A field evaluation of four strains of Salmo introduced into seven Montana waters by Michael Elmer Hensler A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Fish and Wildlife Management Montana State University © Copyright by Michael Elmer Hensler (1987) Abstract: The food habits, growth rates, and condition factors of three strains of rainbow trout (Salmo gairdneri) and one strain of cutthroat trout (Salmo clarki bouvieri) were evaluated in seven limnetic waters in Montana during the summers of 1985 and 1986. Analysis of stomach contents revealed that Daphnia was the most important food item in all populations with trout <350 mm TL. Daphnia remained important for DeSmet rainbow trout with total lengths ≥350 mm, while the other strains switched to insects, fish, and Leptodora kindti. The study indicated that at least 500 daphnids of lengths ≥2 mm per m^3 were needed to produce condition factors of 1.0 or greater in trout up to approximately 350 mm TL. Arlee rainbow trout appeared to more efficiently utilize low Daphnia densities than other strains. Eagle Lake rainbow trout did not feed on forage fish as they were reported to do elswhere. In contrast, McBride cutthroat trout ≥350 mm TL fed heavily on cottids in one area, but they did not feed on them or Utah chubs (Gila atraria) in two other situations. The McBride strain's potential for piscivory indicates it may be more useful where forage fish are available than is presently recognized. Condition factors of fish ≥350 mm TL that relied on Daphnia were lower than in smaller fish. The effective gill raker straining area in fish ≥350 mm decreased for food items of ≤2 mm for all trout strains suggesting this was the cause of the lower conditions factors in these larger fish. Condition factors for Eagle Lake rainbow trout were excellent in the high pH environment of a study reservoir with a daphnid/hemipteran food base. McBride cutthroat trout survived in waters with a wide pH range. The results indicated that these latter two strains might be successfully used in waters that might be unsuitable for other strains of trout. The suitability of the other two strains in this type situation was unknown.  A FIELD EVALUATION OF FOUR STRAINS OF SALMO INTRODUCED INTO SEVEN MONTANA WATERS . by' Michael Elmer HensiIer A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Fish and Wildlife Management MONTANA STATE UNIVERSITY Bozeman, Montana December 1987 ii APPROVAL of a thesis submitted by Michael E. Hensler This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, citations, bibliographic style, and consistency and is ready for submission to the College of Graduate Studies. ~ltnrr^ S'; /W/ Date 7 iz? Au* As. Chairperson, Graduate Committee Approved for the Major Department f ) J ( T V f /350 mm, while the other strains switched to insects, fish, and Leptodora kindti. The study^indicated that at least 500 daphnids of lengths >2 mm per m were needed to produce condition factors of 1.0 or greater in trout up to approximately 350 mm TL. Arlee rainbow trout appeared to more efficiently utilize low Daphnia densities than other strains. Eagle Lake rainbow trout did not feed on forage fish as they were reported to do elswhere. In contrast, McBride cutthroat trout >350 mm TL fed heavily on cottids in one area, but they did not feed on them or Utah chubs (Gila atraria) in two other situations. The McBride strain's potential for piscivory indicates it may be more useful where forage fish are available than is presently recognized. Condition factors of fish >350 mm TL that relied on Daphnia were lower than in smaller fish. The effective gill raker straining area in fish >350 mm decreased . for food items of <2 mm for all trout strains suggesting this was the cause of the lower conditions factors in these larger fish. Condition factors for Eagle Lake rainbow trout were excellent in the high pH environment of a study reservoir with a daphnid/hemipteran food base. McBride cutthroat trout survived in waters with a wide pH range. The results indicated that these latter two strains might be successfully used in waters that might be unsuitable for other strains of trout. The suitability of the other two strains in this type situation was unknown. IINTRODUCTION . Stocks of rainbow trout (Salmo gairdneri) and cutthroat trout (S. clarki) have diverged into different strains with different characteristics both in hatcheries and in the wild. Calhoun (1966) suggested that intraspecific variability might be an important management tool. The variances could be exploited to potentially improve fisheries in areas by planting strains into environments for which they were well adapted. As a result, many evaluations of traits such as feeding habits (Trojnar and Behnke 1974), growth rates (Rawstron 1973 and 1977; Hudy 1980; Dwyer and Piper 1984), migratory behaviors (Moring 1982), and catchability and survival (Cordone and Nicola 1970; Mueller 1985) of different strains have been undertaken in the last two decades. In 1985, the Montana Department of Fish, Wildlife and Parks (MDFWP) began evaluating performances of rainbow and cutthroat trout strains in different habitats throughout the state. In this study, wild, domestic, and introduced strains of trout were to be evaluated for longevity, catchability, food habits, growth rate, maximum size, habitat preference, adaptability, and other characteristics in the reservoirs and lakes in which they had been planted. The objectives of this portion of that larger study were to evaluate the food habits, growth rates and conditions of Eagle Lake, DeSmet, and Arlee rainbow trout, and McBride cutthroat trout 2in several Montana lakes and reservoirs with different morphological and physical/chemical parameters. In addition, the gill raker morphologies of the study strains were examined. This feature was investigated because gill raker morphology is correlated with food habits and habitat preferences of many fish (Galbraith 1967; Martin and Sandercock 1967; Kliewer 1970; Bodaly 1979; Lindsey 1981). 3STRAIN HISTORIES The DeSmet strain of rainbow trout originated in Lake Desmet, Wyoming. Prior to 1957, rainbow trout from many sources were planted in Lake DeSmet (both spring and fall spawning varieties). The DeSmet stock is the result of selecting for the spring spawning variety beginning in 1958. After that time the stock was maintained by trapping wild DeSmet-type Rainbow trout, spawning them, and rearing them to juvenile stage in the hatchery and then returning the young to the lake (Mueller and Rockett 1980). The strain has since been discontinued in Lake DeSmet in favor of Eagle Lake rainbow trout. DeSmets were established in Willow Creek Reservoir, Montana, by a series of four plants from Lake DeSmet in 1977, 1978, 1980, and 1981 (Richard Vincent, MDFWP, pers. comm.). The DeSmet strain is a March-early May spawner in the wild. It is considered to be a planktivore and characteristically prefers the upper portion of the water column in the pelagic zone. The longevity of the strain in the wild averages 5 years (yr) with individuals living up to 8 yr in Willow Creek Reservoir (Richard Vincent, MDFWP, pers. comm.). The Eagle Lake strain of rainbow trout (Salmo gairdneri aquilarium) is indigenous to Eagle Lake, California. The stock now is maintained entirely by an artificial spawning program whereby progeny are returned to the lake annually (Vernon King, California 4Department of Fish and Game [CDFG], mimeo). The strain was brought to Montana in 1980 and propagated in the Creston National Fish Hatchery (Jack Boyce, MDFWP, mimeo). Eagle Lake rainbows are March-mid April spawners in the wild. They are known for their large size, adaptability to highly alkaline waters, and piscivorous tendencies. They prefer the littoral zone in spring and fall and deep water in summer (Vernon King, CDFG, pers. comm.). Longevity averages 3 yr but individuals have been known to live 11 yr (McAfee 1966). The Arlee strain of rainbow trout originated in 1955 at the State Fish Hatchery in Arlee, Montana, from a cross between the Donaldson rainbow strain and McCloud River rainbow/steelhead cross from Missouri (Jack Boyce, MDFWP, mimeo). The brood stock of this strain has been confined to the hatchery system. The Arlee strain has been widely planted in the state by MDFWP. The strain is currently being phased out due to its low survival and poor spawning ability in the wild (Richard Vincent, MDFWP, pers. comm.). The Arlee strain is a mid August-early January spawner in the hatchery but probably does not spawn successfully in the wild (Jack Boyce, MDFWP, mimeo). The strain is known for its exceptional hatchery performance, disease resistance, fast growth rate, and high catchability. It is characterized as an invertebrate feeder with short longevity: most die within 2 yr but some live up to 4 yr (Richard Vincent, MDFWP, pers. comm; Jack Boyce,"MDFWP, mimeo). 5McBride cutthroat trout are native.to McBride- Lake, Wyoming in the Slough Creek Drainage of Yellowstone National Park. They are considered to be a distinct strain of the Yellowstone cutthroat (Salmo clarki bouvieri) (Robert Gresswell, United States' Fish and Wildlife Service [USFWS], pers. comm.). The brood stock was developed in Big Timber Hatchery, Montana from eggs collected from fish in McBride Lake in 1971 (Dean 1972). McBride cutthroat were chosen for Montana lakes due to their rearing success, high post­ planting survival, and success in high mountain lakes (Richard Vincent, MDFWP, pers. comm.). " McBride cutthroat trout spawn in late May-June.. The strain is considered to feed mainly on invertebrates. They live to an average age of about 4 yr but can live to 8 yr (Richard Vincent, MDFWP, pers. comm.). 6DESCRIPTION OF STUDY WATERS Seven bodies of water, six reservoirs and one lake, containing target strains were sampled (Table I). Water bodies were chosen to include sites with different levels of productivity, climatic influences and fish communities. Willow Creek Reservoir (Harrison Reservoir) is located in southwestern Montana near the town of Harrison. Its main purpose is to supply water for irrigation which leads to extensive waterlevel drawdowns during the summer months. Dense algal blooms of primarily Aphanizomenon and Gleotrichia species are common in late summer and early fall. This reservoir contains a self- reproducing population of DeSmet rainbow trout that were first planted in 1977 (Appendix Table 22). Other fish found in the lake are white suckers (Catostomus commersoni), longnose suckers (C. catostomus), and brown trout (S . trutta). Hyalite Reservoir is located in southwestern Montana in the Gallatin Mountain Range near the city of Bozeman.■ It is used for irrigation and as a municipal water source (Zubik 1983). Dense algal blooms of Aphanizomenon species are common in late summer and early fall. The reservoir first received McBride cutthroat trout in 1976 (Appendix Table 23). It now contains naturally reproduced fish and hatchery-reared fish. Arctic grayling (Thymallus Table I. The location and principal characteristics of the study waters and trout strains present. References: Anonymous (1968); Robert Domrose, MDFWP, mimeo; Richard Vincent, MDFWP, pers. comm. ' lake (L) Mbter body or name reservoir (R) Location County Sec. T. R. Ifaximum capacity or vplune (m ) . Abundance, of rooted ^ macrophytes maximum depth (m) Target strains^ present Elevation above sea level (m) WLllow Creek 26,27 I & very Reservoir R Madison 34,35 2S IW 22,204,800 lew 33.4 DR 1440 Ifyalite very Reservoir R Gallatin 15,16 4S 6E 9,902,107 low 27.0 MO ' 2012 Hebgen lake (Grayling Arm) R Gallatin 22 IlS 2E 9,220,870 low 7.3 MG 2003 Notellun Reservoir ' R Flathead 16 26N 25W 2%, 830 high 6.7 AR 1225 Waods Lake L Flathead 18 31N 22W 288,662 high 5.5 ER 1031 very Axolotl lake #2 . R Ifadison 8DC 7S 2W 92,000 high 5.0 MC 2430 Grasshopper very Reservoir R Blaine 29 • 3 IN 19E 100,000 low 6.1 ER 820 1. Macrophyte abundances: very lew = < 20% of water body; low = 20 - 40% of water body; moderate = 40 - 60% of water body; high = 60 - 80% of water body; very high = > 80% of water body. 2. ER = Desnet rainbow trout; ER = Eagle Lake rainbow trout; AR = Arlee rainbow trout • MO = McBride cutthroat trout. 8arcticus), brook trout (Salvelinus fontinalis) and mottled sculpln (Cottus balrdi) are also found in the lake. Hebgen Reservoir is located in a high valley in southwestern Montana near West Yellowstone. The reservoir supplies water for power generation. It is also subject to dense algal blooms of Aphanizomenon in late summer. The lake contains a naturally reproducing population of McBride cutthroat trout. This strain was initially planted in the reservoir in 1979 (Appendix Table 24) and has been continually planted since then. The lake also contains several strains of rainbow trout, mountain whitefish (Prosopium williamsoni), Utah chub (Gila atraria), and brown trout. The study area consisted of the Grayling Arm in the eastern part of the reservoir. Notellum Reservoir is located in northwestern Montana near the City of Kalispell. The reservoir supplies water for irrigation. It contains Arlee rainbow that are planted each year (Robert Domrose, pers. comm.) and westslope cutthroat trout. Blooms of Aphanizomenon are common during the summer and fall. Woods Lake is located in northwestern Montana near the town of Whitefish. It is a closed-basin lake. The lake was planted with 1000 Eagle Lake rainbow trout and 1000 Arlee rainbow trout in 1983 (Robert Dbmrose, MDFWP, pers. comm.). Redside shiners (Richardsonius balteatus) are also present. Axolotl Lake #2 is part of a series of small irrigation reservoirs located in the Gravelly Mountain Range of southwestern 9Montana near the town of Ennis. It contains a self-reproducing population of McBride cutthroat trout that were first planted in 1980 (Richard Vincent, MDFWP, pers. comm.). There is also a population of mottled sculpin present in the reservoir. Grasshopper Reservoir is located in eastern Montana near the town of Chinook. It is used for irrigation and is subject to dense algal blooms of Aphanizomenon in the summer and fall. The reservoir contains Eagle Lake rainbow trout that were planted in 1985 and 1986 and Arlee rainbow trout that also were planted in 1985 (Kent Gilge, MDFWP, mimeo). Other fish are found in the reservoir and include Iowa darters (Etheostoma exile), fathead minnows (Pimephales promelas), and brook stickleback (Culaea inconstans). 10 METHODS Collection of Fish Trout were collected with floating and sinking experimental gill nets between the months of June and October of 1985 and 1986. All experimental nets were 38.1 meters (m) long, 1.8 m deep and consisted of five panels of equal length. Panel mesh sizes were 19, 25, 32, 38, and 51 millimeters (mm). Nets were placed perpendicular to the shoreline with the small mesh inshore. Nets were set on one afternoon and retrieved the following morning. Age and Growth Lengths at Age and Growth Increments The length of trout collected was measured as total length (TL) to the nearest millimeter. Whole weight was measured to the nearest gram with a Homs Temperature Compensated Model 1000 Gram Scale. All trout weighing more than 1000 g were cut in pieces and weighed. All scales were taken from the left sides of fish in an area above the lateral line and between the dorsal and anal fins. Cellulose acetate impressions of the scales were examined at 42X magnification using a microfiche reader. Distances were measured in a straight line from the focus to the annuli and mid-anterior margin of the scales using a millimeter ruler. 11 Age and growth information was analyzed using the Fire I computer program as modified by the Montana Department of Fish Wildlife and Parks. Body length-scale radius relationships were most accurately described using log-log plots generated from the CURVE67 program. The slope of the regression created by CURVES7 was used in the MONASK program to calculate lengths at age for fish based on the Monastyrsky method. Condition Factors The FREQCON program was used to calculate condition factors at specified lengths for trout with the formula: (10^)(w) K = _________ L3 where K = condition factor w = total weight (g) L = total length (mm) Food Habits The stomach of each study specimen was removed and its contents emptied into a labeled glass vial containing a solution of 4 percent (%) formalin with 40 grams (g) per liter (I) sucrose (Haney and Hall 1973). Trout with empty stomachs were not considered in this study. The numbers, volumes,. and frequency of occurrence of identified food items were then evaluated. 12 The numbers of each food item were determined by direct enumeration, except for the numbers of Cladocera which were determined by subsampling. Each Cladocera sample was diluted to a 50 milliliter (ml) suspension volume and I or 2 ml subsamples were taken from it using a Hensen-Stempel pipette. The numbers of Cladocera in three to five subsamples of each sample were counted so that 50 to 100 organisms were counted (Bowen 1983). Subsamples were enumerated using a Ward plankton counting wheel and a binocular dissecting microscope at 25X magnification. The mean number of Cladocera counted from the subsamples was multiplied by the suspension volume and divided by the subsample volume to estimate the total number of Cladocera in the stomach sample. The number of food items in each category in the stomach was then converted to a percentage of the total number of food items in the stomach. Volume of the stomach contents was determined by fluid displacement. Individuals of each type were pooled, blotted to remove excess preservative and placed in a measured amount of the solution in which they were preserved to guard against differences in buoyancy. Organisms with volumes less than 10 ml were measured in a 12 ml graduated centrifuge tube to the nearest 0.05 ml. . Fish remains and invertebrate items with volumes greater than 10 ml were measured to the nearest 0.5 ml in a 50 ml graduated cylinder. Any organisms displacing less than 0.05 ml were arbitrarily assigned a volume of 0.01 ml. The volume of each food item then was calculated / ' " / 13 as a percentage of the volume of the combined food items in each stomach. After the numbers and volumes of the food items were determined, the contents were pooled and frequency of occurrence was determined. The frequency of occurrence of a given food item was determined by dividing the number of stomachs that contained at least one of that food item by the total number of stomachs examined (Bowen 1983). The representation of food habits by each of these three techniques contain inherent biases (George and Hadley 1979; Hyslop 1980; Bowen 1983). Because a combination of indices can be more valuable than single indices (WindelI 1971), a modification of the Relative Importance Index (RIa) (George and Hadley 1979) was used to compare diets. The RI^ for a particular food item was determined by the formulas 100 Al, RIa = ______ c_ where AI^ = % frequency of occurrence + % total numbers + % total weight for food item a. a = a particular food item n = total number of different types of food items For this study, volume was substituted for weight in the Z equation. The values from this index range from 0 to 100/ where the I value 100 indicates exclusive use of a particular food item. 150 mg/1 calcium carbonate CaCO^, respectively (APHA 1975). All alkalinity measurements were reported as total alkalinity in milliequivalents/1 (meq/1). 18 Light transmittance was measured with a submarine photometer fitted with a Weston B56 photocell. Measurements were made from the unshaded side of the boat at I m intervals until the euphotic zone (level of 1% light transmittance) was found. Invertebrate Identification The food items in each stomach were identified to the lowest taxon practical using references by Pennak (1978), and Merrit and Cummins (1984). Zooplankton taxa were identified with the use of Brooks (1.959) and Pennak (1978). Cladocerans were identified to species. Copepods were identified to the suborders cyclopoid, calanoid, or harpactacoid. Statistical Analyses Statistical tests were made following the methods of Snedecor and Cochran (1980). Analyses were performed with the computer program MSUSTAT (Lund 1986). Statistical differences were considered to be significant at the p < 0.05 level. 19 RESULTS Age and Growth Calculated Lengths at Age and Growth Increments The back calculated lengths at annuli determined for the study populations are given in Appendix Tables 25-31.' Because some sampled stocks were planted, and planted at different sizes, and others were from naturally reproducing populations, the lengths at annuli among strains are not directly comparable. Length at annuli were converted to mean growth increments to facilitate growth comparisons among the populations, at least after the first year of life (Table 2). Zubik (1983) found that growth increments in wild and hatchery trout were similar after the first year. Growth increments for the second year of life showed that trout from Axolotl Lake #2, Grayling Arm of Hebgen Reservoir, and Harrison Reservoir had non-significant differences from each other but had significantly greater increments than the strains in the other locations. The growth increments of fish from Hyalite Reservoir, Woods Lake, and Notellum Reservoir, were all significantly different from each other. The Grasshopper Reservoir population did not have any 2 yr old fish. 20 Table 2. Calculated mean growth Increments (standard deviations) of the study trout strains from 1985-1986. Mean growth increments at annuli Strain Study area N I 2 3 4 5 DeSmet rainbow trout Harrison Reservoir 89 104 (15.3) 123 (43.3) 129 (41.4) 82 25 (41.4) (3.5) Eagle Lake rainbow trout Woods Lake 10 222 (17.8) 84 (12.7) 67 (19.9) Eagle Lake rainbow trout Grasshopper Reservoir 57 203 (19.0) Arlee rainbow trout Notellum Reservoir 42 208 (15.0) 69 (11.1) McBride cutthroat trout Hyalite Reservoir 78 H O (16.2) 103 (27.9) 83 (24.5) 84 (7.0) McBride cutthroat trout Hebgen Reservoir 27 151 (30.4) 130 (50.5) 98 (25.0) McBride cutthroat trout Axolotl Lake #2 21 77 (11.8) 136 (37.3) 130 (47.7) 87 (22.9) In the third year, growth increments of strains in Axolotl Lake #2 and Harrison Reservoir were not significantly different from each other but were significantly greater than those in Grayling Arm of Hebgen and Hyalite Reservoirs which had similar growth 21 increments. Increments from trout in Woods Lake were the lowest and were significantly different from all other populations. The-fourth year growth increments could be compared among only three strains. The fish from Axolotl Lake #2 had the greatest growth followed by trout from Hyalite and Harrison Reservoirs, although they were not significantly different from each other. Mean growth increments at annuli were not used in further comparisons because there were not consistent age classes among all populations of trout. This is because the various strains were not planted in the same years at the water bodies studied. Condition factors were considered to be a more immediate measure of the well­ being of the studied strains as related to factors occurring in the summer. Condition Factors Initial examination of the spacing between gill rakers and food habits in the study populations indicated that changes occurred in fish at about 350 mm TL. Mean condition factors, therefore, were calculated for fish with total lengths of less than 350 mm and for those 350 mm or greater from each study population (Table 3). A multiple comparison test showed that mean condition factors for DeSmet rainbow trout in Harrison Reservoir and McBride cutthroat trout in Hyalite Reservoir were significantly greater at total lengths of fish less than 350 mm than they were in larger fish. In contrast, McBride cutthroat trout in Axolotl Lake #2 had a 22 significantly greater condition factor in trout 350 mm or greater than in the smaller size group. Table 3. Mean condition factors in study strains with total lengths of less than 350 mm and 350 mm or greater (standard deviations) during 1985 - 1986. Strain Study area N Total length <350 mm N Total length > 350 mm DeSmet rainbow trout Harrison Reservoir ■ 31 1.09(0.13) 5.8 1.01(0.09) Eagle Lake rainbow trout Woods Lake 10 0.86(0.06) Eagle Lake rainbow trout Grasshopper Reservoir . 42 1.19(0.13) 15 1.20(0.09) Arlee rainbow trout No telIum Reservoir 41 1.10(0.12) 0 McBride cutthroat trout Hyalite Reservoir 70 1.04(0.14) 8 0.97(0.07) McBride cutthroat trout Hebgen Reservoir 13 1.03(0.09) 8 0.99(0.07) McBride cutthroat trout Axolotl Lake #2 13 0.93(0.05) 8 1.08(0.14) Condition factors for the two size groups of McBride cutthroat trout in Hebgen Grayling Arm were not significantly different. Both size classes of Eagle.Lake rainbow trout in Grasshopper Reservoir 23 were represented by age 1+ fish.. Growth in length was exceptional for that summer, although differences in condition factors between size classes were not significantly different. Mean condition factors for all populations of trout less than 350 mm TL were compared in a multiple comparison test. Analysis showed that condition factors for Eagle Lake rainbow trout taken from Grasshopper Reservoir were greater than in all other populations. There were no Eagle Lake rainbow trout less than 350 mm.TL taken in Woods Lake. The two other rainbow trout populations had significantly higher condition factors than all McBride cutthroat trout populations. Condition factors for McBride cutthroat trout in Hebgen Grayling Arm.and Hyalite Reservoir were similar and significantly greater than that of McBrides from Axolotl Lake #2. McBride cutthroat trout from Axolotl had the lowest condition factors of all populations. Analysis of mean condition factors for trout 350 mm TL or longer again showed Eagle Lake rainbow trout from Grasshopper Reservoir were significantly greater than those in all other populations. The condition factors of the remaining populations were similar with the exception of the Eagle Lake rainbow trout population from Woods Lake which was significantly lower than those in all other populations. No Arlee rainbow trout equal to or greater than 350 mm TL were taken from Notellum Reservoir. 24 Food Habits After initial analysis of food habits, it appeared that the utilization of Daphnia decreased with increasing length. When fish length was plotted against percent volume of Daphnia in their stomachs, a decline occurred at about 350 mm TL. For this reason, trout food habits for fish less than 350 mm TL and those 350 mm TL or longer were separated from each other. DeSmet Rainbow Trout From Harrison Reservoir Daphnia pulex was the most important food item in the diet of DeSmet rainbows less than 350 mm TL (Table 4). Insects and water mites, the only other food items found, had about one half the relative importance value of the Daphnia. Table .4. The Index of Relative Importance (IRI) and its components for food items in the stomachs of DeSmet rainbow trout less than 350 mm total length in Harrison Reservoir, 1985- 1986. Frequency of Food item occurrence (%) Volume (%) . Number (%) IRI Daphnia pulex 100.0 83.5 98.3 65.9 Diptera larvae 50.0. 11.3 1.5 14.6 Diptera pupae 55.6 3.6 0.2 13.9 Diptera adults 11.1 1.5 0.1 3.0 Hemiptera 5.6 0.1 <0.1 1.3 Hydracarina 5.6 <0.1 <0.1 1.3 25 Daphnia was also the most important single food item in the diets of DeSmet rainbow trout 350 mm TL or greater (Table 5). However, there was more utilization of insects in these larger fish. Collectively, insects were slightly more important than daphnids in these larger fish. Terrestrial insects included Hymenoptera, Orthoptera, and Lepidoptera. The semi—aquatic Hemiptera included Corixidae. Table 5. The Index of Relative Importance (IRI) and its components for food items in the stomachs of DeSmet rainbow trout 350 mm total length or greater in Harrison Reservoir, 1985- 1986. Frequency of occurrence Volume Number Food item (%) (%) (%) IRI Daphnia pulex 69.6 42.7 97.8 45.0 Diptera pupae 91.3 25.8 1.0 25.4 Diptera larvae 43.5 5.4 0.4 10.6 Terrestrial insects 21.7 7.2 0.1 6.2 Hemiptera 13.0 10.9 1.0 5.4 Coleoptera 17.4 6.2 0.1 5.1 Diptera adults 4.3 1.6 <0.1 1.3 Trichoptera larvae 4.3 0.1 <0.1 1.0 Eagle Lake Rainbow Trout From Woods Lake Only trout equal to or greater than 350 mm TL were captured at Woods Lake. The single most important food item in the stomachs of these fish were snails (Table 6). Again, insects collectively made up over one-half of the IRI of these larger fish. . The fish remains 2 6 were probably of AFF balteatus which were abundant in the lake. Table 6. The Index of Relative Importance (IRI) and its components for food items in the stomachs of Eagle Lake rainbow trout 350 mm total length or greater in Woods Lake, 1986. Food item Frequency of occurrence (%) Volume (%) ' Number (%) IRI Gastropoda 33.3 37.1 21.8 22.4 Diptera larvae 33.3 0.7 25.5 14.5 Trichoptera larvae 33.3 18.9 7.3 14.5 Diptera pupae 33.3 0.9 14.5 11.9 Odonata 22.2 11.1 12.7 11.2 Hirudinea 22.2 12.5 3.6 9.3 Amphipoda 22.2 0.3 12.7 8.6 Fish remains 11.1 18.4 . 1.8 7.6 Eagle Lake Rainbow Trout From Grasshopper Reservoir The importance of IEF pulex and Hemiptera (No tonectidae and Corixidae) were about equal for Eagle Lake rainbow trout less than 350 mm TL (Table 7). The fish remains were of C. inconstans and P. promelas. In Eagle Lake rainbow trout 350 mm TL or larger, Hemipterans (Notonectidae and Corixidae) were nearly twice as important as the next most important food item, Gastropods (Table 8). Daphnia declined to about one-fifth the importance of the most important item. Fish remains (C. inconstans, E. exile, and P. promelas) were more than twice as important for larger trout than they were for the smaller fish. 27 Table 7. The Index of Relative Importance (IRI) and its components for food items in the stomachs of Eagle Lake rainbow trout less than 350 mm total length in Grasshopper Reservoir, 1985-1986. Food item Frequency of occurrence (%) Volume . (%) Number (%) IRI Daphnia pulex 55.2 11.5 95.2 36.5 Hemiptera 100.0 56.7 . 3.8 35.9 Diptera pupae 31.0 0.8 0.3 7.2 Odonata 24.1 5.9 0.4 6.8 Gastropoda 6.9 19.4 0.1 5.9 Amphipoda 13.8 0.2 0.1 3.1 Fish remains 6.9 3.8 <0.1 2.4 Trichoptera larvae 3.4 1.8 <0.1 . 1.2 Diptera larvae 3.4 <0.1 <0.1 1.0 Table 8. The for 350 1985 Index of Relative Importance (IRI) and its components food items in the stomachs of Eagle Lake rainbow trout mm total length or greater in Grasshopper Reservoir, 1-1986. Frequency of occurrence Volume Number Food item (%) (%) (%) IRI Hemiptera 90.9 39.1 68.9 49.7 Gastropoda 45.4 50.1 10.6 26.6 Daphnia pulex 18.2 0.1 19.3 9.4 Fish remains 18.2 6.3 . 0.4 6.2 Odonata 18.2 4.4 0.4 5.7 Goleoptera 9.2 <0.1 0.4 2.4 28 Arlee Rainbow Trout From Notellum Reservoir Only Arlee rainbow trout smaller than 350 mm TL were captured in Notellum Reservoir. Daphnia pulex were about twice as important as the next most important item in the diet of small Arlee rainbows (Table 9). However, again insects collectively made up about two thirds of the IRI. Table 9. The Index of Relative Importance (IRI) and its components for food items in the stomachs of Arlee rainbow trout less than 350 mm total length in Notellum Reservoir, 1986. Food item Frequency of occurrence (%) Volume (%) Number (%) IRI Daphnia pulex 66.7 21.0 92.7 32.3 Diptera larvae 76.2 13.5 5.1 16.9 Terrestrial insects 42.9 39.3 1.5 14.9 Diptera pupae 61.9 2.1 0.3 11.4 Coleoptera 38.1 5.4 0.1 7.7 Hemiptera 28.6 11.3 0.1 7.1 Odonata 23.8 4.4 <0.1 5.0 Diptera adults 9.5 1.4 <0.1 1.9 Amphipoda 9.5 . 0.1 <0.1 ■ 1.7 Trichoptera larvae 4.8 0.3 <0.1 1.1 McBride Cutthroat Trout From Hyalite Reservoir In Hyalite Reservoir, Daphnia was the most important food item in the stomachs of small McBride cutthroat trout and comprised nearly 52 % of the IRI (Table 10). Dipterans, Hymenoptera (Formicidae), and Orthoptera combined provided about 40 % of the IRI. The presence of Plecoptera, Trichoptera, and Ephemeroptera 29 suggested that some McBride cutthroat trout might have been using stream drift or actually moving into the inlet streams to feed. Table 10. The Index of Relative Importance (IRI) and its components for food items in the stomachs of McBride cutthroat trout less than 350 mm total length in Hyalite Reservoir, 1985- 1986. Food item Frequency of occurrence (%) Volume (%) Number (%) IRI Daphnia 96.4 46.6 97.1 51.7 Diptera pupae 75.0 16.5 1.9 20.0 Diptera larvae 41.1 4.8 0.5 9.9 Terrestrial insects 19.6 26.4 0.5 9.9 Ephemeroptera naids 8.9 1.0 <0.1 2.0 Diptera adults 5.4 0.1 <0.1 1.2 Coleoptera 3.6 <0.1 <0.1 1.0 Hemiptera 3.6 <0.1 <0.1 1.0 Gastropoda 1.8 2.5 <0.1 1.0 Hydracarina 3.6 <0.1 <0.1 0.8 Trichoptera 1.8 ■ 0.6 <0.1 0.6 Odonata 1.8 0.4 <0.1 0.5 Plecoptera 1.8 0.2 <0.1 0.4 Terrestrial insects (Hymenoptera, Formicidae) were the most important food items McBride cutthroat trout 350 mm TL or greater (Table 11). Diptera pupae and D. pulex were about of equal importance and slightly less important than terrestrials. Unidentified fish remains were about one-half as important as Daphnia and could have been young McBride cutthroat trout, brook trout, Arctic grayling, or mottled sculpin. 30 Table 11. The Index of Relative Importance (IRI) and its components for food items in the stomachs 350 mm total length or greater 1986. of McBride in Hyalite cutthroat Reservoir, trout 1985- Food item Frequency of occurrence (%) Volume (%) Number (%) IRI Terrestrial insects 16.7 56.8 33.3 29.1 Diptera pupae 66.7 13.1 2.1 22.4 Daphnia pulex 16.7 1.1 63.0 22.0 Gastropoda 33.3 20.5 1.2 15.0 Fish remains 33.3 8.5 0.4 11.5 McBride Cutthroat Trout From Grayling Arm of Hebgen Reservoir . For the smaller size group (less than 350 mm TL) of McBride cutthroat trout in Hebgen Reservoir, Daphnia was the most important food item (Table 12). Diptera pupae, Diptera adults, and L. kindti, each comprised over 10% of the index of relative importance. All. . other, food items were of substantially less importance. In 350 mm TL or larger McBride cutthroat the zooplankter L. kindti was the most important food item, providing about 25% of the IRI closely followed by Daphnia sp. (Table 13). Once again, the combined dipteran forms comprised the majority of the importance index. McBride Cutthroat Trout From Axolotl Lake #2 The single most important food item in the stomachs of the smaller size group of McBride cutthroat trout was Daphnia pulex 31 Table 12. The Index of Relative Importance (IRI) and its components for food items in the stomachs of McBride cutthroat trout less than 350 mm total length in the Grayling Arm of Hebgen Reservoir, 1985-1986. Frequency of occurrence Volume Number Food item (%) (%) (%) IRI Daphnia sp. 84.6 21.6 82.9 31.3 Diptera pupae 100.0 35.5 3.8 22.8 Leptodora kindti 69.2 19.3 11.6 16.4 Diptera adults 69.2 9.3 0.2 12.9 Terrestrial insects 23.1 7.5 0.9 6.4 Diptera larvae 30.7 0.8 0.1 5.2 Ephemeroptera naiads 7.7 5.7 0.6 1.4 Gastropoda 7.7 <0.1 <0.1 1.3 Hemiptera 7.7 <0.1 <0.1 1.3 Hydracarina 7.7 . <0.1 <0.1 1.0 Table 13. The Index of Relative Importance (IRI) and its components for food items in the stomachs of McBride cutthroat trout 350 mm total length or greater in the Grayling Arm of Hebgen Reservoir, 1985-1986. Frequency of occurrence Volume Number Food item (%) (%) (%) IRI Leptodora kindti 87.5 38.9 30.2 25.6 Daphnia sp. 62.5 . 7.0 62.2 ' 21.4 Diptera pupae 100.0 17.2 4.4. 19.9 Diptera adults 75.0 10.2 0.5 14.0 Terrestrial insects 25.0 . 21.7 2.4 8.0 Diptera larvae 25.0 0.1 0.9 4.2 Hemiptera 12.5 3.5 <0.1 2.6 Ephemeroptera adults 12.5 1.1 0.1 2.2 Odonata 12.5 0.4 <0.1 2.1 32 (Table 14). Together with Diptera larvae and pupae, they accounted for about 55% of the IRI. Fish remains were of C. bairdi, and terrestrial insects were from Hymenoptera (Formicidae). Table 14. The Index of Relative Importance (IRI) and its components for food items in the stomachs of McBride cutthroat trout less than 350 mm total length in Axolotl Lake #2, 1986. Frequency of occurrence Volume Number Food item (%) (%) (% ) IRI Daphnia sp. 84.6 9.1 81.9 25.9 Diptera larvae 84.6 9.6 12.3 15.7 Diptera pupae 84.6 4.3 1.6 13.3 Diptera adults 61.5 2.5 0.2 9.4 Coleoptera 30.8 24.9 2.9 8.6 Trichoptera larvae 46.2 . 3.4 0.4 7.4 Fish remains 23.1 14.5 <0.1 5.5 Gastropoda 30.8 5.7 0.1 5.4 Terrestrial insects 15.4 7.8 0.4 4.0 Hemiptera 23.1 1.0 0.1 3.6 Amphipoda 7.7 0.2 ' <0.1 . 1.2 Fish were twice as important as the next food item for the larger category of McBride cutthroat (Table 15). The forage fish utilized was bairdi. The zooplankter Daphnia was not found in any stomachs of cutthroat trout 350 mm TL or greater. . Gill Raker Characteristics Gill Raker Numbers The mean number of gill rakers taken from samples of fish in the study strains are given in Table 16. There were no significant differences in gill raker numbers among strains. 33 Table 15. The Index of Relative Importance (IRI) and its components for food items in the stomachs of McBride cutthroat trout 350 mm total length or greater in Axolotl Lake #2, 1986. Food item Frequency of occurrence (%) Volume (%) . Number (%) IRI Fish remains 85.7 97.2 8.8 40.6 Diptera pupae 28.6 0.4 . 66.3 20.2 Gastropoda 42.9 2.2 10.0 11.7 Ephemeroptera naiads 28.6 0.4 3.1 6.7 Hemiptera 28.6 <0.1 1.3 6.4 Terrestrial insects 28.6 <0.1 1.3 6.4 Diptera larvae 14.3 <0.1 8.8 4.9 Odonata 14.3 <0.1 0.6 3.1 Table 16. Numbers of gill rakers in the four study strains of trout Number of Mean number Strain fish of gill rakers Range DeSmet rainbow 22 19.0 18-21 trout Arlee rainbow trout 20 19.2 17-22 Eagle Lake rainbow trout 22 19.2 18-22 McBride cutthroat trout 65 18.5 16-20 34 Gill Raker Mean Lengths All strains of trout studied showed a positive relationship between mean gill raker length and fish total length with correlation coefficients of 0.86 - 0.94 (Figure I). Ah F-test comparison of the regression lines showed that both DeSmet and Arlee rainbow trout had a significantly longer mean gill raker lengths than McBride cutthroat trout. There were no other significant differences among the strains. Gill Raker Mean Widths All study strains showed an increase in mean gill raker widths with increasing total length. Correlation coefficients ranged from 0.78 - 0.94 (Figure 2). The only significant difference in mean gill raker widths among strains was that Eagle Lake rainbow trout had greater widths than Arlee rainbow trout. Total Straining Area All trout strains showed a positive correlation between total straining, area and total length of trout because all gill rakers grew longer and farther apart as trout length increased (Figure 3). Correlation coefficients were 0.88 - 0.94 and there were no significant differences among strains. Effective Straining Area An effective straining area for prey was calculated by using the area capable of straining a 2 mm long prey item. The 2. mm size was chosen after determining the mean length of Daphnia found in a M EA N G IL L RA KE R LE NG TH ( M M ) ARLEE RA INBOW TROUT R = 0 .8 6 DESMET RA INBOW TROUT R = 0 .9 4 EAGLE LAKE RA INBOW TROUT R = 0 .8 7 MCBRIDE CUTTHROAT TROUT R = 0 .9 0 2 0 0 3 0 0 4 0 0 TOTAL LENGTH OF FISH (MM) Figure I. Regression of mean gill raker lengths (mm) with total lengths of study trout (mm). ARLEE RA INBOW TROUT R = 0 .7 8 2 . 5 - DESMET RA INBOW TROUT R = 0 .8 9 EAGLE LAKE RA INBOW TROUT R = 0 .9 4 MCBRIDE CUTTHROAT TROUT R = 0 .8 8 0 . 5 - 2 0 0 3 0 0 4 0 0 TOTAL LENGTH OF FISH (MM) Figure 2. Regression of mean gill raker widths (mm) with total lengths of study trout (ram). 100-1 LU OZ < ZD Of < LU OZ < O Z Z < o: I ARLEE RA INBOW TROUT R = 0 .8 8 DESMET RA INBOW TROUT R = 0 .8 9 EAGLE LAKE RA INBOW TROUT R = 0 .9 4 MCBRIDE CUTTHROAT TROUT R = 0 .9 0 TOTAL LENGTH OF FISH (MM) Figure 3. Regression of total straining area (square mm) with total lengths of study trout (mm). LO 38. random sample of trout stomachs taken from all study populations containing that item (Table 17). Table 17. Mean lengths (standard deviations) of Daphnia found in the stomachs of the study specimens. Strain Study area Number of trout sampled Mean length of Daphnia (standard deviations) DeSmet Harrison 10 2.1(0.26) rainbow Reservoir trout Eagle Lake Grasshopper 10 1.9(0.16) rainbow Reservoir trout Arlee Notellum 10 1.9(0.16) rainbow Reservoir trout McBride Hyalite 10 2.0(0.19) cutthroat Reservoir trout McBride Hebgen 10 1.9(0.20) cutthroat Reservoir trout McBride Axolotl 5 1.6(0.24) cutthroat Lake #2 trout All trout 55 1.9(0.21) combined 39 Plots of effective straining areas with total length for the strains ,indicated that in fish 350 mm TL or longer, effective areas had peaked and began to decrease. This is due to the increased spacing distance between adjacent gill rakers. Therefore, strains were separated into length groups of fish less than 350 mm TL and those 350 mm TL and longer for further analyses. Correlation coefficients were 0.80 to 0.97 for trout strains for fish less than 350 mm TL and effective straining area (Figure 4). There were, no significant differences among strains. The correlation coefficients of trout strains with specimens 350 mm TL or longer were -0.26 to -0.59 (Figure 5). This suggests that at lengths of 350 mm TL or longer, food items 2 mm or smaller will progressively be less efficiently strained by the gill rakers. Study Water Zooplankton Eight forms of zooplankters were identified from the study waters (Table 18). Daphnia pulex and Calanoida were found in all study waters. Leptodora was only found in one study water. Densities of carapaced Cladocera of all sizes, and those 2 mm or longer were determined for the study waters (Table 19). Cladocera population densities varied by 600%, but the density of Cladocera 2 mm or greater in length only differed by 200% in waters with this size organism. These larger size Cladocera comprised about 10-18% of their respective total populations. EF FE CT IV E ST R AI N IN G A RE A (S Q U AR E M M ) 6 0 - i 5 0 4 0 3 0 - 2 0 - 10- 0 ARLEE RA INBOW TROUT R = 0 .8 0 DESMET RA INBOW TROUT R = 0 .8 2 _ EAGLE LAKE RA INBOW TROUT R = 0 .9 8 y MCBRIDE CUTTHROAT TROUT R = 0 .8 6 *- O I I I I I I I I I I I I I I 5 0 100 150 2 0 0 2 5 0 3 0 0 3 5 0 TOTAL LENGTH OF FISH (MM) Figure 4. Regression of the effective gill raker straining area (square mm) for a 2 mm object with total lengths of study trout less than 350 mm. EF FE CT IV E ST R AI N IN G A R EA ( SQ U AR E M M ) DESMET RAINBOW TROUT R = - 0 . 2 6 EAGLE LAKE RAINBOW TROUT R = - 0 . 5 9 MCBRIDE CUTTHROAT TROUT R = - 0 . 4 8 TOTAL LENGTH OF FISH (MM) Figure 5. Regression of the effective gill raker straining area (square nun) for a 2 mm object with total lengths of study trout 350 mm or greater. Table 18. Distribution of zooplankton identified in the study waters during 1985-1986. Study waters* Plankton type Har. Res. Wds. Lake Grs. Res. Ntl. Res. . Hya. Res. Heb. Res. Axl. Lake #2 Cladocera Daphnia pulex X X X X X X X Daphnia galeata mendotae X X X Diaphnasoma leuchtenbergianum X X X X Ceriodaphnia reticulata X X X X . Bosmina lbngirostris X X x. Leptodora kindti , X Copepoda Calanoida X X X X X X X Cyclypoida X X X X * Har. = Harrison Reservoir; Wds. = Woods Lake; Grs. = Grasshopper Reservoir; Hya.= Hyalite Reservoir; Heb. = Hebgen Reservoir; Axl. = Axolotl Lake #2. 43 3Table 19. Densities (number/m ) of carapaced Cladocera In the study waters, 1985-1986. Density Study water Total Organisms >2 mm Harrison Reservoir 21501 2103 Woods Lake 37588 O Grasshopper Reservoir 14343 1861 Notellum Reservoir 6139 902 Hyalite Reservoir 6831 1120 Hebgen Grayling Arm 6703 1215 Axolotl Reservoir 12852 0 Two bodies of water did not contain Cladocera with lengths of 2 mm or greater. The reason for their absence from Axolotl Lake #2 is not understood, but their absence from Woods Lake may be due to the R. balteatus (Robert Domrose, MDFWP, pers. comm.) present. Johannes and Larkin (1961) reported that high redside shiner populations may reduce populations of Daphnia to a point that rainbow trout may not be able to feed on them as rapidly as they would during years when shiners are not present. In addition. Brooks and Dodson (1965) suggested that fish predation may influence the size structure of herbivorous zooplankton by removing the larger organisms. In Hebgen Reservoir, L^ kindti were present at a 3density of 8/m but were not considered with the above Cladocera because sample specimens became fragmented and non-measurable. They 44 also represent a potential food source not restricted by gill raker widths because of their large size (Pennak 1978). Total density of Cladocera regressed against mean condition factors for fish less than 350 mm TL in all populations had a correlation coefficient of only 0.19. The correlation coefficient of densities of carapaced Cladocera 2 mm or greater in length regressed against condition factors of trout less than 350 mm total length was 0.82, indicating the importance of this food item to growth (Figure 6). A similar analysis with trout 350 mm TL or greater resulted in a correlation coefficient of 0.45. Study Water Limnology The physico-chemical characteristics of the study waters contained a wide range of values in some characteristics (Table 20). Conductivity and alkalinity values varied 18- and 13- fold, respectively. Hydrogen ion concentrations ranged from slightly acid to highly alkaline. Mean depths and euphotic depths were more similar, differing by factors of 3 and 12, respectively. The percent of the total water volume that was euphotic, temperature regimes and dissolved oxygen levels were more similar among the waters than the other measured parameters. None of the maximum temperatures exceeded the the maximum temperature of 25.6°C tolerated by trout (Piper et al. 1986). The only measured dissolved oxygen levels that were below the desirable M EA N C O N D IT IO N F A C TO R S (K ) O F TR O U T K = 0.95 + 9.0 X IC 5(D) R = 0.80 0.8 - 0.6- 0 .4 - 0 . 3 - 750 1000 1250 1500 1750 2000 DENSITY OF CLADOCERA (D) >2MM (NO ./M 3) 2250 2500 Figure 6. Regression of the mean condition factors of trout less than 350 mm TL with densities of Cladocera 2 mm or longer in the study waters during 1985 - 1986. Table 20. Physico-chemical measurements made on study waters during 1985-1986. Study Conductivity water (umho) Alkalinity (meq/l) pH Mean depth (m) Euphotic depth (m) Euphotic volume (%) Maximum/minimum summer temperatures ( ° c ) Mean (range) DO levels (mg/1) Harrison Reservoir 346 3.42 7.8 7.0 7.4 95 23.0/13.1 5.0(2.3-7.7) Woods Lake 171 2.00 8.7 3.8 6.0 100 21.5/19.0 9.1(8.3-10.0) Grasshopper Reservoir 1009 • 7.16 8.6 4.3 3.5 93 18.1/10.5 7.4(6.0-8.2) Notellum Reservoir 55 0.70 6:9 4.6 5.0 91 21.0/9.0 6.0(0.6-8.9)* Hyalite Reservoir 65 0.54 7.3 11.8 27.0 100 17.0/7.1 7.5(6.7-8.I) Hebgen Grayling Arm 237 1.38 8.6 3.9 7.0 99 18.0/15.7 7.9(7.6-8.I) Axolotl Lake #2 192 1.92 9.1 3.7 5.0 100 14.0/11.5 10.5(9.9-11.5)* * Dissolved oxygen levels were based on measurements from single trips. 47 5 mg/l level (Piper et al. 1986) were found in Harrison Reservoir and Notellum Reservoir below depths of 7.5 m and 4.5m, respectively. Limnological variables were regressed with condition factors for fish less than 350 mm TL in all populations (Table 21). Positive correlation coefficients greater than 0.80 were found between mean condition factors and conductivity and alkalinity, while the strongest negative correlation was with condition factors and the percent euphotic volume of the total volume of the water body. These three parameters often are indicators of general productivity of waters. Table 21. Correlation coefficients for limnological variables with mean condition factors of trout less than 350 mm total length in all study waters, 1985-1986. Limnological variable Correlation coefficient Alkalinity 0.87 Conductivity • 0.84 Minimum summer water temperature 0.54 Mean dissolved oxygen level 0.29 Hydrogen ion concentration 0.19 Maximum summer water temperature -0.20 Mean depth -0.42 Euphotic depth -0.56 Minimum dissolved oxygen level -0.59 Maximum dissolved oxygen level -0.69 Percent euphotic volume of total -0.75 48 SUMMARY AND DISCUSSION Food habits of trout less than 350 mm TL were similar regardless of study strain. All strains primarily utilized Daphnia and had an efficient gill raker morphology to do so. The food habits found for this size group of trout were similar to those McMullin (1979) reported in wild rainbow trout and westslope cutthroat trout (Salmo clarki lewis!) at lengths less than 330 mm. It appeared that the condition factors of smaller size group of fish increased as the density of daphnids larger than 2 mm increased. The regression of condition factors in fish less than 350 mm TL with the density of large daphnids in this study showed that populations of at least 500 dapnids 2 mm or more in length per 3 m would be needed to maintain this sized trout in condition factors of 1.0 or greater. Galbraith (1975) reported that summer plankton hauls containing 150 or more daphnids greater than 1.34 mm in length were characteristic of good quality rainbow trout fishing lakes. However, quality of fishing was subjectively judged by the reports of trout fisherman, the size of fish caught was not mentioned. The Arlee strain appeared to be particularly adept at utilizing Dahpnia even in the absence of a morphological advantage in gill raker structure. The volumes of Daphnia in the stomachs of Arlee strain fish were equal to or greater than the like volumes in other strains from lakes with substantially greater daphnid densities. This suggests that Arlee strain fish may be the better type to plant 49 in zooplankton poor waters. More investigation is needed though, to determine the effectiveness of the larger size class of Arlees under similar circumstances. The food habits of trout 350 mm TL or longer diverged within and among strains. The study population of DeSmet rainbow trout continued to be primarily planktivorous even at lengths larger than 350 mm TL. This is consistent with the reports on this strain (Mueller and Rockett 1980; Jack Boyce, MDFWP, mimeo; Richard Vincent, MDFWP, pers. comm.), although there have been instances where the strain has been found to be piscivorous (Boyce 1985). Eagle Lake rainbow trout fed almost exclusively on tui chubs • (G. bicolof) during summer months in their native lake and fed very little oh invertebrates even when they were abundant (McAfee 1966). This strain was introduced into Montana because it was reported to be a fast growing piscivore (Richard Vincent, MDFWP, pers. comm.; Jack Boyce, MDFWP, mimeo) and had the potential to be useful in reducing unwanted forage fish. However, the two populations of this strain planted in Montana waters, showed very little piscivory. They mostly fed on gastropods and hemipterans even though the study waters contained good populations of redside shiners (Robert Domrose, MDFWP, pers. comm.) and brook sticklebacks, fathead minnows, and Iowa darters (Kent Gilge, MDFWP, pers. comm.). It is possible that these forage species may have been undesirable or unavailable to the Eagle Lake trout, but these explanations seem unlikely. There were remains of each forage 50 species in a few trout stomachs and McMullin (1979) reported that the redside shiner was an important food item in the diets of wild rainbow trout greater than 330 mm. Also, since the trout in this study were in small, shallow waters, this probably forced the potential predators and prey into the same habitat even though there appeared to be abundant escape cover at one site. Like DeSmet and Arlee rainbow trout, McBride cutthroat trout are reported to feed primarily on insects and zooplankton (Sharp and Arnold 1967; McMullin and Dotson 1987). However, this study's findings also showed that the McBride strain could be piscivorous. They utilized cottids in one study water, but they did not feed on cottids in another water, or lake chubs (Couesius plumbeus) in their native lake (Varley et al. 1976; Jones et al. 1983). Although they did not feed on Utah chubs during this study, remains of that forage fish have been found in stomachs of some McBride cutthroats in subsequent studies (Richard Vincent, MDFWP, pers. comm.). It may be possible that this form only switches to fish when other food resources are scarce. In the two situations in this study in which fish were not utilized, terrestrial insects and Leptodora were abundant in stomachs. The lower condition factors in some populations of trout with fish greater than 350 mm TL is probably the result of energetics. Werner (1979) reported that for fish to be energy efficient, they must take prey of sufficient size and number to more than compensate for the energy lost in chase and capture. In this study, the larger 51 fish (_> 350 mm TL) in some populations continued to feed heavily on zooplankton despite their reduced effective gill raker straining areas. This may account for the lower condition factors in these larger fish. Mueller and Rockett (1980) also found that DeSmet rainbow trout primarily utilizing Daphnia after approximately 360 mm had lower condition factors than smaller trout. Conversely, trout populations in this study that used larger prey item more heavily, were not significantly lower in conditon factors compared to the smaller fish. These data indicate that it is unrealistic to attempt to manage for large, high condition factor trout in situations without a desirable and available food resource larger than dapnids. Two strains of trout were found to have promising prospects for use in managing waters with high pH levels. The Eagle Lake stock comes from a lake that has a pH that approaches 10.0 (McAfee 1966; Vernon King, CDFG, mimeo) and in this study, they had excellent condition factors for both size classes in waters with a pH of 8.6. The same strain had poor condition factors in a pH of 8.7 which was likely due to a poorer food supply. Also, the McBride cutthroat strain which is used primarily in the state's planting program in high mountain lakes (McMullin and Dotson 1987; Richard Vincent, MDFWP, pers. comm.) were found to have excellent condition factors in waters with a pH of 9.1. In its native lake, the strain survives pH ranges of 8.7 to greater than 10.0 during the summer (Sharpe and Arnold 1967; Varley et al. 1976). 52 The abilities of the Arlee rainbow strain and the DeSmet rainbow strain to sustain themselves in high pH situations are unknown. The results of this study suggest some strain characteristics that could have important management implications, but they are based mainly on single population measurements of a given strain alone in different water types. Additional testing is needed to document characteristics of the test strains. It is important to compare strains raised under the same conditions. A series of lakes/reservoirs should be selected to represent the major kinds of waters receiving trout plants. Each test strain should be marked differently and planted in significant numbers in each of the representative waters during one short time period, if possible. These plants should be made for three consecutive years to produce a series of size and age class samples for analysis. These situations were not as available during this study as originally believed because introductions of some strains were made only recently and other strains did not provide adequate samples. Only after these additional tests have been performed can the most efficient use of the strains be assured. 53 REFERENCES CITED Anonymous. 1968. A comprehensive water and related land resources plan for the state of Montana: Inventory Series Report Number 3. Montana Resources Board. Helena, Montana. APHA (American Public Health Service). 1975. Standard methods for the examination of water and waste water. 14th edition. Washington D.C. Bodaly, R.A. 1979. Morphological and ecological divergence within the lake whitefish (Coregonus clupeaformis) species complex in Yukon Territory. Journal of the Fisheries Research Board of Canada. 36:1214-1222. Bowen, S.H. 1983. Quantitative description of diet. Pages 325-336 in, L.A. Nielsen and D.L. Johnson, editors. Fisheries Techniques. American Fisheries Society. Bethesda, Maryland. Boyce, J. 1985. Rainbow evaluation: report of the hatchery bureau meeting. Montana Department of Fish Wildlife and Parks. . Helena, Montana. Brooks, J.L. 1959. Cladocera. Pages 578-663 in, W.T. Edmondson, editor. Freshwater Biology. John Wiley and Sons, Inc. New York, New York. Calhoun, A. 1966. The importance of considering the strains of trout stocked. Pages 181-184 in, A. Calhoun, editor. Inland Fisheries Management. State of California, The Resources Agency. Department of Fish and Game, Sacremento, California. Cordone, A.J. and S.J. Nicola. 1970. Harvest of four strains of rainbow trout,- Salmo gairdnerii, from Beardsley Reservoir, California. California Fish and Game. 56(4):271-287. Dean, J.L. 1972. Annual project report, fishery management investigation in Yellowstone National Park. Bureau of Sport Fisheries and Wildlife Technical Report for 1971. Yellowstone National Park, Wyoming. Dwyer, W.P. and R.G. Piper. 1984. Three-year hatchery and field evaluation of four strains of rainbow trout. North American Journal of Fisheries Management. 4:216-221. 54 Galbraith, M.G. 1967. Size-selective predation on Daphnia by rainbow trout and yellow perch. Transactions of the Americaon Fisheries Society. 96(1):1-10. Galbraith, M.G. 1975. The use of large Daphnia as indices of fishing quality for rainbow trout in small lakes. Internationale Vereinigung Fur Teoretische und■angewandte Limnologie, Verhandlungen. 19:2485-2492. George, E.L. and W.F. Hadley. 1979. Food and habitat partitioning between rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomleui) young of the year. Transactions of the American Fisheries Society. 108:253-261. Haney, J.F. and D.J. Hall. 1973. Sugar-coated Daphnia; A preservation technique for Cladocera. Limnology and Oceanography. 18(2):331-333. Hudy, M. 1980. Evaluation of six strains of rainbow trout (Salmo gairdneri) stocked as fingerlings in Porcupine Reservoir, Utah. M.S. Thesis, Utah State University, Logan, Utah. Hyslop, E.J. 1980. Stomach content analysis— a review of methods and their application. Journal of Fish Biology. 17:411-429. Jones, R.D., P.F. Bigelow, R.E. Gresswell, L.D. Lentsch, and R.A. Valdez. 1983. Annual Project Report. Fishery and aquatic management program for Yellowstone National Park. United States Fish and Wildlife Service Technical Report for 1982. Yellowstone National Park, Wyoming. Kliewer, E.V. 1970. Gillraker variation and diet in lake whitefish Coregonus nasus, in northern Manitoba. Pages 147-165, in, C.C. Lindsey and C.S. Woods, editors. Biology of Coregonid fishes. University of Manitoba Press, Winnipeg, Manitoba. Lindsey, C.C. 1981. Stocks are chameleons: plasticity in gill rakers of coregonid.fishes. Canadian Journal of Fisheries and Aquatic Sciences. 38:1497-1506. Lund, R.E. 1986. A user's guide to MSUSTAT— statistical analysis package. Department of Math and Science, Montana State University, Bozeman, Montana. Martin, N.V. and F.K. Sandercdck. 1967. Pyloric caeca and gill raker development in Lake Trout, Salvelinus namaycush, in Algonquin Park, Ontario. Journal of the Fisheries Research Board of Canada. 24(5):965-974. 55 McAfee, R.A. 1966. Eagle Lake rainbow trout. Pages 221-225, in, A. Calhoun, editor, Inland Fisheries Management. State of California, The Resources Agency. Department of Fish and Game. Sacremento, California. McMullin, S.L. 1979. The food habits arid distribution of rainbow and cutthroat trout in Lake Koocanusa, Montana. M. S. Thesis. University of Idaho. Moscow, Idaho. McMullin, S.L. and T. Dotson. Use of McBride Lake strain Yellowstone cutthroat trout for lake and reservoir management in Montana. Montana Department of Fish, Wildlife, and Parks, Helena, Montana. Merrit, R.W. and K.W. Cummins. 1984. An introduction to the aquatic insects of North America. Kendal/Hunt Publishing Company. USA. Moring, J.R. 1982. An efficient hatchery strain of rainbow trout for stocking Oregon streams. North American Journal of Fisheries Management. 2:209-215. Mueller, M.A. 1985. Field evaluation of four strains of rainbow trout (Salmo gairdneri). M.S. Thesis, Montana State University., Bozeman, Montana. Mueller, J.W. and L.C.Rockett. 1980. Lake De Smet, history and management. Fishery Research Report number 3: Wyoming Game and Fish Department. Pennak, R.W; 1978. Fresh water invertebrates of the United States. John Wiley and Sons, Inc. USA. Piper, R.G., I. B. McElwain, L.E. Orme, J.P. McCraren, L.G. Fowler, and J.R. Leonard. 1983. Fish hatchery management. United States Department of the Interior. Fish and Wildlife service. Washington D.C. Rawstron, R.R. 1973. Harvest, mortality, and cost of three domestic strains of tagged rainbow trout stocked in large California impoundments. California Fish and Game. 59(4):245-265. Rawstron, R.R. 1977. Harvest, survival, and weight returns of tagged Eagle Lake and Coleman rainbow trout stocked in Lake Berryessa in 1972. California Fish and Game. 63(4):274-277. Sharp, J.L. and R.F. Arnold. 1967. Annual Project Report, fishery management investigation in Yellowstone National Park. Bureau of Sport fisheries and Wildlife Technical Report for 1966. Yellowstone National Park, Wyoming. "I 56 Snedecor, C.W. and W.G. Cochran. 1980. Statistical methods, 7th edition. Iowa State University Press. Ames, Iowa. Trojnar, J.R. and R.J. Behnke. 1974. Management implications of ecological segregation between two introduced populations of cutthroat trout in a small Colorado Lake. Transactions of the American Fisheries Society. 103:423-430. Varley, J.E., R.E. Gresswell, D.E. Jennings, and S.M. Rubrecht. 1976. Annual project report. Fishery and aquatic management program for Yellowstone National Park.• United States Fish and Wildlife Service Technical Report for 1975. Yellowstone National Park, Wyoming. Werner, E.E. 1979. Niche partitioning by food size in fish communities. Pages 311-322, in, H. Clepper, editor. Predator- prey systems in fisheries management. Sport Fishing Institute, Washington D.C. Wetzel, R.G. and G.E. Likens. 1979. Limnological Analyses. W.B. Saunders Company. Philadelphia, Pennsylvania, USA. Windell, J.T. 1971. Food analysis and rate of digestion. Pages 215-226, in, W.E. Ricker, editor. Methods for assessment of fish production in fresh waters. IBP Handbook no. 3. International Biological Programme, London, England. Zubik, R.J. 1983. The fishery of Hyalite Reservoir, Montana, with ah evaluation of cutthroat trout reproduction in its tributaries. MS. Thesis. Montana State University, Bozeman, Montana. 57 APPENDIX Table 22. Trout stocking records for Harrison Reservoir, Montana (Richard Vincent, MDFWP, 1986). Year Strain Number stocked 1977 DeSmet rainbow trout 80,000 1978 " 72,160 1979 no stocking — 1980 DeSmet rainbow trout 74,820 1981 " 143,497 1982 no stocking — — 1983 • DeSmet rainbow trout 40,000 1984 H 1,210 1985 no stocking — 1986 DeSmet rainbow trout 10,000 Table 23. Trout stocking records for Hyalite Reservoir, (Richard Vincent, MDFWP, 1986). Montana Year Strain Number stocked 1976 McBride cutthroat trout 20,070 1977 " 19,834 1978 " 19,534 1979 21,006 1980 . 21,269 1981 " 22,178 1982 no stocking — 1983 McBride cutthroat trout 21,328 1984 t 30,047 1985 tt 25,116 1986 " 30,000 58 Table 24. Trout stocking records for Hebgen Reservoir, Montana (Richard Vincent, MDFWP, 1986). Year Strain Number stocked 1979 McBride cutthroat trout 208,000 1980 " 220,863 1981 " 281,921 1982 " 328,735 1983 ■“ 363,970 1984 " 83,000 1985 " 12,065 1986 " 135,313 Table 25 The calculated mean total lengths (mm) at annuli for DeSmet rainbow trout in Harrison Reservoir, Montana, 1986. 1985- .Mean Annulus length at ______________________ capture. Age Number (mm) I 2 3 4 5 I 14 215 102 2 36 349 ■107 243 3 22 414 107 232 367 4 15 432 95 194 314 391 5 2 453 92 149 286 400 424 Total 89 Grand mean 104 227 342 392 424 59 Table 26. The calculated mean total lengths (mm) at annuli for McBride cutthroat trout in Hyalite Reservoir, Montana, 1985-1986. Mean Annulus Age Number length at capture (mm) I 2 3 4 I 29 188 114 2 26 275 106 223 3 19 317 112 199 2 79 4 4 412 109 201 295 378 Total 78 Grand mean H O 212 282 378 Table 27. The calculated mean total lengths (mm) at annuli for Arlee rainbow trout in Notellum Reservoir, Montana, 1986. Age Number Mean length at capture (mm) I Annulus 2 3 I 2 218 ■ 174 2 39 306 209 • 278 3 I 381 236 . 324 366 Total 42 Grand mean 208 279 3 66 60 Table 28 The calculated mean total 'lengths (mm) at annuli for Eagle Lake rainbow trout in Grasshopper Reservoir, Montana, 1985-1986. Age Number Mean length at capture (mm) 0 Annulus I 0 32 179 I" 25 359 203 Total 57 Grand mean 203 Table 29. The calculated mean total lengths (mm) at annuli for Eagle Lake rainbow trout in Woods Lake, Montana, 1986. Mean length Annulus Age Number at capture (mm) I 2 3 3 10 395 222 306 373 Total 10 Grand mean 222 306 373 6 1 Table 30. The calculated mean total lengths (mm) at annuli for McBride cutthroat trout In Hebgen Reservoir, Montana 1985-1986. 9 Mean length at capture Age Number (mm) Annulus 1 2 3 I 11 246 144 2 8 338 168 297 3 6 392 141 245 344 Total 25 Grand mean 151 275 344 Table 31; The calculated mean total lengths (mm) at annuli for McBride cutthroat trout in Axolotl Lake #2, Montana, 1986. Mean Annulus length at ___________________ capture Age Number (mm) I 2 3 4 2 11 317" 77 235 3 7 378 80 204 315 4 3 502 68 152 329 416 Total 319 416Grand mean 21 77 MONTANA STATE UNIVERSITY LIBRARIES 3 1762 10021381 6