Mollusks on the Move

On a stretch of shore northwest of Santa Barbara, success looked no bigger than a half-dollar. Well, three half-dollars to be precise. This February, researchers from the University of California, Santa Cruz spied a trio of diminutive black abalone clinging to sharp rocks, holding their own against the tides.

They were the first juveniles detected following the experimental move two years earlier of 250 adults from the Channel Islands, an archipelago off the coast of Ventura that is largely managed by the National Park Service. Reaching this milestone was no mean feat: It required decades of data collection, collaboration across agencies and a certain amount of dogged optimism on behalf of a beleaguered species.

Black abalone are marine mollusks that range in hue from onyx to cerulean and max out at about 8 inches in length. The species is historically significant to the Chumash people, who for millennia harvested the snail for food and used its distinctive shell for ceremony, trade and decoration. Thriving in the turbulent intertidal zone from the southern tip of Baja California in Mexico to northern California, the oblong creatures once numbered in the millions, their presence a visual touchpoint for many people growing up along the coast.

Over the last century, however, the fate of the abalone took a decidedly downward turn. First came the fishermen, rapacious in the face of a seemingly inexhaustible supply of the single-shelled delicacies. Then in the 1980s, a disease that causes death by starvation began its northward march through the abalone’s range. The devastation was particularly acute in the Channel Islands. “They were going from thousands and thousands to, like, three, essentially overnight,” said Pete Raimondi, a professor at UC Santa Cruz who has been studying the mollusk for more than 30 years. “There were just piles of shells everywhere.”

Though the harvesting of black abalone was outlawed in California in 1993, poachers kept collecting them. In 2009, the animal’s outlook was so dire that the snail became just the second marine invertebrate designated as a federally endangered species. The National Marine Fisheries Service appointed experts to map out a recovery plan, but disaster — in the form of devastating landslides in 2017 and 2020 — continued to plague the abalone. “These guys don’t move very fast, so they can’t get out of the way of bad things,” Raimondi said.

When the debris flows entombed some abalone and threatened many others, staff from a host of agencies embarked on a series of risky rescue missions. The animal attaches itself to intertidal crevices using its muscular foot, which is the most visible part of its body. If that foot is sliced in the process of prying the creature from its rock of choice, it can easily die. “There was a concern up until that point that you couldn’t move black abalone because they were too fragile,” said Walter Heady, a senior scientist with the Nature Conservancy’s California chapter. As the alternative to human intervention was certain burial, the rescuers took a chance. They managed to free a few hundred snails and return them to the wild. Since the species has never been successfully propagated in the lab, the scientists’ best hope was that those released would spawn on their own.

Members of the recovery team — newly confident in the animal’s hardiness — began eyeing non-emergency translocation as a viable restoration option for the species. When compensatory mitigation funding from a 2015 oil spill materialized, Raimondi and others proposed relocating abalone from an area teeming with mollusks to a site with low densities. The question became: Where would they collect the transplants?

Fortunately, staff at Channel Islands National Park have been monitoring black abalone on four of the park’s five islands since the early 1980s and on Santa Cruz Island since 1994, said Stephen Whitaker, the park’s lead marine ecologist and a member of the species recovery team. “Our data were critical for identifying populations of black abalone that were robust enough to serve as donor populations for restoration efforts,” he said.

The healthiest abalone communities wound up being on a section of Santa Cruz Island’s coastline where the marine snails could be found stacked three high in places. Whitaker’s data indicated that the population had been slowly, if mysteriously, rebounding since 2015. (Though the Park Service monitors all of Santa Cruz and has jurisdiction over the waters from the shoreline to 1 mile offshore, it owns only 24% of the island’s land mass. The rest, including the abalone donor site, is owned by the Nature Conservancy.)

As for where they would release the abalone, the scientists had a ready answer for that, too: the Jack and Laura Dangermond Preserve, where only a few dozen snails remained. Located on a jut of mainland north of the Channel Islands, this 24,000-acre Nature Conservancy property is closed to the public and free from poachers. Better still, with 30-odd years of Dangermond monitoring data in Raimondi’s figurative pocket, “we knew where the black abalone used to live, I mean, to the crack,” he said. “So it was really easy to figure out what the best places would be to put animals back.”

Nate Fletcher, who works with Raimondi as a research specialist, coordinated the first black abalone translocation in March 2023, followed seven months later by a second. Each time, the process took about four days, from the initial survey at Dangermond to the collection of the animals on Santa Cruz Island to their transfer via coolers and boats to a lab in Santa Barbara where they were weighed, measured, tagged and genetically sampled, to their placement the following day in the preserve. Incredibly, 246 of the 250 individuals collected survived the ordeal.

Fletcher and his colleagues returned to Dangermond monthly for the first year to check on the new inhabitants before throttling back to quarterly visits. The abalone haven’t made the respotting particularly easy. Not only did they immediately crawl into new homes, but some managed to shed their identifying tags while nestling between rocks. Add the fact that other organisms can grow on abalone shells, further camouflaging them, and “they can be pretty cryptic,” Fletcher said.

Despite the challenges, the monitoring team routinely counts 70% or more of the transplants each visit. But one thing they hadn’t clocked before February was a juvenile. Until genetic testing is complete, Fletcher can’t say for sure whether the three glimpsed this winter are the product of the relocated abalone or of the 50-odd mollusks that were already there, but the size was right for animals spawned after the move. If success is defined by two criteria, namely survival and reproduction, Raimondi said, “I think we’ve got them both.”

Members of the species recovery team are now considering future translocations. The overall goal, Heady explained, is to establish strongholds of black abalone along the mainland and throughout the Channel Islands so that subsequent generations of what he calls this “very charismatic invertebrate” might one day recolonize its historic range.

“This body of work highlights the importance of protected lands and waters for the recovery of imperiled species,” Heady said. “In this case,” he added, the conservation of Santa Cruz Island “facilitated the natural recovery of black abalone populations to the larger region.”