Ecological Effects of Winter Conditions on Trout and Trout Foods in Convict Creek, California, 1951
- 1 January 1952
- journal article
- Published by Oxford University Press (OUP) in Transactions of the American Fisheries Society
- Vol. 81 (1) , 202-217
- https://doi.org/10.1577/1548-8659(1951)81[202:eeowco]2.0.co;2
Abstract
In 1951, winter studies were conducted at the Convict Creek Experiment Station of the U. S. Fish and Wildlife Service located at 7,200 feet elevation in the Sierra Nevada Mountains near Bishop, California. These were designed to extend knowledge of winter conditions in stream environments and to bring to light problems requiring further investigation at this season. Common stream survey methods were employed to procure and analyze data. Snowfall was meager at Convict Creek in 1951, but freezing temperatures induced extensive ice formations. Surface ice immobilized screens and other objects protruding from the water, yet provided the trout with abundant shelter. Frazil and anchor ice had a more pronounced effect on stream life and water temperatures than surface ice. When subsurface ice was present, the water was at or very close to the freezing point, regardless of weather conditions or time of day. Anchor ice formed and dispersed in a daily cycle that caused wide fluctuations in stream flow. Minimum water flow at night often left secondary channels empty, while morning peak flows scoured the stream with ice fragments, washing loose debris and bottom fauna. Trout were active in the freezing water and fed regularly throughout the winter. Trout were caught on bait when the water was 32° F. Large numbers of aquatic organisms were dislodged by fluctuating flows and became available as food for trout. Clear indications were obtained of high seasonal fluctuations in the abundance of bottom organisms. Adult stoneflies and dipterans emerged on warm days during the winter. A comparison between the numbers of stream bottom organisms present, drift foods, and foods consumed by trout, gave a positive correlation. In cold weather, trout consumed large numbers of mayfly and stonefly nymphs, while dipterans predominated in trout stomachs over the entire winter. Rainbow and brown trout of similar lengths and stomach volumes differed in the number of organisms eaten by each in that rainbow trout ingested larger quantities of small organisms than did brown trout. Wild trout suffered an initial mortality in early January that was caused by heavy subsurface ice which blocked stream flow into side‐channels. Very few dead trout were found after this occurrence. The over‐winter survival of marked trout approximated 50 percent in 1950–51.This publication has 0 references indexed in Scilit: