Science in Action: Threatened Amphibians of Elkhorn Slough

In California red-legged frog, Freshwater, Reptiles and Amphibians, Santa Cruz long-toed salamander, Science in Action Article by Administrator

October 2004 by Kerstin Wasson, ESNERR Reseach Coordinator

In the past years, we have documented a dramatic decline in California Red-legged Frog (CRLF) populations on the Reserve. On summer nights at the end of the last millennium, the eyeshine of hundreds of CRLF could be seen in the beam of a flashlight, and the waters teemed with their tadpole young. This past summer (2004), only a dozen adults were seen at the same pond, and extensive searches turned up but a single tadpole. This decline likely resulted from a number of contributing factors, interacting together: a spell of dry years, pollution from upstream agriculture, malformations induced by a trematode that embeds itself in limb buds, and a fungal infection.

Our research and stewardship teams realize that to better conserve threatened amphibian populations, we need to look beyond Reserve boundaries. We want to identify threats that may occur at larger spatial scales, so we can manage them appropriately, and we also hope to detect new opportunities for conservation, for instance source populations of threatened amphibians outside Reserve boundaries that could be linked through protected corridors.

From January to August, Reserve amphibian interns (and UCSC doctoral students) Valentine Hemingway and Nina D’Amore roamed the watershed and searched (with permission from local propeerty owners) for amphibians, their freshwater habitats, and threats to them. The results of this first season of regional amphibian monitoring are now in.

Overall, Nina and Valentine monitored 40 freshwater habitats (mostly ponds, but some riparian areas and marshes) in about a 5 mile radius from the Reserve. Unfortunately, they did not find a single abundant CRLF population in any of these. Thirteen of the ponds had a few CRLF adults, and eight of these were new records for the Fish and Game database that tracks listed species. However, only five of these thirteen ponds had successful CRLF reproduction, all in low numbers. These results are of concern, because central California is considered a stronghold for this threatened species, the last region with abundant, stable populations. Clearly in 2004, populations are neither widespread nor abundant in this area.

This map of freshwater ponds in this study. The white dots are freshwater ponds; the yellow dots are freshwater ponds with populations of CRLF.

What appears to be limiting the distribution and abundance of CRLF? Valentine and Nina carried out an analysis correlating CRLF presence with various habitat parameters. Most basically, CRLF do not breed successfully in ponds that dry down before June, and that was true for twenty of the forty ponds. So lack of available breeding sites may be one major factor. In addition, they found non-native bullfrogs at fourteen of the ponds – and did not observe successful CRLF reproduction in the presence of bullfrogs. Luckily, there were no bullfrog populations near the Reserve (or we would have culled them). However, bullfrogs are common at many of the otherwise appropriate ponds on the Packard Ranch, across the Slough; Nina is encouraging their eradication and monitoring the benefits to CRLF, as a part of her graduate research.

Other threats were also identified. Many of the ponds on private property were stocked with non-native, predatory fish (catfish, bass), and CRLF never breed successfully in their presence. Nina and Valentine also found that CRLF were absent from the most nutrient-enriched ponds (of which there were a few, probably due to agricultural inputs), and that ponds throughout the region were infected with the chytrid fungus.

In their regional survey, Valentine and Nina also found Santa Cruz Long-toed Salamanders (SCLTS) at four ponds, all of which were previously known to harbor them. These ponds are quite widely spaced throughout the watershed, and we had hoped to find new intermediate locations that might serve as connections between them. SCLTS have a very limited range, along the coast from Aptos to Moro Cojo, and face significant threats at their few breeding ponds. The four ponds with SCLTS either had bullfrog and introduced fish or high rates of malformations, and all receive agricultural runoff.

The results of this regional survey are sobering, and are motivating additional efforts by our stewardship and research teams to help threatened amphibians in the watershed. We have applied for grant funding to restore and enhance breeding ponds, and to cull bullfrogs, both on and off the Reserve. Outreach is also essential – as our ambassadors, you can do your part to talk to our neighbors and highlight the troubles these frogs and salamanders are facing, and the benefits to them of keeping ponds wet until August, and free of bullfrogs and large fish.