Temperature relationships in a pink salmon stream in Alaska

Sheridan, William

The temperature regiment in 2 pink salmon spawning riffles in Cabin Creek, southeast Alaska, were studied for a period of 14 months in 1949-50. These studies were undertaken because little was known of the temperature regimens of streams in the area and because survival of both adult and young pink salmon in freshwater depends in part upon suitable water temperatures. Temperatures of the air, stream water, intragravel water, and bank groundwater were measured. A multiple thermocouple system was installed in each of 2 spawning riffles to measure temperatures in the gravel and in the banks. Analyses of temperature data showed the following: 1. Although the extent of relationship between temperatures of the various media varied with the season, air temperatures were found to dominate and govern all water temperatures during a large part of the climatic year. During the summer and fall months, the closest relationship existed between temperatures of stream water and intragravel water (r = 0.99); the least between air and groundwater temperatures (r = 0.63). Because of close agreement between air and stream and intragravel water temperatures, abnormal air temperatures can affect pink salmon adult spawners as well as eggs and larvae. 2. Winter stream temperatures depend to a large extent on whether the stream is covered with ice and snow. If the stream is clear of ice, stream temperatures are usually higher than when the stream is covered. If the stream is covered, temperatures in the stream are less influenced by air temperatures. The protective influence of an ice and snow layer was evident in Cabin Creek during one of the coldest winters on record. 3. In the spring, melting snow subdues the effect of high air temperatures on water temperatures. Variable yearly water temperatures in the spring, caused by an interaction of air temperatures and accumulated snow, can influence the number of temperature units available to develop pink salmon larvae, hence may cause fry to migrate to sea at unfavorable times. 4. Temperature gradation was more pronounced in groundwater of the banks than in water within the gravel of the streambed, and was more marked in the intertidal zone than in the stream above tidal influence. In the intertidal zone, temperature gradation was the result of ebb and flow of water saltwater over the area. Temperature changes in the intertidal zone depend mainly on tide level, temperatures of stream and saltwater, and permeability of streambed gravels. Saltwater bathing intertidal zones may give salmon eggs and larva protection against freezing during extremely cold winters and may accelerate developmental rate because of higher temperatures than in the stream above the tides. Pink salmon eggs reared in dilute saltwater also have a higher survival than eggs reared in freshwater controls.

Temperature relationships in a pink salmon stream in Alaska

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