. Commercial fisheries review. Fisheries; Fish trade. 38 stations and in water of maximum surface ° C; also, that the south- ern limit of salmon catch (lat. 49° N. at this longitude) coincided with a subsurface (below 50 m.) temperature front which marks the southern limit of the temperature-minimum stratum. Data obtained subsequently have shown this feature to be permanent for the region and to extend across the ocean. The southern limit of the temperature minimum stratum has withstood the test of time as an indicator of the southern limit of salmon dis- tribution in the cent
. Commercial fisheries review. Fisheries; Fish trade. 38 stations and in water of maximum surface ° C; also, that the south- ern limit of salmon catch (lat. 49° N. at this longitude) coincided with a subsurface (below 50 m.) temperature front which marks the southern limit of the temperature-minimum stratum. Data obtained subsequently have shown this feature to be permanent for the region and to extend across the ocean. The southern limit of the temperature minimum stratum has withstood the test of time as an indicator of the southern limit of salmon dis- tribution in the central part of the ocean in summer; it also indicates the southern limit of sockeye salmon, O. nerka, year round in the central part of the ocean (fig. 2). In the easternpart of the ocean, the south- ern boundaries of the temperature-minimum stratum and the limit of sockeye salmon dis- tribution diverge; the southern limit of the temperature-minimum stratum (as defined) turns northward into the Gulf of Alaska, whereas the southern limit of sockeye salmon distribution continues eastward toward the Oregon coast. Skeptics may point to this di- vergence as evidence that the relation between temperature front and salmon does not hold. Inmany instances, when a scientist measures only one variable that has a direct effect on natural phenomena, the skeptics are right. In the present situation, however, the signifi- cance of the subsurface temperature boundary in this area is supported by other data. The environment north of the subsurface temperature boundary appears to be prefer- able for adult sockeye salmon in the Gulf of Alaska, where they are found in winter and early spring before their shoreward migra- tion to spawn. Figure 3 shows the distribu- tion of sockeye salmon (from longline catches) in this area in spring 1962.^/ The large con- centration in the central Gulf is in the general area of the temperature-minimum stratum (fig. 4). Particularly significant is the 60° N. ISCW.
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