In the late summer and fall of 1999, a study of the mainstream of the Blue River, a fourth order tributary of the Ohio River, was conducted to estimate the populations of three species of endangered darters found there and to gather other ecological information about the area. The population estimates were conducted by using a multiple repeated removal method know as the Zippin Method. This study was a continuation and evaluation of similar studies done in 1986 and 1995.
Water levels in the Blue River at the time of the 1999 study were at record low levels due to a continuing drought. Stream-side vegetation and riparian cover were very similar to those conditions encountered in 1995 when a comprehensive bioassessment on the area was undertaken. At one of the study sites located at Stagestop Campground, riffle rocks had been rearranged to produce an easy canoe passage. Despite these low water levels, the Pollution Tolerance Index (PTI), which was generated from macroinvertebrate identifications, indicated that the water quality remained in the good to excellent range which is typical for the Blue River. In support of this, the dissolved oxygen content of the riffles was found to be in a range that could support a wide array of aquatic life. The dissolved oxygen content of the pools, however, was found to be somewhat lower as expected. While the Fecal coliform levels fell in the safe range for recreational usage of the stream, increased levels of nitrate and phosphate may have led to the noticeable increase in algal mats along the Blue River.
In all, 399 fish, representing 15 species, were removed from the seven different riffle areas studied. Of these 399 fish, 118 were spotted darters, giving a population estimate of almost nine darters per 100 square feet of riffle. The populations of bluebreast darters dropped to less than one fish per 100 square feet, while at Rothrock's Mill the low water had apparently forced the variegate darters to concentrate in the riffle area. It was at this site alone that the bluebreast darter population had risen to more than five per 100 square feet. Based on this analysis, the populations of two species of endangered darters studied in the Blue River are maintaining a functional number, while one has dropped. Future samples should be taken to determine if this decline is a long-term trend, or whether it is a short-term trend brought on by the drought.