Hakai Magazine

Coastal science and societies

A diver swims with fish in a marine reserve in Belize. Photo by Norbert Wu/Science Faction/Corbis
A diver swims with fish in a marine reserve in Belize. Photo by Norbert Wu/Science Faction/Corbis

Are Marine Reserves Working?

A new scientific review explores if marine reserves are doing what we hoped.

Authored by

by Becca Cudmore

Article body copy

Near the turn of the millennium, marine conservationists veered from thinking about protecting individual species to a more holistic view: protecting ecosystems. Facing harsh statistics—half the world’s fish stocks were fully depleted by 2004, and big predatory fish have declined 90 percent globally since record keeping began—this new thinking asked: rather than preserving single creatures, why not sustain the whole system on which they thrive?

From just five no-public-access marine refuges in the early 1900s, and the first “no take” area near the US Virgin Islands established in 1961, the number of marine reserves on the planet has since swelled. Of the various forms of marine protected areas, marine reserves are the ocean’s only “no touch, no take” zones. Within these underwater havens, all extractive (read: fishing) and destructive (read: oil drilling) activities are completely expelled. Globally, they account for less than one percent of the ocean. For comparison, national parks and wildlife preserves safeguard 12 percent of the land.

Though prized among conservationists, these new marine reserves are not always welcomed with open arms. For some fishermen, for instance, reserves pose an insurmountable restriction.

Marine reserves are highly political, but underlying the concept is scientific hope—that protecting an ecosystem will conserve species, boost fisheries yields in neighboring water, and create a system that sustains both ecological and human interests.

It’s been 15 years since marine reserves took off in earnest, and last month fisheries ecology PhD candidate Lewis Barnett and marine ecologist Marissa Baskett published a review of the science of marine reserves.

We asked the scientists to give us the gist of the latest scientific understanding of these oceanic refuges.


Are all reserves the same?

The size, design, and spacing between reserves influence their success. Fish don’t need wildlife corridors to move between safe zones like terrestrial animals do, but spacing still matters. The bigger a reserve’s area relative to the range of the fish species it targets, the more genetic diversity it sustains, says Baskett.

But the ecosystem, and the target species, always dictates the design. One species of intensively harvested rockfish, for instance, has only a small home range off the North American west coast. The Atlantic cod, in comparison, goes on impressive large-scale migrations. While a reserve to protect the rockfish might be big enough to protect its adult home range, a reserve targeting Atlantic cod would focus on localized spawning or feeding grounds.

Are marine reserves doing their job?

Within these small slices of protected sea, we know that fish populations are denser than outside of them, Baskett says. “And for certain fish genotypes, scientists also see greater diversity within reserve boundaries.” This assortment of mixed genetics is essential to keeping a population healthy and able to adapt to environmental change. On the other hand, the prey of reserve-protected fish can actually decline, due to the stronger predator population.

Reserves also grant fish a safe place to mature. Commercial fishermen often seek the biggest fish in the sea. This bias for what are sometimes termed “Big Old Fat Fecund Female Fish,” or BOFFFFS, hampers future fish populations and can selectively drive fish to mature earlier. “Fish basically [have] to reproduce before they’re harvested,” Baskett says. This fisheries-induced evolution means fish have been getting smaller. Marine reserves are starting to reverse this trend.

Do reserves benefit fishermen?

Unlike many terrestrial conservation efforts, marine reserves have an added goal of supporting a sustainable fishing community. “Fish move a lot,” Baskett says, so there’s a strong connectivity between protected areas and those open to fishing. “These different types of areas are constantly affecting each other.”

By restricting harvest in certain portions of the ocean, “reserves may help grow source populations of fish for both areas,” Baskett says. Ocean anglers are actually known for “fishing the line,” or casting their poles and nets along a reserve’s edge. To a fisherman’s benefit, this boosts the odds of “catching those bigger fish that flip over the reserve boundary,” she says. In the interest of marine life, this nips fishermen’s freedom to trawl the entire ocean floor.


Lauren Wenzel, the director in charge of marine protected areas for the US National Oceanic and Atmospheric Administration, says that the latest science shows that marine reserves are essential for achieving specific ocean conservation goals, such as restoring our most heavily harvested fish populations and protecting some of the biggest, oldest individuals in them. But the science also reminds us, she says, that reserves have limitations. We do not know how these human-free zones will respond to the threats of land pollution and climate change.

Most importantly, Wenzel says, Baskett and Barnett’s review is a crucial reminder that scientists need to continue monitoring and evaluating the state of our oceans.

Marine reserves have had 15 years to prove themselves, but scientists have a lot to do to understand their total influence on the ocean. Ecosystems reveal change slowly—“The cascading effects throughout a whole community,” Baskett says, “tend to take a bit longer to see.”