A special type of marine protected area (MPA) called a “no-take zone” bans the removal of marine life from designated areas. At first glance, they seem like a hard sell to fishermen and other people who make a living from harvesting fish. But scientists have found again and again that they ultimately result in more fish, benefiting local people and fostering healthier ecosystems.
No-take zones are not walled-off aquariums surrounded by thick glass; instead, these protected havens allow healthy fish to come and go. The migration rates are especially high during the fishes’ young larval stages. Fishermen, therefore, can take advantage of the fish moving across the no-take zone boundary, a phenomenon called “spillover” and collect greater numbers of fish that settle in homes outside these protected zones.
It sounds good in theory, but it can be hard to convince local fishermen that closing off a portion of their fishing ground indefinitely will bring more fish. So scientists have proven it by studying fish populations in and around no-take zones all over the world.
Among these scientists is ecologist Dr. Glenn Almany of the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Australia. His team works in a part of the Great Barrier Reef Marine Park called the Keppel Islands, where no-take fishing zones account for 28% of the local reef area. To determine how many young coral trout (Plectropomus maculatus) living in fishing areas were born to parents living within no-take zones, Dr. Almany and his team took advantage of rapid advances in genetics and used “parentage analysis”—paternity and maternity testing for fish.
In human paternity testing, doctors take cheek swabs from a father and child to determine their relatedness; in fish, scientists collect tissue from the fins of adults inside the protected area and juvenile fish living outside the boundaries. By comparing specific DNA markers, scientists can determine if the fish are related. In one study, Dr. Almany calculated that more than half of the coral trout living in the local reef area—up to 30 kilometers (18 miles) away—were offspring from the no-take zones.
Why do protected areas create more fish? The obvious answer is that, when protected from capture and imminent death, fish have more opportunities to reproduce. However, there could be a subtler but even more important reason: size matters.
Fish living in protected areas typically live longer and are consistently larger than fish in unprotected areas. Dr. Almany said that larger mothers will produce more babies, and “if the pattern holds, the numbers magnify,” sending out more larval fish to inhabit reef systems. Other studies have found similar patterns of increased fish size within no-take fishing zones worldwide, from the Red Sea to the waters off the California coast. The contribution of “big fat mammas” can be large; for example, a 20 inch-long coral trout produces 1 million eggs, whereas a coral trout only 3 inches longer at 23 inches can produce 3 million eggs.
Scientific evidence that marine protected areas boost fish populations, such as Dr. Almany’s research, may encourage countries to protect more ocean habitat. Right now, less than 2% of the world’s ocean is protected, and no-take zones comprise just half of that.
As no-take zones produce more fish, biodiversity should also increase, growing healthier ecosystems. Just as healthier humans are able to fight the flu more effectively during flu season, healthier coral reef systems are better equipped to combat threats such as coral bleaching events or coral disease—an effect known as reef resilience. This effect may be seen in other types of ocean ecosystems as well.
“Marine protected areas are critical to supporting fishing communities,” Almany explained. The more we can learn about the dispersal of larval fish from protected areas, the better we can manage these protected networks to create healthier ecosystems and more fish globally.