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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Dec 18

Salmon Secrets Revealed

Posted on December 18, 2015 at 3:25 PM by Emma Detwiler

The coho salmon run on Lagunitas Creek has been off to a slow start, but spawning ramped up significantly this week. We observed 140 coho spawners and 37 new redds this week – the most coho seen in one week since 2006! In one pool we saw approximately 38 coho (I say “approximately” because counting that many moving fish isn’t easy). Last weekend’s rain allowed a small number of coho to enter San Geronimo Creek but flows in Devil’s Gulch are still too low for salmon to swim up there.

We’re also documenting coho swimming past our antenna, just upstream of Point Reyes Station. The antenna detects tags that were implanted in the fish when they were fry. Each tag has a unique number that allows us to identify which fish are coming back. So far we’ve detected seven returning coho. Two of these were originally tagged in Olema Creek, which is interesting because they had to have passed Olema Creek before swimming past our antenna. One of them has since turned around, apparently realizing it missed the exit.

What’s more interesting are the unique biographies of each fish. Five of the seven fish were born in 2013, were detected heading to the ocean in 2014, and have returned in 2015, which exemplifies the typical three-year life cycle for coho salmon. One fish was born in 2014 and came back as a “jack” after spending only about nine months in salt water. The seventh coho was tagged in 2013 as a rare “holdover” fish – one that stayed in the creek for a second year. We detected it going to the ocean in 2014 and it just returned as a four-year-old coho, which is a life history strategy we knew was possible, but hadn’t documented previously. Even a small group of fish can teach us something new.

Additional rain is in the forecast which should encourage more coho to come upstream and hopefully into the tributaries to Lagunitas Creek. We’ll be out there counting them whenever there’s a break in the weather.

 coho female with worn tail
A female coho worn out from digging her redd


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