. Commercial fisheries review. Fisheries; Fish trade. 37 38»N. :^SAN ^FRANCISCO H C8AY 36" ^. yOBAY 38"^ — 36* SURFACE SALINITY {7oo) TEMPERATURE CO Fig, 1 - Distribution of surface temperature and salinity off San Francisco Bay showing plume of low salinity extending seaward, un- detectable in the temperature distribution, February 1969, Station locations are shown by dots. recording device (fig. 1). The seaward gradi- ent of salinity is fairly well defined because the stations are only about 20 km. ( m.) apart. But stations along the coast are 60 km. apart and, obv
. Commercial fisheries review. Fisheries; Fish trade. 37 38»N. :^SAN ^FRANCISCO H C8AY 36" ^. yOBAY 38"^ — 36* SURFACE SALINITY {7oo) TEMPERATURE CO Fig, 1 - Distribution of surface temperature and salinity off San Francisco Bay showing plume of low salinity extending seaward, un- detectable in the temperature distribution, February 1969, Station locations are shown by dots. recording device (fig. 1). The seaward gradi- ent of salinity is fairly well defined because the stations are only about 20 km. ( m.) apart. But stations along the coast are 60 km. apart and, obviously, it is impossible to as- certain whether or not a sharp front exists at the northern and southern edges of the plume. It is also obvious that surface temperatures provide no indication of the plume's presence. The Columbia's Plume The area offshore of the Columbia River is a much better example. Not only can the plume be seen from the air--extending into the ocean during late spring, straight as a superhighway--but the demarkation line be- tween the surface lens of silt-laden runoff and the relatively clear blue-green coastal water is obvious even aboard ship, when the north and south edges of the plume are crossed many miles at sea. In fact, the plume's sea- ward extent, as determined by dilute surface water, can be traced at times over 500 km. offshore. However, just north of the Columbia River, the runoffs from rivers in Washington and southern British Columbia flow seaward through the Strait of Juan de Fuca. Tidal and turbulent mixing from sills in the inland wa- ters reduces the possibility of this fresh wa- ter formiing a dilute surface lens, and there- by maintaining its identify in the ocean. Even up to the present, observations in the Strait at 10 to 30 km. intervals, made largely by local research vessels, have indicated only a slight salinity gradient from the Strait's inner reaches into the ocean, and no indica- tions of a sharp salinityfront at the entran
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