The black abalone’s road to recovery has been long and brutal. In the 1980s and 1990s, mass mortality events swept across most of the species’ range, driven by withering syndrome, a fatal disease caused by the bacterium Candidatus Xenohaliotis californiensis. In many areas, populations crashed by more than 95 percent. The species was listed as endangered under the U.S. Endangered Species Act in 2009, and the National Marine Fisheries Service published a formal recovery plan in 2020 that identified translocation as a key restoration tool. Yet the approach remained stalled for years by regulatory hurdles, logistical challenges, and genuine biological risks, including the potential to spread disease, disrupt local genetics, or harm donor populations.

What changed, according to the researchers, was a convergence of new evidence that tipped the risk-benefit calculus. The threat of withering syndrome appears to have lessened, with signs of genetic resistance in surviving populations and the discovery of a bacteriophage that reduces the lethality of the pathogen. Population genetics work revealed low genetic structure and high diversity among California black abalone populations, easing concerns about mixing animals from different sites. Meanwhile, two coastal sedimentation events had served as emergency test cases, demonstrating that abalone could be removed and moved without substantial injury or death. And crucially, several populations on the California Channel Islands had recovered to densities high enough to serve as donor sources, since black abalone have never been successfully reared in captivity.

The project was made possible by decades of data from the Multi-Agency Rocky Intertidal Network, or MARINe, a partnership that has monitored black abalone populations since the early 1980s. These long-term records allowed the team to select a restoration site with a documented history of a large pre-disease abalone population, and donor sites with abundant, healthy animals. The Dangermond Preserve was an ideal destination: it had high-quality habitat, restricted public access that prevents illegal harvest, protection within a no-take State Marine Reserve, and proximity to the healthy donor population on a nearby Nature Conservancy preserve on Santa Cruz Island. Funding came from the Refugio Beach Oil Spill Damage Assessment and Restoration Plan, with additional support from The Nature Conservancy.

The translocation itself was executed in two phases in 2023. In March, 115 abalone were collected from one donor site, and in October, 135 more were taken from a second, even denser site. Animals ranging from 60 to 130 millimeters in shell length were pried from the rock with abalone irons and thin metal spatulas, tagged with numbered Floy tags and colored epoxy, measured, weighed, photographed, and sampled for genetics before being transported across the channel in coolers lined with damp towels. Total transport time was about six hours, and animals were held in flow-through seawater tanks for 38 to 60 hours before release into ten pre-established crevice plots where habitat had been restored by clearing encroaching mussels, sandcastle worms, and other fouling organisms.

Survival through the entire collection-to-release process was remarkably high. In Phase 1, the pre-release mortality rate was 2.6 percent, with nine abalone requiring rehabilitation at a state wildlife veterinary facility; eight of those recovered and were released weeks later. In Phase 2, after the team refined its techniques by timing collections with the outgoing tide, targeting animals that were not yet clamped tightly to the substrate, and using thinner removal tools, mortality dropped to 0.74 percent. Detailed injury assessments showed that 36 percent of Phase 2 animals had no injuries, 49 percent had mild scrapes, and 16 percent had moderate injuries, with none classified as severe. Notably, injured animals survived at rates similar to uninjured ones, overturning the long-held assumption that even a small foot cut would likely kill a black abalone.

Post-release monitoring delivered the most striking numbers. Assuming no crypsis, meaning abalone hiding in crevices where surveyors could not see them, retention of translocated animals stood at more than 80 percent three years after release. When adjusted using conservative crypsis rates from prior abalone studies, which range from 28 to 63 percent, true retention was likely close to 100 percent. Site-wide surveys found the mean density of abalone in high-quality habitat rose from 0.2 per square meter before the translocation to 1.0 per square meter by 2026, right at the threshold scientists consider necessary for successful broadcast spawning, in which densely aggregated adults release gametes into the water column for external fertilization. Densities within the restored plots stabilized at 3 to 5 per square meter, well above the team’s long-term target of 2 per square meter.

The translocated abalone moved more than the researchers expected, with some individuals traveling 20 to 30 meters in a single day. That unexpected mobility scrambled the experimental design, which had intended to compare plots receiving only habitat restoration against plots receiving both restoration and abalone. But it also produced a valuable insight: abalone showed a strong preference for restored habitat, with densities inside cleared plots roughly 10 to 30 times higher than in adjacent unrestored habitat of the same quality. The finding suggests that habitat restoration, particularly clearing mussels and sandcastle worms that colonized crevices after sea star wasting disease removed a key predator of mussels, should be built into future translocation efforts. Donor populations, meanwhile, showed no detectable impact, with removals representing less than 1 percent of local abundance and far below the 10 percent allowed by permits.

Perhaps the most exciting discovery came in February 2025, when researchers found three juvenile abalone, 25 to 35 millimeters long, in the West Block, followed by more juveniles in subsequent surveys, including twelve in February 2026. No juveniles had been observed at the site since disease-related declines began in 1993. Given typical juvenile growth rates of 10 to 20 millimeters per year, the sizes align with animals settling roughly two years after the translocation, raising the tantalizing possibility that the translocated adults are already reproducing. Genetic parentage analyses, using tissue samples collected from adults and minimally invasive swabs from some juveniles, will be needed to confirm whether the young abalone are offspring of the translocated population or recruits from elsewhere.

The researchers caution that it is too early to declare full victory. Conservation translocations fail 50 to 70 percent of the time, and true recovery success will require decades of monitoring to confirm population growth, self-sustaining recruitment, and eventual spillover of larvae to neighboring areas, in line with the federal recovery plan’s metrics. Still, the team has clearly achieved the first stage of establishment, and the effort demonstrates a model that could reshape endangered species recovery more broadly. By embedding the translocation within a decades-old monitoring network and leveraging partnerships among federal and state agencies, universities, and nonprofits, the team moved quickly and efficiently while keeping risks low. The next challenge is scale: mainland southern California populations remain critically sparse 30 to 40 years after the disease declines, and expanding translocations to that densely populated coastline will require substantial public engagement and support. For now, though, a few hundred relocated sea snails have shown that with patience, data, and cooperation, even a species on the brink can be given a second chance.

Subject of Research: Conservation translocation of endangered black abalone as a population restoration tool

Article Title: Translocation of endangered black abalone (Haliotis cracherodii) as a population restoration tool

Article References: Fletcher, N. C., Miner, C. M., Heady, W. N., & Raimondi, P. T. (2026). Translocation of endangered black abalone (Haliotis cracherodii) as a population restoration tool. Frontiers in Conservation Science, 7, Article 1952618. https://doi.org/10.3389/fcosc.2026.1952618

Image Credits: AI Generated

DOI: 10.3389/fcosc.2026.1952618

Keywords: black abalone, conservation translocation, endangered species, withering syndrome, rocky intertidal, habitat restoration, MARINe, population recovery, California Channel Islands, marine conservation, recruitment, Dangermond Preserve