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was likely the case for the Bonneville cutthroat population in Birch Creek, Beaver County, Utah. Population Dynamics During recent studies on cutthroat trout in Birch and Trout creeks, popula- tion estimates were made to determine standing crops and biomass in these small streams. Sampling areas on Birch Creek consisted of four sections, each covering a distance of 161 m (528 ft). The sections were electro-fished using the two sample method (Ricker 1958) to estimate the population. A section on Trout Creek was also sampled and provided comparative data (Table 6). Table 6. Density of Bonneville cutthroat trout (S. c. utah) in Birch Creek, Beaver County, and Trout Creek, Juab County, Utah.' Birch Creek Trout Creek NoJkm (NoJmile) NoJha (NoJacre) No./km (No/mile) NoJha (No./acre) Section 1 ----~ Section 2 96 (154) 702 (284) Section 3 378 (608) 2948 (1193) 752 (1210) 2135 (864) Section 4 287 (461) 2234 (904) Total estimate 1962 (794) 2135 (864) 'Stream reach sampled was 161 m (528 ft.). 'Only one fish was sampled in this section. The total estimated stream population for Birch Creek was calculated to be 4,190 fish based on a total area of 2.14 ha (5.28 acres) for the 16.1 km (10 miles) of stream inhabited by cutthroat trout. The biomass estimates for the Birch Creek stations were 25.2 kg/ha (22 lbs/ac), 46.5 kg/ha (411bs/ac), and 48.9 kg/ha (44 lbs/ac), respectively. Total estimated biomass in Birch Creek was 40.3 kg/ha (42.41bs/ac) or 86.2 kg (190 lbs) offish. Total estimated biomass in Trout Creek was 379.3 kg (827 lbs). The larger biomass (standing crop) for the Trout Creek population habitat 3.5 ha (8.6 ac) versus 2.14 ha (5.3 ac). Population estimates were not available for other populations of Bonneville cutthroat found in Utah. It can be speculated that"their numbers would also be limited because of restricted habitat where they are found. The year 1977 was considered to be the driest on record and many smaller streams in Utah were severely affected. Birch Creek became dry in the lower 4.8 km (3 miles), thus reducing habitable area from 16.1 to 11.3 km (10 to 7 miles). It was estimated that approximately 0.32 ha (0.79 acres) of good habitat and 225 trout (5 percent of total population) were lost. The drought had a lesser effect on cutthroat trout in Trout Creek. Water conditions were not monitored in other streams containing Bonneville cutthroat trout but these populations were prob- ably affected. Old, partially functional log structures were credited for the survival of half the know population of Gila trout (Salnzo gil¢e) during two consecutive drought 18