by Eric Ettlinger
Long before sub-prime mortgages became a household term, coho salmon were suffering through their own housing crisis. For more than a century, dam construction has blocked salmon from returning to the birthplaces of their ancestors. In Marin County, dams and urbanization have eliminated most of the habitat for salmon, and much of the remaining habitat is highly degraded. Some of the best remaining habitat is in Lagunitas Creek, which runs through Water District, State Park, and federal land. But even here the creek bears the scars of logging, hydrologic manipulation, and land management practices that included removing logs from the channel. These logs, which once included massive old-growth redwoods that could remain stable for decades, provided deep water, protection from predators, refuge from floods, and even insects for food. Without these log houses, young salmon are essentially living on the streets, vulnerable to predators, the weather, and hunger.
Starting in 1999, the Marin Municipal Water District began collecting logs from Kent Lake and using them to build log structures for juvenile coho salmon. The first structures were fairly simple: one to three cut logs, held in place with boulders and cables, and often protruding a short distance into the creek. Over time we learned that structures that collect sticks and small logs also tend to create the deepest pools with the most fish. We now build larger, more elaborate structures and arrange them in groups to transform simple, straight channels into complex meanders. In September, using funding provided by the California Department of Fish and Wildlife, we completed four new structures in a straight, shallow section of Lagunitas Creek. By next summer the creek will hopefully be meandering between complex debris jams housing hundreds of juvenile coho salmon.
So how do we know that these log homes are actually benefitting salmon? We monitor them extensively, measuring water depths, observing them during winter storms, and snorkeling around them to count the juvenile salmon using them through the summer. The results have been encouraging. Coho numbers at enhancement sites quadrupled within two years of construction. In the last 15 years the summer survival rate of juvenile coho throughout Lagunitas Creek has increased by approximately six times. While we can’t prove that the log structures are responsible for the increase in coho survival, the evidence suggests that providing more homes has made Lagunitas Creek a safer neighborhood for coho salmon.