For the multibillion-dollar marine park industry, the decision has implications far beyond the fates of these 18 belugas. It is part of a darkening picture for the industry.

This summer has been a rocky one for marine parks generally, as the NOAA decision followed—by just 10 days—the opening of the documentary film Blackfish, an exposé of cruelty, dishonesty, and worker abuse by SeaWorld, the biggest player in the business. The film details the deaths of three humans caused by SeaWorld's killer whale Tilikum, the biggest orca in captivity, and the company's cover-up of these homicides. (Related: "Opinion: SeaWorld vs. the Whale That Killed Its Trainer.")

Environmentalists and animal-rights activists, long opposed to the captivity of marine mammals for human entertainment, are