| Popis: |
Following the abatement of domestic sewage pollution xii in the lower Logan River, the fish population was investigated in terms of abundance, growth, fecundity, production, mortality, age class structure, species diversity, distribution and movements during 1970 and 1971. Three general groupings of fish were identified in the study area on the basis of species composition, abundance and distribution using a cluster analysis technique. These were located in 1) the tributary stream (7-Mile Creek) which previously transported sewage to the river and 2) above and 3) below 7-Mile Creek in the main stream of the Logan River. A "transition" population was present in the river near the confluence of 7-Mile Creek. Species diversity was predictable on the basis of four physical variables including percent riffle, a measure of bank cover, stream sinuosity and gradient. Percent riffle appeared to be the most important variable in predicting the "Trophic Condition Index" of the fish population. An information theory function was used to determine the extent of fish movement within the study area. Of the four dominant species in the river (carp, mountain whitefish, Utah suckers and brown trout) only the brown trout demonstrated an apparent response to the pollution abatement by reducing the extent of its movements at this time. Seasonal growth patterns were strikingly similar among the species examined with maximum growth occurring during the spring months. Extensive weight losses, attributed to high population densities and a decline in the invertebrate forage base, occurred during the summer of both 1970 and 1971, particularly in the older age classes of mountain whitefish and brown trout. Production of carp, mountain whitefish and brown trout and Utah suckers was assumed to approximate total fish production in the river. Whitefish production above and below 7-Mile Creek was estimated to be 3. 87 and 1.65 gm/m 2/yr respe ctive ly for the period June 1970 to May 1971. Carp production in these two areas was estimated to be 22.86 and 10.45 gm/m 2/yr for the same period. Brown trout production was estimated to be 5.94 gm/m 2/yr above 7-Mile Creek while production of Utah suckers in the study area was estimated to be 2-3 gm/m 2/yr. Weighted production for the entire study area was estimated to be 23.5 gm/m 2/yr. Evidence is presented which suggests that fish production has increased following the pollution abatement. |
