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Trout and Salmon Movements in Two Idaho Streams as Related to Temperature, Food, Stream Flow, Cover, and Population Density
Author(s) -
Bjornn T. C.
Publication year - 1971
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1971)100<423:tasmit>2.0.co;2
Subject(s) - fish migration , streams , trout , fishery , population , juvenile , ecology , spring (device) , biology , environmental science , fish <actinopterygii> , mechanical engineering , computer network , demography , sociology , computer science , engineering
Many juvenile salmon and trout migrated from the Lemhi River drainage each fall‐winter‐spring period. Seaward migration of anadromous trout and salmon normally occurred in the spring but pre‐smolt anadromous and non‐anadromous fishes also left the stream usually beginning in the fall. I compared data on temperature, food abundance, stream flow, cover and population density with movements and conducted field and laboratory tests to determine reasons for the two types of movements. Smolts of the anadromous species migrated for an obvious reason but none of the factors I examined appeared to “stimulate or release” their seaward migration. Movement frequently coincided with changes in water temperature and stream flow, but I could not establish a consistent causal relationship and concluded that photoperiod and perhaps growth must initiate the physiological and behavioral changes associated with seaward migration. Non‐anadromous and pre‐smolt anadromous species emigrated from the streams for different reasons than the smolts. I postulated that fish found the stream environment unsuitable during the winter. Stream temperature declined in the fall as fish began moving from the streams but I could not induce more fish to stay in test troughs with 12 C water versus troughs with 0–10 C water. Fish emigrated before abundance of drift insects declined in winter. Emigration occurred in spite of the relatively stable flows in both streams. Population density modified the basic migration pattern by regulating the number and percentage of fish that emigrated and to a limited extent time of emigration. Movements of non‐smolt trout and salmon correlated best with the amount of cover provided by large rubble substrate. Subyearling trout emigrated from Big Springs Creek which contained no rubble substrate but remained in the Lemhi River which did. In both field and laboratory tests more fish remained in troughs or stream sections with large rubble substrate than in troughs or sections with gravel substrate. Trout and salmon in many Idaho streams enter the substrate when stream temperatures declined to 4–6 C. A suitable substrate providing adequate interstices appears necessary or the fish leave.