Page 4 - bell1978fishes

4 CONTRIBUTIONS IN SCIENCE No. 295

be brought forth to support the hypothesis that a species is introduced. The failure of

a species to be obseived or collected (negative data) until recent times may be a result

of recent introduction or from erroneous observation, identification or incomplete col-

lection in the past. Even if there is a record of introduction, the species may already

have been present before the introduction. The confidence pl~ced in the conclusion

based on historical data that a species is introduced depends on the quality of the

original observation. Reasoning based on distribution patterns, the presence of ap-

propriate habitats and dispersal routes is inferential. Fishes do not always occur in

habitats that they can disperse into and that appear to be appropriate for them. Thus,

as much evidence as possible must be brought to bear on the question of whether a

fish species is native, and the answer obtained may never be satisfactory.

RESULTS

DESCRIPTION OF STREAMS

The Santa Clara River system is composed of the Santa Clara River and a large

number of tributaries primarily draining from the north (Fig. 1). The drainage is

bounded on the southwest by the Santa Susana Mountains and on the southeast by the

San Gabriel Mountains. No substantial tributaries of the Santa Clara River drain these

mountain ranges. The Santa Susana Mountains are drained to the south by Calleguas

Creek and its tributaries. The southern slope of the San Gabriel Mountains is drained

by tributaries of the Los Angeles and San Gabriel Rivers.

In the west, the headwaters of Sespe and Piru creeks are interctigitated with those

of the Cuyama River, a tributary of the Santa Marie River and tributaries of the small

Ventura River system.

Drainage north of the Santa Clara River system is by creeks which eventually

disappear into the southern San Joaquin Valley. The eastern corner of the Santa Clara

River system is bounded by these creeks as well as those of the Los Angeles River

system and some draining into the Mojave desert.

The Santa Clara River, Santa Paula, Sespe, Piru and Castaic creeks, San Fran-

cisquito and Arrastre canyons and Todd Barranca were studied. Other tributaries east

of Saugus were not studied because J. N. Baskin (personal communication) reported

no fishes there. Some tributaries in the western portion of the drainage could not be

studied or received cursory examination because of limitations of time, funds or

access.

The Santa Clara River was examined from its headwaters to its mouth. Flow is

intermittent over substantial lengths of the stream (dotted lines, Fig. I) and the geo-

graphic extent and duration of desiccation varies yearly. The sectior1 between Lang

and Saugus is dry except during heavy downpours, a condition that apparently has

existed since at least the middle of the last century (Miller 1960). The Santa Clara

River and its tributaries are subject to flooding some winters. The river flows through

a broad, primarily sandy-bottomed valley. In most places, the flood plain is lined by

earth and rock or wire and debris barriers. The Southern Pacific Railroad runs the

length of the Santa Clara River, built across the flood plain on elevated grades in

places. Upstream of Saugus the flood plain is occupied by gravel pits, small recrea-