In one small canyon, on one small Island, there is a unique snail called the Catalina Mountainsnail (Radiocentrum avalonense). This species, one of the rarest land mollusks in the Channel Islands, is listed as Critically Endangered by the International Union for Conservation of Nature. It is only found on steep south-facing slopes on the southeast side of Catalina Island and, on a late January morning, that is exactly where a team of biologists, along with Catalina Island Conservancy Wildlife Biologist Emily Hamblen spotted this incredibly rare species.
“We were pretty excited, particularly when you realize that this particular snail has only been seen a couple of times over more than 100 years,” said Charles Drost of U.S. Geological Survey, one of the team members. “In talking about this afterwards, we realized that there have been fewer than five people who have ever seen this species alive. It is all the more special that this snail is so distinctive, is only found on Catalina, and only on a small area of the Island. This speaks to the importance of this area, and this habitat, to the native land snails of the Island – and probably to other members of Catalina’s unique native plants and animals, as well.”
The species is distinctive not only due to its scarcity, but also its visually unique aspects. The Catalina Mountainsnail is small, with a height of 6-8 mm and diameter of 11-14 mm (about half an inch). The shell is comparatively ornate and sculptured, as well as resting on a slight angled bias. The species also occupies a distant, lonely outpost, as it nearest relatives are 300-500 miles away, in the mountains of southeastern Arizona and central Baja California, Mexico.
The Catalina Mountainsnail was originally described in 1905, based on specimens found on Catalina in 1902 by a shell collector named Henry Hemphill. It was believed to be extinct until 1982, when Drost’s colleagues, Barry Roth and Eric Hochberg of the Santa Barbara Museum of Natural History, found both shells and live individuals.
“Between that time and now, the species continued to be almost unknown,” Drost added.
A trip to the Island last September produced empty Mountainsnail shells, but the researchers didn’t give up. With the assistance of the Catalina Island Conservancy, the group set out again in January, this time with great success.
“There is still so much to learn about the land snail fauna of the Island,” said Drost, who added that it is not even certain yet how many different snail species are present on the Island, let alone such things as their overall distribution, what habitats they occur in, their relative abundance and trends in numbers.
“One of the motivations [of this research] is to gain a more complete understanding of the land snails of the Channel Islands in part for scientific knowledge, but also for conservation,” said Drost.
The snail species of Catalina primarily feed on dead plant material and leaf litter, helping to build and enrich the Island’s soil. Currently, a total of 27 land, freshwater and semi-aquatic snail and slug species are known on Catalina Island (including 10 non-native species).
Of the 13 native land snail species, eight are endemic to the Channel Islands, and five are found only on Catalina — found nowhere else in the world.
“It’s a group that has the highest rate of endemism of any plant or animal group that occurs on the Islands,” Drost continued. “These are unique species that literally can’t be replaced.”
