title
Cutthroat trout spawning activities on Bear Lake, 1975-1989
author
Array ( [0] => Nielson, Bryce R. [1] => Birdsey, Paul W., Jr. )
abstract
UDWR Publication Number 91-11
date
1991-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
file_path
https://grey-lit.s3.wasabisys.com/cutthroat-trout-spawning-activities-on-bear-lake-1975-1989.pdf
thumb
https://grey-lit.s3.wasabisys.com/cutthroat-trout-spawning-activities-on-bear-lake-1975-1989-pdf-1-793x1024.jpg
content
• CUTTHROAT TROUT SPAWNING ACTIVITIES ON BEAR LAKE, 1975-1989 Bryce R. Nielson Project Leader Paul W. Birdsey, Jr. Special Projects Biologist Dingle-Johnson Project Number F-26-R Publication Number 91-1 Utah Department of Natural Re'sources Division of wildlife Resources 1596 West North Temple Salt Lake City, utah 84116 An Equal Opportunity Employer Timothy H. Provan Director March 1991 TABLE OF CONTENTS INTRODUCTION . .. .. . Project Background Historical Background METHODS . . . . . . . Trap Installation and Operation Spawning . . . . . . . . . . . Captive Broodstock Replacement Data Analysis RESULTS DISCUSSION Influence of Flow Timing of Spawning Run Between Year Variation in Mean Total Length Within Year variation in Mean Total Length Population Structure . . . . • . . . . Mark and Age Composition . . . . . . . Influence of Growth Rate on Maturation Egg Size vs. Female Total Length Post-spawning survival Repeat Spawning RECOMMENDATIONS LITERATURE CITED - iii - Page 1 1 3 7 7 8 11 12 15 23 23 27 27 34 38 43 53 55 57 58 65 67 Table 1. 2. 3 • 4. 5. LIST OF TABLES Trapping dates for the three Bear Lake cutthroat trout spawning traps, 1975-1989 . . . . . . . Summary of Bear Lake cutthroat trout trapping operations, 1975-1989 ........... . . Summary of Bea'r Lake cutthroat trout egg collection, 1975-1989 . . . . . . . . . Summary of Bear Lake cutthroat trout repeat spawners, 1975-1989 . . . . . . . . . . . . . . Results of t-tests between sexes by trap for the study period . . . . . . . . . . . . . . - v - Page 8 16 . . . 19 . . . 21 33 LIST OF FIGURES Figure 1 . Map of Bear Lake showing major tributaries 2. Map showing the location of the 19 75-1988 and 1989 st. Charles Creek trap sites 3 . 4 . Flows (cfs) in Swan and st. Charles creeks in 1981 and 1982 . . . . • • • • • Number of Bear Lake cutthroat trout captured by year at the spawning traps, 1975- 1989 5. Number of Bear Lake cutthroat trout captured by week at the spawning traps . . . . . 6 . Mean total length with 95 % confidence limits for Page 2 4 24 25 28 males and females captured in the Bear Lake spawning traps, 1975- 1989 •• . • • . • . • • . • . • • . • . 31 7 . Mean total length with 95 % confidence limits by date for the Bear Lake spawning traps . . . . . • . . 35 8 . Length-frequency histograms captured in the st. Charles 1975-1989 . • • ••• •. of males and fema l es Creek trap, 9. Length-frequency histograms of males and females 39 captured at the Swan Creek trap, 1975- 1989 ••• 4 1 10 . Length- frequency histograms of males and females combined from the st. Charles Creek spawning trap, 1975-1989 ..• •.•...•..•. . . 44 11. Length-frequency histograms of males and females c ombi ned from the Swan Creek spawning trap, 1975- 1989 ... ...... . ..•..•..• 46 12 . 13 . Percentage of examined spawn i ng Bear Lake c~tthroat trout which were marked , 1981- 1,989 Composition of known age fish in the Bear Lake cutthroat trout spawning popula tion, 1981- 19 8 9 - v ii - 4 8 50 LIST OF FIGURES (cont.) Figure 14 . Mean total length with 95 % confidence limits for known age Bear Lake cutthroat trout captured in the Page spawning traps . . . . . . . . . . . . . . . . • . 54 15. 16 . 1 7 . 18 . An example of change in total length (with 95% confidence limits) by mark group . . . . . . Number of repeat spawning Bear Lake cutthroat trout captured in the spawning traps, 1977- 1989 • • . • • • • • • . . • . Year returned after initial capture repeat spawning Bear Lake cutthroat multiple trap returns • . . • . . . for all trout and .. Percent unmarked repeat spawning Bear Lake cutthroat trout, 1981- 1989 • • . . • . • • - i x - 56 59 60 61 INTRODUCTION Project Background The Bear Lake Cutthroat (Oncorhynchus clarki utah) Enhancement Project was initiated in 1973 with two main objectives; 1) to determine if the native Bear Lake cutthroat trout still existed in a pure, morphologically distinct form and, 2) if the native cutthroat trout existed, develop methodologies to enhance the population. An important aspect of this latter objective was the operation and maintenance of cutthroat trout spawning traps on the primary tributaries to collect spawn for arti£icial propagation. Artificial propagation was necessary because flows in the tributaries were either partially or entirely diverted for irrigation purposes during late summer, severely impacting potential natural recruitment to the lake. A trap has been installed and operated by Utah Division of Wildlife Resources personnel on Swan Creek (Figure 1) annually since 1973. The present site is 30 m upstream from the historic trap site utilized from 1939 to 1953. The trap was originally covered by a metal framework and canvas tent. Improvements to the trap were made in 1978 with the construction of a wood building over the holding pens, and in 1981 with the installation of power. The Idaho Fish and Game Department has installed and operated a temporary weir and .trap on St. Charles Creek annually since 1975. Fish from st . Charles Creek were transported to the St Charles Creek Swan Creek BeClr River Inlet/Outlet • Biq_Spring i::; reek rOAHO -UTAH Figure 1. Map of Bear Lake showing major tributaries. - 2 - ~ , 2 "!I .... ki lometers 10 UT Swan Creek trap for holding until spawning because of lack of holding facilities and security at the temporary trap. Except for 1989, the st. Charles Creek trap has been located on the property of Mr. Wayne Transtrum in the vicinity of the historic trap site (Figure 2). Slight upstream or downstream yearly variations in actual trap site were dictated by anticipated runoff and lake levels. In 1989, the trap was moved downstream below the high water elevation of the lake because of extremely low lake levels. Under low lake level conditions, st. Charles Creek flows for a considerable distance over mud flats prior to reaching the lake. The mouth of the stream is braided and very shallow in these conditions. A temporary weir and trap has been installed and maintained by the Utah Division of wildlife Resources on Big spring Creek at the south end of Bear Lake (see Figure 1) since 1987. Nielson (1986) noted that runs of spawning cutthroat trout were apparently increasing in this tributary possibly as the result of straying by un imprinted cultured fish. The trap was located approximately 1 km upstream from the mouth, inside the fenced boundaries of Rendezvous Beach State Park for increased security. Fish captured in Big Spring Creek were transported to the Swan Creek trap and held until spawning. Historical Background Spawning traps were established on Swan and st. Charles creeks in 1939. The traps were run as part of a U. S. Bureau of - 3 - ni ddla For~ W 5 ' r ) H < J, E -~ For~ _ . SL Cll~rlls Cra!~ . OAI.r. U:NIC! a:UHc.a~Y -'-.. ..,. - .... --- .. __ ... _ ..... . : .... . ,. - : ... .. _"" .......... -.. ..•. -... _ ,- , .. ,.-.-:" :," ' .. ~.­ ~­-" . Figure 2. ... - ... -.. --.--...... ~ ••• __ ··-....... 4 Hi gll':'!':y 39 Littla C:-~!~ ~"-' .f 975 1988 (I ) and 1989 (. ) Mao show'...r:g t.'1e l=ation of t.'1e 1 - - i - - k (Li· ~-le ~-~k) trao s_ ~es. St. Cha=les <:=ee.. _~ '-__ _ - 4 - Fisheries project, in cooperation with the states of Utah and Idaho, under the direction of Dr . stillman Wright . operation of the traps from 1939 to 1943 typically commenced about mid-March and ran through mid-June (S. Wright, 1942, unpub. memo). Egg collection totals for the two traps in 1939 were 900,000 and 200,000 for Swan and st. Charles creeks, respectively. Low lake levels in the early 1940's impacted egg collection efforts, especially at st. Charles Creek. Totals for 1940 were 662,000 and 38,000 from Swan and st. Charles creeks, respectively . The st. Charles Creek trap was apparently not operated between 1941 and 1946. Egg collection at the Swan Creek trap totaled 788,000 in 1941, 505,000 in 1942, and 117,000 in 1943. The trapping records are incomplete for subsequent years, but egg totals apparently continued to decline. Egg collection was discontinued at Swan Creek in 1954 . Only 40,000 eggs were collected from Swan Creek during that year. Trapping continued on st. Charles Creek until 1960 . A total of 152,160 eggs were collected at that time. Resumed trapping efforts at Swan Creek in 1973 and 1974 y ielded 439,896 and 357,845 cutthroat trout eggs, respectively (Nielson and Archer 1977) . A total of 140 fish, 115 females and 25 males, were spawned in 1973 . In 1974, 141 females and 95 males were spawned . Average total length of spawned fish in 1974 was 447 mm and 386 mm for females and males, respectively . Length data were not collected in 1973 . - 5 - METHODS Trap Installation and Operation The Swan Creek trap required annual cleaning, and installation of a weir and water regulation structure to become operational. Trapping typically commenced in the first half of April to insure capture of all spawners (Table 1). The st. Charles Creek temporary weir and trap were erected approximately 1 May each year except for 1975 and 1987-1989. Because of the later installation time of this trap, a significant number of early migrants were probably missed. Twenty percent of all spawners entering the "St. Charles Creek trap were released upstream unspawned to insure the perpetuation of this run. Trapping activities continued until the latter part of June in most years. Earlier cessation dates of trapping occurred in 1981 due to low flows, and in 1982 because of inundation of both traps during extremely high flows. The st . Charles Creek trap was also shut down early in 1986 because of high flows. Every other bar in the weir at Swan Creek was removed during 1982-1986 because of high flows. Swan Creek and portions of St. Charles and Big Spring creeks were close9 to fishing during the spring to protect spawning cutthroat trout. The area of the lake immediately adjacent to the mouths of Swan and st. Charles creeks was also closed to fishing during the "spawning runs. Other species entering the - 7 - Table 1. Trapping dates for the three Bear Lake cutthroat trout spawning traps, 1975-1989. Tra22ing Season BeginLEnd st. Charles Swan Big Spring Year Creek Creek Creek 1973 3/1 - 6/18 1974 3/9 - 6/18 1975 4/4 - 6/19 4/3 - 6/24 1976 5/1 - 6/15 4/2 - 6/29 1977 5/1 - 6/15 4/16 - 6/21 1978 5/9 - 6/16 4/4 - 6/19 1979 5/3 - 6/11 4/16 - 6/27 1980 5/1 - 6/20 4/19 - 6/21 1981 4/30 - 6/6 4/6 - 6/10 1982 5/3 - 6/8 4/6 - 6/16 1983 5/2 - 6/20 4/20 - 6/20 1984 5/7 - 6/15 4/26 - 6/20 1985 4/30 - 6/18 4/22 - 6/19 1986 4/29 - 6/1 4/22 - 6/25 1987 4/14 - 6/12 4/15 - 6/17 4/24 - 6/17 1988 4/7 - 6/22 4/16 - 6/29 4/20 - 6/14 1989 4/11 - 6/16 4/11 - 6/28 4/24 - 6/15 - 8 - traps such as Utah sucker (Catostomus ardens), Utah chub (Gila atraria), and carp (Cyprinus carpio) were destroyed during the early years of the project. More recently, they have been released upstream so their natural migration patterns would continue. Rainbow trout (Oncorhynchus mykiss) were stripped and released upstream prior to 1986. Since that time all rainbow trout entering the traps have been sacrificed to avoid any potential hybridization with cutthroat trout. Cutthroat trout fingerlings raised at the Mantua Hatchery have been exposed to a constant concentration of morpholine for possible imprinting since 1984. Morpholine drip stations were established at the Swan Creek trap 1987-1989 and at the st. Charles Creek trap in 1987 and 1988. The drip station at the Swan Creek trap utilized a 120 liter plastic carboy filled with a stock solution of morpholine and water. Delivery to the stream was accomplished using a peristaltic chemical pump. A 20 liter plastic carboy filled with stock solution was used at st. Charles Creek. Gravity flow was used to deliver the solution to the stream. Concentrations of morpholine in the stock solutions, drip rates and final concentrations were calculated using the methods of Scholz et al. (1975). Spawning After sufficient numbers of spawners were captured, spawning occurred on a weekly basis. Broodfish were selected according to a specific set of criteria to avoid including rainbow trout x - 9 - cutthroat trout hybrids and Yellowstone type cutthroat trout in the spawning stock. Fish selected for spawning had distinctive round spots concentrated posteriorally above the lateral line with very few spots on the head. Cutthroat trout males used in spawning were typically the largest individuals and highly colored with rose-orange hues. Females had a drab gray-brown cast, often with a yellow spot located on the ventral portion of the body. Size was not used as criteria for females. , Neither sex exhibited the typical crimson maxillary slash (Nielson 1978). Further separation of Bear Lake and Yellowstone cutthroat trout was also possible by egg color . Bear Lake cutthroat trout eggs were pale yellow, whereas eggs from Yellowstone type cutthroat trout were blood red. These morphological criteria have been sUbstantiated by electrophoresis (Martin 1983, unpub . data). On spawning days, the fish were anesthetized with tricaine methane sulfonate (MS-222) to facilitate handling then tagged with a numbered tag prior to spawning. Because of observed tag loss in the trap and on repeat spawners, several different tag types were used throughout the project; spaghetti, clinch, and lock-on, all manufactured by Floy Tag of Seattle, WA . Total lengths were recorded for each fish along with tag number, sex and tributary ascended. Weight prior to spawning was taken on all fish from 1975 through 1980. Each fish was examined under an ultraviolet light to detect fluorescent grit marks to determine hatchery stock and age-class composition of the run. Methods for examination were described - 10 - by Nielson (1990). Prior to 1982, only cutthroat trout in size classes corresponding to stocked groups of fish were examined. Beginning in 1982, all fish were examined except those released upstream at st . Charles Creek. The dry pan method was used in spawning . Five to ten females were spawned into a net covered pan . . The eggs were then transferred to a bucket and fertilized with 3 or 4 selected males . Sperm diluent was added to the bucket to increase sperm motility and egg fertilization. The diluent has been used annually since 1980. Before transportation to the hatchery the eggs were water hardened and disinfected. All spawned fish were allowed to recover from the anesthetic prior to release downstream at the Swan Creek trap. Hand stripping of broodstock was used in all years except 1980 when compressed air was used. Greater mortality of brood fish resulted from the compressed air technique due to the inability of the fish to vent the air and hemorrhaging of internal organs. Captive Broodstock Replacement A captiv e broodstock has been maintained at the J. Perry Egan Hatchery in Bicknell, Utah since 1973 to supple~ent the number of eggs taken from the wild . Development of the broodstock began in 1973 when 10,000 eggs were sent to the hatchery from the Swan Creek trap. An additional 10,000 eggs were sent each year through 1977, except 1975. However since - 11 - Egan Hatchery is in the Colorado River drainage, disease protocol established by the Colorado River wildlife Council prevented the hatchery from receiving eggs from non-certified sources after that time. The required disease protocol was satisfied by 100% lethal sampling of the selected parent stock. Four females and eight males from each tributary were selected and spawned as family groups. Eggs from the brood stock were quarantined at the Fisheries Experiment station as family groups until the required disease inspections on the parents were completed. After hatching, the fish were raised to fingerling size, then transported to the Egan Hatchery for rearing. Broodstock replacement was done using this method in 1979, 1983, 1987, and 1989. Nine females and twenty-seven males were used for broodstock replacement parents in 1989 in an effort to increase genetic diversity. Broodstock replacement parents were typically selected from different dates in the run to further enhance diversity. Data Analysis Original raw data from the trapping operations were coded and entered onto the project's microcomputer. The data were entered into the Paradox database management system (ANSA 1987) and checked a minimum of three times for accuracy. Data summaries and analyses were accomplished using the Number Cruncher statistical system (Hintze 1987) . Unless otherwise - 12 - noted, all analyses are significant at ~ . 05. The original data sheets from the 1976 trapping operations had been misplaced and the only data a vailable from that year were a listing of the tag numbers, total lengths, sex, and capture location . Data on repeat spawners and the disposition of captured fish were not available for 1976. For this reason, most of the summaries for the 1976 data were taken from the original annual report (Nielson and Archer 1977) . All other years were r e - summarized because of mi nor error s in the initial summaries . Therefore, the summaries presented in this report may not exactly correspond with pr e v ious annual reports . Egg totals for the traps were calculated by summing the total lengths (or weights) of spawned females from each trap and dividing by the summation of all spawned females total lengths (or weights) . This ratio was then multiplied by the number of eggs collected to get the totals for each trap . - 13 - RESULTS A total of 6990 cutthroat trout were tagged at Bear Lake between 1975 and 1989 (Table 2). The tagging totals consisted of 4181 females, 2774 males, and 35 immatures. Some of the fish released upstream at st. Charles Creek between 1983 and 1986, and a l l fish released since 1987 were tagged and included. in the t otals . Data from untagged cutthroat trout released upstream were not included in any of the summaries. Cutthroat trout trapping operations at Bear Lake have y ielded over 11 million eggs during the project (Table 3). The total number of eggs collected annually has varied between 225,210 in 1982 and 1,204,944 in 1975. Egg eye-up was typically in excess of 85% . (R . Roubidoux, UDWR, pers . comm. 1990). variations in environmental conditions probably accounted for the wide range in the number of eggs collected. Drought conditions and low stream flows in 1977, 1981, and 1987 through 1989 impeded upstream migration by cutthroat trout and subsequently reduced the number of eggs collected. Dewatering of st. Charles and Big Spring creeks occurred throughout most of the 1988 and 1989 trapping seasons . Conversely, high flows during the period from 1982 through 1986 severely impacted trapping efficiency at Swan and st . Charles creeks. Although stream flows were not excessive in 1980, the efficiency of the Swan Creek trap was influenced by high lake - 15 - T a b le 2 . S u m m ar y o f B e a r L a k e c u tt h r o a t tr o u t tr a p p in g o p e ra ti o n s , 1 9 7 5 -1 9 8 9 . N O . Q M EA N S T D N O . d M EA N ST D N O . IM M . M EA N ST D Y E A R T A G G E D T L Q D E V Q T A G G E D T L d D E V d T A G G E D T L IM M . D EV IM M . s t . C h a rl e s 1 9 7 5 2 5 3 6 1 3 6 2 .8 9 9 6 2 3 7 7 .0 0 1 9 7 6 2 6 0 5 6 9 7 0 . 6 1 2 9 6 1 9 8 8 .7 0 I- ' 1 9 7 7 8 5 5 4 1 8 5 . 0 6 7 5 0 4 9 7 .0 0 '" 1 9 7 8 1 5 4 5 7 1 6 9 .7 8 9 6 1 9 8 3 .9 2 4 9 3 1 9 7 9 1 4 4 5 7 0 5 8 .3 9 8 6 2 3 6 9 .2 1 4 1 2 1 9 8 0 2 0 2 5 9 7 6 0 . 6 1 0 2 6 3 7 9 2 .6 0 1 9 8 1 8 1 5 9 4 6 6 .8 6 2 5 8 8 9 3 .3 0 1 9 8 2 3 3 5 6 2 5 4 .0 3 6 5 8 0 7 6 .8 0 1 9 8 3 1 0 5 5 5 8 6 3 . 1 7 0 6 0 5 7 0 .1 0 1 9 8 4 9 4 5 9 4 5 6 .2 5 2 5 9 8 7 1 .3 0 1 9 8 5 1 1 3 5 4 4 5 8 .9 6 0 5 6 2 7 1 .2 0 1 9 8 6 4 4 5 4 8 5 7 .1 2 6 5 4 6 7 2 .5 0 1 9 8 7 1 6 0 5 5 2 5 3 .7 7 3 5 6 6 7 6 .8 1 4 8 4 1 9 8 8 1 7 0 5 6 5 5 8 .2 1 1 5 5 7 2 7 4 . 3 0 1 9 8 9 1 4 1 5 6 3 5 1 . 5 1 0 7 5 6 4 6 4 . 5 0 T a b le 2 . c o n ti n u e d . N O . <;> M EA N ST D N O . d M EA N ST D N O . IM M . M EA N ST D Y EA R TA G G ED T L <;> D EV <;> TA G G ED T L d D EV d TA G G ED T L IM M . D EV IM M . S w an 1 9 7 5 5 5 5 8 1 6 4 .4 1 0 5 5 7 1 1 4 . 1 0 1 9 7 6 5 8 5 3 8 8 3 . 5 3 1 5 4 8 1 1 1 .5 0 1 9 7 7 8 2 5 0 4 8 5 .2 1 1 9 4 6 7 9 1 .5 0 1 9 7 8 2 1 2 5 3 3 5 8 .7 1 8 5 5 5 4 7 4 .5 1 8 3 9 0 3 1 . 2 1 9 7 9 1 6 8 5 4 4 6 5 . 5 1 1 6 5 8 8 8 0 .8 2 3 8 1 1 9 8 0 6 0 5 3 7 6 1 .0 3 9 5 3 4 9 1 . 5 1 4 0 7 1 9 8 1 1 6 8 5 2 0 6 9 .9 1 5 4 5 0 4 7 9 .7 0 1 9 8 2 7 2 5 3 6 5 4 .4 8 8 5 5 3 6 1 .0 0 >- " 1 9 8 3 1 1 6 5 4 7 5 2 .2 8 5 5 8 2 7 9 .9 0 -.- J 1 4 7 5 6 3 8 5 5 7 3 9 6 .7 1 3 3 0 1 9 8 4 7 1 . 0 1 9 8 5 1 6 0 5 5 4 7 3 . 0 1 1 6 5 3 4 8 7 .9 3 4 3 8 3 4 .7 1 9 8 6 1 1 8 5 2 0 6 3 .5 4 0 4 9 9 6 8 . 3 2 4 1 2 1 9 8 7 2 1 0 5 3 0 6 1 . 5 1 0 8 4 9 7 1 0 0 .8 2 4 1 4 1 9 8 8 1 8 3 5 2 9 6 4 .6 1 5 1 5 1 3 9 6 . 3 0 1 9 8 9 2 3 5 5 3 0 6 9 .7 2 1 0 5 1 0 9 5 .3 1 3 9 5 B ig S p ri n g 1 9 8 7 7 6 5 6 4 6 0 . 1 3 7 5 6 8 6 0 .3 1 4 5 6 1 9 8 8 1 9 5 4 5 4 1 .6 1 2 5 2 9 4 6 .4 0 1 9 8 9 3 5 0 8 2 4 .9 3 6 0 7 6 2 . 0 0 T a b le 2 . c o n ti n u e d . N O . 9 M EA N ST D N O . d M EA N ST D N O . IM M . M EA N ST D Y EA R TA G G ED T L 9 D EV 9 TA G G ED T L d D EV d TA G G ED T L IM M . D EV IM M . T o ta l C o m b in ed 1 9 7 5 3 0 8 6 0 7 6 7 .1 1 0 9 6 1 7 8 2 .7 0 1 9 7 6 3 1 8 5 6 3 7 4 .0 1 6 0 6 0 5 9 7 .3 0 1 9 7 7 1 6 7 5 2 3 8 6 .8 1 8 6 4 8 0 9 4 .9 0 1 9 7 8 3 6 6 5 4 9 6 6 .1 2 7 4 5 7 5 8 3 .3 2 0 4 0 0 5 0 .5 1 9 7 9 3 1 2 5 5 6 6 3 .5 2 1 4 6 0 4 7 7 .5 3 3 9 1 1 8 .7 f- -' co 1 9 8 0 2 6 2 5 8 3 6 5 .6 1 4 1 6 0 8 1 0 2 .8 1 4 0 7 1 9 8 1 2 4 9 5 4 4 7 7 .2 2 1 6 5 2 8 9 1 .9 0 1 9 8 2 1 0 5 5 4 4 5 5 .4 1 2 4 5 6 0 6 6 .8 0 1 9 8 3 2 2 1 5 5 2 5 7 .8 1 5 5 5 9 2 7 6 .2 ' 0 1 9 8 4 2 4 1 5 7 5 6 7 .2 1 3 7 5 8 2 8 8 .5 1 3 3 0 1 9 8 5 2 7 3 5 5 0 6 7 .6 1 7 6 5 4 4 8 3 .4 3 4 3 8 3 4 .6 1 9 8 6 1 6 2 5 2 8 6 2 .9 6 6 5 1 7 7 3 .2 2 4 1 2 1 9 8 7 4 4 6 5 4 4 6 0 .0 2 1 8 5 3 2 9 3 .8 4 4 4 2 4 3 .1 1 9 8 8 3 7 2 5 4 6 6 3 .0 2 7 8 5 3 8 9 0 .6 0 1 9 8 9 3 7 9 5 4 2 6 5 .2 3 2 0 5 2 9 8 9 .8 1 3 9 5 T O T A L 4 1 8 1 2 7 7 4 3 5 t- ' '" T a b le 3 . S u m m ar y o f B e a r L a k e c u tt h r o a t tr o u t e g g c o ll e c ti o n , 1 9 7 5 -1 9 8 9 . Y E A R 1 9 7 5 1 9 7 6 a 1 9 7 7 1 9 7 8 1 9 7 9 1 9 8 0 b 1 9 8 1 1 9 8 2 c 1 9 8 3 c 1 9 8 4 c 1 9 8 5 c 1 9 8 6 c 1 9 8 7 1 9 8 8 1 9 8 9 T O T A L S T . C H A R L E S 9 7 5 ,0 9 3 7 2 1 ,5 9 2 2 6 4 ,2 0 1 5 3 3 ,1 1 4 4 4 3 ,1 2 4 7 0 7 ,9 3 3 2 9 2 ,9 8 6 6 6 ,8 2 7 2 1 5 ,8 4 3 2 6 6 ,2 4 9 3 2 1 ,2 9 7 1 0 8 ,5 6 1 3 3 9 ,8 8 7 4 0 0 ,9 0 0 3 7 7 ,2 2 2 6 ,0 3 4 ,8 2 9 SW A N 2 2 9 ,8 5 1 1 9 1 ,9 1 4 2 1 3 ,4 0 8 6 4 7 ,3 0 0 4 9 8 ,3 1 2 1 9 7 ,5 3 2 3 7 7 ,5 5 0 1 5 8 ,3 8 3 2 7 0 ,0 3 9 4 2 2 ,5 4 7 5 1 0 ,8 4 3 2 7 1 ,1 3 5 4 7 7 ,1 5 6 4 2 3 ,2 4 6 6 1 4 ,3 9 5 5 ,5 0 3 ,6 1 1 B IG S P R IN G 2 0 7 ,4 8 8 4 3 ,3 3 6 9 0 9 4 2 5 9 ,9 1 8 T O T A L N O . 1 ,2 0 4 ,9 4 4 9 1 3 ,5 0 6 4 7 7 ,6 0 9 1 ,1 8 0 ,4 1 4 9 4 1 ,4 3 6 9 0 5 ,4 6 5 6 7 0 ,5 3 6 2 2 5 ,2 1 0 4 8 5 ,8 8 2 6 8 8 ,7 9 6 8 3 2 ,1 4 0 3 7 9 ,6 9 6 1 ,0 2 4 ,5 3 1 8 6 7 ,4 8 2 1 ,0 0 0 ,7 1 1 1 1 ,7 9 8 ,3 5 8 a - to ta ls fr o m o r i g in a l su m m a ri e s . S e e te x t fo r e x p la n a ti o n . T O T A L O Z . # /O Z . 5 0 5 3 3 2 8 8 1 7 3 0 4 4 4 9 3 6 0 5 4 0 2 2 2 7 3 8 9 6 8 2 2 3 1 3 3 5 2 3 6 2 4 1 6 7 7 4 5 6 1 4 0 9 1 4 6 4 5 5 0 ,0 3 4 2 3 9 2 7 8 2 7 6 2 6 5 2 6 1 2 2 5 2 4 5 2 3 3 2 1 8 2 0 6 2 3 0 2 2 6 2 2 5 2 1 2 2 1 5 2 3 6 b - S w an C re e k a n d S t. C h a rl e s e g g s w e re k e p t s e p a ra te a t th e ti m e o f c o ll e c ti o n . T o ta ls re p re s e n t a c tu a l m e a su re d v a lu e s . c - In e ff e c ti v e tr a p p in g d u e to h ig h fl o w s . levels at that time. Lake water backed up into the trap to a depth of approximately 1 m (Nielson and Johnson 1981). Trapping efficiency was reduced because fish could swim out of the trap or bypass the weir. Numbers of repeat spawning Bear Lake cutthroat trout were low throughout the project (Table 4). A total of 212 cutthroat trout, 164 females and 48 males, were recaptured in the traps. Fish with obvious scars indicative of tag loss were included in these totals. The majority of repeat spawners returned to the same trap where they were originally tagged and usually the same week as the initial capture . Only 11 cutthroat trout returned multiple years during the period from 1977 through 1989 . - 20 - Table 4. Summary of Bear Lake cutthroat trout repeat spawners, 1975-1989a . Data includes fish with lost tags. NO. 9 MEAN STD NO. d MEAN STD YEAR RETURNED TL 9 DEV 9 RETURNED TL d DEV d st. Charles 1975 0 0 1977 5 660 15 . 8 0 1978 0 1 601 1979 5 615 37.4 0 1980 21 622 48 . 0 3 640 54.6 1981 20 635 41.3 2 482 1982 1 565 0 1983 2 678 0 1984 3 659 46 . 4 1 645 1985 1 514 0 1986 2 630 0 1987 1 650 0 1988 1 661 0 1989 15 621 42 . 5 2 614 Swan 1975 2 585 0 1977 5 634 99 . 6 0 1978 3 546 2 0 . 1 2 543 1979 6 581 41.4 2 619 1980 18 590 42.7 3 605 11.8 1981 9 636 69 . 3 2 490 1982 1 556 5 500 46.5 1983 6 594 60 . 6 4 588 55.9 1984 15 623 46 . 9 6 520 44.9 1985 10 614 50.3 0 1986 4 626 71 . 6 2 587 1987 2 597 0 1988 2 584 0 1989 7 605 55.4 8 549 52.5 a - 1976 data not available. See text for explanation. - 21 - Table 4. Continued. NO . Q MEAN STD NO. d MEAN STD YEAR RETURNED TL Q DEV Q RETURNED TL d DEV d Big Spring 1987 1 601 1 585 1988 0 0 1989 0 0 Total Combined 1975 2 585 0 1977 10 647 68 . 6 0 1978 3 546 20.1 3 562 36.3 1979 11 597 41. 6 2 619 1980 39 607 47 . 9 6 623 40 . 3 1981 29 636 50.3 4 486 8 . 3 1982 2 561 5 500 46.5 1983 8 615 64.1 4 588 55.9 1984 18 629 47.5 7 538 62 .5 1985 11 605 56 . 5 6 628 55 . 5 1986 2 587 0 1987 4 611 51. 8 1 585 1988 3 609 98.3 0 1989 22 616 46.2 10 562 56.4 TOTAL 164 48 - 22 - DISCUSSION Influence of Flow Tributary flows varied widely throughout the course of the study. Droughts occurred in 1977, 1981, and 1987 through 1989. Flooding occurred from 1982 through 1986 . Flows in Swan Creek ,(Bear Lake Regional Commission 1983) varied from approximately 5 cfs during the 1981 trapping season to greater than 200 cfs in 1982 (Figure 3) . Observations in 1986 indicated that flows in Swan Creek were even higher at that time but no measurements were taken. Ineffective trapping occurred during both drought and flood periods . For example, during June 1986 water depths inside the st . Charles Creek trap were approximately 1 . 5 m, nearly the height of the weir . Cutthroat trout were observed jumping over the weir at that time. Fish were also able to bypass the Swan Creek trap during periods of high flows when e very other bar was removed from the weir. Electroshocking in Swan Creek in fall 1986 revealed unmarked cutthroat trout f i ngerlings upstream from the trap . No adult resident cutthroat trout have been observed in Swan Creek indicat'ing that these fingerlings were natural recruits from spawners which had bypassed the trap . Despite differences in trap efficiencies with flow, a trend in numbers captured was evident (Figure 4). Cutthroat trout catches have increased in Swan Creek during the study and - 23 - -e- St. Charles - Swan 250 200 (j) ..... 150 .9 ~ 0 ...J 100 LL 50 Ot:~i~i~i~i~i iii M J J A SON D J F M A M J 1981 1982 Figure 3. Flows (cfs) in Swan and st. Charles creeks in 1981 and 1982. Data from Bear Lake Regional Commission (1983) . - 24 - -€- St. Charles - Swan Creek -.- Big Spring 500 400 I U) u: LL 0 300 U) a: w 200 01 :2 ~ 100 o I ~ 1975 1977 1979 1981 1983 1985 1987 1989 YEAR Figure 4. Number of Bear Lake cutthroat trout captured by year at the spawning traps, 1975-1989. - 25 - declined at st. Charles Creek. The reasons for the decline in st. Charles Creek are unclear but may be related to changes in the habitat or a reduction in the overall efficiency of the trap structure. Changes to the habitat or water quality of st. Charles Creek may have occurred as a result of improvements to the irrigation diversion located on Transtrum's property (see Figure 2) in fall 1978. These improvements allowed less water leakage through the structure and better regulation of the downstream flow. The new structure may also have impeded upstream migration of the cutthroat trout released from the trap (20% of the total run), especially during periods of low flows. Reduced efficiency of the trap structure may also have accounted for the trend in st. Charles Creek. Mean total length of spawning cutthroat trout has declined during the study and distances between the bars on the weir appeared to be sufficient to allow passage of smaller cutthroat trout. Therefore, a greater percentage of the run may have escaped the trap. Conversely, improved efficiency of the Swan Creek trap operation may account for some of the overall increase in the numbers of fish caught at that trap. The four-fold increase in the number of cutthroat trout captured at the Swan Creek trap, however, probably indicates an enhancement of the population. Large quantities of gravel were transported downstream and deposited below the Swan Creek trap during the flood period 1982-1986. As a result of this deposition, significant spawning - 26 - activities have been observed below the trap during 1987-1989. Timing of the Spawning Run Gresswell (1985) noted that the greatest catches of Yellowstone cutthroat trout occurred during periods of decreasing streamflow and increasing temperatures. In Bear Lake, cutthroat trout catches were greatest during the period of highest runoff. The peak of the run typically occurred during the latter half of Mayor the first part of June (Figure 5) . Immature cutthroat trout captured were not included in th~ figure because immatures were not always tagged. An interesting aspect to the timing of the run through time is the apparent shift in the st. Charles run from a late to an early run . Overall the run has extended in duration. since 1986, the run has begun earlier than the historic run and continued for 1- 2 weeks longer. The increase in duration of the run may be a reflection of an overall increase in the population. Between Year Variation in Mean Total Length The average size of cutthroat trout in both tributaries declined during the study (Figure 6) . Decline in mean total lengths were especially apparent since 1979. Significant decreases in mean total length were determined for st. Charles males (r2=O.68, p < .05). Regression coefficients were significant only when the 1977 data were excluded from the analyses. The low stream flows in 1977 apparently excluded larger fish from the - 27 - 1975 1977 '00 '00 , .. ,,. !!i '00 Ii '00 • • ~ -St.Ow ... ~ 70 ~ ......... St. Ct.., ... ! 7' ! ............ ........ Sw~ "" "" 2' ,., 0 0 5/13 6120 5127 .13 6110 6il6 .,.. 619 &13 ~17 15124 15131 ef7 61146121 """ DA7E 1978 1979 '00 ,"0 ,.. , .. Ii ' 00 !Ii '00 • " ~ -+-St..a-... ~ 7' ~ -+- Sf. a. ... ~ 7' ~ ~ f'---., " ........... -e- ..... "" A .. 0 519 15116 5123 &/30 6115 6113 6111~ 5/11 6118 5J2!5 611 618 61 t 5 6122 6f29 DA7E DATE 1980 1981 '00 '"" , .. ,.. ~ '00 ~ '00 ~ -$t.0' ... ~ 70~ -+- $t. o.'-$ ~ 7' ! J'\ --- s ... ........ ..... 00 00 2' 2. 0 0 5/1. 5122 5129 ." 6'11 61HI 6125 OM .m 5'20 .127 &3 '''0 DATE DATE Figure 5. Number of Bear Lake cutthroat trout captured by week at the spawning traps. Repeat spawners and immatures are not included in the figure. - 28 - 1982 1983 '00 "'0 , .. ... ili ~ < '00 ' 00 1J -St.Ow," 1J 7. ~ /\ ........ St. o.t"lH ~ 7. ~ -<>- ... ~ -<>- -! 00 00 2. 2. 0 0 t5/1~ .,2. 012 .,. 6/16 6/18 6/25 ." .,. .no 0120 OATE CATE 1984 1985 '"" '"" , .. ,.. Ji ili • '00 < '00 b ~ S< """" 1J ,. ~ - St. 0.'" I 10 --<>- - ~ "" --<>-~ "" 00 2. 2. 0 0 .". on. 15130 .,. .m on<> .". 0122 .129 "'. 6/12 6/19 O"TE DATE 1986 1987 '00 '"" ... ... ili ~ _SLOw," < '00 ' 00 1J ........ St. OW,- 1J --<>- Sw~ ! 10 --<>-~ ! 70 ~ - BiG ScrII"'Q 00 "" 2' .. 0 0 ' 6J6 6/145/21 ens 15014 &1161196125 "'30 M5 61t3 6/20 6127 613 6110 6117 DATE DATE Figure 5. continued. - 29 .li " ~ j 1988 '50 ... ">0 -Sl.OW ... 7. ~...., - BoQ SprIl'lO 50 2. O1---- 514 Sf11 "'8512561'1 6Ie &/156'2261'29 DATE Figure 5. continued. ~ ~ ! 30 1989 '50 ,. . ,,>0 -St.OIetI .. --<>- ,,"on ~ BoO $orrog O~+-~db~~~~~ &3 Sll0Sl17at2451Jl &17 &/''''61226128 DATE -- St. Charles Females 700 I F ~ 600 ,,\;; ILJ/' - ...J « I- 0 500 I- ~ 400 1975 1977 1979 ] i!: 700 ~600 ~ g 500 ~ -e- Swan Creek Females T 400 1 - I -- St. Charles Males ~ :/"~T 1981 1983 1985 YEAR -- Swan Creek Males 1975 1977 1979 '1981 1983 YEAR 1985 T T 1987 1989 I I 1987 1989 Figure 6. Mean total length with 95% confidence limits for males and females captured in the Bear Lake spawning traps, 1975-1989. - 31 - tributaries and the data, therefore, were considered to be an outlier. Significant declines in the mean total length of Swan Creek males, and st. Charles females were also identified by the analysis (p<. 05), however, the regression coefficients were indicative of high variability (r2=0.31 and 0 .29, respectively) and the significant p value may be an artifact of the data. No change in the mean total length of Swan Creek females was determined by the regression analysis. A decline in the mean total length of spawned females during the project was evident for both traps, excluding the 1977 data. The data were again highly variable with r2 values less than 0.40. A decrease in the average size of spawned females from the Swan Creek trap was apparent despite no change in the overall size of the females captured in that tributary. This indicates that the larger fish ascending the stream were not maturing prior to the discontinuation of spawning operations. The reason for the lack of maturation by the larger females in Swan Creek is unclear and requires further investigation. T-tests (Hintze 1987 ) determined that, except for 1985, st. Charles Creek fish of both sexes were significantly larger than Swan Creek males and females, respectively. In 1985, there were no significant differences between females from the two traps. Male cutthroat trout from st. Charles Creek were significantly larger than Swan Creek males that year, however. Males were significantly larger than females at the st. Charles Creek trap five years during the study (Table 5). - 32 - Table 5. Results of t-tests between sexes by trap for the study period. Significantly larger fish (~ .05 ) are indicated by asterisk. st. Charles Creek Swan Creek Year Females Males Females Males 1975 NSD NSD 1976 * NSD 1977 * * 1978 * * 1979 * * 1980 * NSD 1981 NSD * 1982 NSD NSD 1983 * * 1984 NSD NSD 1985 NSD * 1986 NSD NSD 1987 NSD * 1988 NSD * 1989 NSD * NSD - indicates no significant differences between sexes. - 33 - Females were significantly larger than males only one year. The remaining years there were no significant differences. In Swan Creek females were usually larger, with males significantly larger only three years during the study. Except for 1975 and 1976, instances of no significant differences between the sexes coincided with unusual water flows, either drought or flooding . Males appeared to be mor~ responsive to changes in environmental conditions than females. Average size of males increased during periods of flooding and decreased during drought. within Year variation in Mean Total Length Mean total length of cutthroat trout captured at the spawning traps typically showed a pattern of a significant increase between the first and second weeks, no change the following 2-3 weeks, and then declining during the last portion of the run (Figure 7). Data from repeat spawners and immatures captured in the traps were included in these analyses. Gresswell (1985) reported a similar pattern in Yellowstone cutthroat trout of larger fish entering the traps early in the run . However, he did not observe the initial significant increase in total length noted for the Bear Lake run. No intra-year differences in mean total lengths were determined during several years. These periods were usually associated with flood events and occurred more frequently at the st. Charles Creek trap. It is possible that the smaller and - 34 - -+- St. ow,.. 800 I 700 ~ ~ 000 ~ 000 0 ~ ~ 400 300 S/13 "'20 ___ sc. 0.. ... 800 I 700 ""7 1975 --- .. ~ 6/3 ",'0 o.TE 1978 ----...,. .". ~ ~ 000, ~ I t -=t ; k ~500 ~400 6/24 3OOCI----~--~--~~--~--~----~--­.,. erg &/16 5/23 6J3O &Ie 6113 &119 OATE 1980 ~ St. Ow .. --- .. ~ 800 i 700 ~ ~ : f ! -==+ '=------1 + -I ~ ~400 3OO LI ~ __ ~ __ ~ ____ ~ __ ~ ____ ~ __ _ /!if,.. om ~ &'4 6(11 OATE om 012. 1977 ___ St. Cherles --- .... 800 I 700 ~ 000 ~ 000 ~ 400 300 .'" e113 om 0/24 om et7 6/,. om ""TE 1979 -- SL 0wIM --- Sw~ 800 ] 700 i 000 ~ 5 000 .. ~ 400 3OO 1c---~--~----~--~----~--~---- &/', Slt8 &126 611 618 61115 6122 6129 800 I 700 _ StOW," ""'" ""TE 1981 --- Sw~ ~ ~ :t==: ~ --! ==t=1 ~ ~ 400 3OO 'L---~----~----~----~----­"'. om eil20 !5f27 013 0/10 "" TE Figure 7. Mean total length with 95% confidence limits by date for the Bear Lake spawning traps. NSD indicates no significant differences between dates. - 35 - 1982 1983 -e-- st. o-.w ... ....... .. ~ __ S1. 0... .. ....... s _ ..." ""'" ..." BOO 800 I 700 I 700 <. I -, KL ~600 i ~ f ~600 ~500 g ~ 400 ~ 400 300 300 15119 SI26 "" 0'" 151115 5/ 18 "". ." .,. .". M10 OATE DATE 1984 1985 ___ ~ 0. ... ....... .... ___ st. OwIM --- .... NSO> BOO BOO I I 700 700 ~ <. ~600 600 ~eoo .. 5 !>OO • ~ .00 ~ .00 300 300 .". ""'. ISI30 .... 0", ""'" .". om .= .,. "'2 .". DATE DATE 1986 1987 ........ St. 0.... ... ....... .. ~ -- St. c:r-. --- .... ..." BOO BOO I I 700 700 <. ~ooo ~eoo .. .. ~ !>OO • !>OO g 0 ~ ~ .00 ~ 400 300 300 "'0 51'4 ."" ., .. 0" 0/" 0/'8 612' 4130 510 .113 5120 .127 ." 6110 .,,, DATe DATe Figure 7 . continued. 36 1988 ~St.o...~ __ s-n BOO I 700 ~ eo<> ~ eo<> ~ """ ~L-~ __ ~ __ ~~~~ __ ~ __ ~ __ 5/4 !!\Ill 61'8 ~/2~ 611 6180 6110 6122 6129 DATE Figure 7. continued . - 37 1989 _ SW&r\ 800 I 700 ~ XQL-~ __ ~ __ ~ __ ~~ __ ~ __ ~ __ &/3 15110 6/17 05/2. 1S13, 61'1 6/14 6122 6128 OATE larger fish were either excluded from the trap or were able to escape during these periods. The observed pattern of smaller fish entering the traps early and late in the spawning runs coupled with the increased duration of the runs during the project led to the development of the following hypotheses: Ho: Ha : There is no significant decrease in mean total length of spawners when comparing similar time periods of the spawning run. There is a significant decrease in mean total length of spawners when comparing similar time periods of the spawning run. The hypotheses were tested using one- way analysis of variance (Hintze 1987) of total lengths of all fish captured versus year for the trapping period from approximately 10 May through 20 June (F10 ,524S=68 . 34, p <. 001). Data from the 1981 through 1983 spawning runs were not inc"luded in the analysis because of the limited duration of the runs those years. The 1976 data were also not included because no tagging date information was available for that year. Multiple comparisons of " the means from the analysis revealed that, except for 1977 and 1984, mean total lengths from the more recent spawning runs were significantly smaller than the earlier runs rejecting the null hypothesis. Population structure Length-frequency histograms for st. Charles (Figure 8) and Swan Creek (Figure 9) illustrated similar patterns. Females - 38 - 1975 1976 = ........ - ..... =~ --- ~ ~ i ~ ~nn I ~ a n~~ & I: I: .. • - - - - - -- - - - - - 'I'OT .... ....:n'H _ TOT .... ~TH_ 1977 1978 =--- --- =-- -- ~ ~ ~ m t ~ t & & I : I .. • • - - - - - - - - ... - - -TQT .... I.B'CJ1H _ l'Of .... LJ!Io4n'I_ 1979 1980 =- --- =- ---.. m t .. t a ~ I: _nn~llnn.JI_ I .. • - - ... - - - - - - - - ... lOT .... ..-.rrnt ... TOT .... ..a«nM _ 1981 1982 =--- --- =-- ---.. .. .. .. t .. t ~ ~ ~ I : I: •• .. • • - - ... - - - - - - - - -'I'OT .. ..--_ 'I'OT .... ~_ Figure 8. Length-frequency histograms of males and females captured in the St. Charles Creek trap, 1975-1989. Interval width equals 25 mm. 39 1983 1984 =--- -~ =~ -- ~ ~ .. .. f ~ ! ~ ~ ~ I .. I .. .. to ~ ,. • • ,.. - - - - -,.. - ... ... ... ... TOT~~_ TOT" ....0""_ 1985 1986 =-- -- =- --.. .. ! ! ~ ~ ~ I I .. .. ~ • ,.. - - ,.. - - ... - -fOT ..... IJt«lTH ..... 1987 1988 =--- --- =-... --- ~ .. .. .. ! ~ ! .. ~ a I .. I .. to to ~ ~ • • ,.. - ,.. ... ,.. - - - ,.. -fOT ..... ~_ 1989 =- --.. .. ! ~ ~ I .. to ~ • ,.. - ... ... ,.. ... 'f'O~"'~_ Figure 8. continued. 40 1975 1976 = ........ _-... =- -~ ~ ~ ~ ~ t ~ t ~ ~ ! I: I: ~ " • • - - - - - -- - - - - - TOT .... ~_ TOT .... -"'OTH ..... 1977 1978 =- --- 0_ -~ ~ ~ t ~ i ~ ! ! I : .1 I: ~ • - - - - - - - - - - - -tOT ..... I.BC'I'H _ TOT"'- La«J1H ..... 1979 1980 0 ....... --- 0 __ --m ., t ~ t ~ ! ! I : nd~~r.I. I: ~ • - - - - - -'IOT ..... ...-_ TOTAL LaG'TW _ 1981 1982 0_ --- 0_ -~ ., ., ., ., t ~ t ~ ! ! I : ! : " ~ • • - - - - - - - - - -TOT"~_ f'OT"~_ Figure 9 . Length-frequency histograms of males and females captured at the Swan Creek spawning trap, 1975-1989. Interval width equals 25 mm . - 41 - 1983 1984 =~ -~ =- -- ~ ~ .. ~ t ~ I ~ ~ ! " I " I .. ., ~ ., , , - - - - - -- - - - '" - TOT-'~_ TOT ..... .....0"'_ 1985 1986 =- -- =- --.. ~ ~ .. t ~ I ~ ~ ~ I " I " .. ., .. .. , , - - - - - - - - - - '" -TOT"'- L.oT'H _ 'I'OT .... UtCITH_ 1987 1988 = ..... -....... =--- - ..... ~ .. .. .. t ~ I ~ ~ ! I " I " ., ., .. .. , , - - - - '" - - - - - '" -'IOT ..... ~_ TOT","~_ 1989 = ....... -- ~ .. I ~ ~ I " " .. , -TOT"~_ Figure 9 • conti nued . 42 were approximately normally distributed throughout the study. Males however, shifted from a skewed-right distribution to a more normal distribution. Histograms of males and females combined revealed a declining percentage of fish in the larger size classes through time. In st. Charles Creek (Figure 10) the mode decreased from approximately 600 mm TL to 570 mm TL between 1975 and 1989. The mode in Swan Creek (Figure 11) declined from 570 rnrn TL to 530 mm TL during the same period. The skewed distribution of fish captured in the 1977 and 1981 runs reflects the low water conditions experienced during those years . However, a similar pattern was not apparent for the drought period from 1987 through 1989 . Changes in trap operations, occurrence of spawning below the traps, or overall changes in the population structure likely masked the influence of low water . Mark and Age Composition Cutthroat trout examined for marks in the Swan Creek trap r evealed a higher percentage of marked fish entering the Swan Creek trap than st . Charles Creek (Figure 12) . Because only cutthroat trout in size classes corresponding to stocked fish were examined in 1981, the value for that year is probably inflated. Only three fish were captured in the Big Spring Creek trap in 1989, and the percentage shown in the figure for that year is probably not representative of the population. - 43 - i 8 I ~ t " 8 r ~ 1975 TOT"'I.~_ 1977 0 1 lI yp tf ~ EI , ~ t " 8 I : :100:Il10 __ 100 ___ 100 __ fOT .... ~'""_ 1979 .Q •• lOO:JIO <10 _____ J'OO 1110 100 l"af ... laGTH _ 1981 , I ... oJtrwllIllI lOO:JIO __ eoo ___ l'OO __ l'OTAL laG,"" _ ~ t " ~ I : 1976 , I . do>JJ [lI1i i & ! t 8 I lOO :JIG _ 40 too NO «10 NO 100 '60 .., TOT ..... IJNI,",,_ 1978 )00 :Il1O _ .-eo too NO _ NO 1'00 7.0 .., TOT ..... I.aGIIoO _ 1980 .I . .m ."'"llilli~ 11 1111111 ~ i " 8 I : lOO:JIO ___ MOeooM 1'OToIIL 1.8G111 ..... 1982 0 1 p qaMU 1tD1W"Dn On q 100 :JIG _ .-eo _ NO _ _ 100 760 too T01'IIoI.. ~1'H_ Figure 10. Length-frequency histograms of males and females combined from the st. Charles Creek spawning trap, 1975-1989. Interval width equals 10 mm. - 44 - 1983 1984 ~ ! » ! ~ ~ I ,. I ~ • ,~~ TOT .... ~...., 1985 1986 ~ ~ ~ » ! » ~ ~ i ,. I ,. " ~ • • :IOO :MO _ ~ _ &IIO_ IMO 100 7110_ TOT .... ""OlH _ 1989 ~ i » ! I ,. " • n;m"ol. '--lM _ Figure 1 0. c ont i nue d . 45 ~ ~ ~ ~ i: 0 ~ t ,. ~ r t ,. ~ I: t ~ I 1975 300 leO .00 ..00 IlOO NO 4100 NO '/'00 760 toO TOT""-~"" 1977 ]I)O:JeO __ _ .., __ 1'1)0 78:)_ TOT .... I.8'GTH '_ 1979 .~ XIO )110 __ ____ 1'OO7~_ TCT' ..... utGTH ... 1981 :lOCI leO _ .. eoo NO toO NO 700 710 _ TOT ..... I.8'GTH _ ~ l ,. & I : 0 t & ! .I ~ t ,. & ! : 0 ~ t ,. & ! : 1976 XIO leO ..:JIO 460 IlOO _ toO NO 700 760 aoo !'Or ..... Ul'lQTH _ 1978 .JblllIIill~IIIIIIIIIIIIII~ •• XIO :MoO .- __ NO toO _ l'GO 760 _ fOT ..... ~TH_ 1980 lOG :JeO ___ Il1O _ NO 700 760 _ TOT .. laGTH ..... 1982 0' n fb=s11 lOG 3110 _ .oleO eoo !leO eoo NO 700 700 toCI l'OT ..... ~TH_ Figure 11. Length-frequency histograms of males and females combined from the Swan Creek spawning trap, 1975-1989. Interval width equals 10 mm. - 46 ~ ! ~ ~ I ~ 1983 TOT ...... 1..AJG1Io4_ 1985 1987 3OO:MO _____ MO700 tlIO_ 1'Of .... ....ant _ 1989 XlO:MO __ eoo560eooM07007lI01OO 1'OT .... ....un. _ Figure 11. continued. ! & I 47 1984 roTAI.~TloI_ 1986 300 3lICI _ G€ Composition of known age fish in the Bear Lake cutthroat trout spawning population, 1981-1989. - 50 - 1987 1988 n. n. '"0 '''' Ii ". Ii .. . • • ~ '00 ~ '00 ! " I " '" '" •• •• ° ° •• , • • • , • • '0 " .. 2 , • • • , • • '0 " .. """ - 1989 '" '''' t , .. ~ '00 ! , . .. • , • • • , • • '0 " .. ... Figure 13. continued. - 51 - cutthroat trout did not appear to fully recruit to the spawning population until VI+. The minimum observed age in the spawning population was 11+ in 1989, and the maximum observed age was XII+. Mean age of Bear Lake cutthroat trout in 1989 was 6.4 years and 40% of the marked spawners were greater than VII+. In contrast, the mean age of cutthroat trout in the 1984 Yellowstone Lake spawning population was 5.3 years, and only 11.2 % of the ,fish in the run were greater than VII+ (Gresswell 1985). An interesting aspect to the age composition of the Bear Lake spawning run was the wide variation in age at maturity for the same cohort. Fish from the same cohort were observed entering the traps as first-time spawners between the ages of 111+ and X+. The largest fish entering the traps on an annual basis were always first-time spawners. It has been assumed during the Bear Lake project that trap returns have been low, in part, due to a lack of imprinting by stocked fish. For this reason, it was theorized that return of morpholine imprinted fish would skew the distribution of age- classes downward as precocious fish which had previously been unable to locate a spawning tributary entered the traps. Although an increase of younger aged fish was observed in 1989, it is unclear whether this was an impact of the morpholine, a reflection of year class strength, or a result of shifts in the population due to other factors. It will be necessary to continue monitoring of the spawning population to fully determine the impact of morpholine. - 52 - Influence of Growth Rate on Maturation Growth rates may influence age and size at maturation. Thorpe (1987) cited two examples of changes in the population structure of sockeye salmon (Oncorhynchus nerka) as a result of increased juvenile growth rate. In both cases the percentage of precocious males increased in the runs when growth rates of the juveniles increased. Furthermore, Thorpe (1987) stated that conditions existing in fish culture situations; i . e . , abundant food and constant temperatures, may result in early maturation . Growth rates from known age marked fish in the spawning runs were determined . Large intra-year variation in size at a known age existed resulting in r2 values for the yearly age-growth regressions of less than .60. Combining t he 1981-1989 data however reduced the intra-age class variation and increased the r2 to 0.9 (Figure 14). The linear nature of the growth curve is unique ~iven the span of years examined. Comparison of the growth curve from the spawning population with the curve generated from gill- netted Bear Lake cutthroat trout (Nielson and Lentsch 1988) revealed that age 11+ and 111+ fish from the spawning population were approximately 100 mm and 50 mm longer, respectively, than similarly aged cutthroat trout from the gill nets . These data suggest that the fastest growing Bear Lake cutthroat trout mature earliest. Considerable evidence suggests that growth rates and age at maturity are heritable c haracteristics for a variety of salmonid species (Thorpe and Morgan 1978, Naevdal 1983, Thorpe 1987, - 53 - 800 ~ (31 T ~ 700 r (1~2~ 1 I r- l'J z 600 r ~ (31 W ...J ...J (3361 <{ (3041 f- 500 I 0 (621 ~ (5971 f- Z Y = 352.42 + 32.99x <{ 400~ (1601 W :z (41 r2=O.90 300 2 3 4 5 6 7 8 9 10 1 1 12 AGE Figure 14. Mean total length with 95% confidence limits for known age Bear Lake cutthroat trou t captured in the spawning traps , 1981-1989. Sample size in parentheses. - 54 - Gall et al. 1988). The diversity of ages in the Bear Lake cutthroat trout spawning population, the wide variation in age at maturity for the same cohort, and the apparent differences in growth rates within each cohort suggests that these characteristics are heritable in this species also. Thus, increased numbers of smaller fish in the spawning population at Bear Lake may be a reflection of increased diversity within the population . Two anomalies exist in the growth data that makes further interpretation difficult. Data from known age cutthroat trout were separated by age class and analyzed us i ng one- way analysis of variance (Hintze 1987) by mark group . In general, fish stocked as 225 rom TL catchables were significantly smaller at the same age than fish stocked as 125 rom TL fingerlings (Figure 15). -Additionally, fingerlings stocked since 1984 returned to the traps at a smaller mean size than. fingerl i ngs stocked prior to 1980. These relationships held true only for fish less than eight years old. Further investi gation of the relationship between size at stocking and size at maturity i s required. Egg Size vs. Female Total Length From 1975 through 1979, the number of eggs per ounce was determined using a Von Bayer trough . The trough was closed at both ends and all eggs placed in the trough were counted (T. Miles, UDWR, pers . comm . , 1990) . Two different methods were used after 1979. From 1980 through 1984 three ounces of eggs - 55 - 700 ~ 001 I 600 ROil GOLP f- GOII T pONe ~ • ! 0011 w ORP ± • ...J - 500 GO ROlli ...J 600 rom also was assigned to each fish and used as a factor . contingency table analysis (Hintze 1987) was used to determine the inter-relationship between the individual factors and whether or not the fish returned in a subsequent year. Results from the analyses indicated that sex, the number of days held in the trap initially, and whether or not the fish was . marked influenced the rate of return. Females returned at a higher percentage than males, at approximately the same ratio as the angler tag returns . Fish held in the traps less than eight days during the initial year of capture were the most likely to return in a subsequent year . Unmarked fish returned at a higher rate than marked fish, suggesting that most of the repeat ' spawners were naturally recruited from the tributaries. The increase in the number of repeat spawners in 1989 is consistent with this theory. Sizes of - 62 - the 1989 returned fish suggest they were produced from spawners which bypassed both traps during the high water years. The relationship between mark and rate of return questions the benefits of morpholine as an attractant. Cutthroat trout in the 500-599 rom size class were also the most likely to return in . subsequent years, but other factors such as age and growth rate may have been the determining factors for this result. Larger fish may have simply been close to the end of their normal lifespan. Whereas, the smaller fish were most likely the fastest growing members of their cohorts and growth rate has been shown to be inversely related to longevity (Dillinger 1989). Disposition of the fish, that is whether it was spawned, released unspawned, or released upstream at st. Charles was not related to the rate of return. Julian date of initial capture and trap site also did not appear to influence the return rate. Mann and Mills (1979) stated that one-time spawning fish such as the Atlantic salmon (Salmo· salar) can achieve the benefits of multiple spawning by the production of individuals of the same year class which mature at different ages. Thorpe (1987) suggested the threshold level of biochemical indices necessary to trigger maturation vary throughout the population. He further related this variation to the ability of salmonids to occupy a wide variety of geographic and climatic regions. Evidence presented from other salmonid species suggests that semelparity is common for salmonids. From the low rate of repeat - 6 3 - spawning in Bear Lake, the wide diversity of age at maturity for the same cohort, and the fact that the largest fish in the spawning population are always first-time spawners, it can be concluded that the majority of Bear Lake cutthroat trout are one-time spawners. Lahontan cutthroat trout also appear to be semelparous (P.Coffin, NDW, p~rs. comm., 1990). However, the influence on return rate of the factors analyzed earlier and the average longevity estimated from the tag returns suggests that a higher rate of repeat spawning could be expected in Bear Lake . Repeat spawning rates for Lahontan cutthroat were two to three times greater than the rate experienced in Bear Lake (P. Coffin, NDW, pers. comm., 1990). - 64 - RECOMMENDATIONS Several aspects of the Bear Lake cutthroat trout spawning run require further investigation and should be undertaken during the next phase of the project: 1 . Additional effort is required to more closely estimate post- spawning mortality and angler e xploitation. Reward tags should be utilized in the future to provide an estimate of reporting bias from previous years, and hopefully increase the t otal number of tags r eturned . 2. Consultation with a genetic ist should be done concerning current methods of spawning wild broodstock, including review of the broodstock se l ection cr i teria used in the trap and t he male to female spawning ratio . The number of parents selected for broodstock replacement needs to be def i ned for maximizing genetic diversity while still working within the constraints of the cult ure system to maintain isolated lots of eggs for disease purposes . 3 . The use of only wild origin fish as captive broodstock parents should be considered . This would require differential marking of any stocked fish from eggs produced at the J . Per ry Egan Hatchery. 4 . Fur ther investigation of the apparent r elationship between size at stocking and size at maturity should be done . An important aspect of this project would be defining the size of natural recruits . 5 . Natal stream imprinting by Bear Lake cutthroat trout appears to occur . Additional work on the timing of juvenile imprinting and refinements to the methodology of artificial imprinting need to be undertaken . 6 . Investigate the magnitude of natural reproduction in the tributaries below the traps . Other drainages (e . g. Fish Haven · creek) should be surveyed to determine e xtent of use by spawning Bear Lake cutthroat trout . - 6 5 - 7. The possible influence of weather patterns on daily trap catches should be investigated further by the acquisition of a recording thermometer to monitor diel changes in stream temperature at Swan Creek. Monitoring of flow patterns, minimum and maximum air temperature, and percent cloud cover should also be considered. - 66 - LITERATURE CITED ANSA . 1987. Paradox relational database . Ansa Software, San Francisco . Bear Lake Regional Commission. 1983 . The Bear Lake 314 clean lakes study . Bear Lake Regional Commission, Fish Haven, ID . Beverton, R. J . H. , and S. J. Holt. 1957 . On the dynamics of e xploited fish populations. Fishery Investigations Series II, Volume XIX, London . Brownie, C., D. R. Anderson, K. P. Burnham, and D. S . Robson . 1985. statistical inference from band recovery data - A h a ndbook . Second edition. U. S. Fish and wildlife Service Res ource Publication No . 158, Washington, D. C. Coffin, P . 1990 . Personal communication . Chief of Fisheries, Nevada Department of wildlife . Dillinger, Jr., R. E. 1989 . An analysis of the taxonomic status of the Coregonus autumnalis species complex in North America, and an investigation of t he l i fe histories of the whitefishes and ciscoes (Pices : Coregoninae) in North America and Eurasia. Ph . D. Dissertation, Memorial University of Newfoundland, st . John's . Gall, G. A. E. 1974. Influence of size of eggs and age of female on hatchability and growth i n ra i nbow trout . California Fish and Game 66 : 26 - 35 . Gall, G. A. E., J. Baltodano, and N. Huang . of age at spawning for rainbow t r out . 102. 1988 . Heritability Aquaculture 68 : 93 - Gresswell, R . E . 1985. Clear Creek cutthroat trout spawning run. Pages 17 - 27 in R. D. Jones (Project Leader) Fishery and aquat i c management program, Yellowstone National Park . United States Department of the Interior, Annual Pro j ect Technical Report for 1984 , Washington , D. C. Hintze, J . L. 1987 . Number Cruncher statist ical SOftware . J. L . Hi ntze, Salt Lake City. Mandis, T . , and L . E. Harris . 1984 . Accuracy of various rainbow trout egg- counting methods . Fishery Information Leaflet, Colorado Division of wildlife . Mann, R. H. K., and C. A. Mills . 1979 . Demographic aspects of fish fecundity . Zoological society of London Symposium 44 : 161-177. - 67 - Martin, M. 1983. Unpublished data. Utah Division of wildlife Resources, Salt Lake City . McConnell, W. J., W. J. Clark, and W. F. Sigler. 1957. Bear Lake its fish and fishing. Utah Department of Fish and Game, Idaho Department of Fish and Game, and wildlife Management Department, Utah State University, Logan, Utah. Miles, T. 1990. Personal communication. Fisheries Experiment station Hatchery Superintendent . Utah Division of wildlife Resources. Naevdal, G. 1983. Genetic factors in connection with age at maturation. Aquaculture 33:97-106. Nielson, B. R. 1978. Bear Lake cutthroat fishery enhancement program, Utah Division of wildlife Resources, Federal Aid in Fish Restoration, F-26-R-3, Annual Completion Report, Salt Lake City. Nielson, B. R. 1985. Bear Lake cutthroat fishery enhancement program, Utah Division of wildlife Resources, Federal Aid in Fish Restoration, F-26-R-11, Annual Completion Report, Salt Lake City. Nielson, B. R. 1990. Twelve-year overview of fluorescent grit marking of cutthroat trout in Bear Lake, Utah-Idaho . American Fisheries Society Symposium 7:42-46. Nielson, B. R., and D. L. Archer. 1977. Bear Lake cutthroat fishery enhancement program, Utah Division of wildlife Resources, Federal Aid in Fish Restoration, F-26-R-2, Annual Completion Report, Salt Lake city. Nielson, B. R. , and J. Johnson. 1981. Bear Lake cutthroat fishery enhancement program, Utah Division of wildlife Resources, Federal Aid in Fish Restoration, F-26-R-6, Annual Completion Report, Salt Lake City. Nielson, B. R. , and L. D. Lentsch. 1988. Bonnevil
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