Fishing pressure blamed for depletion of old fish

Source: Xinhua| 2017-09-20 14:50:30|Editor: Yang Yi
Video PlayerClose

SAN FRANCISCO, Sept. 19 (Xinhua) -- A study by University of Washington (UW) researchers has found that for dozens of fish populations around the globe, old fish are greatly depleted, mainly because of fishing pressure.

Like old-growth trees in a forest, old fish in the ocean play important roles in the diversity and stability of marine ecosystems. The longer a fish is allowed to live, the more likely it is to successfully reproduce over the course of its lifetime.

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. Older fish in a population have more years to produce eggs, increasing the chance for success over time.

In the new study, published online in Current Biology, the researchers looked at model output gathered from commercial and recreational fisheries and scientific observations that describe the status of fish populations over the years and analyzed 63 populations living in five ocean regions worldwide.

They found that the proportion of fish in the oldest age classes has declined significantly in 79 to 97 percent of populations, compared with historical fishing trends or unfished figures, respectively.

And the magnitude of decline was greater than 90 percent in 32 to 41 percent of the groups.

The decline is mainly due to fishing pressure, according to the researchers. In general, the longer a fish lives, the more encounters it has with fishing gear, and the greater the likelihood it will be caught.

Meanwhile, some environmental factors like disease and pollution might also contribute to the loss of old fish.

To impact fisheries management, the authors suggest fishing methods to protect young and old fish by prohibiting the harvest of fish below and above a specific size range, closing certain areas to fishing permanently, or rotating areas where fishing can take place each year to let fish grow older and bigger.

"In the marine world, the success rate of producing new baby fish is extremely variable," co-author Trevor Branch, a UW associate professor of aquatic and fishery sciences, said in a news release. "I think of old fish as an insurance policy - they get you through those periods of bad reproduction by consistently producing eggs."

TOP STORIES
EDITOR’S CHOICE
MOST VIEWED
EXPLORE XINHUANET
010020070750000000000000011100001366239331