere and Ocean.
In forestry, a tree farm with only 20-year-old trees may be healthy and productive, but the loss of old-growth trees should not go unnoticed. The giant trees have unique traits that support a number of animal and plant species and make for a diverse, robust ecosystem. In a similar sense, the same is true for old fish.
“More age complexity among species can contribute to the overall stability of a community,” Barnett said. “If you trim away that diversity, you’re probably reducing the marine food web’s ability to buffer against change.”
The designation of an “old fish” varies from species to species, depending on life history. Some types of rockfish might live to 200 years, while few herring live past age 10.
After female fish release eggs, many factors must align for a healthy brood to hatch and grow to adult size. Because the marine environment is so variable, species might go a whole decade between successful broods. Older fish in a population have more years to produce eggs, increasing the chance for success over time.
“In the marine world, the success rate of producing new baby fish is extremely variable,” said co-author Trevor Branch, a UW associate professor of aquatic and fishery sciences. “I think of old fish as an insurance policy — they get you through those periods of bad reproduction by consistently producing eggs.”
In addition to having more opportunities to reproduce, older fish also behave differently than younger fish. As they age, some fish change what they eat and where they live in the ocean…
Read the full article here: https://www.sciencedaily.com/releases/2017/09/170914152343.htm