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Fish need wilderness reserves in which they can grow old

Posted January 20, 2016

Permanent marine protected areas and wilderness are critical to the effective protection of marine fish, according to a study conducted by the Wildlife Conservation Society, James Cook University, and Lancaster University.


Unlike previous research that focused primarily on the weight of fish (biomass) as a measure of reef recovery, this study evaluated the life histories of fish, such as growth rates and length.

The researchers found:

  • Fish life history characteristics recovered at a much slower rate than biomass, which typically took 20 years to recover;
  • The time needed to fully recover from overfishing can exceed 100 years;
  • Young and small marine parks fall short of protecting ocean fish communities.

The findings underline the importance of permanent marine protected areas and wilderness in the effective protection of marine fish.

The study combined fish censuses from more than 300 coral reefs to examine how they changed in terms of fishing methods as well as how many years reef reserves had been closed to fishing.

They also compared the reefs in marine reserves with the remote Chagos Archipelago, a relatively pristine marine ecosystem off limits to exploitation due to its status as a large military base in the Indian Ocean.

The authors built on previous work that had largely concluded that recovery times for reefs can be reliably based on the biomass of the fish.

When looking at this and other factors, the authors found that biomass was one of the few measures that leveled after a limited number of years, whereas metrics including body sizes, age, and feeding habits continued to change for 40 years and growth rates were projected to decline for over 100 years.

The study appears in the online version of Proceedings of the Royal Society B. The authors are: Tim R. McClanahan of WCS; and N.A.J. Graham of James Cook University and Lancaster University.

Professor Nick Graham of Lancaster University’s Environment Centre, co-author on the study said: “If you want to protect the longer-lived, slower growing species, you need old, large, and high compliance marine reserves. The effective protection of the full suite of fish species and life history characteristics will depend on the establishment of large reserves with strict enforcement.”

“Fish biomass has been the common way to evaluate fish communities, but what our research shows is that it does not tell the entire story,” said Dr. McClanahan, Senior Conservationist for WCS and co-author of the study. “Analyses based primarily on fish biomass produces an incomplete and somewhat misleading scenario for fast recovery from overfishing. What we found in our study was a slow and continuous reorganization of the fish community well past the stabilization of biomass. A full evaluation of marine reserves needs to look at the life histories of the fish species and, when we do that, we see the important role of protecting ocean wilderness and making permanent and large reserves.”

“By giving marine managers a reliable assessment of how fish life histories influence reef health, the authors have completed the how-to manual for rebuilding fish communities that we all rely on,” said Dr. Caleb McClennen, Executive Director of WCS’s Marine Conservation Program.

Source: Lancaster University

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