Maria Slough

Shane Green checking trap. Photo: Isabelle Groc


Kristina Robbins catching Oregon Spotted Frog. Photo: Isabelle Groc

Although egg mass surveys are crucial to monitoring populations, they can only provide a crude glimpse into the health of the population. Egg mass numbers provide an indication of whether the population is declining, but don’t give any indication of why.

The Capture-Mark-Recapture program (CMR) has been ongoing at Morris Valley and Maria Slough since 2011, since it was begun by a team of researchers at Simon Fraser University led by PhD candidate Amanda Kissel

Frogs are captured over five weeks during breeding season around known breeding sites in soft-sided traps – up to 150 at a single site. Every day our team of field researchers checks the traps, and measure, weigh, and individually tag each Oregon Spotted Frog captured with a with Passive Integrated Transponder (PIT) tag that is about the size of a grain of rice. Frogs are then released, and hopefully recaptured in the same season and in future years.

With this information, we can infer population sizes around those breeding sites, but most importantly we can track survival of individual frogs over the years and learn about the age structure of the population. For example, a population with lower adult survival will rely more on annual recruitment (breeding survival) to maintain a stable population, but annual variation in temperature and rainfall during breeding season can severely impact breeding success. Just one or two years of poor breeding and rearing conditions could tip the population towards extirpation. A population with higher annual survival would be less susceptible to annual climate variation leading to recruitment.

Over time, we hope to correlate differences in habitat, hydrology or climate with survival and recruitment, and inform management strategies to ensure the few remaining populations remain stable, or even grow, over time. We also hope to answer questions about site fidelity (do the frogs return to the same breeding site each year?), breeding frequency (do females breed annually?), growth patterns, health indicators, start of breeding age, etc.