A total of 7,485 fish, representing 49 species, 25 genera, and 11 families, were electroshocked from three stations on the Middle Fork of Drake's Creek during the period January, 1972 through January, 1973. Community structure was influenced by seasonal changes in both numbers of species and numbers of individuals. The number of species per collection was at its highest, at all stations, during the month of September. The total number of species and individuals collected at each station progressively increased toward the upstream areas. Eleven of the forty-nine species collected during the course of the study provided 91.8% of the total number collected. Diversity (D) values were used to compare average diversities for each of the monthly samples at each station. Monthly diversity values tended to fluctuate erratically, with the greatest stability being observed at the "mid-stream" study area. Individual species' contribution to diversity were computed using "information units" expressed as a percentage of the total diversity to find dominant species at each station and during each season. Species were categorized, according to frequency of occurrence, into permanent residents, seasonal residents, and transients. Monthly contributions to diversity, expressed in per cent, were used to compare dominant species of each category at each station. Transient species were observed to be most prominent in the lower stream reaches during the period June through September. Attempts were made to detect movement of stream fishes by mark-and-recapture techniques. The recapture of marked fish represented a return of 10.9%, as 16 of 146 marked fish were recaptured. The home range concept of some stream fishes was supported in some instances; however, streams were found to be open systems which do not lend themselves readily to mark-and recapture studies.

Accidental conservation isolation characterizes a situation when a barrier created for a non-conservation purpose happens to fragment a population that now holds conservation value. This study established baseline genetic structure for the isolated populations of Colorado River cutthroat trout in the North Fork Little Snake River drainage, Wyoming. In many cases of accidental isolation, the populations above the barriers have limited habitat and small population sizes that make them vulnerable to extinction and may hold evolutionary value to the species as a whole. All the isolated populations in the drainage currently have high genetic differentiation among tributaries, low genetic diversity within each tributary, a suggestion of isolation by distance, and effective population sizes that are below the recommendation for long- term persistence. This structure represents natural and anthropogenic influences, but the presence of the human-constructed barriers in the headwater tributaries puts the larger core conservation group at risk into the future. Although the genetic diversities within the populations are low, the high genetic differentiations among populations suggest that each population may have its own unique contribution to the evolutionary value to the drainage as a whole and each is important to conserve into the future.

With an ever increasing fishing pressure on our natural and artificial lakes every measure possible must be taken to preserve the sport for its many thousands of participants. Hyrum Reservoir is easily accessible to the fishermen of northern Utah. In recent years the lake has offered little in the way of fishing. It is hoped that the information accumulated in this study will help pave the way to a successful stocking program and that Hyrum Reservoir will be one of the productive fishing areas available to Utah anglers. The objectives of this investigation were: 1. To determine the extent of area suitable to fish life at the critical seasons of the year. 2. To determine the chemical, physical and biological factors which may affect fish population numbers. 3. To study critical aspects in the ecology of the rainbow trout in the impoundment.

Changes to rivers that alter physical and thermal habitat may cause fish population abundance to decline, due to fewer individuals maturing and entering the adult population. The Weber River has become highly degraded with many dams and diversions altering fish habitat, river volume, velocity, and temperature, and limiting movement between reaches. Bluehead suckers (Catostomus discobolus) occupy only 47% of their historical range and the genetically-distinct Weber River (northern UT) population is declining and contains few young, juvenile fish. My objectives were to determine whether spawning and rearing habitat available in the Weber River may be limiting bluehead sucker reproductive success and population growth. I used reach-based surveys to locate and quantify spawning habitat in the Weber River and Ferron Creek (central Utah), a relatively unaltered river for comparison. I sampled slow-water backwaters near (< 1 km) spawning reaches for juvenile sucker and surveyed habitat characteristics. I conducted laboratory experiments to evaluate the effect different temperature and velocity treatments (12-19°C, 0.004-0.18 m/s) have on juvenile bluehead sucker growth. In the Weber River and Ferron Creek, reaches with gravel (4-64 mm diameter), cobble (64-256 mm diameter), and pools (6-26 pools/km) were used by spawning bluehead sucker. In Weber River backwaters, deeper backwaters contained significantly more juvenile sucker (18-378 sucker; range: 19-87 cm max depth). Laboratory results indicated that juvenile bluehead sucker growth was greatest in the cooler temperature and slower velocity treatments. Collectively these results suggest spawning habitat is limited by the availability of small, rocky substrate and pools and rearing habitat is limited by the availability of deep, slow backwaters at the optimal temperature. By evaluating factors that may limit bluehead sucker population growth, this study will provide a template for future restoration efforts directed at recovering this imperiled population.

The phytoplankton, or plant plankton, live in the open water throughout their life cycle and obtain the necessary nutrients from the water. They are important contributors to the total plant production of lakes and ponds.

Any method used in aging fish must fulfill certain requirements to be satisfactory. If the method is inaccurate, naturally little reliance can be placed upon its use. If considerable study of the method and much practice are required before accurate readings can be obtained, the method will not come into widespread us ~. The requirements of an aging method, then are that . it must be accurate and comparatively easy. The scale method for aging lake trout (Salvelinus namaycush Walbaum) unfortunately does not fulfill these requirements.

The channel catfish, Ictalurus punctatus (Rafinesque), was first introduced into Utah Lake in the summer of 1911, and has since been stocked in the lake on numerous occasions. It has only been in the last few years that the channel catfish has become an important game fish in Utah. As the value of the channel catfish, as a game fish, increased, it has become increasingly important to the state to maintain this species for present and future generations. This study was initiated in 1958 and completed in 19 60, and was financed by the Utah State Department of Fish and Game. Data on certain phases of the channel catfish life history were investigated to provide information to aid in management of this species. The following phases were studied: age and rate of growth; age composition of the population; reproduction success; food habits; movements; and extent of the fishing pressure.

As part of an investigation of the non-game fish resources of Utah, a study of the age and growth rate of the carp was instituted. A preliminary investigation indicated that the opercular method was superior to several other methods of determining age and growth in the carp. Age and growth were calculated from the opercular bones of 330 carp collected at Ogden Bay Refuge in 1950-51. Distances to annuli were measured directly. The relationship between the posterior radius of the opercular bone and the standard length of the carp was curvilinear. Past growth was calculated with a logarithmic nomograph. Expected number of annuli on opercular bones of known age carp, agreement of ages assessed by length frequency modes and those assessed from opercular bones of the same fish agreement of empirical and calculated lengths for the first three years of life, agreement between ages assessed by scales and opercular bones, and increase in age with increase in size were accepted as evidence of the validity of the opercular method. Decrease in growth rate at any year of life for successive age groups is attributed to a gradual change of the environment.

Microhabitat use by cutthroat trout and macrohabitat use by both cutthroat and rainbow trout were studied i n the Green River below Flaming Gorge Dam during the winters of 1988 and 1989. Microhabitat parameters used by cutthroat trout, such as focal velocity, depth, and fish elevation, differed significantly in eddies, runs, and riffles. Mean focal velocities in runs were 0.79 body lengths/seconds (bl/s), in riffles 0.66 bl/s, and in eddies 0.24 bl/s. Cutthroat trout size also varied significantly with macrohabitat; larger fish were found in riffles. Macrohabitat use by cutthroat trout and rainbow trout differed significantly among species, macrohabitat types, and months. Both rainbow trout and cutthroat trout macrohabitat use shifted from lower velocity habitats during winter to faster velocity habitats in summer. Cutthroat trout and rainbow trout used macrohabitats at seasonally differing rates. Riffles were never selected in proportion to their abundance, especially during high winter discharges. Cutthroat trout implanted with radiotransmitters exhibited little movement during diel monitoring and did not change their occupation of macrohabitats.

The Logan River heads in the southeastern corner of Franklin County, Ida.ho, and runs in a south and westerly direction.· It enters the state of Utah through the northern boundary in the northeast corner of Cache County. The main stream is fed by two tributary streams which head in separate directions a few miles a.part. The Franklin Basin branch is the main contributing tributary while the Beaver Creek branch is nearly as large.