ESNERR freshwater ecologist, Nina D’Amore, and UCSC graduate student Valentine Hemingway are actively researching different aspects of California red-legged frog ecology here on the Central Coast. As part of these research efforts, they have been conducting a mark-recapture study since 2005, with approximately 150 frogs tagged on the Reserve and an additional 500 tagged in another part of the watershed.
This means going out to each pond at night (at least once a season) to capture
as many individuals as possible. Each time they catch a frog, they measure its length, weigh it, mark it with a Passive Integrated Transponder (PIT) tag inserted under its dorsal skin and take a small skin swab to test for amphibian disease. Each time an animal is recaptured, they are then able to find out how much it has grown, how long it has survived, whether its disease status has changed and whether it has moved between different ponds.Nina then enters each animal’s recapture history into a computer program, MARK, and through some mathematical modeling is able to estimate how well frogs of different age and sex categories survive. Below you can see the estimate of seasonal (3 month) survivorship for three different categories of frog here on the reserve: juveniles, adult males and adult females.
With the detailed disease information that Valentine has collected, she may later be able to tease apart how amphibian disease, like amphibian chytrid, affect survivorship of these threatened amphibians. For more information about amphibian chytrid, please click here. For more information about Valentine’s research, please click here.
Other past amphibian research projects from the reserve examined how habitat characteristics and human alteration of the landscape affect the distribution of amphibian species in the Elkhorn Slough watershed, whether California red-legged frogs exhibit metapopulation dynamics and how invasive American bullfrogs impact the behavior and habitat use of California red-legged frogs.
Another aspect of our ongoing freshwater conservation efforts focuses on habitat restoration. Our basic research has identified a suite of factors that are problematic for amphibians in our watershed, particularly California red-legged frogs. These factors include: high nutrient levels, invasive species (such as bullfrogs and invasive fish species), inadequate hydroperiod and lack of connectivity to other sites. We have used our knowledge of freshwater habitat throughout the watershed to prioritize restoration efforts. We focus our restoration on sites that: 1) have suffered an obvious decline in amphibian populations 2) are natural sites, rather than man-made 3) have multiple listed species and most importantly 4) have a clear-cut problem that is within our power to change. For an example of some of this work, please read our case-history of restoration efforts in one ESNERR site, Lower Cattail Swale.
Case history – Lower Cattail Swale
Cattail Swale is the largest pond on the reserve, at nearly 2 acres. This pond has provided important breeding habitat for two amphibian species protected under the Endangered Species Act: California red-legged frogs and Santa Cruz long-toed salamanders. Populations of these animals have been present since at least 1997, when rigorous monitoring of amphibian populations at the reserve began. Pacific chorus frogs are also known to breed in the pond in high numbers. Over the past ten years of monitoring data, there have been maximum nightly adult California red-legged frog counts of over 300 individuals seen in the pond and hundreds of larval and metamorphosing Santa Cruz long-toed salamanders seined and dip-netted in the site by UC Davis researcher Wesley Savage. Savage’s work indicated that this Santa Cruz long-toed salamander population is genetically distinct from other local populations and therefore has high conservation priority.The counts of amphibians in Lower Cattail Swale began to fall between 1999 -2001 and this change in numbers was coincident with noticeably higher levels of sediments and nutrients in the water.
Much of the water that filled the site was thought to come directly off of upstream strawberry fields. The hypothesis about the origin of water in the site was confirmed in 2007 when the Elkhorn Slough Foundation was able to buy the farm directly upstream from Lower Cattail. As a condition of the sale, it was taken out of production and a cover crop was planted on the slopes above the pond. The intention was to reduce the amount of agricultural contaminants and sediments being fed into the pond and to allow the water table to recover from overdraft. With this change in land-use, the clarity of the water was significantly improved, but the amount of water in the pond was drastically reduced. In 2008, Lower Cattail Swale had a maximum depth of less than a foot, down from over six feet in other years. It dried down much too early to support amphibian breeding.
In order to tackle this new problem, we hired Ivano Aiello of Moss Landing Marine Labs to create a detailed topographic map of the pond using terrestrial laser scanning. We were then able to procure permits and excavate a small pond within the greater Lower Cattail Swale site, in the deepest existing portion of the pond. This deepened area should hold water longer, provide more suitable breeding habitat and allow some of the amphibian larvae time to metamorphose. If there are amphibian larvae in the smaller pond and it seems in danger of drying, we could easily supplement water to this smaller pond in a way that would be impossible for Cattail Swale as a whole.
We track the distribution, reproduction, and abundance of three frog species (California red-legged frog, Pacific chorus frog and invasive American bullfrogs) throughout the watershed and monitor the quality and characteristics of their habitats. We currently monitor approximately forty different freshwater sites, owned by a variety of organizations and private individuals. We carry out: 1) daytime surveys of aquatic habitats to monitor water quality and characterize pond attributes such as pond size, vegetative cover and upland habitat type; 2) dip-netting and seining for larval amphibians 3) evening listening surveys to identify sites used by breeding males; and 4) night-time eye shine surveys to assess adult population size.