. Commercial fisheries review. Fisheries; Fish trade. 30 140 60°N. 50 N. 40°N. I60°W. ISCw. I40°W. I30°W. I20° 60°N. 50°N. I40°E. ISO-E. leO-E. ITCE. 180° ITO'W. leO'W. ISCW. I40°W. ISO"*. I20°W. Fig, 2 - Schematic diagram of extent of two salmon environments--one characterized by a subsurface temperature-minimum stratum and the other a transition zone," with neither a temperature- nor salinity-minimum stratum. The Subarctic-Subtropic Boundary de- notes the southern limit of Pacific salmon in the open ocean. The location of the Subarctic-Subtropic boundary also was found later to
. Commercial fisheries review. Fisheries; Fish trade. 30 140 60°N. 50 N. 40°N. I60°W. ISCw. I40°W. I30°W. I20° 60°N. 50°N. I40°E. ISO-E. leO-E. ITCE. 180° ITO'W. leO'W. ISCW. I40°W. ISO"*. I20°W. Fig, 2 - Schematic diagram of extent of two salmon environments--one characterized by a subsurface temperature-minimum stratum and the other a transition zone," with neither a temperature- nor salinity-minimum stratum. The Subarctic-Subtropic Boundary de- notes the southern limit of Pacific salmon in the open ocean. The location of the Subarctic-Subtropic boundary also was found later to be an area of distinct changes in type and amount of planktonic forms. But no investigation has been made of the tongue-like intrusion of typically subarctic water, which extends as a salinity-minimum stratum south of lat. 40° N under the surface lens of the saline subtropic surface water. A number of years ago, be- fore we were able to conduct winter salmon fishing, I speculated that some salmon might winter in this deep stratum far removed from the winter storms prevalent at the surface. Although we caught enough salmon at the sur- face at higher latitudes during winter to challenge this hypothesis, we have never caught them in sufficient quantities to estab- lish a winter distribution pattern. Indeed, it would be interesting to investigate the bio- mass in this stratum during winter. The distribution of salinity at depth also provides some clue as to cause of the tem- perature-minimum stratum. A plot of depth at which the 34 %o isohaline occurs (fig. 3) indicates that it rises closest to the surface in a plateau-like structure around the tem- perature-minimum stratum. If we accept the premise of a northward flow of deep or bot- tom water from the Antarctic region into the North Pacific Ocean, the physical barrier im- posed by the boundary of the Gulf of Alaska and Aleutian Islands could deflect this water upward and cause a certain type of water structure. The s
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