Michigan Department of Natural Resources
Institute for Fisheries Research Report No. 1786, 1972
The Effects of Stream Improvement upon the Anglers' Catch and Standing Crop of Trou in The Pigeon River, Otsego County, Michigan
W. C. Latta
Abstract.-In the fall of 1953, at the end of the trout fishing season, experimental Section A (1.3 miles long) of the Pigeon River was improved as habitat for brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) by the addition of sheet-piling deflectors, stumps, and sodded logs. The anglers' catch and standing crop of trout were estimated in order to evaluate the effects of the improvement structures. Variations in the catch and standing crop were such that control for environmental variability was essential. Therefore Section B (1. 2 miles long), the experimental water immediately upstream, was designated as the control. The yearly parameters of catch and standing crop in Section A were related to those in Section B through a ratio of A to B. The experimental design called for a comparison of the parameters for the 5 years before stream improvement, 1949-53, with the 5 years during stream improvement, 1954-58, i. e., while the improvement structures were in place. From the first 5-year period through the second, there was a statistically significant increase in the catch (A to B ratio) but not in any aspect of the standing crop. However, because of high fishing pressure in Section B during the "before" years, the increased catch could not be regarded as valid. Therefore, the experiment was extended for another 5 years, 1960-64. For this experimental extension, in 1959, the improvement structures and cover were removed from Section A and sand was added to fill the holes created by the deflectors. The changes in physical environment were recorded by detailed mapping of 13 randomly selected 100-foot segments of Section A and 10 like segments of Section B. Mapping was first done in 1958, before the improvement structures were removed; then in 1960, after they were removed; and finally, in 1964 at the end of the experiment. Square footage for three parameters was recorded: bottom soil types, water depth, and cover. In the fall of 1959 and 1961, during the estimates of standing crop in experimental waters, large numbers of trout were marked by clipping a fin, distinctive for each section. Movement between sections was noted, by returns in the catch and in succeeding fall population estimates. From the maps it was determined that there was a decline in the area of water over 3 feet deep and a decline in amount of cover, but little or no change in bottom soil types, after removal of the stream structures. An assessment of the movement data indicated little interchange of trout with the water outside of the experimental area, but substantial interchange between sections. A comparison of the means of A:B ratios for the "before" years (1949-53), with the "during" years (1954-58), and the "after" years (1960-64), for catch and standing crop, showed a consistent increase of brook trout for the years (1954-58) when the structures were in the stream. However, for the-brown trout there appeared to be a steady increase throughout the three time periods, independent of the addition or removal of structures. For brook trout, a statistically significant increase occurred in numerical catch, in fall standing crop (pounds), in fall standing crop plus catch (pounds), and in numbers of age-I and older fish. Fishing pressure remained constant for the during (1954-58) and after (1960-64) years. The increase in brook trout as recorded in catch-and standing crop must be attributed either to better survival or to migration of trout in response to the addition of cover.