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SPAWN’s smolt monitoring program began about 10 years ago as a way to measure the health of endangered fish populations in San Geronimo Creek – an important tributary to Lagunitas Creek. Monitoring the population of coho smolts is an extremely important gauge for the population as a whole because it indicates how well the baby salmon fared during their juvenile freshwater life. Lots of big, strong smolts are an indication of healthy streams that are providing the proper food, shelter and cold, clean water that salmonids need to thrive.

Juvenile coho salmon often have a difficult time surviving the winter season as they need a lot of room to feed and grow in cool, deep water with access to side channels and floodplains – features that the San Geronimo Creek Watershed in it’s more developed state lacks. Counting the number of smolts is a good indicator of how productive the stream has been for raising fish. It is also one way in which we can gauge the success of our restoration projects in the watershed.

To monitor smolts, SPAWN sets up large v-shaped nets in the creek to funnel the fish swimming downstream to a single point that then runs into a trap made of nets and mesh. At this point, SPAWN and trained citizen scientist volunteers catch and identify the fish, weigh them, measure their length and give a general health assessment of the fish. Once data has been collected, SPAWN re-releases the fish back upstream to observe if they are captured again, and accurately estimate the population. Once the fish have been counted, they are released downstream to continue their journey to the ocean.

SPAWN smolt traps are set up and run every single morning by teams of two to four people. The traps run from March to June for roughly 80 days in a row. Volunteers are essential to SPAWN’s smolt monitoring program. No experience is necessary, only a commitment to attend a training and be involved in hands-on-science at least once a week. Learn more about the next training here.