The Arroyo Chub (gila orcutti), a Southern California native fish, once thrived in the Arroyo Seco, along with trout, steelhead and other fish. After the deadly flood of 1914, Los Angeles County flood engineers built Devilís Gate Dam to deal with the flood threat. Later in the 1930s and 1940 the Arroyo Seco stream was reconfigured and lined with concrete along most of its course as it flows from the San Gabriel Mountains toward the Los Angeles River. Urbanization and the paving over of substantial portions of the watershed compounded these severe impacts on the natural ecologgical functions of the Arroyo Seco stream. Now there was more flood flow, and it traveled faster than before. Runoff polluted by oil, grease and trash damaged the rich riparian vegetation that once lined the banks of the stream. These factors all negatively impacted the survival of the arroyo chub and other aquatic species to the point of extirpation.
The chub is found only in the streams of Southern California and generally in relatively flat stretches. Although it is not present in the Arroyo anymore, it is still found in Big Tujunga Canyon, the Santa Ana River and Malibu Creek. The State of California has listed the Arroyo Chub as a Species of Special Concern.
The fish is quite distinctive. Like the carp and minnow, the Arroyo Chub belongs to the cyprinid family, but its gray-olive green back, white bellies, big eyes, and small mouth differ from the average cyprinids. The average size for an adult Chub is around 7-10 centimers (3-4 inches). Arroyo Chubs are omnivorous, consuming algae, insects, and crustaceans off of plants or in the bottom of the stream. They enjoy a slow-moving, warm mud/sandy bottomed stream with a depth of 40 cm. (16 in.).
The Arroyo Chub is an important species in the Arroyo Seco watershed. It is a good indicator of a healthy riparian or stream habitat. Arroyo Chubs are prey and predators in the ecosystem. The presence of Arroyo Chubs in the stream shows that the environment has what the this species and others need. It is a good indicator for other species like steelhead and the threespine stickleback which rely on the arroyo chub as food.
One of the primary goals of the Central Arroyo Seco Stream Restoration Program is to restore favorable habitat for the arroyo chub to repopulate the stream. The plan is to find several sites to reintroduce the arroyo chub. The prime locations are the northern area between the 210 freeway and above the concrete channel and the southern area between the Holly Street Bridge channel and the stately Colorado Street Bridge. In these sites, which are not channelized, we will create backwater and sediment basins to improve the habitat for the Chub. In addition, we will install weirs, wing deflectors, and snags to slow down the water flow, deepen the local area, and give the arroyo chub a more favorable environment for sprawning and refuge during flood events.
The Central Arroyo Stream Restoration Project will be completed by September 1, 2008. We are currently seeking permission from the California Department of Fish and Game to allow us to release several hundred arroyo chubs into the stream before the completion of the project.
Scientists have recently learned that the arroyo chub is effective in mosquito control, even more effective than non-natives species that have been commonly used in Southern California.