To be fair, few realized the extent to which recreational fishing can damage marine ecosystems. Commercial fishing, with its capacity to scoop up whole schools in a single trawl, or deploy thousands of hooks in a night, was perceived to be the enemy, not a bunch of weekend anglers trying to catch a feed. Only later, as fish numbers dwindled and some species became rare, was the scale of the problem realized.

A curious thing happens when fish stocks decline: People who aren't aware of the old levels accept the new ones as normal. Over generations, societies adjust their expectations downward to match prevailing conditions. The concept of a healthy ocean drifts from greater to lesser abundance, richer to poorer biodiversity.

For those who live through the changes, who witness the emaciation of the sea at firsthand, it is a dispiriting experience. "I take visitors out to the Poor Knights today, and they're so excited by the fish life they're just about walking on water," says Wade Doak, one of the country's pioneer divers and underwater naturalists. "And all I can think is that they're seeing a crumb, a skerrick of what it once was."

Marine reserves are an antidote to this collective amnesia. They provide a scientific benchmark against which changes in the wider ocean—the exploited ocean—can be measured. "If nothing is left intact or pristine, how can you know that damage has occurred?" Ballantine asks. Indeed, how do you even imagine an undamaged state?

Seen in this light, marine reserves are the reference collections of the sea, or, as Doak likes to call them, "wet libraries." Like libraries on land, they should be regarded as essential public amenities. And, as the Poor Knights experience shows, they must be fully protected. Allowing fishing in a marine reserve makes as much sense as allowing the most popular books in the library to be borrowed and never returned.

Doak dreams of the day when establishing marine reserves becomes as automatic as building a school in a new residential area, or opening a medical clinic, or planting a park.

We're not there yet. So far, the acquisition of most reserves in New Zealand has been a slow and contentious business involving the voluntary effort of community groups, dive clubs, conservation organizations, Maori communities, and even a group of high school students.

During the late 1980s, Ballantine traveled the country holding adult education courses for anyone interested. "The subject was marine studies, but everything was oriented to making marine reserves," he says. "Several small groups sprang up as a result, and some of those groups went on to propose reserves, and a few of those proposals were successful. This is the way it has been."

Ballantine likens the creation of a marine reserve to a drunk trying to get a key into a lock: "You have to be at the right door, and be holding the right key, but beyond that it's just persistence."