Jun 14, 2024

May 2024 Field Updates: Bioassessment Season Begins

Spring is a busy time for the Estuary Program’s monitoring team. In the last week of April, we kicked off our annual bioassessment monitoring effort. During these surveys, our staff and volunteers collect creek health data from various sites across the Morro Bay watershed. This dataset spans over two decades and helps us assess changing conditions in the watershed. 

What is Bioassessment?

Bioassessment is a monitoring tool that we use to evaluate creek health. Each survey involves gathering around 1,500 measurements to assess stream conditions throughout our watershed. Each measurement helps determine if the creek can support sensitive aquatic species.

A key component of bioassessment monitoring is the collection of benthic macroinvertebrates (or “BMIs”). These invertebrates are bottom-dwelling insects visible to the naked eye. Macroinvertebrate collection is a critical part of our surveys because the types of BMIs you find in a creek can tell you something about the water quality. While some species are very sensitive to pollution, other species can be very tolerant of it. The presence of sensitive species indicates that the water quality is likely good, whereas a large number of pollution-tolerant species may indicate poor water quality. 

Stonefly larvae, like the one pictured above, are typically an indicator of good water quality conditions since they cannot survive in polluted water.

Unexpected Rainfall

Bioassessment surveys are conducted in the spring, when the creek flows are low and the big winter storms are done. This year we had a unique rainfall event in mid-April, which drastically increased water levels within a short period of time. This sudden rise in water levels caused rocks and cobbles to be transported throughout the channel, dislodging benthic macroinvertebrates from their bottom-dwelling habitats. As a result, our team began the bioassessment survey season later than normal, allowing the macroinvertebrates time to recolonize before sampling.  

Surveys took place throughout May and will wrap up in June. Results from the effort will be shared when they are available in the fall. For more information about our bioassessment monitoring, you can check out some of our past bioassessment blog posts  

Bioassessment surveys are conducted in the spring when the creek water levels are low since high flows can disrupt macroinvertebrate communities

Wildlife Encounters

While in the field, our staff are fortunate to come across a wide variety of wildlife. Along the water’s edge, we see fish and frogs, and in the tree canopy, we often spot hawks and songbirds.   

This season, our staff encountered an adult California red-legged frog (Rana draytonii) on upper Dairy Creek. California red-legged frogs are the largest native frog in the western United States and are federally-listed as threatened, meaning their population is likely to become endangered in the foreseeable future. Spotting an adult during our survey was an exciting find.  

An adult California red-legged frog (Rana draytonii) was spotted on Dairy Creek. This frog was approximately four inches long. 

Other wildlife encounters included a number of juvenile Pacific chorus frogs (Pseudacris regilla), southern alligator lizards (Elgaria multicarinata), a ring-necked snake (Diadophis punctatu), various hawks, fish, and a lot of bugs!  

Many Helping Hands

Conducting these assessments would not be possible without the support of our dedicated partners and volunteers. For the past three years, students from Cal Poly’s Natural Resources Management and Environmental Sciences (NRES) Department have come out for the surveys. Through volunteering, Cal Poly students gain real-life monitoring skills that support their future environmental careers.   

We’ve also had help from AmeriCorps Watershed Stewards Program (WSP) Corpsmembers.  To learn more about WSP, visit: https://ccc.ca.gov/what-we-do/conservation-programs/wsp-watershed-stewards-program/  

A Watershed Stewards Program (WSP) Corpsmember uses an auto level to collect creek slope data.

A big thank you to everyone who joined our survey effort to support this meaningful work. 

Thank You, Harold J. Miossi Trust

The Harold J. Miossi Charitable Trust has supported bioassessment monitoring in the Morro Bay watershed since 2013 and provided over $140,000 to make this work possible. This critical dataset has benefitted our program by helping us track long-term changes over time and assess watershed health, and we are grateful for the Trust’s generous support. 

An Estuary Program staff member collects data on San Bernardo Creek during a bioassessment survey.

Help us protect and restore the Morro Bay estuary!