FISHES OF STREAMS TRIBUTARY TO MONTEREY BAY 
51 
less than 3 miles of land separating them. The San Lorenzo flows into the bay at some 
distance north of the Pajaro, there being between their mouths more than 15 miles of 
coast, much of which is high, ascending rapidly to the foothills and the mountains 
beyond. 
THE RELATIONSHIPS AND DISTRIBUTION OF THE FISHES. 
The fishes of the Pajaro system may be said to belong to two fairly distinct 
groups. In the first of these may be assembled the anadromous forms and others which 
descend freely to salt water. They are the lampreys, trout, salmon, sticklebacks, and 
cottoids {Entosphenus tridentatus , Salmo irideus, Oncorhynchus tschawytscha, O. kisutch, 
Gasterosteus cataphractus , Cotius asper, C. gulosus, and C. aleuticus). Since the ocean 
presents no barrier to the dispersal of these species they have a wide distribution along 
the coast, occurring in all the streams of sufficient volume to support them. 
To the second category belong the fresh-water fishes, the suckers, minnows, sunfish, 
and viviparous perch (Catostormis mniotiltus, Orthodon microlepidotus , Ptychocheilus 
grandis, Hesperoleticus subditus, Lavinia ardesiaca, Agosia carringtoni, Archoplites 
interruptus, and H ysterocarpus traski). These fishes are regarded as being strictly 
fluvial — not able to withstand long immersion in salt water. This assumption, though 
not based on experimental evidence, appears to be sufficiently established to accept 
without further discussion. Hence these species, living in isolated basins like those 
of the Pajaro or Salinas, occupy positions almost exactly analogous to those of reptiles 
or mammals inhabiting oceanic islands. 
The present study shows that the fluvial fishes of the Pajaro system are all repre- 
sentatives of Sacramento River forms. In fact five of them, O. microlepidotus , P. grandis, 
A. carringtoni, A. interruptus, and H. traski, appear to be identical with Sacramento 
species, no distinctive local peculiarities having been observed among them. On the 
other hand, representatives of the Sacramento forms, Catostomus occidentalis , Hespero- 
leucus venustus, and Lavinia exilicauda, have become measurably differentiated, and 
so modified that they may be regarded as distinct species which are characteristic of the 
Pajaro system. The Pajaro basin alone contains a complete representation of the 
fluvial fauna of the region. The Salinas has six species, C. mniotiltus, O. microlepi- 
dotus, H. subditus, L. ardesiaca, A. carringtoni, and H. traski; the San Lorenzo three, 
C. mniotiltus, H. subditus, and A. carringtoni. Soquel and Aptos Creeks, which at times 
nearly dry up, have no fresh-water fishes at all. 
If the relationships of the Pajaro fauna have been correctly determined, then one 
may safely pass to the conclusion that the Pajaro system received its species from the 
Sacramento,® and it may further be assumed that there was once an open passage 
between them, or an intermingling of their waters which enabled fishes to migrate from 
one basin to the other. The Sacramento, not the Pajaro, is thought to be the region 
from which the migration took place, as it contains not only a full representation of the 
“ There are no fluvial species in the coastal streams between the San Lorenzo River and the Gulden Gate, nor are there any 
in the rivers immediately south of the mouth of the Salinas. 
