Stream-dwelling Amphibian & Invasive Species Monitoring

Light-colored frog with a brown line extending from its eye, blending in well with the rocks and leaves around it
Pacific tree frogs can be found in streams in the Santa Monica Mountains


Why We Care

When Inventory and Monitoring Program biologists survey the native frog, toad, or newt populations in the Santa Monica Mountains, we see a group of species that is uniquely vulnerable to changes in air and water quality. We see indicators of the health of the ecosystem. We see the impacts of urban development.

Urbanizing as little as just 8% of a watershed can strain native amphibian populations. It can mean habitat destruction and fragmentation, degraded water and air quality, changes in streamflow, and the introduction and spread of non-native species that weaken native populations. Each side effect comes with its own set of negative consequences for stream-dwelling species.

Amphibians in particular have permeable skin that’s excellent at absorbing what it touches. It’s useful for taking in water and oxygen but also leaves amphibians at risk in sullied streams and air, both of which can hold harmful, hitchhiking chemicals that the amphibians absorb. Some species can live for over ten years, and during that long decade, they can accumulate toxins that limit their lifespans and their ability to reproduce.

Critters in Santa Monica Mountains’ streams are nestled in the hills beside swelling Los Angeles, the second largest city in the US, with nearly unparalleled sprawl and no end to development in sight.

By monitoring native amphibians and invasive species in these streams, we are tracking the welfare of animals that need human protection from human-caused threats. Using amphibian health as an indicator of the degree of impact of nearby urban development, we are also gauging the health of the greater ecosystem, including air, water, soil, flora, and fauna alike.

We began this work in the Santa Monica Mountains in 2000 with an inventory to assess population status and reproductive success of the park’s five native species of wet, warty, and webbed amphibians, including the Baja California treefrog, California treefrog, California newt, western toad, and the rare California red-legged frog. The California red-legged frog nearly vanished from the park entirely in 2014 but is now making a recovery after our team moved to reintroduce the species.

The initial amphibian inventory effort provided experience and baseline data that guided the development of our long-term monitoring strategy for native, stream-dwelling amphibians in the Santa Monica Mountains. We also monitor non-native species like the amphibian-egg-eating red swamp crayfish, the everything-eating bullfrog, and various fish species.

How We Monitor

  • Every year, we sample 22 "sentinel" sites retained from the initial inventory effort conducted between 2000 and 2005. In addition, we survey 36 randomly-selected sites over a three-year rotation (12 per year).
  • Sampling occurs from April to July to coincide with the amphibian breeding season. We visit each sampling location twice during the season: once to collect a full suite of biological and environmental data, and again to determine the presence or absence (occupancy) of target stream-dwelling amphibians and non-native species.
    • Biological data:
      • For each target species within each stream segment, we document population sizes and age classes (egg, larvae, juvenile, adult).
      • For invasive species within each stream segment, we document presence/absence of fish and crayfish, and abundance estimates for adult and juvenile crayfish.
    • Environmental data:
      • We measure length and depth of stream segments and categorize them by habitat type, e.g., pools (slow or non-moving bodies of water), riffles (quick, shallow moving water), runs (deep, slow moving water), or dry.
      • We also track habitat conditions (vegetation type, boulders, erosion).
    • Occupancy:
      • We walk 250 meters upstream, and use dip nets and aquascopes to find and capture larvae and adults. Then, we verify their species.
        • The undersides of rocks, submerged logs, and floating vegetation are popular spots for eggs.

        • Banks, exposed rock, and floating vegetation are stomping grounds for juveniles and adults.

      • Later, we use a statistical framework that addresses differences in detectability between species to account for any critters we may have missed.

A biologist standing next to a fallen tree with a pen and notepad in hand.
Dr. Katy Delaney conducting an aquatic amphibian survey


Our Goals

  • Understand the status and long-term trends in the distribution and relative abundance of native amphibians and invasive species in order to inform better park decision-making around stream habitat conservation.
  • Determine environmental factors—like drought or wildfire—and stream characteristics—like temperature and depth—that may be affecting amphibian populations in the Santa Monica Mountains.

Why It Matters for Park Managers

  • Monitoring the status of native amphibians in the Santa Monica Mountains helps us to detect changes over a broad landscape involving multiple watersheds subjected to various levels of urbanization, pollution and non-native species, which can help to inform resource management decisions and actions.
  • Invasive species, such as crayfish, fish, and New Zealand mud snails, have a detrimental effect on our native amphibians. Pacific treefrog tadpole density is severely reduced in streams with crayfish, as compared to streams without. Our data confirm that in the overwhelming majority of streams where invasive fish, crayfish, or bullfrogs have been found, native California newts and California treefrogs have been absent.
  • New Zealand mud snails have recently invaded many of our streams, and it is unknown how their presence will affect native species. Studies from other areas of the U.S. have shown that native aquatic invertebrates, prey for amphibian larvae, are negatively affected by the presence of New Zealand mudsnails.

For More Information

Download 1-2 page PDFs about the Mediterannean Coast Network's monitoring programs.

Source: Data Store Saved Search 3516. To search for additional information, visit the Data Store.

The Mediterranean Coast Network documents its findings in reports published in the NPS Natural Resource Publication Series.

Source: Data Store Saved Search 1500. To search for additional information, visit the Data Store.

Protocols describe in detail the procedures used to collect, manage, analyze and report monitoring data. They follow strict guidelines for content and format, and are reviewed and revised by subject-matter experts in each field.

Source: Data Store Saved Search 1513. To search for additional information, visit the Data Store.


Katy Delaney

Last updated: November 30, 2023