NOTES ON THE FISHES OF THE STREAMS FLOWING INTO SAN 
FRANCISCO BAY. 
By JoHN OTTERBEIN SNYDER, 
Assistant Professor of Zoology, Leland Stanford Junior University. 
The territory drained by the streams flowing into San Francisco Bay 
comprises a catchment basin which is partly bounded by mountain 
ranges of considerable height. It is thus sharply separated on the 
east from the San Joaquin Valley, and on the west from a much more 
restricted area drained by a series of small streams flowing directly to 
the ocean. On the south a comparatively low, though perfectly dis- 
tinct, watershed divides it from the valley of the Pajaro River. All 
of the streams connected with the bay are to be considered as belong- 
ing to a single system, none apparently having remained isolated for 
any considerable period of time. Complete isolation is prevented by 
an occasional intermingling of the waters of two or more streams near 
their mouths, and also by a reduction of the salinity of the water of the 
bay during periods of excessive rainfall, the surface at such times occa- 
sionally becoming quite fresh. 
Most of the streams of this basin converge toward the southern end 
of the bay, which is there bordered by extensive salicornia marshes. 
The constant wash of the tides has cut into the surface of these 
marshes a network of sloughs, to some of which the water from the 
creeks eventually finds its way. Before reaching the sloughs, however, 
this water often spreads out, forming large ponds. The union of two or 
more of these temporary ponds, the shifting of a creek channel caused 
by some obstruction, the change in the direction of a slough, ora com- 
bination of these conditions may form between two streams a continu- 
ous passage well adapted for the migration of fresh-water fishes. @ 
Such a union of two creeks has actually been observed, one of themas 
a result having become stocked with an additional species. A dense 
growth of willows recently deflected San Francisquito Creek to the 
a Such conditions are possible only during the height of the rainy season. On the approach of the 
dry season all the streams of the region rapidly shrink, both in volume and length, only one of them, 
Coyote Creek, discharging water into the bay during the entire summer. Much ofits bedis dry, how- 
ever, for part of the year, the water sinking soon after leaving the mountains, and appearing again 
about 2 miles aboye its mouth. : 
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