Once the Arroyo Seco was full of a diverse range of freshwater fishes. Today the rainbow trout (Oncorhynchus mykiss) in the upper watershed and the Arroyo Chub, restored in 2008 in the Central Arroyo, may be the only native fish species that still occur in the Arroyo Seco, but there is great potential for the restoration of the native fish that once thrived in the Arroyo stream.
The Arroyo's native fish included:
The southern steelhead (Oncorhynchus mykiss irideus) is a federally endangered, anadromous form of the rainbow trout. While anadromous steelhead can no longer return to the Arroyo Seco due to dams and flood control facilities, it has been observed that individuals from the existing rainbow trout population migrate downstream during typical steelhead outmigration times, particularly during flooding. We believe some of these native trout become steelhead and may attempt to return to the Los Angeles River or other coastal streams but are thwarted by human barriers.
Many fisherman in the Arroyo Seco claim that there are still native rainbow trout in the stream in the San Gabriel Mountains. For many years, the California Department of Fish and Wildlife have stocked the upper Arroyo Seco with rainbow trout of different strains. The genetic makeup of the current population of trout in the upper watershed is unknown.
The Unarmored threespine stickleback (Gasterosteus aculeatus williamsoni) in 1917 as “one of the most abundant fishes in the lowlands of the Los Angeles Basin. The stickleback was to be extirpated from the watershed in the 1940’s, coinciding with the completion of the flood channel in the lower Arroyo canyon. Populations of this unique stickleback subspecies currently exist in the upper Santa Clara River and San Antonio Creek to the north. This species is a state and federally listed endangered species. The 1985 USFWS Recovery Plan for the unarmored threespine stickleback calls for reestablishing two viable populations of stickleback in the Los Angeles River watershed.
Pacific lamprey (Lampetra tridentata) was collected in the Los Angeles River Watershed in 1925 but is now gone from the watershed due to migration barriers associated with downstream flood control projects. Pacific lamprey used to spawn in the Arroyo Seco to spawn. This anadromous species continues to run up Malibu Creek and the Santa Clara River to the north.
Pacific brook lamprey (Lampreta pacifica) This species was collected in the Los Angeles River at Griffith Park in 1930 and is now thought to be extirpated (Swift et al. 1993). It is presumed that this species also utilized the Arroyo Seco. The Pacific brook lamprey still occurs in northern California streams and could be successfully reestablished after habitat conditions are improved.
Santa Ana sucker (Catostomus santaanae) This species was described as “common” in the Arroyo Seco (Culver and Hubbs 1917) and was observed as recently as 1992 upstream of Hansen Dam on Big Tujunga Creek (Los Angles River tributary). It is likely that the sucker has been extirpated from the Arroyo Seco and it may have disappearing from the entire Los Angeles River Watershed. Populations of Santa Ana sucker still exist in the San Gabriel and Santa Ana Rivers (Swift et al. 1993). This species is federally listed as a threatened species.
Santa Ana speckled dace (Rhinichthys osculus) This dace was observed in the Big Tujunga Creek tributary of the Los Angeles River until the mid-1980s and has not been observed since (Swift et al. 1993). It is not known if this species currently exists in the Arroyo Seco or greater Los Angeles River. Populations still exist in the San Gabriel and Santa Ana Rivers (Swift et al. 1993).
Arroyo chub (Gila orcutti) In a 1917 survey, the arroyo chub was described as “common in the Arroyo Seco” (Culver and Hubbs 1917; Swift et al. 1993). In 1993, Swift noted that this species still occurs in the Big Tujunga and Pacoima tributaries of the Los Angeles River and the Sepulveda Flood Control Basin. In 2008 the Arroyo Seco Foundation restored the arroyo chub to two stretches of the Arroyo Seco as part of the Central Arroyo Stream Restoration Project. Chub were collected in Tujunga Canyon and transported to the natural stream areas in the Arroyo just south of Devil's Gate Dam and below the Rose Bowl down to the Colorado Street Bridge.
While each native fish species exhibits unique habitat preferences, many of these species co-occur in the same aquatic habitat and have similar requirements. Restoration efforts geared towards rainbow trout, southern steelhead, and unarmored threespine stickleback would also likely benefit other species including: pacific lamprey (Lampetra tridenta), pacific brook lamprey (Lampetra pacifica), Santa Ana sucker (Catostomus santaanae), Santa Ana speckled dace (Rhinichthys osculus), and arroyo chub (Gila orcutti).
Stewards of the Arroyo Seco, PO Box 92722, Pasadena, CA 91109-2722 (323) 405-7326 firstname.lastname@example.org