Over the past nine weeks, SPAWN biologists have traversed the banks along tributary creeks of the San Geronimo Valley in search of coho salmon spawning. A total of 15 nests (called “redds”) have been counted on Arroyo creek and 16 redds have been counted on Woodacre creek, for a total of 31 confirmed redds so far this season. No fish or redds were observed on any of the other tributaries including Larsen, Willis Evans, Montezuma, or North Fork of San Geronimo, despite ample rains.
The tributaries of San Geronimo Creek, including Woodare, Arroyo, and Motezuma creeks, are critical to the overall health of the coho population. In spite of these creeks being small with water flowing seasonally, they support a large proportion of the spawning that occurs in the San Geronimo Valley. So far this season a total of 77 redds have been observed in the entire San Geronimo Valley, including the main stem of San Geronimo Creek. Of these, 31 redds have been found in the small tributaries of Woodacre and Arroyo Creeks, which represents over 40% of all coho spawning in the San Geronimo Valley! You might not guess it by looking at these small quiet streams, but these are where many coho prefer to spawn and where many young fish like to rear. It’s critically important that these streams receive better protections from streamside development that erode stream banks and lead to degraded habitats.
Of the 31 redds, 29 are confirmed coho and two are steelhead. We have counted 44 live fish and five carcasses. The coho redds were first observed in the tributaries on December 13th and the first steelhead redds were observed on January 17th. The coho spawning season is complete but the steelhead run will likely continue into February. The total coho redd count for the watershed is around 150 nests, below the 20-year average of 250 redds, and far below the endangered species recovery goal of 1,300 redds. The large storm events in December and January, made worse by streamside development and channel degradation, likely caused damage to many redds by smothering the gravel beds with sand and mud or blowing out completely.
It’s critical now more than ever to protect streamside habitats from damaging and illegal development. These small seasonal tributary creeks play an especially important role in the life of salmon and are the often the areas of highest spawning densities. Please help protect these keystone species by volunteering with SPAWN on habitat restoration projects or with our citizen scientist program, and reporting illegal development to the County.