White abalone, which once numbered millions along the California coast, are on the brink of extinction following decades of overfishing, researchers say. Overfished until protections were put in place in the 1990s, the endangered shellfish has experienced ongoing population declines, scientists for the National Oceanic and Atmospheric Administration reported. Underwater surveys found a 78 percent drop in the number of white abalone off the coast of San Diego since 2002, with most of those remaining either so old or isolated from one another they can no longer reproduce, the Los Angeles Times reported Wednesday. Without the ability to spawn a new generation, the abalone, which can live as long as 35 years, will not be able to recover on their own, researchers said. \"At this point, without human intervention, the species could go extinct within our lifetimes,\" study co-author Melissa Neuman of NOAA\'s National Marine Fisheries Service said. The researchers urged \"immediate, proactive conservation\" by breeding white abalone in captivity and releasing them in the wild. \"The case of the white abalone,\" they wrote in the journal Biological Conservation, \"illustrates that marine invertebrates, and particularly species with high commercial value, are unarguably vulnerable.\"