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21 <br />Table 1. Distribution of native fishes in the San Pedro River <br />Basin, Arizona, since 1963• <br />Mainstream Aravaipa Babacomari <br />Species San Pedro Creek River <br />Agosia chkyAog"ten X X <br />Ca to stomws imign.us X <br />Ca,tastomuz .tati.p inndvs * <br />Cypxinodon macutaxiuz* <br />G.c to .intamedia. X <br />Gila ubwsta g&a.ham.i X <br />Meda Futg.ida X <br />Pantoztews ctaAii. X X <br />Poeciti,ops-c.b o. occidentaW** <br />Ptychocheitws .tuciu.5* <br />Rh.in.ichth yb o s cu a X <br />T.cahaga cobitiz X <br />Xynauchen zexanws* <br />* Extirpated in early 1900's <br />Population discovered and extirpated in 1978 <br />Further reduction of the already-depleted San Pedro native <br />ichthyofauna occurred in February 1978, when pollutants from copper <br />mining operations on the San Pedro headwaters in Sonora, Mexico <br />apparently eliminated all fishes in the upper portion of the main- <br />stream. Reestablishment of fishes in this section must occur from <br />tributaries such as the Babocomari River where small populations of <br />native species occur. <br />A recent occurrence south of Mammoth, Arizona, illustrated what <br />is generally happening to fish and wildlife habitat along much of <br />the San Pedro. A new locality for the Gila topminnow, Poec ti.opAiZ <br />occidenta,4 6 occi.dentaLL6, was identified in July 1978, in the <br />outflow of an artesian well. At that time, clearing of mesquite <br />immediately adjacent to the site was underway. By September, the well <br />piping had been partially capped and dense mesquite around the well <br />was removed by bulldozer. Much of the outflow area had become silted <br />in and few fish could be observed. By early October, the well had <br />been completely capped and connected to an irrigation system in the <br />adjacent cleared area, resulting in complete drying of the former <br />habitat and extirpation of the topminnow population. This incident <br />is particularly significant because the well outflow was the only <br />known locality in the entire San Pedro basin where PoeciXiopA.us <br />was still present, and was one of only seven naturally-occurring <br />populations presently known in the U.S. Thus, in a matter of three <br />months, an important endangered species population was both discovered <br />and extirpated.