San Diego Management & Monitoring Program


Arroyo chub
Gila orcuttii

Vertebrata

Vertebrata
Kingdom Phylum Subphylum Class Order Suborder Family

Current distribution rangewide

Native to the Los Angeles, San Gabriel, San Luis Rey, Santa Ana, and Santa Margarita rivers and to Malibu and San Juan creeks [1 cited from 2]. Absent from much of their native range. Abundant only in the upper Santa Margarita River and its tributary De Luz Creek, Trabuco Creek below O’Neill Park and San Juan Creek (San Juan Creek drainage), Malibu Creek [3] and the West Fork of the upper San Gabriel River below Cogswell Reservoir as of 1991 (CDFG, unpubl. data). Successful introductions into the Santa Ynez, Santa Maria, Cuyama, and Mojave river systems and other smaller coastal streams [4;5 cited from 2]. Scarce occurrences in: Big Tujunga Canyon, Pacoima Creek above Pacoima Reservoir, and in the Sepulveda Flood Control Basin, Los Angeles River drainage; and middle Santa Ana River tributaries between Riverside and the Orange County line [3].


Known Populations in San Diego County

Occurrences found in Santa Margarita River Park, Sycuan Peak Ecological Reserve, and Vista Irrigation District.


List status

SSC


Habitat affinities

Found in slow-moving or backwater sections of warm to cool (10-24°C) streams with mud or sand substrates [2]. Does best in lower gradient streams that have largely disappeared [3]. Depths are typically greater than 40 cm [2]. Physiologically adapted to hypoxic conditions and wide temperature fluctuations, conditions common in southern coastal streams [6].


Taxonomy and genetics

Morphologically and genetically distinct. In the subgenus Temeculina with the closely related Gila purpurea[7]. Able to hybridize with two other cyprinids native to California: Mohave tui chub (Siphatales mohavensis) and California Roach (Lavinia symmetricus) [8;9;13].


Seasonal activity

Spawn primarily in June and July, however can breed continously from February through August [10 cited from 2,11, and 12].


Life history/ reproduction

Occurs in pools or in quiet edge water at 14 to 22 degrees Celcius. Egg release initiated by the rubbing of the male's snout to the area below the female's pelvic fins. More than one male may fertilize the eggs as they are being laid [10 cited from 2 and 12]. Embryos adhere to plants, rocks, and debris and hatch in 4 days at 24 degrees Celcius. After hatching, fry remain attached to or in the substrate for several days and swim to the surface, presumably to fill the swimbladder, once the yolk sac is absorbed [10 cited from 2 and 11]. Females can begin reproducing after one year. Females grow larger than males after second year. Life expectancy rarely more than 4 years [2;11;12].


Diet and foraging

True omnivores. Feed on algae, insects, and small crustaceans. Algae made up most (60-80%) of the identified stomach contents [13 cited from 11]. Also feed on roots of a floating water fern (Azolla), whih is generally infested with nematodes [8;5 cited from 14 and 2].


Dispersal

Natural dispersal is typically up- or downstream as conditions and suitable habitat permit. Typically facilitated by flooding events [5 cited from 12]. Dispersal within the mainstem of the Santa Margarita River appeared to increase dramatically after El Nino rains produced flood waters that heavily scoured the vegetation within the drainage, widening channels and reducing channel depths, creating habitat conditions that favor the chub and reduce exotic fish presence [15 cited from 12]. Larvae and juveniles tend to invade standing backwaters and/or disperse downstream from upstream spawning areas within the Santa Ana River [16 cited from 12]. Dispersal within both watersheds is currently limited by several large dams that serve as migration barriers. Many tributaries within each watershed are limited for chub occupation because of artificial or natural upstream migration barriers [15;16; both cited from 12].


Threats

Threatened by habitat degradation, fragmentation, nonnative species [2;11;17], dams, urbanization, mining, transportation, fire, and climate change [17].


Arroyo chub sources