While targeted conservation efforts seeminly boost threatened animal populations, researchers suggest permanent marine protected areas, in which fish can thrive and grow old, are a vital component of conservation that is often overlooked. A new study led by the Wildlife Conservation Society (WCS), James Cook University, and Lancaster University revealed that focusing primarily on the weight or biomass of fish is not an accurate measure of reef recovery.

"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," Dr. McClanahan, co-author of the recent study and a Senior Conservationist for WCS, said in a news release. "Analyses based primarily on fish biomass produces an incomplete and somewhat misleading scenario for fast recovery from overfishing. What we found 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 species and their life histories and, when we do that, we see the importance of protecting ocean wilderness and making permanent and large reserves."

For their study, researchers examined fish census of more than 300 coral reefs to evaluate how they have responded to fishing regulations implemented to better protect them. Additionally, researchers compared reefs located in marine reserves to those along the remote Chagos Archipelago, which is a relatively untouched marine ecosystem located in the Indian Ocean and off limits to exploitation due to its status as a large military base.  

Their analysis revealed a slow, long road to recovery: While biomass measures leveled off after a fairly low number of years, other factors such as age, feeding habits and body size continued to change for approximately 40 years, and growth rates would continue to decline for more than 100 years.

"The slow-growing species in marine reserves could require a century to fully recover, indicated the importance of permanent and large reserves," McClanahan explained.

"If you want to protect the longer-lived, slower growing species, you need old, large, and high compliance marine reserves," co-author Nick Graham added. "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."

When examining how the size of a protected area, the length of closure time, and how successful the protected area was at eliminating fishing combined to impact a species' overall recovery, researchers found closures with weak compliance recovered to only half the biomass levels of the high compliance closures and also produced small and younger fish. This, researchers say, indicates an incomplete recovery. 

"With governments around the world committed to protect 10 percent of the oceans by 2020, this study provides important insight into the long term horizon needed to fully realize the benefits of today's ocean conservation efforts," Dr. Caleb McClennen, Executive Director of WCS's Marine Conservation Program, said. "The importance of designing scientifically defensible large marine reserves only solves the first pieces of the equation - long term capacity to enforce and ensure compliance will take the long term focus of the ocean conservation community."

Their study was recently published in the Proceedings of the Royal Society B.

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