Gila orcutti

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General Information
Common Name: 
Arroyo chub

Conservation Status in California: Class 2, Vulnerable (Moyle et al. 2011).
Vulnerable to extinction in its native range in the next 100 years. Several populations exist outside the native range but no arroyo chubs are truly secure and many (if not all) populations face extinction within the next 50-100 years.

Life History: 

Life History: Arroyo chubs spawn primarily in June and July, but can breed more or less continuously from February through August, as the eggs of females ripen in small batches (Tres 1992). During spawning, a group of males pursue a ripe female and rub their snouts against the area below the female's pelvic fins, stimulating egg release. More than one male may fertilize the eggs as they are being laid (Tres 1992). Embryos adhere to plants, rocks, and debris and hatch in 4 days at 24 ?C. After hatching, fry remain attached to or in the substrate for several days, swimming to the surface, presumably to fill the swimbladder, once the yolk sac is absorbed (Tres 1992). Juveniles spend the next 3-4 months in the water column, usually in habitats with still water and vegetation or other submerged cover.
Arroyo chubs in the Santa Clara River are about 60 mm SL after their first year and grow about 10 mm each year after, reaching 80-90 mm SL by their fourth year (Tres 1992). Females can begin reproducing after the age of one year. Females generally grow larger than males after their second year. The life expectancy of arroyo chubs is 1-4 years.
Arroyo chubs are true omnivores that feed on algae, insects, and small crustaceans, but they apparently prefer to feed on algae. In one study, algae made up most (60-80%) of the identified stomach contents (Greenfield and Deckert 1973). They also feed extensively on the roots of a floating water fern (Azolla) which is generally infested with nematodes (Greenfield and Greenfield 1972).

Dispersal Capability: Only capable of natural colonization via hydrologic stream connection. Arroyo chub have been spread to many Southern California coastal streams via interbasin water transfers and possibly through hitchhiking during trout stocking.

Habitat Requirements: 

Habitat Requirements: Arroyo chub are physiologically adapted to survive in habitats with low oxygen concentrations and wide temperature fluctuations, conditions common in southern coastal streams (Castleberry and Cech 1986). They are found in habitats characterized by slow-moving water, mud or sand substrate, and depths greater than 40 cm (Wells and Diana 1975). However, they have also been found in habitats with gravel, cobble and boulder substrates, albeit in lower numbers (Feeney and Swift 2008). They are most common in streams with gradients of less than 2.5% slope (Feeney and Swift 2008) where water temperatures range from 10 to 24 ?C. Thus, Deinstadt et al. (1990) found them in only small numbers (compared to rainbow trout) in the West Fork San Gabriel River, above Cogswell Reservoir where water was cool in summer (maximum temperatures


Distribution: The native distribution of arroyo chubs is restricted to southern California. They were once found only in the Los Angeles, San Gabriel, San Luis Rey, Santa Ana, and Santa Margarita rivers and in Malibu and San Juan Creeks (Wells and Diana 1975). Introductions expanded their distribution into the Santa Ynez, Santa Maria, Cuyama, Santa Clara, and Mohave River systems and other smaller coastal streams (e.g., Arroyo Grande Creek) (Miller 1968, Moyle 1976). The northern-most population was the result of an introduction into Chorro Creek, San Luis Obispo County (Moyle 2002). Absent from much of their native range, arroyo chubs currently are 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 (Swift et al. 1993), and the West Fork of the upper San Gabriel River below Cogswell Reservoir (as of 1990; J. Deinstadt, CDFG, pers. comm.). They also occur in low numbers in the Big Tujunga Canyon, Pacoima Creek above Pacoima Reservoir, Sepulveda Flood Control Basin, Los Angeles River drainage and middle Santa Ana River tributaries between Riverside and the Orange County line (Swift et al. 1993). They have recently been documented in the headwaters of the San Jacinto River near Forest Service Cranston Station on the mainstem and Indian Creek on the Soboba Indian Reservation (S. Loe, pers. comm. 2009). They have been found in recent years up to the North Fk. and South Fk. confluence in the mainstem San Jacinto River and have been found up the South Fork to near the Lake Hemet dam (G. Abbas, USFS, pers. comm. 2009).

Abundance Trends: 

Trends in Abundance: Little information is available on the abundance of arroyo chubs at various locations. Arroyo chubs are thought to be common at only four places within their native range: upper Santa Margarita River and its tributary, De Luz Creek; Trabuco Creek below O'Neill Park and San Juan Creek; Malibu Creek (Swift et al. 1993); and West Fork San Gabriel River below Cogswell Reservoir (J. Deinstadt, CDFG, unpubl. data 1990?). The decline in arroyo chub abundance has been largely attributed to the habitat degradation of low-gradient streams within their native range (Swift et al. 1993). Arroyo chub numbers appear to respond favorably to a decrease in flows. From 1986-1990, arroyo chub numbers temporarily increased due to low-water conditions in the West Fork of the San Gabriel River. Numbers decreased again after rains in 1991-1992 but increased in 1993. Arroyo chubs are common and widely distributed in some of the streams where they were introduced, particularly in the Santa Clara River.


Description: Arroyo chub are relatively small fish. Adults can reach lengths of 120 mm SL but are typically 70-100 mm long. They are sexually dimorphic. Males have larger fins than females and develop tubercles on the upper surface of the pectoral fins during breeding (Tres 1992). Both males and females have thick bodies, large eyes, and small mouths. Pharyngeal teeth arrangement can vary but is generally closely spaced with a formula of 2,5-4,2. Fin ray counts are 7 and 8 for anal and dorsal fins, respectively. Gill rakers number from 5 to 9. The lateral line is straight and complete with 48-62 scales extending to the caudal peduncle. Their body color varies from silver or grey to olive-green dorsally, with white ventrally, and a dull grey lateral band (Moyle 2002).
Larvae and juveniles from the Los Angeles and Santa Ana River drainages were described by Feeney and Swift (2008). Larvae are deep-bodied with 36-39 myomeres, pectoral fin buds, continuous dorsal, caudal and anal finfold, and a preanal finfold that extends to near the pectoral fin base. Caudal fin rays become visible at 6.5 mm, while dorsal and anal fin rays become visible at 8.3 mm and become fully developed at 10 mm, at which point pelvic fin buds appear. Pectoral fin rays become visible at 13 mm. The preanal finfold is retained until about 18 mm. Larvae body color is characterized by pigment that is heart-shaped over the midbrain and line along their backs. The snout, lower jaw, dorsal body, lateral midline, gill arches, dorsal gut, postanal ventral body and caudal fin are all heavily pigmented. By the time they reach 5.4 mm larvae have a functional almost terminal mouth and gas bladder, pigmented eyes and have used up the yolk sac. Notochord flexion occurs between 7 and 8.3 mm. At lengths greater than 10 mm, numerous small melanophores pigment the area above the lateral midline. A noticeable dark patch also appears on the dorsal end of the opercle. At this stage, the snout, head, later midline and upper parts of the body become darkly pigmented. Pigment in the dorsal and anal fins becomes noticeable at about 9 mm. Pigment also becomes noticeable in an arc along the pectoral fin base.