UNARMORED THREESPINE STICKLEBACK Gasterosteus aculeatus williamsoni (Girard, 1854 

 Order: GASTEROSTEIFORMES Family: GASTEROSTEIDAE 



Distinguishing characteristics : A threespine stickleback which usually lacks lateral 

 plates and averages fewer than 1 plate in a random sample of 10 specimens; dorsal spines 

 weak; pectoral and caudal fins rounded. 



Present distribution : Now native only in the headwaters of the Santa Clara River in 

 Soledad Canyon, Los Angeles County, and presumably in the Santa Maria River drainage 

 in San Luis Obispo County, California; established by introduction in the upper part of 

 the Mohave River , California . 



Former distribution : Once abundant in the rivers that cross the Los Angeles Plain 

 (Los Angeles, San Gabriel, Santa Ana and connecting streams) upper Santa Clara River, 

 and tributaries of the Santa Maria River basin. Became extinct on the Los Angeles Plain 

 between 1942 and 1961. 



Status: Jeopardized because of very restricted distribution and the likely contamination 

 of stocks established in Mohave River by genetic hybrids. 



Estimated numbers : No definite data. 



Fecundity : Unknown . 



Reasons for decline : Introduction of the exotic predator, Gambusia affinis , and other 

 alien species; destruction and desiccation of habitat. 



Protective measures already taken : Classed endangered and protected under California 

 State law . 



Measures proposed : Protection in the headwaters of the Santa Clara River . 



Number in captivity : None . 



Breeding potential in captivity : Unknown, but the species has been successfully reared. 



Remarks: Data provided by Dr. Robert R. Miller, University of Michigan, Ann Arbor. 



References : 



Miller, R. R. 1960. The type locality of Gasterosteus aculeatus williamsoni and 

 its significance in'the taxonomy of California sticklebacks. Copeia, 1960, 

 No. 4, p. 348-350. 



. 1961. Man and the changing fish fauna of the American Southwest. 

 Pap. Mich. Acad. Sci., Arts, and Letters , No. 46, (1960), p. 365-404. 



and C . L. Hubbs . 1969. Systematics of Gasterosteus aculeatus , with 



particular reference to intergradation and introgression along the Pacific Coast 

 of North America: a commentary on a recent contribution. Copeia, No. 1, 

 (1969). p. 51-69. 



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