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Effects of Myxobolus cerebralis on the Population Dynamics of Kokanee in Porcupine Reservoir, Utah
Arthur E. Butts Utah State University
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Recommended Citation Butts, Arthur E., "Effects of Myxobolus cerebralis on the Population Dynamics of Kokanee in Porcupine Reservoir, Utah" (2002). All Graduate Theses and Dissertations. 4436. https://digitalcommons.usu.edu/etd/4436
This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. EFFECT OF MYXOBOLUS CEREBRALIS ON THE
POPULATION DYNAMIC OF KO KANEE
IN PORCUPINE RE ERVOLR, UTAH
by
Anhur E Butts
A thesis submitted in panial fulfillment of the requirements for the degree
of
MASTER OF SCI NCE
in
Fisheries Biology
Approved
UTAH TATE IVERSITY Logan, Utah
2002 UMI Number: 1408258
UMI Microform 1408258 Copyright 2002 by ProQuest lnformalion and Learning Company. All rights reserved. This microform edition is protecled againsl unaulhorized copying under Title 17, United Stales Code.
ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml48106-1346 ABSTRACT
Effects of Myxobolus cerebra/is on the Population Dynamics of
KokJinee in Porcupine Reservoir, Utah
by
Arthur E. Butts, Master of Science
Utah State University, 2002
Major Professor: Dr. David A. Beauchamp Depanment. Fisheries and Wildlife
This study tracked the chronology and severity of Myrobo/us cerebra/is infection and related it to
survival of age-0 kokanee to determine whether M cerebra/is represented a significant agent ofmonality
in the population. Environmental conditions and losses to predation were identified and linked to age-0
kokanee survival to identifY other sources ofmonality in the population. We attempted to track survival of
age-0 kokanee from the outmigrati on into the reservoir until the end of the first growing season in
September of each year. The number of age-0 kokanee that entered the reservoir was calculated by
obtaining estimates of total egg deposition and egg-to-fry survival for the 1999 brood year.
Age-0 kokanee were primarily infected by the parasite after they had entered the reservoir in
spring Prevalence and severity increased rapidly throughout the summer and nearly all age-0 kokanee
were infected by August of both years. In total, 495 age-0 kokanee were examined for clinical lesions
associated with M cerebra/is in 1999 and 2000, but only one fish displayed a cranial abnormality in 2000.
Low survival rates of age-0 kokanee from July through September were observed and coincided with
increased prevalence and severity. However. because of high reservoir temperatures, low food levels,
predation, and entrainment, evidence forM cerebra/is acting as a direct source of monality on age-0
kokanee was elusive during our study. In age-l and older kokanee, we did not find any evidence that M cerebra/is had an effect on growth and overall condition of the fish. Infection severity and presence of clinical signs varied between years and were likely more related to limitations of the diagnostic techniques.
Any effects that M cerebra/is may have had on kokanee are likely to occur during the first growing season iii and may impact the host 's abili ty to cope with the other environmental stressors identified at Porcupine
Reservoir.
Despite high mortality rates. the kokanee population at Porcupine Reservoir was considered to be overabundant based on estimated densities and length distributions of spawning fish. M. cerebra/is did not appear to have a significant effect on the abundance of the kokanee population but we were unable to detemline whet her or not the parasite was a source of direct mortality because of other potential sources of mortality. {Ill pages) iv ACKNOWLEDGMENTS
I would like to thank the Utah Division of Wildlife Resources and United States Geological
Service/Biological Research Division for funding and cooperative efforts. Craig Schaugaard, Kent
Sorenson, Chris Wilson, and Eric Wagner provided valuable assistance and insight during the initital stages of this research. Matt Helm, Mike Golden, Jon Flinders, Mark Smith, and Brett Thompson provided invaluable support and friendship in the field and laboratory. Without my technicians, I would not have been able to accomplish this research.
Special thanks to my advisor, Dave Beauchamp, for his invaluable assistance, patience, mentoring, and friendship. No class, book, or other individual could have taught me more about fisheries or being a professional than Dave.
I will never be able to thank my parents, Charles and Alice, enough for the endless sacrifices that they have made so that I could receive an education. At times, I'm sure they didn't know if! would make it out of high school. so I hope that my compl etion of this degree is a reward for their perseverance.
And finally to my beautiful wife and best friend, Kresta, and my "children," Niezhone and
Scooter. Kresta provided friendship, support, and reason when I most needed it and was always willing to help in the field when nobody else could. Thanks for putting up with me. Niezhone and Scooter, my four legged techs, were always ready to give me a lift when so many things went wrong.
Arthur E. Butts v CONTENTS
Page
ABSTRACT ...... ii
ACKNOWLEDGMENTS .iv
LIST OF TABLES ...... vi
LIST OF FIGURES ...... viii
CHAPTER
INTRODUCTION ...... •...... •...... 1
References ...... ············ 5
2 AN ASSESSMENT OF THE I 998 AND I 999 SPA \Vli.'ING ESCAPEMENTS AND FRY RECRUITME TIN A POPULATION OF KOKANEE INFECTED BY MYXOBOLUS CEREBRA U S AT PORCUPINE RESERVOIR, UTAH ...... 9
Abstract ······· · 9 Introduction ...... ····················· ...... 9 Study Site ...... 12 Methods ...... 12 Results . .... ···························· ...... 21 Discussion ...... 37 References ...... 43
2 SURVIVAL OF AGE-0 KOKANEE IN A POPULATION INFECTED BY MYXOBOLUS CEREBRAU S IN PORCUPINE RESER VOIR, UTAH ...... 46
Abstract ...... 46 Introduction ...... 46 Methods ...... 50 Results ...... 61 Discussion ...... 84 References ...... ··· ··························· ...... 94
4 CONCLUSION ...... ·················· ······ ····· ...... 100 vi LIST OF TABLES
Table Page
2-1 Sum of observed ranked deformities, percent fish with deformities, deformity ranking, infection prevalence, and average spores per I 00 fields for spawning kokanee at Porcupine Reservoir for 1996-1999 spawning runs. Sample size fo r all years was 60 fish ...... 22
2-2 Live spawner counts from daily visual surveys and abundance estimates from area-under-the-curve (AUC) calculations for each survey interval during the 1998 and 1999 escapement period...... 25
2-3 Est imated kokanee egg deposition in the East Fork Little Bear River in 1998 and 1999. Estimates are based on a size-specific fecundity model, female size distribution, total abundance of females (26, 118 in 1998; 11 ,299 in 1999), and an average egg retention rate of3.59 eggs/female ...... 28
2-4 Values for parameters used to estimate total fry outrnigration during spring 2000 at Porcupine Reservoir. Total number of fry captured and estimates for total fry abundance using both flow expansion and trap efficiency techniques are shown as well. The mean trap efficiency estimate of 4.6% for days when recaptures were greater than zero was assumed for all dates in which marked fry were not recapu ted in the trap ...... 35
2-5 Comparison between reponed kokanee and sockeye egg-to-fry survival rates from various western populations. Estimates !Tom Bradford (1995) were estimated !Tom a summary graph of35 different populations of sockeye that were compiled from various sources ...... 42
3-1 Parameters used during the collection and analysis ofhydroacoustic data ...... 54
3-2 Diet composition of prey, as wet weight percentages of the stomach contents for two size classes ofbrown trout, cutt hroat trout, and rainbow trout during spring and summer 2000. Prey energy densities (Jig) that were used in the bioenergetic simulations are shown and were assumed to be constant throught the modeling period ...... 60
3-3 Average extinction coefficient s and Secchi depths for dates that routine limnological measurements were taken ...... 66
3-4 Estimated values for instantaneous monality (Z) and survival (S) of age-0 kokanee for three time periods during the 1999 and 2000 summers, wbere abundance estimates were obtained !Tom monthly hydroacoustic surveys ...... 76
3-5 Sum of observed ranked deformities, percent fish with deformities, deformity ranking, infection prevalence, and average spores per I 00 fields for kokanee coll ected during the summer and spawning runs at Porcupine Reservoir, 1998- 2000. Percent offish with observed deformities and deformity ranking are higher during spawning runs, after fish have undergone morphological changes associated with sexual maturity in kokanee ...... 82 vii 3-6 Average spores/100 fields for age-l and older kokanee collected during 1999 and 2000 summer venical gillnening and spawning runs. Fish were processed using the pepsin-trypsin digest. No age-l fish were collected in 1999 because of problems with gear selectivity ...... 83
3-7 Monthly consumption of kokanee (kok) by all cohons of salmonids for 2000 summer. Population structure for 1,000 individuals was calculated from survival rates obtained from a regression of age frequencies from fish fully recruited to gillnets for brown trout. Because age frequency data were incomlere for cutthroat trout, we assumed that the population structure for both species was the same for purposes of the model. The population of 1,000 predators was panitioned into 354 age-3, 251 age-4, 178 age-5, 127 age-6, and 90 age-7 individuals for both brown trout and cutthroat trout ...... 85
3-8 Various estimates of degree-days until onset of clinical signs associated with M cerebra/is in various laboratory studies...... 88
3-9 Various survival rates for age-0 kokanee and time periods over which survival was measured. When possible, an error was calculated from published data using two standard errors ...... 90 viii LIST OF FIGURES
Figure Page
2- 1 Map of Porcupine Reservoir and the surrounding watershed. The East Fork Little Bear River and Cinnamon Creek contain spawning grounds that are utilized by kokanee ...... 13
2-2 Linear regression of fecundity (In( eggs/female)) on mid-orbital length (mrn). The model was constructed using egg counts from 1998 and 1999 spawners ...... 17
2-3 Visual counts of spawning kokanee vs. time in East Fork Little Bear River during the 1998 and 1999 brood years. Counts were conducted over the entire length of stream that was utilized by the spawners. In 1998, peaks of 5,0 19 males, 5,112 females, or 9,851 total fish were observed. In 1999, peaks of 2,065 males, 1,934 females, or 3,728 total fish were observed ...... 23
2-4 Mean daily stream temperatures for East Fork Little Bear River during the spawning and early incubation periods in 1998 and 1999. The beginning, peak., and end of each spawning run are shown. Temperature data were not avai la ble after 15 January 1998 and 22 December 1999 ...... 26
2-5 ex-specific length frequency distribution of spawning kokanee in the East Fork Linle Bear River for both the 1998 and 1999 brood years . A random sample of 60 fish was collected each year fo r length, weight, fecundity, and Myrobolus cerebra/is testing ...... 27
2-6 Percentage contributi on of each age class for female and male spawners from the 1998 and 1999 brood years...... 29
2-7 Nightly kokanee fry catches during 1999 (a) fi-om the beginning of fry trapping until 18 March when vandalism and high flows disrupted fry trapping. Flows in the East Fork Little Bear River (b) during the fry trapping period. Flows were interpolated between dates ...... 31
2-8 Length fi-equency distribution of ou tmigrating fry caught in fry traps on the East Fork Little Bear River in 1999 and 2000 ...... 32
2-9 Spring 2000 nightly kokanee fry catches (a) fi-om the beginning of fry trapping until 8 May 2000 when fry outmi gration ceased. Also shown are the flows in the East Fork Little Bear River (b) and mean daily stream temperatures during the fry outmigration ...... 34
2- 10 Comparison between survival curves generated from both trap efficiency and flow expansion estimates of total fry outmigration and actual observed abundance obtained from hydroacoustic sampling. Theoretical July population abundances were calculated for both techniques using an observed survival rate of0.17. Because of the proximity of the July abundance estimate obtained usi ng trap efficiency to observed hydroacoustic abundance, we determined that trap efficiency estimates were more realistic ...... 4 1 ix 3-1 Diagram of Porcupine Reservoir denoting upper, mid, and lower reservoir sections. Hydroacoustic sampling transects used to assess limnetic fish densities in 1999 and 2000 are shown as well ...... 52
3-2 Porcupine Reservoir elevation (m) measured at the darn fTom I 5 August 1998 to 15 May 1999 and the period when increasing numers of fTy were entering the reservoir. The conservation pool was at 1600 m fTom 30 December 1998 to mid-February 1999. The reservoir is completely empty at an elevation of I 598 m ...... 62
3-3 Venical temperature (solid line) and dissolved oxygen (dashed line) profiles measured in Porcupine Reservoir in 1999. Reservoir depth declines considerably due to drawdowns for irrigation during July-September ...... 63
3-4 Venical temperature (solid line) and dissolved oxygen (dashed line) profiles measured in Porcupine Reservoir in 2000. Reservoir depth declines considerabley due to drawdowns for irrigation during July-September...... 64
3-5 Density (niL) estimates (a) and average total length of Daphnia (b) on 1999 and 2000 sampling dates at Porcupine Reservoir...... 67
3-6 Venical distribution offish captured in venical gillnets for the entire 1999 and 2000 summers. Nets were set prior to hydroacoustic surveys for target verification and sample collection. Kokanee comprised 99"/o of the total catch in 1999 and 93% of the total catch in 2000...... 68
3-7 Age-0 kokanee le01,'1h distribution from tow-netting (June), and gillnetting (August and September) surveys at Porcupine Reservoir during 1999 ...... 69
3-8 Age-0 kokanee length distribution fTom tow-netting (May-August) and venical gill netting (August-September) at Porcupine Reservoir in 2000 ...... 70
3-9 Length distribution of age-l and older kokanee captured in vertical gillnets during July-August surveys in 1999 and 2000...... 71
3-10 Density(± 2 SE) of three size classes of pelagic fish by depth at dusk and night (right) during 1999 hydroacoustic surveys. The 25-80 mm size class was comprised of mainly age-0 kokanee. ote the range of target densities for night surveys ...... 72
3- 11 Density (± 2 SE) of three size classes of pelagic fish by depth at dusk and night (right ) during 2000 hydroacoustic surveys. The 25-80 mm size class was comprised of mainly age-0 kokanee. Note the range of target densities for night surveys ...... 73
3-12 Monthly total abundance estimates (± 2 SE) for three size classes of kokanee at Porcupine Reservoir during 1999 and 2000 hydroacoustic surveys ...... 75
3-13 Growth curves for age-0 kokanee at Porcupine Reservoir during the 1999 and 2000 growing seasons. Data points denote the mean length for each month and error bars denote tbe 95% Cl ...... 78
3-14 Monthly total abundance(± 2 SE) estimates (a) and results ofPCR testing for the presence of Myrobolus cerebra/is for age-0 kokanee at Porcupine Reservoir during summer 1999. Age-0 kokanee were not captured during April, May, and July. Estimated degree-days were calculated based on the collection date ...... 79 3- I 5 Monthly total abundance(± 2 SE) estimates (a) and results ofPCR testing for the presence ofMyrobolus cerebra/is for age-0 kokanee at Porcupine Reservoir during summer 2000. Estimated degree-days were calculated based on the collection date...... 80
3-16 Porcupine Reservoir volume for June through September 1999 and 2000. The reservoir experiences an average drawdown of22 m or 50"/o of the full volumetric capacity during the four prime irrigation months...... 93 CHAPTER I
INTRODUCTION
Myxobolus cerebrolis, the etiological agent for whirling disease, has been implicated in the
devastating declines of several popular trout fisheries in the western United States. Fisheries in Colorado
and Montana have been panicularly hard hit , but the parasite ha s also spread to Washington, Oregon,
California. Idaho, Wyoming, and Utah. Utah Division of Wildlife Resources (UDWR) biologists have
tracked the spread of the disease in Utah, since it was first discovered in the state in 1991.
The presence of a pat.hogen such as M. cerebra/is does not necessarily result in a disease outbreak
within an individual or population. A disease can be described as a process that is characterized by .. any
impainnent that interferes with or modifies the perfonnance ofnonnal functions, including responses to
environmental factors such as toxicants and climate, nutrition, infectious agents; inherent or congenital
defects, or any combination of these factors" (Wobeser 1981 ; cited by Hedrick 1998, p. 107). Diseases
result from a series of complex interactions between the host, pathogen, and environment, and are an
inherent and imponant component of aquatic ecosystems (Hedrick 1998). According to an epidemiological
model developed by Snieszko (1974}, the host and pathogen must resi de together in an environmental
situation that is stressful to the host in order for the disease to occur. Environmental stressors such as
temperature, pH. dissolved oxygen, and contaminants can impact a host by altering physiological
parameters. such as osmoregulation. respiration, and immune responses (Sniesz.ko 1974; Lafferty and Kuris
1999, Lenihan et at. 1999). The presence of a pathogen or disease may also alter the behavior of a host and
reduce the ability to avoid predation (Mesa 1994; Mesa et al. 1998}, compete with others (Price et at . 1988;
Kiesecker and Blaustein 1999}, and may even alter the life history of a host (Sorenson and Minchella
1998). All of these potential impacts may cause changes in the growth, fecundity, and abundance of an
individual or population of organisms.
Understanding the life cycle of the parasite is irnponant for determining the potential impacts and severity of infection in a species or population offish hosts. M. cerebra/is is a microscopic parasite chat auacks the cartilage of infected trouc (Hoffman 1990). Cli nical signs include skeletal deformities, panicularly cranial, venebral, and mandibular, darkening of the caudal area, an apparent loss ofequilibriurn in the fish that is characterized by a "tail chasing" behavior, and death. Evidence suggests that this 2 "whirling" behavior is caused by a granulomatous inflammation, associated with parasitic invasion of the
sku ll and vertebral column, which may cause restriction within the spinal cord and possible compression or
deformation of the lower brain stem (Rose et al . 2000). The life cycle of M cerebra/is begins when mature
myxospores are released from the skeletal tissue of a dead fish . The spores can survive in the benthos for
an extended period, awaiting ingestion by their secondary host Tubifex tubifex, an aquatic oligocheate
worm (Wolf and Markiw 1984). in the gut epithelium ofT. tubifex, the spores develop into the next life
stage known as triactinomyxon (TAM). These T A.Ms are the life stage of the parasite that infects
salmonids and their development within the worm and subsequent release is clearly temperature dependent
(EI-Matbouli and Hoffinan 1998). After the TAMS are mature, they are released from the worm in feces,
where they enter the water column (Gilbert and Granath, in press). The longevity of the TAM is
apparently temperature dependent, but appears to be no longer than a week (EI-Matbouli et al. 1999).
When a TAM comes in contact with a salmonid, it enters the epidermis via the firing of polar capsules.
Sporoplasm is released into the fish, which migrates into the neural tissue where it is free from host
immune responses (EI -Matbouli et al. 1995). Generally, the sporoplasm co ntinues to migrate through the nervous system. and many ultimately reside in the canilaginous area su rrounding the brain. Here the parasite, now in its vegetative plasmodium stage, is referred to as a trophozoite The canilaginous matri~ which surrounds the trophozoite, is lysed as the trophozoites develop (EI-Matbouli et al. 1995).
Approxima tely 3 months afier infection, the parasite develops into the mature myxospore. These myxospores will not be released until the fish dies and the carcass decomposes. Because the parasite affects cartilage, younger fish that have not yet undergone ossification are especially susceptible to severe deformities and death.
Whirling disease can potentially affect the growth, survival, and abundance of its fish host
(Uspenskaya 1957; Markiw 1992b; Schisler et al . 1999). Severe M. cerebra/is infections can lead to canilaginous lesions or developmental deformities. The parasite may also indirectly limit an infected individual 's ability to forage, compete, avoid predation, and carry out certain behaviors characteristic of their species' life hi story strategies (timing oflife stage recruitment, age at reproduction). Much of the recent research on the parasite's impacts on salmonids has focused on its effects on rainbow
(Oncorhynchus mylriss), brown (Salmo truua), and cutthroat trout (0. clarki). Substantial declines in wild rainbow trout, in relation to the other species, have been important for both ecological and economical
reasons in Montana and Colorado (Nehring and Walker 1996; Walker and Nehring 1995; Vincent 1996).
This decline has been evident in the lack of recruitment of age-0 fish, suggesting that the disease causes
signifi cant mortality in younger rai nbow and cutthroat trout. Brown trout were introduced from Europe
and therefore may have coevolved with the parasite, which was inadvertently introduced to the United
States in 1964 fro m Europe (Hoffman 1998). Therefore, rainbow and cutthroat trout are naive hosts and
have not developed abilities, such as immunological responses, to cope with the disease. Aside from the
possibility of developing host-defense mechanisms, i.e., immune responses (Hedrick et al. 1999), the
differences in timing of certain aspects in the species' life histories may also allow brown trout to cope with
infection. Brown trout spawn in th e fall , whereas rainbow and cutthroat trout spawn in the spring.
Subsequently, juvenile trout that arise from fall spawners hatch and live their first few months during
periods of potentially low TAM releases. In contrast, progeny from spawning rainbow and cutthroat trout,
hatch and live their first few months during periods when water temperatu res are wanner and coincide with
higher TAM releases (El-Matbouli and Hoffman 1998). Age and dose response studies on rainbow and brown trout have suggested that development and severity of whirling disease are dependent on both age at firs t exposure and parasi te dose (Markiw 1991; Markiw 1992a; Ryce et al . 1999). In these experiments, survival was significantly lower for younger fish (<9 weeks post hatch). Fish that were infected after 7 weeks post hatching developed few clinical signs and suffered no mortality, and fi sh exposed at II weeks post hatch did not develop clinical signs, regardless of parasite dose.
Because of the economic importance of wild rainbow and cu tthroat trout in many western states, a vast amount of resources has been dedicated to the study of whirling disease on these species, but little is known about effects on kokanee or other fall-spawning salmonids that have not coevolved with the parasite. Kokanee are the land-locked form of sockeye salmon (Oncorhyncims neriw) and the life history and di stribution differences of kokanee in relation to other western salmonids could be important in determining the susceptibility and role of a semelparous species in the life cycle of the parasite. Unlike trout, adult kokanee die en masse after spawning. This heavy accumulation of carcasses may release a tremendous number of spores over a short period. This large annual release of spores could have significant implications for other salmonids, as well as the ecosystem because it may result in large releases 4 ofTAM s during periods that cutthroat or rainbow trout are young and vulnerable. Large releases of
mature myxospores into the environment from decomposing fish also should increase the chance that
Tubijex tubifex individuals ingest and become infected by M. cerebra/is. As the disease continues to spread
throughout the western U.S., baseline information on the impact of this disease on other fishes will become
increasingl y irnponant. This will be especially evident as the parasite spreads to areas that contain
endangered Pacific salmon.
Porcupine Reservoir has maintained a suong population and spawning run ofkokanee for the past
rwo decades Because of the success of the population, it was utilized as a wild broodstock source of
kokanee eggs in 1991 and 1992. In accordance with the Utah wild broodstock program, kokanee were
collected !Torn 1988 to 1992 during the spawning run and tested for prohibited pathogens, which included
M. cerebralis. The broodstock program at Porcupine Reservoir was abandoned after the 1992 brood year
because of the characteristically small fish and the success of other kokanee populations in the state.
During the period of di sease testing, no evidence of any prohibited pathogen was detected (Wil son et al.
1998).
However. in the 'vinter of 1993, M. cerebra/is was detected at a private hatchery on the East Fork
Linle Bear River, below Porcupine Reservoir. Intensive sampling effons immediately followed to determine the spatial extent of the parasi te in the drainage. During this testing, UDWR biologists failed to find evidence of the parasite in the reservoir. However, in the spring of 1994, gill netting samples revealed a rainbow trout with a severe venebral deformity that later tested positive forM. cerebra/is. Subsequent sampling revealed that young of the year (YOY) kokanee were also infected with the parasite.
Beginning in 1996, Utah Division of Wildlife Resources biologists decided to begin monitoring the disease prevalence and proponion of deformities in spawning individuals collected during the escapement period. An annual monitoring program was initiated in the Porcupine Reservoir drainage because of the lack of knowledge on whirling disease in kokanee, and uncenainty about how the parasite operated in reservoirs. The close proximity of the reservoir to Logan, Utah, the early stages of infection in the reservoir, and the history of pathogen testing also made it an attractive site for research.
Results !Tom the first two years of monitoring revealed that a significant increase in prevalence of the disease had occurred in the population (Wilson et al. 1998). The number of infected fish had increased !Tom 18/60 in 1996 to 44/60 in 1997, a jump !Tom 30"/o to 73%. ln addition, the mean number of spores
per 100 fields, a methodology used to enumerate spore load, increased !Tom 2. 1 to 128.9. These results
suggested that the prevalence ofM . cerebra/is was rapidly increasing in the population.
In this study, I examined the potential effects of M cerebra/is on a kokanee population. Stage
specific abundance and survival, in relation toM cerebra/is infection, was estimated for age-0 kokanee
during 1999 and 2000 !Tom fry trapping during outmigration and dual beam hydroacoustics during the
summers. Timing and intensity of infection in kokanee at Porcupine Reservoir were examined in age-0 and
older fish collected throughout the study period. The temporal aspects of stage-specific survival and the
onset of infection in age-0 kokanee were examined while concurrently tracking alternative sources of
monality. Egg-to-fry survival, environmental condit ions such as water temperature, dissolved oxygen, and
food supply, predation by piscivores in the reservoir, and entrainment were monitored so that any loss of
age-0 kokanee to M cerebra/is infection could be examined more directly. Potential nonlethal effects of
infection on growth of age-0 and older kokanee were also examined !Tom length and weight measurements
and otoliths.
Knowledge of potential impacts by M cerebra/is on kokanee should provide better understanding of the ecology of the parasite within lentic habitats and interactions with nalve hosts. The results of our
study may also provi de valuable information for the management of kokanee populations and perhaps anadromous salmonids, particularly as the parasite continues to rapidly spread across western U.S. watersheds.
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show alternation of invertebrate and vertebrate hosts. Science 225:1449-145 9 CHAPTER2
AN ASSESSMENT OF THE 1998 AND I 999 SPAWNING ESCAPEMENTS AND
FRY RECRUITMENT TN A POPULATION OF KOKANEE INFECTED BY
MYXOBOLUS CEREBRA US AT PORCUPTNE RESERVOIR., UTAH
Abslrac/.- We described and quantified the I 998 and I 999 kokanee spawning escapements and fry
recruitment at Porcupine Reservoir, Utah, to characterize infection by the parasiteMyrobo/us cerebra/is in the population. In addition, we generated an expansion factor for annual ]-{lay spawning index surveys to assist in the management of the kokanee fishery. Infection prevalence and severity was monitored by testing 60 randomly collected spawners each year forM. cerebrali. using the pepsin-trypsin digest technique. Clinical lesions associated with infection were ranked and recorded to generate a deformity index for each year. Prevalence increased from 68% in I 998 to 93% in I 999 but the number of fish with deformities dropped from 48% to 25%. Mandibular and cranial deformiti es were the two types of lesions most often observed in both years. Total escapement was estimated using the area-under-the-curve (AUC) technique and total egg deposition was calculated using estimates of length-specific fecundity and egg retention rates for the population According to AUC estimates, a total of25,65 I males (mean residence time = 3.8 days) and 26, 118 females (mean residence time = 4.2 days) entered the spawning tributary in
1998. In I 999, I 2,898 males and I I ,299 females entered the stream based on residence time estimates from I 998. By comparing AUC estimates with I -{lay spawner counts from both years, we suggest that a reliable estimate of total spawner abundance (within ± 25% of true abundance) could be generated by applying an expansion factor of5.8 times the I -day spawner count during the peak of the run (around I 9
September). An estimated 20, 159,809 eggs were deposited during the 1998 brood year and 5,768,578 were deposited in 1999. Efforts to quantifY fry recruitment failed in 1999, but we estimated that 1,241 ,452 fry outmigrated into the reservoir in 2000, for an estimated egg-to-fry survival rate of22%.
Introduction
Kokanee (Oncorhynchus nerka) are the landlocked form of sockeye salmon (0. nerka) and function as an important forage base and recreational fishery throughout much of the western United States 10 (Foerster 1968; Burgner 1991 ; Paragamian, 1995; Rieman and Maiolie, 1995). Kokanee life history
differs considerably from other inland salmonids Kokanee feed and grow in lakes for 2.5-3.5 years, then
spawn and die in tributaries or beaches during aurumn. Eggs incubate over winter in the streambed or
shoreline gravels until hatching in late wi nter, and a Ievins remain in the gravel for several more weeks before emerging at night and migrating immediately to the lake or reservoir. Fry commonly migrate directly to the limnetic region (Foerster 1968), but can spend time feeding in the littoral zone, particularly in lakes or reservoirs with pronounced littoral regions (Gemperle 1998; Burgner 1991).
Kokanee were introduced into Porcupine Reservoir, Cache County, Utah, in 1963 and 1967. The population has since become well established and relies on an annual spawning run (escapement) for production. The kokanee at Porcupine Reservoir provide a rare and valuable spon fishery in nonhero Utah, and function as a forage base for adfluvial brown trout and cutthroat trout. The annual spawning run has become a popular event for residents in Cache Valley and much of nonhero Utah, due to its close proximity to many cities nonh of Salt Lake City. Spawning kokanee also provide an abundant food source for birds and mammals that li ve along the East Fork Little Bear River. Resident stream-dwelling fish feed upon kokanee eggs during the spawning run and the decomposing carcasses transpon imponant nutrients in and downstream of spawning areas (Richey et al . 1975; Bilby et al. 1996).
The Utah Division of Wildlife Resources (UDWR) began monitoring the kokanee population with a research project in 1981 (Janssen 1983) and has continued with annual redd counts conducted by non hem region biologists to record an index of spawner abundance. The annual counts serve as a tool for monitoring the kokanee abundance in the reservoir, where the population has been considered over abundant for some time (Janssen 1983). Redd counts usually occurred after the peak of the spawn to enable biologists to collect carcasses for length data. The use of 1-day surveys, including spawner or redd counts. as a tool for monitoring population trends can be problematic, because it may severely underestimate the total number of spawners if run timing and the shape of the spawning curve is variable or unknown (Beauchamp et al. 1994). Beauchamp et al. ( 1994) found that total abundance of spawning kokanee in a Lake Tahoe tributary was 19 and 141 times higher in 1991 and 1992, respectively, than the fixed date, 1-day surveys oo ovember I indicated. These 1-day surveys also do not address important characteristics of a typical spawning run. such as the beginning and end of the spawning run, the peak or II multiple peaks of the run, and the residence time of the spawners, which is the duration that an average
fish spends in the stream before it dies. The underestimation of kokanee abundance may confound abilities
to properly manage the population.
In 1994, Myxobolus cerebra/is, the microscopic parasite that causes whirling disease, was
discovered in rainbow trout (0. mykiss) and juvenile kokanee at Porcupine Reservoir. Whirling disease has
been linked to severe declines in survival of some wild trout populations in the western United States.
Substantial declines in wild rainbow trout have been imponant for both ecological and economic reasons in
Montana and Colorado (Nehring and Walker 1996; Vincent 1996; Walker and ehring 1995). The parasite infects all species ofsalmonids, but the severity of infection is dependent upon species, age and size offish, and parasite dose at first exposure. The disease can be panicularly devastating to young developing fish because the parasite affects canilage. The majority of research on effects of M cerebra/is on fish populations has focused on rainbow trout. brown trout, and cutthroat trout (Thompson et al. 1999; Nehring and Walker 1996; Vincent 1996). The initial lack of infected kokanee populations has left the potential impacts of the disease on kokanee unknown. UDWR biologists began monitoring the prevalence of infection and presence of clinical lesions associated with infection in spawning kokanee in 1996. Because of the close proximity of Porcupine Reservoir to the UDWR's Fisheries Experiment Station and Utah State
University, a research project was init iated to address the potential impacts of whirling disease on kokanee.
The objectives of this study were to (I) describe and quantify the 1998 and 1999 kokanee spawrting escapements, and provide the UDWR with an expansion factor for annual I -day index surveys to aid in the management of the population; (2) assess the prevalence of M. cerebra/is infection and quantify associated clinical deformities observed in spawrting kokanee and compare this to previous years; (3) obtain estimates of total egg deposition for each brood year; and (4) estimate the total number of fry that enter Porcupine Reservoir during spring 1999 and 2000 This research was a segment of a study conducted at Porcupine Reservoir in which an attempt was made to track the chronology ofinfection in relation to survival of age-0 kokanee to determine whether whirling disease represents a significant agent of monality in this population. In order to properly assess survival, an initial estimate of the number of age-0 kokanee entering the reservoir in spring was needed. This estimate of total fry outmigration can then be used for subsequent studies on lake phase survival of age-0 kokanee, in relation to whirling disease. 12 Stud y Site
Porcupine Reservoir is a smal l mesotrophic impoundment located on the E.F . Little Bear River in
Cache county, non hem Utah (Figure 2-1 ). The reservoir is located I ,640 m above sea level and contains
16. 024, 7 13 m' water at full pool with a mean depth of22 m, and a maximum depth of44 m. Porcupine
Reservoir is managed almost exclusively as an irrigation reservoir and experiences an average annual
drawdown of20 m. Porcupine Reservoir is a narrow water body, with steep shorelines and very limited
littoral region because of drawdown associated with irrigation. The surrounding landscape, including the
reservoir, is largely privately-owned ground. and is subjected to a variety of uses including logging, intense
grazing, and recreation.
The reservoir contains a variety of species including self-perpetuating populations of brown trout
(Salmo trulla). cutthroat trout (0. clarkt), and kokanee (0. nerka). Rainbow trout (0. mylriss) are both self
perpetuating and are stocked periodically after which they often hybridize with the cunhroat trout. During the fall of 1998, the reservoir was drained to a small conservati on pool for dam repairs. It remained at low levels unt il March of 1999 when dam repairs were completed. and the reservoir was allowed to fi ll during spring runoff Gill nening during maximum drawdown and after ice-off in March indicated good survival for fish confined in the small pool
A number of small springs feed int o Porcupine Reservoir, but the primary sources of water are
Porcupine Creek and the East Fork Little Bear River, which is th e lone tributary utilized by kokanee for spawning Approximately 4.8 km upstream from the reservoir, Cinnamon Creek joins the E. F. Little Bear.
When the spawner densit y is high enough, the kokanee continue upstream into Cinnamon Creek exclusively, ignoring areas of the E.F. Litt le Bear River upstream from the confluence of Cinnamon Creek.
Methods
1998 and / 999 Spatming Escapemell/s
As pan of an annual survey to track the prevalence of M. cerebra/is infection in kokanee at
Porcupine Reservoir, spawners were examined for deformities and were individually tested for the presence of the pathogen. On II September 1998 and 6 September 1999, 60 fish were randomly collected with an 13
Figure 2-1 .- Map of Porcupine Reservoir and the surrounding watershed. The East Fork Little
Bear River and Cinnamon Creek contain spawning grounds that are utilized by kokanee. 14 electroshocker for whirling disease testing. Coinciding with the deformity index of the Health Condition
Profile (HCP, Goede and Banon I 990), each fish was examined for seven rypes of deformities: vertebral,
mandibular, cranial , opercular, fins, gi ll rakers, and miscellaneous "other" deformities. Percent deformity
was calculated !Tom the number of deformities, each ranked by severity on a I -3 scale ( I= slight, 3=
severe), divided by the total possible number of2 I for each fish . Fish were then measured for total lengths
(nearest mm) in I 998 and total and mid-orbital lengths in I 999. Mid-orbital lengths were taken !Tom the
center of the eye to the hypural plate. Fish were weighed on a calibrated digital scale in I 998 and I 999
(nearest g). Intact ovaries (where eggs were not loose in the body cavity) were removed !Tom females and
frozen for subsequent egg counts in the laboratory to generate length-fecundity estimates. Otoliths were
removed through the roof of the mouth (Schneidervin and Hubert 1986), and placed in 70"/o EtOH for age analysis. Otoliths were sectioned (Beamish I 979) and aged by counting opaque rings laid down during
periods of slow growth in combination with counting ridges formed on the otolith surface. Average size-at age of spawning kokanee was estimated using an age-length key, as described by DeVries and Frie 1996.
Finally, a portion of the head of each fish was taken for individual testing for the presence ofM cerebra/is. at the Fisheries Experiment Station (FES), Logan, Utah. Diagnosis ofM. cerebra/is infection was conducted using a slightly modified version of the pepsin-trypsin digest (PTD) as described by Lorz and
Amandi ( 1994). The resulting residues were placed on slides and stained using Ziehl- oelsen carbo! fuchsin and examined under 200x_ Spores were enumerated by counting the number of spores in I 00 microscopic fields of vision
Escapement was defined as the number of mature kokanee "escaping" the fishery to spawn in the
E. F. Little Bear River. Sex-specific abundance of spawners was estimated using the area-under-the-curve
(AUC) methodology, as described by English et al. ( 1992). The AUC has been widely accepted and used for estimating numbers of various species of Pacific salmon (English et al. 1992; Hilborn et al. I 999).
Visual counts for six different categories of spawners were repeated during visual surveys of the spawning tributary. Spawners were counted on each observation date and estimated counts were interpolated berween observation dates, generating a spawner curve, which estimated the number of spawner-days, or the area-under-the-curve. The total number of spawners was then estimated by dividing the area-under-the curve by an estimate of the residence time, or the average period of time that a spawner spent in the 15 stream prior to death. An estimate of residence time was obtained by marking a group offish, as they
entered the spawning tributary, and the number of marked fish remaining during subsequent surveys was
counted (Lady and Skalski 1998; English et al . 1992; Irvine et al . 1992).
The East Fork Little Bear Ri ver was monitored fo r the presence of spawning kokanee on 30
August 1998 and 27 August 1999. Stream temperatures were recorded every 2 hours using a Hobo Temp
data logger (Onset Corp .) placed midway in the spawning area. Temperatures were recorded throughout the spawning and incubation period. In both I 998 and I 999, the entire length of stream utilized by spawning kokanee was surveyed. Count s of live males and females. dead males and females, and Jive and dead spawners of unknown gender were recorded 2-3 times weekly for the duration of the escapement period All of the following calculations of the AUC method were computed separately for live male and female spawners to obtain sex-specific estimates.
The population estimates (p,) for each sampling date (i) were then combined int o an estimate of the area-under-the-curve using the following algorithm:
0 1/C a l:" ({1,- 1, , ,} ' (p, + p,_,)) / 2 , . J
where 11 was the number of days since the start of the spawning run to the ith survey date and" was the number of surveys in which fish were observed.
Residence time estimates were obtained by calculating the AUC of tagged fish remaining in the stream on the rth sampling date (tag,). The AUC for tagged individuals (auc,) and residence time (rt). the average time that tagged fish remain in the stream, were estimated using the foll owing equations:
auc, = ,l:_ ,{{1 1- 1, _ 1) • (tag,+ tag, _,)) I 2
rl = auc, I relg where g was the tagged group of fish and ret, was the number of tagged fish initially released. Our estimates of residence time from both years were calculated from a large group of tagged fish released in
I 998 and was applied to both J 998 and I 999 because a reliable estimate in 1999 could not be calculated due to an insufficient sample size. Residence times should have been similar for both years, because run 16 timing, duration. and the shape of the spawner-day curves were similar between years. Fmally. the total
escapement for each sex was estimated by:
Escapeme/11 = auc I n
where auc and rl were calculated separately for males and females.
Prior to the peak of the run, a fyke net was deployed near the reservoir confluence, and 77 males and I 00 females were captured. These fi sh were measured to the nearest mm total length and weighed
(nearest g). Males and females were tagged below the dorsal fin with blue and yell ow Floy tags, respective ly. Fish were released the same day (17 September 1998) and were enumerated during subsequent surveys for sex-specific estimates of residence time. Because of the extreme sensitivi ty of the residence time estimate, we conducted visual surveys on three consecutive days after tagged fish were released, and every 2-4 days thereafter. English et al. (1992) found that residence time estimates were extremely se nsi tive to the length of time between the release of tagged fish and the first survey date afterwards.
Fecundity and egg Deposition
Total egg deposition was modeled usi ng a length-fecundity regression, egg ret ention estimates from carcasses sampled in 1998 and 1999, and the size-specific abundance of females. Gemperle (1998) used the following algorithm for estimating total egg deposition for each year:
n I:,. (fe, cundity - egg reteution ,) • ifemales ,), where 1 = I to 4. represented 25- mm size intervals of female spawners (from 225 to 350 mm, mid-orbital length). Fecundity, was obtained !Tom a size-specific fecundity regression. created fi-om the egg counts of intact ovaries of mature females. Egg cou nt s from both years were combined to develop a significant population specific model that allowed us to estimate the fecundity (number of eggs/female) from the mid- orbital length of the fish (Figure 2-2). The followi ng model was then apptied to the abundance and size structure of spawning females in both 1998 and 1999 (r2 = 0.83, N= 59, P FecwJdily = 12.6e (0.014 • mokwt>,> 17 8~------, 014 Fecundity = 12.6e10· 'M""""'> ~ =0 .83, p < 0.0001 7 .~ "'0c:: ~ 6 LL. .E 5 0 • 1998 0 1999 4+----.---.----.---.----.---,,---,----.--~ 160 180 200 220 240 260 280 300 320 340 Mid-orbital length (mm) Figure 2-2.- Linear regression of fecundity (In( eggs/female)) on mid-orbital length (mm). The model was constructed using egg counts from 1998 and 1999 spawners. 18 where mid-orb,= mean mid-orbital length (mm) in each 25-mm size intervaL Throughout the spawning period, female carcasses were collected, frozen, and subsequently measured and examined for egg retention in the laboratory We found no relationship between the length of the females and egg retention and therefore used the mean number of eggs remaining in the body cavity from carcasses collected in 1998 as our estimate of egg retention (N = 46, mean egg retention = 3.6 eggs/female, SO = 8.96). Mid-orbital lengths for females in 1998 were estimated using a regression model based on total and mid-orbital lengths (mm) from the 1999 spawning run (r' = 0.97, N = 32, P mid- The total number of females was estimated using the AUC techniques described above. Fry Outmigration Fry trapping was unsuccessful in 1999 because of access problems from construction around the dam and high runoff. Stream temperature data were recorded throughout the spawning, incubation, and try outmigration periods using a Hobo Temp data logger (Onset Corp.) deployed in the E. F. Little Bear River prior to both the 1998 and 1999 spawning runs. The logger was retrieved periodically throughout the fall and winter, and the temperature data were downloaded and analyzed in relation to the timing of try outmigration. The timing of try emergence was estimated using the temperature-dependent regression embryo-development rate function by Murray et aL ( 1989): log.E = 5.5595 - 0.0308I(Iog.n - 0.2140(log.T)2 (r' = 0.998) where E = days to 500/o emergence and T = mean incubation temperature in •c. Previous studies reponed that the Murray et al . ( 1989) equation tended to underestimate the date of 500/o emergence of naturally incubating embryos by 2-3 weeks (Gemperle 1998). Thermal unit analysis was used to predict when try traps needed to be deployed to begin monitoring the try outmigration. Emergence times were predicted using mean daily stream temperature starting on I September 1998. The equation was used to predict 500/o emergence from tbe stan of the spawning run (September I), the peak of the run (September 19), and the end of the spawning run (October 29). 19 During 2000, fry outmigration traps consisted of a 60-cm x 3-cm x 62-cm frame constructed with 6.4-mm diameter stainless steel rods. Two 10-cm diameter, 91-cm long PVC pipes were attached to each side of the trap frame so that each trap would have two pipes sampling both the upper and lower strata of the stream for a total of four pipes per trap. Four 20-cm x 3-cm openings were cut on the side of each pipe and sealed with a 2-mm plastic mesh to allow water to dissipate before entering the holding net. A 20- cm diameter, 85-cm long, 0.8-mm mesh holding net was securely au ached to the end of each pipe with a hose clamp. Each holding net had a 20-cm long zipper sewn into the end to facilitate the removal of fish . The trap was designed to ensure that trapping would continue even during high flows. The openings on the trap pipes and the length of the holding net were intended to allow water to dissipate within the pipes so that flows would not cause excessive monality for captured fry. Two 10-cm diameter, 80-cm long PVC tubes were sealed off with caps and artached to the top of each trap to provide flotation during periods of high flows. Prior to spring runoff, traps were secured to the stream bortom with four pieces of rebar, pounded into the substrate in each comer of the trap. During high flows, a cable was stretched across the entire chann el and each trap was auached to the cable by leader ropes secured to each side oft he trap frame. Stream velocity was measured with a flow meter to determine both the flow into the entrances of each trap and for the cross-section oft he stream at the trapping site. Stream flows were measured with a Marsh McBimey flow meter at every 0.5 m across the width oft he stream channel at a depth of60% of the total ven.ical depth at each interval. The total water volume sampled during each trapping period was estimated by measuring the flow (m/s) at the center of each pipe entrance and multiplying it by the period between each time the traps were checked. Four traps ( 16 pipes) were set horizontally across the channel on 17 January 2000. The traps fished continuously and were checked 3-4 times weekly from 19 January 2000 to 8 May 2000 except on 5 April, 12 April, and 21 April 2000. Because the reservoir was filling during the entire outmigration period, traps were continuously moved upstream so that the trapping site was always at least 25 m above the encroaching reservoir confluence. Traps sampled between 25% of the total stream discharge during low flows and I% during the extremely high flows. Fry abundance (N) was estimated by two different methods: (I) volumetric expansion of catch densities; and (2) catches corrected by trap efficiency estimates. Individual trapping periods (11, 1 -t,; generally 2-3 days) were the number of days between when 20 traps were set (e.g., from day t, to day 1,. 1 a!ler the stan of the trapping season) and subsequently checked. The total number of fry migrating through the trapping si te between trapping periods was estimated using the volumetric expansion of fry density FD;: 3 FD; (fry I m ) =/;I v, where], was the total number of fry captured and v, was the estimated total volume of water sampled by fry traps during the ith trapping period. Fry density was expanded to abundance during each period M by: . N; = l:FD, •Q; i• l 3 where Q, was the total volume of stream discharge (m ) passing through the trapping site during the ith sampling period and n was the number of santpling periods during the fry outmigration .. Nightly trap efficiency was measured by recapture rates of marked fry released upstream fro m the trapping site 24 times during the fry migration season. A known number of fry were removed from the traps early in the evening, immersed in a Bismark Brown dye solution (250 mg I 19liters (5 gal.) water) for I hour, and then released 100m (several meanders) above the traps. Trap efficiency TE; for the ith sam pling period was calculated by: TE,= R,IM, where R, was the number of marked fry recaptured in fry traps and M ; was the number of fry initially marked and released above the traps at the beginning of the ith sampling period. A trap efficiency of T£1 = 4.6% was assumed during periods when releases of marked fry would have been too small to expect valid recapture rates. This value was obtained by averaging 7'£1 for all days in which marked fry were re- captured in traps. Actual trap efficiency estimates varied between I% and I 7%, and were computed for I 8 trapping periods during the outmigration season. Daily trap efficiency-based estimates of the abundance of fry passing the trap D, were calculated by· D,= j, / TE; 21 where./. was the total number offish captured during the ith sampling period. Finally, the estimate of total migrating fiy abundance was computed by: " N =,. l:, ((D, + D, _1) / 2) • (11- 11_ 1) where n was the number of sampling periods. Egg-to-fiy survival for the I 999 brood year was calculated by dividing the estimated total number of out migrating fiy by the total number of eggs deposited. Egg-to-fiy survival was not calculated for the I 998 brood year because of a failure to estimate the abundance of outmigrating fiy. Results The prevalence ofM. cerebra/is infection, incidence of deformities, and average spores I I 00 fields varied between the I 998 and I 999 escapements and from the I 996 and 1997 spawning runs (Table 2- I). Prevalence jumped from 68% in I 998 to 93% in I 999 but the number of fish with deformities dropped from 48% to 25%. The increase in prevalence was expected because 100"/o ofage-0 kokanee were infected by the end of their first growing season (see Chapter 3). These results were based on DNA-based PCR testing for the presence of M cerebra/is, which was more sensitive for detecting all life stages of the parasite (Andree et al . I 998). Mandibular and cranial deformities were the two types of deformities most often observed in all years. The deformity ranking remained relatively constant from 1996 to I 999, suggesting that the severity oflesions did not measurably change during the period of study. The average spores I I00 fields, which is a measure of parasite burden, also varied among years and individual fish . However, it should be noted that spores I I 00 fields were highly variable, even within the same fish and therefore may not be a true measure of parasite load, panicularly among years. After reaching a peak of 129 (SE = 36.3) in 1997, the mean spore count dropped to 51.7 (SE = 18) in 1998 and 40.6 (SE = 18.8) in 1999. These measurements were still well above the initial estimate of2.12 (SE = 0.8) in 1996, and future monitoring will address whether or not the spore burdens will continue to decrease or reach an equilibrium within the population. 22 Table 2-1.- Sum of observed ranked deformities, percent fish with deformities, deformity ranking, infection prevalence, and average spores per I 00 fields for spawning kokanee at Porcupine Reservoir for 1996-1999 spawning runs. Sample size for all years was 60 fish. Spawning year 1996 1997 1998 1999 Vertebral 0 0 0 0 Mandibular 23 21 32 15 Cranial 7 22 12 9 Opercular 9 10 2 Fins 0 4 0 Raker 0 7 4 Other 0 0 0 0 % fish with deformities 35% 55% 48% 25% Deformity ranking• 10% 7"/o 10% 10% Prevalence 30% 73% 68% 93% Average spores per 2 12 (0.79) 128.97 (36.29) 51.68 (17.97) 40.6 ( 18. 77) 100 fields (S.E.) • Deformity ranking = (no. deformed fish I no. defortned fish • 21) • I 00 1998 and 1999 Spawning Escapements Mature kokanee entered the spawning tributary by 3 September 1998, and 2 September 1999 (Figure 2-3). In 1998, counts of live males peaked at 5,01 9 fish on 19 September, and female count s peaked at 5,11 2 fish on 18 September. Spawners were distributed over approximately 4.8 km of the E.F. Little Bear River, and 2.8-km into Cinnamon Creek, where further migration was blocked by a waterfall (- 2.5 m height), 2.8 km upstream. At the confluence of the two streams, fish were observed entering the E. F. Little Bear River but quickly turning around to continue upstream in Cinnamon Creek. This diJfers from Janssen ( 1983), who reported that kokanee spawned in both streams above their confluence. In 1999, counts oflive males peaked at 2,605 on 19 September, and female counts peaked at 1,934 on 24 September. ln 1999, kokanee only utilized approximately 4 km of the E.F. Bear River and were blocked by a small (0.3 m height) beaver darn. Visual surveys were terminated on 29 October 1998 and 21 October 1999, when only II fish were observed on each date. 23 12000~------~ 1998 10000 --+--Male 8000 ··0 ·· Female --T- Total ,._ g ,._ en Q) en 0 N en Q) en en g N a. N N ..N N N ~ N C) C) "'a. a. ., "' u "'u u "' ., ., a. a. a. a. a. a. a. a. 0 0 0 u u u u u :J :J en ., ., Q) ., < < en en en"' en en en en"' en"' en en"' 0 0 0 0 0 4000 1999 r-T"'~ ..... ~ I 3000 I --+--Male I ··0 ·· Female \" ..... ~Tota l 2000 I ' \ I 1000 I " I . .o 0 ,._ ,._ N en N en 0 ;;: g ~ c;; N "' a. ~ "'N ..N "'N ~ "'u u ~ C) a. a.., ., a. a. a. a. "' u tJ tJ tJ :J a.., a.., ., a. ., ., a.., 0 0 < en"' en en en en en en"' en en"' en en 0 0 0 0 Date Figure 2-3.-Visual counts of spawning kokanee vs. time in East Fork Little Bear River during the 1998 and 1999 brood years. Counts were conducted over the entire length of stream that was utilized by the spawners. In 1998, peaks of5,0 19 males, 5,112 females, or 9,851 total fish were observed. In 1999, peaks of2,065 males, 1,934 females, or 3,728 total fish were observed. 24 During visual surveys, 39,894 male spawner days and 42,301 female spawner days were observed in 1998 and 16,898 male spawner days and 17,221 female spawner days were counted in 1999 (Table 2-2). In 1998, counts of tagged males and females varied initially because a number of spawners returned to the reservoir for a shon period immediately after tagging on 17 September 1998. One hundred tagged-male spawner days and 159 tagged-female spawner days were counted from 18 September 1998 to 19 October 1998 when tagged fish were last observed. According to AUC estimates, a total of25,651 males (mean residence time= 3.8 days) and 26,118 females (mean residence tinne = 4.2 days) entered the spawning tributary in 1998. In 1999, 12,898 males and 11,299 females entered the stream, based on residence time estimates from 1998. Although mean daily stream temperatures over the entire spawning period were warmer in 1998 (9.5 °C) than in 1999 (8.2 °C), stream temperatures up to the peak of the spawning period were quite similar during both years (Figure 2-4), and temperature should not have significantly affected residence time between years. Mean spawner length varied by sex and year (Figure 2-5). Male spawners were separated into two different age/size classes(< 290 mm; > 290 mm) for analysis to account for a smaller fraction of younger, precocious males (termed "jacks"). In 1998, jacks averaged 258 mm total length (SD = 26 mm), older males averaged 339 mm total length (SO = 26 mm), and females averaged 335 mm total length (SD = 20 mm). In 1999, older males averaged 31 I mm total length (SO = 12 mm) and females averaged 304 mm total length (SD = 16 mm), while jacks were not collected Older males (age-2+) were significantly smaller in 1999 than in 1998 (two-sample Hest; P < O.OOOS). Female spawners were also significantly smaller in 1999 than spawners in 1998 (two-sample Hest; P < O.OOOS). Using the mean length for each of the four size intervals (female mid-orbital length, nearest mm), estimates of size-specific fecundity, and a mean egg retention rate of3.6 eggs/female, we estimated that 20,159,809 eggs were deposited in 1998 and S, 768,S78 were deposited in 1999 (Table 2-3). Both the 1998 and 1999 spawning runs were primarily composed of age-4 males and females (Figure 2-6). In 1998, 92% of the females collected were age-4 and 8% were age-S whereas 10% of the males were age-3 , 76% were age-4, and 14% were age-S. Age composition of the fish collected in 1999 varied somewhat to that of 1998. In 1999, 18% of the females collected were age-3, 71% were age-4, and II% of the females were age-S, whereas only age-3 (24%) and age-4 (76%) males were found in 1999. 25 Table 2-2.-Live spawner counts from daily visual surveys and abundance estimates from a rea-under-the-curve (AUC) calculations for each survey interval during the 1998 and 1999 escapement periods. Oa1l~ Sj!"1ler Counts AUCEsumalcS Dme Male Femnle T01at Male Female Total t998 30-Aug 0 0 0 0 0 3-Sq> 25 25 50 0 50 7-Sep 0 t585 50 0 3220 9-Sep 2t5J 1761 3914 2t53 1761 5499 11-Sq> 2137 2833 4970 4290 4594 8884 18-Sq> 3552 51t2 8664 199 12 27808 47719 19-Sep 5019 4832 9851 4285.5 4972 9258 20-Sep 4987 4853 9840 5003 4843 9846 22-Sep 4259 4251 8510 9246 9104 18350 24-Sep 4269 4709 8978 8528 8960 17488 26-Sep 4738 4857 9595 9007 9566 18573 29-Sep 3308 3311 6619 12069 12252 24321 l-Oci 2419 2532 4951 5727 5843 11570 6-0el 1528 1761 3289 9867.5 10733 20600 8-0el 1249 1229 2478 2777 2990 5767 15-0el 175 183 358 4984 4942 9926 19-0el 43 45 88 436 456 892 22-0el 27 27 54 105 108 213 29-0el 6 5 II 116 112 228 Tow ls 39894 4230 1 83780 98605 109043 212403 Residence Time EstunaLeS (Days) 4 AUC Total Esca~ncnt Estunates 25651 26118 5269 1 1999 27-Aug 0 0 0 0 2-Sep 198 129 327 594 387 981 5-Sep 1060 504 1564 1887 950 2837 9-Sep 1303 1017 2320 4726 3042 7768 12-Sep 2023 1573 3596 4989 3885 8874 16-Sep 1911 1582 3493 7868 6310 14178 19-Sep 2065 1663 3728 5964 4868 10832 23-Sep 1802 1837 3639 7734 7000 14734 24-Sep 1789 1934 3723 1796 1886 3681 25-Sep 1246 1894 3140 1518 1914 3432 26-Sep 1047 1765 2812 114 7 1830 2976 30-Sep 1045 1242 2287 4184 6014 10198 J-Oel 841 1002 1843 2829 3366 6195 7-0el 372 663 1035 2426 JJJO 5756 10-0el 140 296 436 768 1439 2207 14-0el 53 112 165 386 816 1202 21-0et 3 8 II 196 420 616 Totals 16898 17221 34119 49011 47455 96465 Residence Time Estim.lleS (Days) 4 4 AUC T&l Esca~t Estimates 12898 11299 24116 26 14~------. 1998 12 u ~ 10 ~ :::> "§ 8 a> a. E ~ 6 E ~ 4 U) 2 o~~~-.~~~~~~~~~~~~~~~~~ Aug Sep Oct Nov Dec Jan Feb Date 14 ~------. 1999 12 E 10 ~ .3 ~ 8 Q) a. E a> 6 I- E ro 4 ~ U5 2 O+-~~~~~~~~~~~~~~~~~~~~~ Aug Sep Oct Nov Dec Jan Feb Date Figure 2-4.- Mean daily stream temperatures for East Fork Little Bear River during the spawning and early incubation periods in 1998 and 1999. The beginning, peak, and end of each spawning run are shown. Temperature data were not available after 15 January 1998 and 22 December 1999. 27 60 1998 50 -Male 40 c:::J Female 30 20 10 ~ >. u c 0 Q) :::J 70 c:r ~ 1999 LJ.. 60 50 40 30 20 10 0 250 300 350 400 450 500 Total Length (mm) Figure 2-5.- Sex-speci.fic length frequency distribution of spawning kokanee in the East Fork Little Bear River for both the 1998 and 1999 brood years. A random sample of 60 fish was collected each year for length, weight, fecundity, and Myrobo/us cerebra/is testing. Table 2-3.-Estimated kokanee egg deposition in th e East Fork Little Bear Ri ver in 1998 and 1999. Estimates are based on a size-specific fecundity model, female size distribution, total abundance of females (26, I 18 in 1998; II ,299 in 1999), and an average egg retention rate of 3. 59 eggs/female. 1998 1999 Mean Mean Mid-orbital length Size- %of females length Size- %of females length in interval specific in size Egg in interval specific in size Egg (mm) (mm) fecundit~• interval de~sition (mm) fecundit~• interval de~si t ion 226-250 24 1 366 5.7% 541 ,298 239 356 IS.6% 622,463 25 1-275 271 557 8.6% 1,239,890 266 520 71.9"/o 4, 191,856 276-300 290 727 45 7% 8,640,692 278 615 9.4% 647,47 1 301-325 307 936 40.0% 9,737,929 303 872 3.1% 306,788 Total Egg Deposition 20, 159,809 5,768,578 0 *Fecundity = 12.6e10· "'"i ...., 29 100 80 - Female c::J Male 60 40 X 20 d) "'>- ..0 c: 0 ·2u; 100 0 1999 0. E 8 80 c ~ d) a. 60 40 20 0 2 3 4 5 Age Figure 2-6.- Percentage contribution of each age class for female and male spawners from the 1998 and 1999 brood years. 30 Fry Ommigratiou and Egg to Fry Sun•iva/ for the 1998 Brood Year During the first two months of the incubation period (starting with I September), the mean daily stream temperature was 6.0 °C, with a maximum of 12.4 °C and a minimum of0.3 °C (Figure 2-4). Temperature data were not collected throughout the entire incubation period because temperature recorders were dislodged and lost during high flows in March. Because the initial warmer stream temperatures were more important in determining the timing of development and emergence, we were still able to estimate the timing of 50"/o emergence from the start, peak, and end of the spawning run using the model developed by Murray et al. (1989). Time until50"/o emergence was estimated at 123 days from the beginning of the spawning run (27 August), 137 days from the female peak oft he spawning run {18 September), and 170 days from the end of the spawning run (which was assumed to be 19 October). Therefore, eggs deposited at the beginning of the spawning run were predicted to achieve 50"/o emergence on 27 December 1998, while we estimated 50"/o emergence for the peak of the run on 2 February 1999, and for the end of the spawning run on 17 April 1999. Out migration traps were placed in the stream on 26 January but fry did not appear in traps until 17 February 1999 (Figure 2-7)_ Outmigrating fry collected during March ranged from 25 to 32 mm (TL) with a mean length of28.5 mm (SD = 1.5; Figure 2-8). Trapping continued until22 March when problems with access, vandalism, and flooding precluded further trapping that year. Fry Outmigratiou and Egg to Fry Survival for the 1999 Brood Year During the first two months of the incubation periods (starting with September 1), the mean daily stream temperature was 6.2 °C, with a maximum of 13.4 °C and a minimum of 1.0 oc (Figure 2-4). The Murray et al. ( I 989) equation predicted that 50"/o emergence would occur I 20 days from the start of the spawning run (27 August I 999), 143 days from the female peak of the spawning run (24 September I 999), and 165 days from the end of the spawning run (21 October 1999). Therefore, eggs deposited at the beginning of the spawning run were predicted to achieve 50"/o emergence on 25 December 1999, whereas eggs deposited during the peak and end of the spawning run were predicted to achieve 50"/o emergence on 13 February 2000 and 2 April2000, respectively. The mean daily stream temperatures in 1999 were0.2 °C 3 1 30 a 1999 25 .c 20 .8 l3 15 .t >- :E 10 z0> 5 0 b 1999 8 til 6 ...§.- ~ u:: 4 2 Figure 2-7.- Nightly kokanee fiy catches during 1999 (a) from the beginning offiy trapping until 18 March when vandalism and high flows disrupted fiy trapping. Flows in the East Fork Little Bear River (b) during the fiy trapping period. Flows were interpolated between dates. 32 0.25 1999 Fry Outmigration 0.20 0.15 0.10 0.05 >- 1.) c Q) :J 0.00 0" 2000 ~ u. 0.25 Fry Outmigration 0.20 0.15 0.10 0.05 0.00 20 22 24 26 28 30 32 Total Length (mm) Figure 2-8.-Length frequency distribution of outmigrating fry caught in fry traps on the East Fork Linle Bear River in 1999 and 2000. 33 wanner than in 1998 during the initial incubation period. This resulted in slightly earlier predictions for 50% emergence, although the timing and duration of the spawning runs were remarkably similar. Outmigration traps could not be deployed until 17 January 2000; however, only six fry were captured on 19 January 2000 and low catches over the following 2 weeks suggested that very little of the fry migration period was missed (Figure 2-9). The catch of outmigrating fry fluctuated during January and February and peaked at 1,464 fish on 29 March 2000 (Table 2-4). Fry marking did not begin until fry catches increased on 21 February 2000. The maximum number of fry marked was 800 on 27 March 2000 but maximum estimated trap efficiency was 17% on 17 March 2000. During the days when marked fish were recaptured, the mean trap efficiency was 4.6 %, which was assumed for all dates that trap efficiency was not estimated either because captured fry were not marked or marked fry were not recaptured. This value represented the mean trap efficiency rate for days when marked fish were recaptured. Outmigrating fry ranged trom 21 mm to 32 mm total length with a mean length of28.7 mm (SD = 1.7), which was nearly ideotical to the length distnbution of fry in 1999 (two-sample t-test, P > 0.44; Figure 2-8). Stream velocity (m/s) was positively correlated with the catch rate of fry (r'- • 0. 71 , P < 0.000 I, N = 44). whereas stream temperature showed a weaker correlation(.-' K 0.40, P < 0.02) trom the begiruting of fry trapping effons ( 19 January 2000) through the beginning of spring runoff (31 March 2000). After 5 April 2000, nightly fry catch was only weakly correlated with stream velocity, which suggested that the traps were not as effective after the floats were attached and faster flows began. This corresponded to the following relationship betweeo natural logarithm of total stream discharge and the natural logarithm proportion of total stream discharge (m3/sarnpling period) sampled by the outrnigration traps, which dropped from an average of 17% trom 19 January through 5 April 2000 to I% trom I 0 April through 8 May 2000 (r' = 0.96, N = 44, P < 0.0001): where P is the proponion of flow sampled by the traps and Q is the estimated total volume of water passing through the traps during a trapping period. The drop in proponion of total discharge sampled is related to the hydrology and basin shape of the reservoir during the spring wheo the reservoir is refilling. 34 1600 1400 .c .B 1200 rl 1000 .t 800 >. ~ 600 Ol z 400 200 0 6 ~ ..,.!!!s 4 ~ 2 u:: 0 12 10 u 8 L. ~ 6 ::::J (;j 4 ~ 2 E Q) 0 ~ -2 -4 8 0 0 0 0 § 0 8 8 8 8 ~ ~ ~ ~ ~ ~ ~ <;; ;;; ~ in co Date Figure 2-9.- Spring 2000 nightly kokanee fry catches (a) from the beginning of fry trapping until 8 May when fry outmigration ceased. Also shown are the flows in the East Fork Linle Bear River (b) and mean daily stream temperatures during fry outmigration. Table 2-4.- Values for parameters used to estimate total fry out migration during spring 2000 at Porcupine Reservoir. Total number of fry captured and estimates for total try abundance using both flow expansion and trap efficiency techniques are shown as well. The mean trap efficiency estimate of 4.6% for days when recaptures were greater than zero was assumed for all dates in which marked try were not recaputed in the trap. F!:): abundance estimates Estimated Proportion of Total no. Fry density No. try No. fry Efficiency Volumetric Daily trap Interval trap Date total Q(m A3) QsamE ied f!:): caEtured (f!:Y/mA3) marked reca2tured est imate ex~ansion efficienc~ efficienc~ 1/19/00 38,016 23% 6 0.001 4.6% 130 130 1/21/00 38,016 23% 18 0.002 4.6% 104 39 1 522 1/24/00 57,024 20"/o 22 0.002 4.6% 284 478 1,304 1126/00 38,016 21% 14 0.002 4.6% 179 304 783 1/28/00 38,016 20"/o 15 0.002 4.6% 142 326 630 1/31/00 57,024 20"/o 10 0.001 4.6% 188 217 815 2/2100 38,016 25% 5 0.001 4.6% 71 109 326 214/00 38,016 24% 17 0.002 4.6% 89 370 478 2/7/00 57,024 24% 47 0.003 4.6% 396 1,022 2,087 219/00 38,016 25% 29 0.003 14 0 4.6% 311 630 1,652 2/11/00 38,016 16% 38 0.006 14 0 4.6% 352 826 1,457 2114/00 57,024 16% 67 0.007 0 0 4.6% 986 1.457 3,424 2/16/00 38,016 16% 35 0.006 0 0 4.6% 635 761 2,217 2/ 18/00 38,016 16% 6 0.001 0 0 4.6% 251 130 891 2121 /00 57,024 22% 19 0.002 0 0 4.6% 186 413 815 2123 /00 67,392 14% 151 0.016 14 0 4.6% 1, 160 3,283 3,696 2/25/00 67,392 14% 91 0.010 49 I 2.0"/o 1,738 4,459 7,742 2/28/00 101 ,088 13% 130 0.010 35 0 4.1% 2,447 3,209 11.502 3/ 1/00 67,392 14% 117 0.012 33 2 6.1% 1,799 1,931 5,140 .... "' Table 2-4.- Continued. 3/3/00 67,392 14% 173 0.01 9 33 I 3.0"/o 2,095 5,709 7,640 3/6/00 101 ,088 14% 309 0.022 53 0 3.5% 5, 192 8,791 21 ,749 3/8/00 62,208 16% 148 0.015 75 4.0"/o 3, 137 3,700 12,491 3/10/00 62,208 IS% 131 0.014 0 0 7.2% 1,786 1,826 5,526 3/13/00 93 ,312 13% 216 0.017 29 10.3% 3,683 2,088 5,872 3/1 S/00 57.024 I S% 178 0.021 24 4 16.7% 2,783 1,068 3,156 3/ 17/00 57,024 15% 176 0.02 1 101 3.0% 2,361 5,925 6,993 3/20/00 85,536 14% 233 0.019 88 3.4% 4,204 6,835 19, 140 3/22/00 57,024 15% 202 0.024 Ill 4 3.6% 2,971 5,606 12,440 3/24/00 60,480 14% 532 0.064 98 9 9.2% 5,215 5,793 11 ,398 3/27/00 90,720 16% 1415 0.097 0 0 5.9% 18,929 23,965 44,637 3/29/00 119,232 II% 1464 0. 11 3 800 21 2.6% 22,290 55,771 79,737 3/31 /00 119,232 8% 734 0.073 179 1 0.6% 22,257 131 ,386 187,157 4/3/00 178,848 II % 1096 0 .054 131 3 23% 27,474 47,859 268,867 4/S/00 212,544 7% 1372 0.096 438 s 1.1 % 30,073 120, 187 168,046 4/10/00 584,064 2% 189 0.020 0 0 4,6% 80,465 4,109 310,740 4/12/00 584,064 2% 146 0.014 40 0 4.6% 20,070 3, 174 7,283 4/ 19/00 812, 160 1% 55 0 005 24 0 4.6% 44,622 1, 196 15,293 4/2 1/00 812, 160 1% 58 0.007 15 0 4.6% 10,377 1,261 2,457 4/26/00 1,01 9,520 1% 0.001 4.6% 17,581 174 3,587 4/28/00 1,019,520 1% II 0,001 4.6% 2,465 239 413 5/1/00 1,0 19,520 1% II 0.001 4.6% 4,245 239 7 17 5/3/00 1,019,520 1% 9 0.001 4.6% 2,551 196 435 515/00 1,019,520 1% 0 0.000 4.6% 1, 148 196 5/8/00 713,664 2% 0 0.000 4.6% To1al 349,293 457,412 1,241 ,452 w "' 37 At full capacity, the inlet extended into a narrow canyon and the stream channel became deep and restricted within the canyon; as the reservoir level advanced, the channel depth could increase by a meter or more overnight. However, the traps had to remain in the slower confluence because the fast flows ( ~ 3 m/s) would have potentially damaged the traps. The relationships between stream flow, fry catch, and trap efficiency were evaluated among all dates and also for instances in which the releases of marked fry were >30, >40, and >50; however, trap efficiency was not significantly correlated with flow or total fry catch. Because no relationships between trap efficiency and other variables were observed, we applied a constant trap efficiency estimate of 4.6% to trapping periods when efficiency estimates were not obtained. We believe this was a conservative and justifiable approach because this trap efficiency estimate was attained over variable conditions (e.g., flows, fry catches, number of marked fry). The magnitude of change in total fry abundance caused by the uncenainty about time-specific trap efficiencies was also examined. If trap efficiencies after 5 April 2000 were changed from 4.6% to 1% to coincide with the higher flows, our final estimate of fry abundance changed from 1,241 ,452 to 1,387,800, or an increase of 12%. This change was considered relatively small considering the potential error in the total fry abundance estimate. Estimates of total outmigrating fry using the volumetric expansion and trap efficiency methods varied greatly (Table 2-4). During the 2000 fry migration, we estimated 349,293 fry using volumetric expansion and 1,241 ,452 fry with the trap efficiency method. Egg-to-fry survival was calculated for the 1999 brood year. Using the estimated 1,241 ,452 fry trom the trap efficiency abundance estimate and the estimated 5, 768,578 eggs deposited during the 1999 spawn, we estimated that egg-to-fry survival was 22%. Dise:ussion The presence of M. cerebra/is does not appear to have seriously affected the abundance of spawning kokanee since first detected in 1994. The peak spawner count during the 1998 spawning run far exceeded previous recorded spawning runs in both number of fish and length of stream utilized, although this is based on comparisons with 1-day spawner counts (C. Schaugaard, UDWR aquatic biologist, personal communication). The population ofkokanee at Porcupine Reservoir has long been considered over- 38 abundant and stunted. Because of this, harvest limi ts were liberalized in the mid 1980s (Janssen 1983). These management changes have had little effect on size of fish and the population is still considered over abundant in relation to the reservoir size. From a management perspective, some monality associated with M. cerebra/is could be absorbed by the population. Research on the effects of M. cerebra/is on survival of age-0 kokanee in the reservoir and on nonlethal effects on growth wi.ll be valuable for assessing potential impacts of the parasite on kokanee. The total abundance of spawners in 1998 was over twice as large as in 1999. During the fall of 1998, Porcupine Reservoir was drained to a small conservation pool. Thus, the decline in spawners in 1999 could be attributed to the loss of fish downstream and monality associated with the drawdown, such as predation, competition, stress, disease, and angling. The drawdown began after spawning in the E. F. Little Bear River was nearly complete in 1998. During this period, many age- l, -2, and -3 kokanee may have been lost to entrainment. The reservoir reached its lowest volume in December 1998 and began refilling by March 1999 as the fry began migrating from the stream i11 t0 the reservoir. Zooplank1on communities, panicularly those of Daphnia .rp. , did not recover to normal densities and sizes until late July 1999 (Chapter 3). The large reduction in fish density may also account for a reduction in stream area utilized by spawning kokanee in 1999. In 1998, spawners continued upstream into Cinnamon Creek and were halted by a barrier that existed approximately 7.6 km from the reservoir, almost twice the distance that fish traveled in 1999 Because the density oflarger, edible-sized zooplankton did not recover until late summer 1999, spawners experienced a sub-par growing season (see Chapter 3). Reservoir temperatures were also excessively warm from surface to bottom which, combined with low prey abundance, would reduce growth significantly. Indeed, both male and female spawners were significantly smaller in 1999 than in 1998 despite considerably lower population densities. Because the length-specific fecundity regression was calculated using lengths and egg counts from both 1998 and 1999, egg deposition estimates should not have been affected by the smaller fish in 1999. Using egg counts from individuals collected during both years allowed us to incorporate a larger size range of fe males. Applying residence time estimates calculated from spawners in 1998 to 1999 may have 39 intToduced some bias into the abundance estimates; however, we believe this bias would be minimal because the stream temperatures and riming of the 1998 and 1999 spawning runs were very similar The similarity between the tinting and duration of the spawning runs for each year is characteristic of populations living in a highly selective environment. Environmental conditions in the area can change drastically between August and October. Therefore, kokanee at Porcupine Reservoir appear to have a rather narrow window of opponunity in which to leave the reservoir and reproduce. The annual I -day spawner counts on 19 September corresponded with the peak counts for the run and represented a reasonably consistent fTaction of total spawner abundance. The AUC estimates of abundance were 5.4 times higher than the 1-day counts on 19 September in 1998 and 6.4 times higher in 1999 These results suggested that a reliable estimate of total spawner abundance (within ± 25% of true abundance) could be generated by applying an expansion factor of 5.8 times the I -day spawner count. During extreme environmental conditions, such as an exceptionally hot and dry fall that may influence the run timing, it may be pragmatic to conduct 2-3 surveys spaced 1-1.5 weeks apan to determine when the actual peak occurs. Live spawner counts would be preferable to redd counts, because fish were easier to detect and will provide more accurate information on sex ratio and abundance estimates. Redds were more difficult to observe and single redds could not be distinguished in mass-spawning areas. The E. F. Little Bear River held 3-4 glides where substrate, depth, and flow conditions were favorable enough to accommodate 3()().. 500 spawners in 50-75-m sections of stream. In these sections, the entire area of stream could be classified as one large redd. The difference in size distribution ofkokanee between the two years may be attributed to the fact that kokanee growth and maturity is very plastic and responds annually to environmental conditions. The presence ofage-4 and age-S cohons diOers from Janssen (1983) who found only age-l , -2, and -3 spawners at Porcupine Reservoir. The difference in reponed age compositions may be a result of missed annuli in Janssen 's (1983) study but is more likely a shift in age at maturity within the population, due to different growth conditions. The reported age composition may reflect sampling methodology more than the actual cohon composition of the spawning run. In order to minimize stress on spawning fish and damage to existing redds, electroshocking ceased immediately after the first 60 fish were collected from a stream 40 reach. Additional effons were not made to ensure collection of all possible cohons that composed the spawning runs. Estimates of the total number of fry entering the reservoir in spring 2000 varied greatly between the flow expansion and trap efficiency methodologies. This discrepancy between the two techniques was caused by the expansion factors used by each technique when accounting for unsampled fry . The volumetric expansion technique assumed that fry density was distributed in proponion to flow across the 3 cross-section of the stream at the trapping site. Fry density (fry/m ) was calculated for each trapping period and the density estimate was simply multiplied by the total volume of water that passed through the trapping site during the collection period. The trap efficiency technique did not assume that fry are evenly proponioned throughout the stream channel and it allowed us to obtain a proximate measure of the variabil ity of fry capture given variation in the temporal and spatial dynamics of stream flows and fry migration. The proponion of recaptured marked fish for a given trapping period provided an estimate of actual trapping efficiency for a specific trapping period. Therefore, the estimates of total fry outmigration into Porcupine Reservoir using the trap efficiency technique should be the most appropriate method for this study. Comparisons were made between survival curves generated from both trap efficiency and flow expansion est imates of total outmigration and actual observed abundance from hydroacoustic sampling during the following summer (see Chapter 3}. Theoretical population abundances were calculated for both techniques using the observed monthly monality rate ofZ = 0.8822 for July to September (Figure 2-10). Because of the proximi ty of July abundance obtained !Tom trap efficiency to observed hydroacoustic abundance, we determined that outmigration estimates obtained using trap efficiency were much more real istic than were estimates obtained using flow expansion. The estimate of egg-to-fry survival at Porcupine Reservoir (22%) is somewhat high, compared io those reponed in other west em systems (Table 2-5). Egg-to-fry survival is related to quality of spawning gravel, density of spawners, frequency of floods, droughts, and stream temperature (Murray et a!. 1989; Burgner 199 1; Bradford 1995; Gemperle 1998). Annual variation in these parameters is the likely source for the large variation in egg-to-fry survival seen in many western populations. For example, in Taylor Creek, a tributary to Lake Tahoe, California, kokanee egg-to-fry survival varied between 15 .9% and 1.5% \ \ ~~ Estimate of N obtained from 100000 I trap efficiency calculations is I 1,471 ,197 fish entering the I reservoir. I I I \ 50000 \ \ / \\ Estimate of N obtained from .t. f flow expansion calculations is 349,293 fish entering the reservoir. o~----.-----.-----.----.-----.-----.-----1 April May June July August September • Observed N (hydroacoustics) Month - · Theoretical N (trap efficiency) ---6-- Theoretical N (flow expansion) Figure 2-10.-Comparison between survival curves generated from both trap efficiency and fl ow expansion estimates of total fry outmigration and actual observed abundance obtained from hydroacoustic sampling. Theoretical July population abundances were calculated for both techniques using an observed survival rate of0.17. Because of the proximity of the July abundance estimate obtained using trap efficiency to observed hydroacoustic abundance, we determined that trap efficiency estimates were more realistic. 42 Table 2-5.---{;omparison between reponed kokanee and sockeye egg-to-fry survival rates from various western populations. Estimates from Bradford (1995) were estimated from a summary graph of35 different populations of sockeye thai were co mpiled from various sources. Mean% Range of egg-to-fry Site Year % survival survival East Fork Little Bear River, Porcupine Res., UT 2000 21.5 Taylor Creek, Lake Tahoe, CA' 1994-95 1.5-15.9 8.7 Metolius River, Lake Billy Chinook, OR' 1997 3.8 Scully Creek. Lakelse Lake, B.C.' 1950-55 9.3-13.8 12. 1 Six Mile Creek, Babine Lake, B.C.' 1951 , 1954 12.0-19.0 15.5 Tally Creek, Port John Lake, B.C.' 1949-59 1.8-19.3 8.4 Chilko Lake, upper Fraser River, B.C.' 1959-55 5.0-11.9 7.9 Williams Creek, Lakelse Lake, B.C.' 1954-56 7.8-17.2 13 .8 Bradford (1995) 9.4-9.55 9.1 'Gemperle, 1998 'Thiesfeld et al ., 1999 '"Foerster, 1968 43 in 1994 and 1995, respectively (Gemperle 1998). However, the low survival in 1995 at Taylor Creek corresponded with extremely wann incubation temperatures through the end of November. Because of the potential for large variation in egg-to-fry survival within a population, we did not attempt to estimate egg survival or fry out migration for the 1998 brood year, using the egg-to-fry survival rate obtained from the 1999 brood year. The mean stream temperature during the initial 2 months of incubation was 6.02 •c. Murray et al. ( 1989) reponed that highest embryo survival rates for kokanee occurred at constant incubation temperature of 6 •c. Therefore, optimal stream temperatures for incubation success during the initial development period may have contributed to the high egg-to-fry survival rate, although eggs experienced a wide range of temperatures during the entire incubation period which may have increased morrality. References Andree, K. B., E. MacConnelL and R. P. Hedrick. 1998. A nest polymerase chain reaction for the detection of genomic DNA of Myxobo/us cerebra/is in rainbow trout Oncorhynchus mykiss. Diseases of Aquatic Organisms 34:145-154. Beamish, J. R. 1979. Differences in age of Pacific hake (Merluccius produc/us) using whole and sections of otoliths. Journal oft he Fisheries Research Board of Canada 36:141-151 . Beauchamp, D. A., P. E. Budy, B. C. Nlen, and J. M. Godfrey. 1994. The timing, distribution, and abundance ofkokanees spawning in a Lake Tahoe tributary. Great Basin Naturalist 54:130-141. Bilby, R. E., B. R. Fransen, and P. A_ Bisson. 1996. Incorporation of nitrogen and carbon from spawning coho salmon into the trophic system of small streams: evidence from stable isotopes. Canadian Journal of Fisheries and Aquatic Sciences 53 :164-173. Bradford, M. J. 1995. Comparative review of Pacific salmon survival rates. Canadian Journal of Fisheries and Aquatic Sciences 52:1327-1338. Burgner, R. L. 1991. Life history of sockeye salmon. Pages 3-101 in C. Groot and L. Margolis, editors. Pacific salmon life histories. UBC Press, Vancouver, British Columbia. 44 DeVries, D. R. , and R. V. Frie. 1996. Determination of age and growth. Pages 483-512 in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2"" edition. American Fisheries Society, Bethesda, Maryland. English, K. K. , R. C. Socking, and J. R. Irvine. 1992. A robust procedure for estimating salmon escapement based on the area-under-the-curve method. Canadian Journal of Fisheries and Aquatic Sciences 49:1982-1989. Foerster, R. E. 1968. The sockeye salmon, Oncorhynchus ner!rLJ . Journal of the Fisheries Research Board of Canada. Bulletin 162. Gemperle, C. K. 1998. Kokanee fry recruitment and early life history in the Lake Tahoe Basi n. Master's thesis. Utah State University, Logan. Goede, R. D., and B. A. Barton. 1990. Organismic indices and an autopsy-based assessment as indicators of health and condition of fish. American Fisheries Society Symposium 8:93-108. Hilborn, R., B. G. Bue, and S. Sharr. 1999. Estimating spawning escapements from periodic counts : a comparison of methods. Canadian Journal of Fisheries and Aquatic Sciences 56:888-896. Irvine, J. R., R. C. Socking, K. K. English, and M. Label le. 1992. Estimating coho salmon (Oncorhy nchus kisu1ch) spawning escapements by conducting visual surveys in areas using stratified random and st ratified index sampling designs. Canadian Journal of Fisheries and Aquatic Sciences 49:1972- 1981. Janssen, P. I. 1983. Investigation of selected aspects of kokanee (OnchorJrynchus nerlw) ecology in Porcupine Reservoir, Utah, with management implications. Master's thesis. Utah State University, Logan. Lady, J. M., and J. R. Skalaski. 1998. Estimators of st ream residence time of Pacific salmon (Oncorhynchus spp.) based on release-recapture data. Canadian Journal of Fisheries and Aquatic Sciences 55:2580-2587. Lon, H. V., and A. Amandi. 1994. Whirling disease ofsalmonids. Pages 1-7 in J. C. Thoesen, editor. Suggested procedures for the detection and identification of certain finfish and shellfish pathogens, 4th edition, version I. Fish Health Section, American Fisheries Society, Bethesda, Maryland. 45 Murray, C. B., J D. McPhail. and M. L. Rosenau. 1989. Reproductive and developmental biology of kokanee from Upper Arrow Lake, British Columbia. Transactions of the American Fisheries Society 118:503-509. Nehring, R. B .. and P. G. Walker. 1996. Whirling disease in the wild: the new reality in the intermountain west. Fisheries 21(6):28-30. Paragamian, V. L. 1995. Introduction to kokanee investigations. North American Journal of Fisheries Management 15: 173 . Richey, J. E., M. A Perkins, and C. R. Goldman. 1975. Effe<:ts ofkokanee salmon (Oncorhynchus nerlca) decomposition on the e<:oloay of a subalpine stream. Journal of Fisheries Research Board of Canada 32:817-820. Rieman, B. E., and M. A Maiolie. 1995. Kokanee population density and resulting fisheries. North American Journal of Fisheries Management 15:229-237. Schneid ervin, R. W. and W. A Hubert. 1986. A rapid techniq ue for otolith removal from salmonids and catostomids. North American Journal of Fisheries Management 6:287. Thiesfeld , S. L .• J. C. Kern. A R. Dale, M W. Chilcote, and M. A Buckman. 1999. Lake Billy Chinook sockeye salmon and kokanee research study: 1996- 1998 Contract Completion Report. Pelton Round Bune Hydroelectric Proje<:t, FERC umber 2030. Research and Development Division, Oregon Department of Fish and Wildlife. Portland. Thompson, K. G., R. B. Nehring, D. C. Bowden, and T. Wygant. 1999. Field exposure of seven spe<:ies or subspe<:ies of salmonids to Myxol>olus cerebra/is in the Colorado River, Middle Park, Colorado. Journal of Aquatic Animal Health II :312-329. Vincent, E. R. 1996. Whirling di sease and wild trout: the Montana experience_ Fisheries 21(6):32-33 . Walker, P. G., and R. B. Nehring. 1995. An investigation to determine the cause(s) of the disappearance of young wild rainbow trout in the upper Colorado River, in Middle Park, Colorado. Colorado Division of Wildlife Report 134, Denver. 46 CHAPTERJ SURVIVAL OF AGE-0 KOKANEE IN A POPULATION INFECTED BY MYXOBOLUS CEREBRA LIS IN PORCUPINE RESERVOIR, UTAH Abs1rac1. - We tracked the chronology and severity of Myrobolus cerebra/is infection and related it to survival ofage-0 kokanee to determine whether M. cerebra/is represented a significant agent of mortality in the population. We also tracked environmental conditions and losses to predation to identity other sources of mortality in the population. Age-0 kokanee were primarily infected by the parasite after they had entered the reservoir in spring. Prevalence and severity increased rapidly throughout the summer and nearly all age-0 kokanee were infected by August of both years. In total, 495 age-0 kokanee were exami ned for clinical lesions associated with M. cerebra/is in 1999 and 2000, but only one fish displayed a cranial abnormality in 2000. Low survival rates of age-0 kokanee from July through September were observed and coincided with increased prevalence and severity. However, because of high reservoir temperatures, low food levels, predation, and entrainment, evid ence forM. cerebra/is acting as a direct source ofmonality on age-0 kokanee was elusive during our study. In age-l and older kokanee, we did not fi nd any evidence that M. cerebra/is had an effect on growth and overall condition of the fish. Infection severity and presence of clinical signs varied between years and were likely more related to limitations of the diagnostic techniques. Any effects that M. cerebra/is may have had on kokanee are likely to occur during the first growing season and may impact the host 's ability to cope with the other environmental stressors identi_fied at Porcupine Reservoir. lntroduction Myrobolus cerebra/is, the etiological agent for whirling disease, has been implicated in the devastating declines of several popular trout fisheries in the western United States. Fisheries in Colorado and Montana have been particularly hard hit, but the parasite has also spread to Washington, Oregon, California, Idaho, Wyoming, and Utah. Utah Division of Wildlife Resources (UDWR) biologists have tracked the spread of the disease in Utah, since it was first discovered in the state in 1991 . Understanding the life cycle of the parasite is important for determining the potential impacts and 47 severity of infection in a species or population offish hosts M cerebra/is is a microscopic parasite that attacks the canilage of infected trout (Hoffman 1990). QinicaJ signs include cranial and venebraJ skeletal defonnities, darkening of the caudal area, and apparent loss of equilibrium in the fish that is characterized by a ··tail chasing" behavior, and death. The life cycle of M cerebra/is begins when mature myxospores are released from the skeletal ti ssue of a dea d fi sh. The spores can survive in the benthos for an extended period, awaiting ingesti on by their secondary host Tubifex tubifex, an aquatic oligocheate wonn (Wolf and Markiw 1984). In the gut epithelium ofT. tubifex, the spores develop into the next life stage known as triactinomyxon (TAM). After the TAMs are mature, they are released from the worm in feces and enter the water column (Gilben and Granath 1998). When a TAM comes in contact with a salmonid, it enters the epidennis via the firing of polar capsules. Sporoplasm is released into the fish, which migrates into the neural tissue where it is free from host immune responses (EI-Matbouli et al. 1995). Generally, the sporoplasm continues to migrate through the nervous system, and many ultimately reside in the canilaginous area surrounding the brain. Here the parasite, now in it s vegetative plasmodium stage, is referred to as a trophozoite. The canilaginous matrix, which surrounds the trophozoite. is lysed as the trophozoites develop (EI-Matbouli et al. 1995). Approximately 3 months after infection, the parasite develops into the ma ture myxospore. These myxospores wiU not be released until the fish dies and the carcass decomposes. Because the parasite affects canilage, younger fi sh that have not yet undergone ossification are especially susceptible to severe deformities and death. Whirling disease can potentially affect the growth, survival, and abundance of its fish host (Uspenskaya !957; Markiw !992b; Schisler et al. 1999). Severe M. cerebra/is infections can lead to canilaginous lesions or developmental defonnities. The parasite may also indirectly limit an infected individual 's abi lity to forage, compete, avoid predation, and carry out cenain behaviors characteristic of their species' life history strategies (timing of life stage recruitment. age at reproduction). Much of the recent research on the parasite's impacts on salmonids has focused on its effects on rainbow trout (Oncorhynchus myki.ss), brown trout (Salmo fruita), and cutthroat trout (0. clarki). Substantial declines in wild rainbow trout, in relation to the other species, have been imponant for both ecological and economical reasons in Montana and Colorado (Nehring and Walker 1996; Walker and Nehring 1995; Vincent 1996). This decline has been evident in the lack of recruitment of age-0 fish, suggesting that the disease causes 48 significant monality in younger rainbow and cutthroat trout. Brown trout were introduced from Europe and may have coevolved with the parasite, which was inadvenently introduced to the United States in 1964 from Eurpoe (Hoffman 1998). Therefore, rainbow and cutthroat trout are naive hosts and have not developed abilities, such as immunilogical responses, to cope with the disease. Aside from the possibility of developing host-defense mechanisms, i.e., immune responses (Hedrick et al. 1999b), the differences in timing of cenain aspects in the species' life histories may also allow brown trout to cope with infection. Brown trout spawn in the fall, whereas rainbow and cutthroat trout spawn in the spring. Subsequently, juvenile trout that arise from fall spawners hatch and live their first few months during periods of potentially low TAM releases. In contrast, progeny from spawning rainbow and cutthroat trout hatch and live their first few months during periods when water temperatures are warmer and coincide with higher TAM releases (El-Matbouli and Hoffinan 1998). Age and dose response studies on rainbow and brown trout have suggested that development and severity of whirling disease are dependent on both age at first exposure and parasite dose (Markiw 1991,1992a; Ryce et al. 1999). In these experiment s, survival was significantly lower for younger fish(< 7 weeks post hatch). Fish that were infected after 7 weeks post hatching developed few clinical signs and suffered no monality, and fish exposed at II weeks post hatch did not develop clinical signs, regardless of parasite dose. Because of the economic importance of wild rainbow and cutthroat trout in many western states, a vast amount of resources has been dedicated to the study of whirling disease on these species, but little is known about effects on kokanee or other fall-spawning salmonids that have not co-evolved with the parasite. The life history and distribution differences of kokanee in relation to other western salmonids could be imponant in determining the susceptibility and role of a semelparous species in the life cycle of the parasite. Unlike trout, adult kokanee die en masse after spawning. This heavy accumulation of carcasses may release a tremendous number of spores over a shon period. This large annual "release" of spores could have significant implications for other salmonids, as well as the ecosystem because it may result in large releases ofT AMs during periods when young cutthroat or rainbow trout are vulnerable. As the disease continues to spread throughout the western U.S., baseline infonnation on the impact of this disease on other fishes will become increasingly imponant. This will be especially evident as the parasite spreads to areas that contain endangered Pacific salmon. 49 Porcupine Reservoir has maintained a strong population and spawning run ofkokanee for the past two decades. Because of the success of the population, it was utilized as a wild broodstock source of kokanee eggs in 1991 and 1992. In accordance with the Utah wild broodstock program. kokanee were collected from 1988 to 1992 during the spawning run and tested for prohibited pathogens, which included M. cerebra/is. The broodstock program at Porcupine Reservoir was abandoned after the 1992 brood year because of the characteristically small fish and the success of other kokanee populations in the state. During the period of disease testing, no evidence of any prohibited pathogen was detected (Wilson et al. 1998). However, in the winter of 1993, M. cerebra/is was detected at a private hatchery on the E.F. Little Bear River, below Porcupine Reservoir. Intensive sampling effons immediately followed to detennine the spatial extent of the parasite in the drainage. During this testing, UDWR biologists failed to find evidence of the parasite in the reservoir. However, in the spring of 1994, gill netting samples revealed a rainbow trout with a severe venebral deformity that later tested positive forM. cerebra/is. Subsequent sampling revealed that young of the year (YOY) kokanee were also infected with the parasite. Beginning in 1996, biologists with the Utah Division of Wildlife Resources decided to begin monitoring the disease prevalence and proponion of deformities in spawning individuals collected during the escapemenl period. An annual monitoring program was initiated in the Porcupine Reservoir drainage because of the lack of knowledge on effects of the parasite on kokanee, and uncenainty about how the parasite operated in reservoirs. The close proximity of the reservoir to Logan, Utah, the early stages of infection in the reservoir, and the history of pathogen testing also made it an attractive site for research. Results from the first two years of monitoring revealed a significant increase in prevalence of the disease had occurred in the population (Wilson et al . 1998). The number of infected fis h had increased from 18/60 in 1996 to 44/60 in 1997, a jump from 300/o to 73%. In addition to this finding, the mean number of spores per 100 fields, a methodology used to enumerate spore load, increased from 2. I to 128.9. These results suggested that the prevalence ofM. cerebra/is was rapidly increasing in the population. The objectives of this study were to {I) track the chronology and severity of M. cerebra/is infection and relate it to survival of age-0 kokanee to detennine whether M. cerebra/is represents a significant agent of monality in this population, (2) identiJY windows of mortality and associated 50 environmental stressors that might trigger these events, and (3) assess and compare the prevalence ofM cereralis infection and associated clinical deformities observed in age-l and older fish. Methods By concurrently modeling predation, on age-0 kokanee in Porcupine Reservoir, testing for pathogens, estimating the forage base, and monit oring water quality, we attempted to account for the relative imparlance of different sources of mortality for age-0 kokanee in Porcupine Reservoir. The timing and abundance of the 1999 and 2000 fry migration to the reservoir and the subsequent abundance throughout the growing season were monitored, while concurrently tracking the prevalence of infection during the different life stages. In 1999, effon s were hampered by vandalism and high flows, and an estimate of total fiy out migration into the reservoir was not obtained. Fry traps designed to sustain high flows were utilized in 2000 and an estimated 1,241 ,452 fiy entered the reservoir by the end of the fiy outmigration period on 8 May 2000 (Chapt er 2). The majority of fry (73%) entered the reservoir before 5 April 2000, which was just after the peak catch offiy. These est imates were helpful in the analysis and interpretation of age-0 kokanee abundance and survival, as well as identifying factors that may have contributed to any observed declines in abundance. Limnologica/ Monitoring /999-2000 Li mnologcal variables were measured monthly at a fix ed station from 18 May through 27 October 1999 and 27 March through 27 September 2000. Vertical temperature (0 C) and dissolved oxygen (mg!L) profiles were measured using a calibrated Yellow Springs Instruments (YSI) data logger (modei 6 10-DM) and depth probe (model 600 XL) Light extinction was measured with a LICOR (model Ll-1000) light meter on most limnological sampling dates. The extinction coefficient k was estimated using the slope from the regression oflight versus depth (Wetzel and Likens t 990). Secchi transparency was also measured at each sampling period except for 10 June 1999. Zooplankton were sampled with a 30-cm diameter, 500-~m mesh Wisconsin-style plankton net and preserved in sucrose formalin, except 18 May 1999 when a 1 53- ~m mesh net of the same dimensions was used. The 500-~ net was used to sample zooplankton that were visually susceptible to predation by kokanee. Venical hauls were taken from the 51 entire water column {bottom to surface). Samples were diluted to at least 40 ml and then subsampled with three 2-ml aliquots. However, in most cases, zooplankton samples were processed in their entirety due to low numbers in 1999 and August and September 2000. Cladocerans and copepods were identified to genus, and were enumerated using a dissecting microscope. For each sampling date, up to 30 Daphnia were measured using a calibrated image analysis program. Lake Phase Surviva/1999-2000 Dual-beam hydroacoustic surveys were carried out during the period of summer stratification (J une-September) to track the monthly abundance and survival of age-0 kokanee in Porcupine Reservoir in 1999 and 2000. Methodologies for hydroacoustic sampling and analysis were the same for both years. Kokanee are an ideal species for quantitative acoustic evaluation for several reasons (Parkinson et al. 1994). At night , schools disperse in the mid-water column allowing the detection of single targets without the associated problems of surface and bottom interactions. Dual-beam acoustic methodologies also allow for adequat e discrimination of age-0 kokanee from age-l fish, although it is not possible to separate age- l kokanees from older year classes. Each survey consisted of at least two dusk (from sunset to astronomical twilight) runs and two night runs (30 minutes after astronomical twilight, complete darkness), except the September survey in which only one dusk transect was conducted in both 1999 and 2000. Porcupine Reservoir was divided into three distinct longitudinal sections (upper, mid, and lower sections; .Figure 3-1 ). Each run (upper + middle + lower tra nsects/time period) consisted of the same series of zigzag transects across the entire reservoir (Figure 3-1 ). All surveys were conducted du ring the new moon period of each month in clear and calm conditions. Hydroacoustic data were coll ected using a Biosonics Model I 05 scientific echosounder with a 420-kHz dual beam (6°, 15°) transducer towed approxi mately 1.0 m deep off the starboard bow of the research vessel. Methods for both acoustic data collection and analysis were obtained from Brandt (1996) and Beauchamp et at. ( 1997). The transducer was towed at a boat speed of 2-3 mls and sampled at a rate of two pingsls. Receiver gain was set at 12 decibels (dB). Signals were adjusted for spreading loss by applying a 40 log 10 R time-varied gain (R is target range in meters). Additional infonnation on the Diagram o f Porcupine Reservoor denotmg u p per, mid, and lower reservoir sections Hydroacoustic sampr ong transects u sed to assess Figure 3-1 - hown as well l_imnetiC. fish densotoes. . .'" I 999 and 2000 are s 53 collection and analyses of the hydroacoustic data are presented in Table 3-1 . A dual beam Biosonics Echo Signal Processor (ESP, model281) was used to process data and determine the acoustic size of individual fish targets in decibels. Echoes within 3° (half angle) of the acoustic beam axis (-6 dB off axis) were used to calculate fish target strength (dB) and fish density estimates. Single fish targets were used with dual beam target strengths ranging from - 58 .6 to - 30 dB to represent fish ranging from 25 mm to 882 mm (TL), respectively (Love 1977). Only echoes that met the single target shape criteria in our analyses were used (Table 3-1). Targets that were within 2m from the bottom and 2 m from the transducer were excluded due to limitations that are characteristic of echosounding gear and parameters (Brandt 1996; Beauchamp et al. 1997). Beauchamp et al. (1997) reponed that their acoustic data often underestimated total lengths, and therefore our density estimates may sli ghtly underestimate age-0 kokanee density because we did not include targets that were smaller than - 58.6 dB (25 mm) in our analyses for each month. Based on length distributi ons of age-0 kokanee for the entire summer, we determine.d that a 25-80 mm size class would be representative of age-0 kokanee for all monthly analyses. Fish densities were calculated in terms oftargets/1000 m3 and analyzed densities by depth interval (3-6, 6-9, 9- 12, 12-15, 15-18, 18-21 , 21-24 m intervals) and three size classes. Because tracking the survival ofage-0 kokanee through time was the primary objective, only three size classes were analyzed for each monthly survey. Monthly abundance estimates for three size classes were calculated by first computing the specific volume of water for each depth strata in the entire reservoir, using reservoir elevation-volume relationships and the actu al reservoir elevation during each survey. Volumetric expansion of nighttime density estimates for the three size classes in each depth strata were then used to estimate abundance. TotaJ reservoir abundances were then calculated by summing over all depth strata. Abundance estimates !Tom each of the two night runs during each survey were averaged and used as the estimator for monthly abundance and error terms. Tow-netting samples and gi ll neuing ( 13-mm stretch mesh) in August and September provided target verification for age-0 kokanee. Fish were not susceptible to either means of capture during the month of July 1999. In 1999, tow-netting was conducted at night using a 1-mm mesh ichthyoplankton net Table 3-1.-Parameters used during the collection and analysis ofhydroacoustic data. Parameter Value Frequency of sound 420kHz Pulse width 0.4 ms Pulse frequency 2/s Depth range of analysis 3-24m Narrow-beam noise threshold 200mV Wide-beam noise threshold 100-120 mV Bottom threshold 7V Single-target criteria, 1/2 peak amplitude 0.4-0.52 ms 55 with a 1-m diameter opening that was towed at roughly I m/s at discrete depths ranging between I 0 and 15 m. In 2000, a larger tow-net was constructed which consisted of 6.4 mm mesh, 2 m diameter opening, and 6-m length, which was towed at 1.5-2 m/s targeting depths containing the highest densities of fry-sized targets (generally 10-15 m). Tow-netting was conducted during complete darkness immediately after the acoustic survey had been completed and on various dates for collection of age-0 kokanee for pathogen testing. Venical gill nets were set prior to the beginning of the August acoustic survey in 1999 and all hydroacoustic surveys in 2000. A series of vertical gill nets of different mesh sizes (13, 19, 25, 38, 51 , 64, and 76 mm stretch mesh) were set in the mid and lower sections of the reservoir. The two 13-mm mesh vertical gill nets consisted of two 5 m x 2 m panels that were set at various depths during the entire netting week. All other venical nets were 2 m wide and sampled the entire depth range of the water column (0-20 m). Nets were set during the late afternoon and retrieved the following morning. Different meshes were set on two different nights to ensure reasonable time for processing fish and resetting nets. Instantaneous monthly mortality rates {Z) for age-0 kokanee were calculated using the following equation (Ricker 1975): Z = -ln(N,JN. )/1 where N, was the abundance at month 1, and N. was the initial abundance, obtained from the July hydroacoustic survey. Survival to month 1 (S,) was calculated using: -z • t s. = e Instantaneous monality and survival were calculated, starting with the July density estimates. During the month of June, age-0 kokanee were distributed too close to the surface and were more concentrated in the inlet area of the reservoir where they could not be effectively sampled by echosounding gear. Myrobolus cerebra/is Testing Age-0 kokanee were collected in fry traps in the tributary in March and in the reservoir with townets or giUnets June, August, and September 1999 and monthly from March through September 2000 using the methods described above and tested for the presence of Myxobolus cerebrolis. We attempted to 56 collect at least 60 fish monthly between March and September; however, samples sizes were often much smaller because low catch rates for age-0 kokanee. Sample sizes were compromised in the laner portion of August and September 2000, because low and rapidly receding reservoir levels prevented launching of a boat large enough to haul the tow-net. All fish were examined for lesions or deformities, and lengths (TL and SL, mm) and weights (nearest g) were recorded. Whole fish (March and June) or heads (August and September) were preserved individually in 70% EtOH and shipped to the Pisces Molecular laboratory in Boulder, Colorado, for testing. M cerebra/is diagnostics were conducted by the DNA-based polymerase chain reaction (PCR) method (Andree et al. 1998; Epp and Wood 1998). The PCR diagnostic method was used because all life stages of the parasite can be detected (Andree et al. 1998). This was critical during the first growing season, because any infections would have been recent, and the parasite would not likely have developed into mature myxospores. The PCR technique is the most sensitive of all the whirling disease diagnostic methodologies, particularly in smaller samples, such as with the head of a age-0 kokanee. The accuracy of PCR is reduced as the sample vo lume increases, because of the apparent patchiness of infection within the canilage and increased chances for sample contamination (Epp and Wood 1998). At the laboratory, the samples were heated, and a tissue lysis buffer was added. Total DNA was extracted from each sample using a spin-column D A purification procedure. The resulting DNA preparation was then assayed for the presence of theM cerebra/is ISS rRNA gene segment by single-round PCR amplification. Each PCR run included the following five controls: (I) positive DNA (DNA from aM cerebra/is spore prep in negative fish DNA), (2) negative DNA (DNA from an uninfected fish), (3) no DNA in reagents (H20 in place of template DNA (capped prior to addition of sample DNA) to serve as a control to detect contaminating DNA in PCR reagents), (4) no DNA carryover (H20 in place of template DNA (uncapped during addition of sample DNA) to serve as a control to detect carryover of positive DNA during reaction setup, and (5) sensitivity (DNA from aM. cerebra/is spore prep diluted in negative fish DNA to serve as an internal control for the limit of sensitivity of each PCR run). Pisces Molecular biologists scored the resulting signals as follows: Scoring: +++ = very strong positive signal ++ = strong positive signal + = positive signal 57 w+ = weak positive signal = no signal/below limit of detection These scores allowed comparisons between variables such as length, weight. condition factor, and observed deformities back to some level of infection or severity in individual fish. Analysis and comparison of these vari ables versus the infection level for each sampling period was conducted by StatXact 3.0 (CYTEL Software Corporation, 1997). PCR data were analyzed for any trends in severity by Goodman-Kruskal Gamma coefficient (Agresti 1984; Wickens 1989), a measure of the differences in proponions for ordinal-ordinal data Because the development of the parasite within the fish is heavily influenced by temperature, we used degree-day analyses to assess and compare infection strength and the onset of any observed clinical signs of infection in age-0 kokanee. Degree-day comparisons between published laboratory experiments and estimated thermal units for periods when age-0 kokanee were collected provided a means for determining the development of infection and potential exhibitition of clinical signs. Degree-days were estimated by calculating the them1al experience of kokanee based on observed diel venical distributions from monthly hydroacoustics and venical temperature profiles measured within the reservoir during the summer. The thermal unit analyses began on 5 April for each year, based on estimates of peak fry outmigration into the reservoir in 2000 (Chapter 2). Therefore, degree-day estimates were only approximations for the thermal experience of individuals based on when the maj ority of age-0 fish entered the reservoir each year and the date at whi ch they were collected for pathogen testing. A net pen experiment was planned for 2000 to assess the onset of infection and presence of clinical signs and monality associated with M. cerebra/is in age-0 kokanee. One hundred fish were placed in a 2-m x 2-m, 3.2-mm mesh net pen on 13 March 2000. The net pen was held I 0 m below the reservoir surface in an area of the reservoir that was 30 m deep. The net pen was retrieved weekly so that zooplankton levels within the pen could be supplemented. Twenty-one fish were collected from the net pens on 17 April 2000 when monality occurred after transferring fish to a larger pen (2 m x 2 m x 7 m). These were the only fish tested forM. cerebra/is because the net pen was vandalized and destroyed soon thereafter. 58 Infection by M. cerebra/is and presence of associated clinical signs in age-l and older cohons were examined in kokanee collected in venical gill nets and during annual surveys of spawning fish in 1998, 1999, and 2000. Following the deformity index of the Health Condition Profile (HCP, Goede and Ban on 1990), each fish was examined for seven types of deformities; venebral, mandibular, cranial, opercular, fins, gill rakers, and if any other type was described, it was listed as "other." The percent deformity was calculated from the number of deformities, each ranked by severity on a 1-3 scale (I = slight, 3= severe), divided by the total possible number of21 for each fish. To determine age, otoliths were removed through the roof of the mouth (Schneidervin and Huben 1986), and placed in 70"/o EtOH for age analysis. Finally, the head of each fish was taken to test for the presence ofM. cerebra/is. Diagnosis of M. cerebra/is infection was conducted using a slightly modified version of the pepsin-trypsin digest cPID) as described by Lorz and Amandi (1994). The resulting residues were placed on slides and stained using Ziehl-Nielsen carbo! fuchsin and examined under 200x magnification. Spores were enumerated by counting the number of spores in 100 microscopic fields of vision. Predation ofoge-0 Kokanee Because age-0 kokanee survival can be influenced by many factors such as predation, disease, food supply, and environmental stressors, attempts were made to assess relative losses ofage-0 kokanee to predation by piscivorous fish in the reservoir. Bioenergetics modeling provides a useful tool for quantifying predation on a daily or monthly time scale for individual predators or entire populations (Beauchamp et al. 1995; Canwright et al. 1998; Baldwin et al. 2000). The purposes of our models were to estimate the relative proponionallosses of age-0 kokanee monality that could be attributed to predation during the summer months in which hydroacoustic surveys for age-0 kokanee abundance were conducted. Samples of potential piscivores were obtained by setting four sinking horizontal gill nets (76-, 89-, 102-, 114-, 127-, and 152-mm stretch mesh) on 15 May, 8 June, 27 June, and 2 August 2000 to obtain samples of large brown, rainbow, and cutthroat trout. Nets were set parallel to the shore at a slight angle so that each net was sampling in a I 0-20 m depth zone. For all fish captured, lengths and weights were measured, otoliths were collected for age determination, and stomachs were removed and preserved in I 0"/o buffered formalin. Stomach contents were examined under a dissecting microscope and separated into 59 seven distinct categories; zooplankton, gastropods, chironomids, benthic invertebrates (oligochaetes, dipterans), terrestrial invertebrates. kokanee, and other fish species, which included rainbow trout, mountain sucker, speckled dace, and unidentified fish portions. Prey fishes were identified to species using similar techniques to Beauchamp and Van Tassell (200 I); kokanee were readily distinguishable from other salmonids. When possible, total, standard, or vertebral lengths were measured on fish prey to discriminate between age-0 kokanee and older kokanee. In total, 159 stomachs were collected during 2000 and monthly diet composition was estimated from 134 non-empty stomachs from brown, cutthroat, and rainbow trout (Table 3-2). Potential predators were separated into two size classes(> 350 mm and < 350 mm) for diet analysis but only piscivores greater than 350 mm were used in bioenergetic models, because of small sample size and fish prey typeS were rare in the smaller size class. The > 350 mm size class corresponded to age 3-7 brown and cutthroat trout. Kokanee were not observed in rainbow trout stomach contents in 2000 and were excluded from model simulations. We used the Wisconsin bioenergetics mode13.0 (Hanson et al. 1997) to estimate monthly consumption rates (grams per day) ofkokanee by predators during the 2000 summer when hydroacoustic urveys were ongoing. April 5 was designated as day I in the model simulations because that was when the majority ofage-0 kokanee had entered the reservoir in 2000. Because diet content information was not available beyond August, consumption beyond August 2000 was interpolated using the observed diet proportions from May 2000 for day 365 of the model run (4 April2001). Parameters for steelhead (0. mylriss) were used as surrogate models for brown trout and modified parameters for coho salmon were used for cutthroat trout (Beauchamp et al. 1995; Cartwright et al . 1998). Prey energy densities (J/g) were obtained from Hanson et al. (1997) and Beauchamp and Van Tassell (2001) and were assumed to be constant throughout the model simulations (Table 3-2). We assumed an indigestible fraction of 40"/o for gastropods, 17% for all other invertebrates, and 3% of total body mass for all fish prey species. Growth for age 3-7 brown and cutthroat trout were calculated from length at age information collected during 1999 and 2000 netting. Lengths at age were subsequently convened to weight using species-specific length-weight regressions from data collected during the same period. Brown trout weight (g)= 0.00000513 • TL' ·t' (? = 3 06 0.99, N = 137; size range, 58-649 mm TL) and cutthroat trout weight (g)= 0.00000741 • TL · (? = 0.99, N = 131; size range, 29-436 mm TL). The following initial and end weights for each brown trout cohort Table 3-2.- Diet composition of prey, as wet weight percentages of the stomach contents for two size classes of brown trout, cutlhroat trout ~ and rainbow trout during spring and summer 2000. Prey energy densities (J/g) that were used in the bioenergetic simulations are shown and were assumed to be constant throughout the modeling period. "'"""'""' ""'""' Ten~ "'"" Silt D aphni~ CiMII'OpOd ...... mwru Kobnc;.c "" s~ ... v- ...... jliOOJ/Il j517lJ .~ ~47<16 1-'12 j«21J~ j5000JJJ!·- S60J I Jill j50liJIIJ "'"' 2 0.0011 o.oro 0.22S 0. 161 0001 0.3?5 0.212 "" 0.000 o.... O.OJO 0,000 0.000 0,000 0.667 R.ntbow "'" 20110 ·-M•y 0.259 00011 0.6o7 007<1 0.0110 0.0011 0.0011 0.0011 """ 0.000 0131 0.000 0000 - 0.29> OJlJ Q ... 0.167 0.000 0.000 0161 ""' ocw 0.6ll O.I IS 0.116 Q_lll 0.0110 0.000 ,,,. ,..,. 0. 169 2000 - o.1n 0.000 0611 O.o.tl 0.02<1 0.000 ,_ ""' QOOO .... 0.0011 0000 0.000 0. 2~ 0.248 00$< o.m O.IS9 o.oso 0.000 0.091 " ""' 0.02S o..t\9 am 0.167 0.0\ 1 0.0011 0. 146 """"' "' "'0 61 wereusedin themodels: age-3, 1200-1331 g; age-4, 1331-1358g; age-5, 1358-1542; age-6, 1542- 1627 g; and age-7, 1627-1742 g. Initial and end weights for cutthroat trout cohons were also computed (age-3, 983-1220 g; age-4, 1220-1326 g; age-5, 1326-1398 g; age-6, 1398-1495 g; and age-7, 1495-1641 g. We assumed an 8% loss of body weight during spawning for all cohons of cutthroat trout (spawning day = 58) and brown trout (spawning day = 211) in model simulations. Diet proponions for > 350 mm size classes were used in the simulations, and proponions were interpolated between sampling dates by the model (Table 3-2}. The thermal histories of brown and cutthroat trout were estimated from venical temperature profiles and the depth intervals at which the nets were set during the study period. An annual survival rate of71% (Z = 0.34) for brown trout was calculated by regressing log. age frequency (ages J-7) against age for samples collected during 1999 and 2000 gillnetting. This survival rate was used to construct age-specific abundances for both brown and cutthroat populations in Porcupine Reservoir such that N3•7 = 1,000, using methods described in Beauchamp and Van Tassell (2001). Small sample sizes prevented the estimation of an annual survival rate for cutthroat trout The number of age-0 kokl!llee consumed was estimated by dividing the proponion of total consu med age-0 kokanee biomass that was age-0 fish by the mean weight of age-0 kokanee for each month. Results Limnologica/ Conditions in 1999 and 2000 Porcupine Reservoir was completely refilled to capacity by I 0 May 1999 reaching a reservoir elevation of 1642 m (Figure J-2). In 1999, the reservoir began to thermally stratifY on 18 May and was we ll stratified from I July until 4 September when the entire water column had become warm and almost isothermal, only varying between 18 •c at the surface and 16 •c at the bottom (Figure J-3). In 2000, the reservoir began to stratifY by 16 May, and the reservoir reached complete stratification by 2 June, which was a month earlier than in 1999 (Figure 3-4). The reservoir remained thermally stratified until the end of August 2000 when the reservoir began to approach isothermal conditions. The rapid annual drawdown of this bottom-withdrawal reservoir for irrigation and the warm summer air temperatures contributed to the destratification in 1999 and 2000. During both summers, temperatures and dissolved oxygen conditions remained within tolerance limits for 0. nerka throughout the entire water column (Brett 1971) . Light 62 1650 ~Spillway elevation (m) 1640 I c: .Q -m 1630 > Q) Qj .... - ~ 1620 Q) (/) ~ 1610 Fry outmigration increasing 1600 Date Figure 3-2.- Porcupine Reservoir elevation (m) measured at the dam from 15 August 1998 to 15 May 1999 and the period when increasing numbers of fry were entering the reservoir. The conservation pool was at 1600 m from 30 December 1998 to mid-February 1999. The reservoir is completely empty at an elevation of 1598 m. 63 D.O. (mg/L) 10 10 ...... I I I I I \, - D.o 11 JIJy 10 15 200 10 15 200 10 15 200 10 15 20 Temperature ("C) D.O. (mgll) 0 10 15 0 10 15 0 10 15 0 10 15 0 1 l J I : I I I 10 > ) J I I 15 { I I I I I I I I I I I ) J I - -- ' 30 11 August 4 September 29 Sep~ember 270dober •o 0 10 15 200 10 15 200 5 10 15 200 10 15 20 Temperature (' C) Figure 3-3.-Vertical temperature (solid line) and dissolved oxygen (dashed line) profiles measured in Porcupine Reservoir in 1999. Reservoir depth declines considerably due to drawdowns for irrigation during July-September. O.O. {mgll) 10 15 10 ;- 15 :s I t 20 1- 00, 25 ~ I 30 I 35 I 27 March I •o 21 Aprit 18M:ay 2.Aine 27 Jlr!e 10 ,. 200 10 15 200 10 15 200 s 10 15 20l 10 15 20 TeJT1)erature ('C) O.O. (mg/L) 0 \0 150 10 150 10 15 0 10 15 0 10 15 0 10 :s 15 20 \ t I ~ 25 I 30 I I _., 35 ~ 12JIIr 25JiA:t 24Au~st 27 Sec;iember 40 3 August 10 15 200 10 15 200 10 15 200 10 15 200 10 15 20 T OJT1)erature (' C) Figure 3-4.- Vertical temperature (solid line) and dissolved oxygen (dashed line) profiles measured in Porcupine Reservoir in 2000. Reservoir depth declines considerably due to drawdowns for inigation during July-September 65 coefficients ranged from 0.36 in May to 0.69 in October 1999 and minimum Secchi depths occurred in July while maximum transparency was measured in August (Table 3-3). In 2000, extinction coefficients and Secchi depths were variable throughout the summer, particularly when compared to 1999. The minimum observed extinction coefficient of0.32 occurred on 26 eptember 2000 and the maximum observed value was 0.98 on 3 August 2000. Minimum transparency occurred on 21 April 2000 and maximum water transparency was recorded on 16 May 2000. Daphnia densities varied considerably between 1999 and 2000 (Figure 3-5). In 1999, Daphnia densities remained low throughout the sampling period, reaching a maximum density of0.2 1 individuals/L on I I August. In 2000, Daphnia reached a peak density of2.66 Daphnia I Lon 2 I April and varied around 0.6-2.3 Daphnia I L until 24 August when they virtually disappeared from the reservoir. Daphnia densities suggested a much berter forage base available to kokanee in 2000 than in 1999, when maximum observed density was 0.21 individuals I L on I I August 1999. The low densities in 1999 were artributed to the draining and refilling of the reservoir during the prior fall and winter. Lake Phase Survival Vertical gill netting in the mid and lower sections of the reservoir revealed that 99"/o of the limnetic fish species assemblage consisted of kokanee in 1999 and 93% were kokanee in 2000 (Figure 3-6). Therefore, hydroacoustic data were not adj usted to account for other species. Only two rainbow trout and one brown trout were captured during I 999 surveys, whereas a variety of species were sampled in vertical nets during 2000 surveys. In I 999, age-0 kokanee ranged from 28 to 48 mm (total length) in June and grew to a size range of62 to 75 mm by September (Figure 3-7). In 2000, age-0 kokanee ranged from 35 to 44 mm and grew to a range of 56 to 82 mm in September (Figure 3-8). Older kokanee captured in vertical gi ll nets in July and August ranged from 186 to 345 mm total length in I 999 and 97 to 397 mm total length in 2000 (Figure 3-9). Despite serting 13· and 19-mm stretch mesh vertical nets, we failed to capture any age- l kokanee in 1999 but the same cohort appeared frequently in our catches in 2000 as age-2 fish (average TL = 174.4 mm). The hydroacoustic data indicated that fish density varied by depth and fish size among months (Figures 3-10 and 3-11). Depth distributions ofage..O kokanee were generally similar between dusk and 66 Table 3-3.-Average extinction coefficient s and Secchi depths for dates that routi ne limnological measurements were taken: Extinction Secchi Date coefficient depth (m) 1999 18May 0.36 2.2 10 June 1 July 2.1 11 July 2.1 11 August 0.68 4.1 4 September 4.0 29 September 0.6 1 2.9 27 October 0.69 2.7 2000 27 March 3.1 21 April 0.59 2.3 16May 047 4.9 2 June 0.55 3.5 27 June 0.66 3.3 12 July 0.86 2.8 25 July 3.5 3 August 0.98 3.3 24 August 2.5 26 September 0.32 3.4 67 4 ---- 1999 -<>- 2000 3 u..i CJi N +I 2 ....1 '- Q) .D E z::> 0 2 u..i CJi N +I 'E .§. .c 0, c Q) ....1 ---- 1999 -<>- 2000 0 >- Q) Q) >- >- u; u; (j; ro c c :; :; :J :J ~ Ci :::;: :J ..., ..., D ro ..: ..., ~ 0> 0> E N :J :J Q) :::;: ~ ,._ ~ N N ..: ..: ,._ N N "' i5. N .... ., "' N Cl) 0> Date N Figure 3-5.-Density (niL) estimates (a) and average total length of Daphnia (b) on 1999 and 2000 sampling dates at Porcupine Reservoir. 68 1999 1999 0-3 F== - Brown trout c::::J KokanM 3-6 c:J Rainbow trout 6-9 p 9-12 0 12-15 D - 15-18 ==::3 = 18-21 ~ [ 21-24 :~- "l iii ""'"·- .,2: >24 ::::::3 .£ .ca. ., 2000 .= 2000 0 0-3 :J = KokaMe - Brown trout 3-6 p r:::::J Rainbow trout - Cufvott trout 6-9 = Spockloddace F"ii' - Mountain Suckw 9-12 - # 12-15 .-, '" "'·==='"' fiiiiiiiiiii" 15-18 ;,·- ~' 18-21 "'# ~ 21-24 ,~· ;- :~ >24 21 0 20 40 60 80 100 120 1400 2 4 6 8 Catch Figure 3-6.- Vertical distribution offish captured in venical gillnets for the entire 1999 and 2000 summers. Nets were set prior to hydroacoustic surveys for target verification and sample collection. Kokanee comprised 99"/o of the total catch in 1999 and 93% of the total catch in 2000. 69 18 16 June 1999 14 12 10 8 6 4 2 0 30 August 1999 25 .c Ol 20 ::> (1) () 15 ~ .D 10 E z::> 5 0 +------~~~~~-L~~--~ 14 September 1999 12 10 8 6 4 2 0 +---.---,--,---,---.---.--,---,L~~~~~-L~ 20 80 Total length (mm) Figure 3-7.- Age-0 kokanee length distribution from tow-netting (June), and gillnetting (August and September) surveys at Porcupine Reservoir during 1999. 70 16 14 May 2000 12 10 6 ,.0 June 2000 12 10 8 .lily 20(X) Augull2000 • ~ • ~ ~ ~ ~ ro n w ~ Total Length (mm) Figure 3-8.-Age-0 kokanee length distribution from tow-netting (May-August) and vertical gillnening (August-September) at Porcupine Reservoir in 2000. 71 1999 50 40 i ' t~ · ~-~ -- 30 :: 20 :c 10 Ol ::> Cll -~- L () -nfln-f (ij 0 .0 E 100 2000 ::> z 80 60 r:--'- 40 20 ~ 0 i · ~~ == rl rh 50 100 150 200 250 300 350 400 450 Total Length (mm) Figure 3-9.-Length distribution of age-l and older kokanee captured in vertical gillnets during July-Auguust surveys in 1999 and 2000. 72 June 1999 dusk .line 19Qg night July 1g9Q dusk I.. ~ .!! .E R August 1999 right ~ 9-12 12-15 15-18 111-21 21-2• Septetn)er 1QQ9 nlgt'C ~e 11-9 9-12 12-15 - 25-aamm 1S.18 ~ 80-150mm 18-21 ->150mm 21-2~ 20 40 20 40 60 100 Targets /1 000 m' ~ 2 S.E. Figure 3-10.- Density (± 2 SE) of three size classes of pelagic fish by depth at dusk and night (right) during 1999 hydroacoustic surveys. The 25-80 mm size class was comprised of mainly age-0 kokanee. Note the range of target densities for night surveys. 73 .AJne 2000 night ~ ..line 2000 dusk I.. 2: $ £ ~ li. t3 I Augu!f. 2000 right I.. 2: ~ t ~ september 2000 nlgt'l I ...... 9-12 2: 12-15 ~ ~ 15-18 25-80mm li. 16-21 80-150mm >150mm t3 21-2. 20 40 20 40 eo 100 Targets / 1000m' !2 S.E. Figure 3-11.- Density (± 2 SE) of three size classes of pelagic fish by depth at dusk and night (right} during 2000 hydroacoustic surveys. The 25-80 mm size class was comprised of mainly age-0 kokanee. Note the range of target densities for night surveys. 74 night sampling periods on all dates, which suggested that there was not a distinct diel vertical migration by kokanee. On all dates, single fish targets increased dramatically during the night runs indicating that fish schools had dispersed. Kokanee were strongly surface-oriented during both dusk and night in June 1999 and 2000. This surface orientation probably caused a significant underestimation of kokanee density and abundance due to the difficulty in acoustically detec1ing and quantifying targets near the surface and other boundaries. During July-September sampling dates in 1999 and 2000, the modal depth ofkokanee were separated from the surface and bottom and were fully detectable by the acoustic gear. In both years, the modal depth of all size classes ofkokanee shifted progressively deeper through August and reflected the changes in water temperature and dissolved oxygen during late summer as the reservoir warmed and approached isothermal conditions. Kokanee occupied the deeper metalimnion where temperatures were somewhat cooler, but also avoided the area near the bon om where dissolved oxygen concentrations were low (e.g., 24 August 1999 on Figure 3-4). Monthly abundance estimates indicated a significant decline in age-0 kokanee during the July September in 1999 and 2000 (Figure 3-12). Age-0 kokanee abundance declined from 225,641 (± 51,271) in July 1999 to 44,040 (± 30,641) in September 1999. Similarly, a decline from 75, 109 (± 4,258) age-0 kokanee in July 2000 to 12,865 (± 2,802) in September 2000 was observed. Instantaneous monality rates and survival were calculated for the July-August, August-September, and July-September time periods for comparison (Table 3-4). The July-September 1999 estimates indicated that a severe monality pressure had occurred that period (Z = 0.82), where only 200/o of age-0 kokanee survived from July to September. In 2000, we estimated that 17% ofage-0 kokanee survived from July to August (Z = 0.85). The August September 1999 monatity rate was much lower (Z = 0.13) and was reflected in the survival rate of age-0 kokanee from the month of August to September (S = 88%). In 2000, the August-September monality remained somewhat constant (Z = 0.92), when we estimated that 400/o ofage-0 kokanee survived the time period. Age-0 kokanee did not recruit to the 13-mm mesh venical gillnets until late August and September 2000, suggesting that the age-0 cohon experienced poorer growth in 2000 than in 1999. This is perplexing because of the abundant forage base in 2000 compared to 1999. Growth curves for 1999 and 2000 age-0 kokanee cohorts suggest that age-0 fish in 2000 experienced bener growth during the initial 3 months in the 75 300000 250000 - 25-80mm c:::::J 80-150 mm - >1 50mm 200000 150000 ui 100000 en N + I Q) 50000 u c <0 1:) c c 100000 ::l .0 <{ ~ I- 80000 60000 40000 20000 0 June July August September Month Figure 3-12.-Monthly total abundance estimates(± 2 SE) for three size classes ofkokanee at Porcupine Reservoir during 1999 and 2000 hydroacoustic surveys. Table 3-4.-Esrimated values for instantaneous mortality (Z) and survival (S) ofage-0 kokanee for three rime periods during the 1999 and 2000 summers, where abundance estimates were obtained from monthly hydroacoustic surveys. Time period in Initial Abundance at Instantaneous Survival (S) months (t) abundance (No) time t Q:!t) mortalit~ (Z) % July to August 1999 ( I) 225,641 50,201 1.50 22% Range (2 S.E.) 174,3 70-276,912 41,185-59,217 1.44-1.54 21-24% August to September 1999 (I) 50,201 44,040 0.13 88% Range (2 S.E.) 41 ,185-59,217 39,217-48,863 0.05-0.19 83-95% July to September 1999 (2) 225,641 44,040 0.82 20% Range (2 S.E.) 174,3 70-276,912 39,217-48,863 0.75-0.87 18-22% July to August 2000 (I) 75, 109 32,231 0.85 43% Range (2 S.E.) 70,851-79,36722,574-41,888 0.64-1 14 32-53% August to September 2000 (I) 32,231 12,865 0.92 40% Range (2 S E.) 22,574-41 ,888 10,063-15,667 0.81-0.98 37-45% July to September 2000 (2) 75, 109 12,865 0.88 17% Range (2 S.E.) 70,851-79,367 10,063-15,667 0.81-0.98 14-20% Z = -ln(Nt / No) I t S = e(·Z " I) 77 reservoir (May-Ju ly) but did not fare as well a.fler August (Figure 3-13). Water temperatures were similar for both years during this period, and the density of fish within the cohort was much less than in 1999, which suggests that competition should not have been an issue. However, in 2000, Daphnia densities were at their lowest levels (0.001 individuals I L) by late September and at much higher levels (0.1 individuals I L) at the same period in 1999. Myxobolus cerebra/is Tesring PCR testing for the presence of M. cerebra/is revealed that infection of age-0 kokanee increased in prevalence and severity through time in 1999 (Figure 3-14) and 2000 (Figure 3-15). Prevalence and severity of infection in age-0 kokanee increased through time in a more pronounced manner in 2000 than in 1999. In 1999, the Gamma coefficient was estimated as 0.57 with a 95% confidence interval of(0.43 to 0.71) and in 2000 the coefficient was 0.84 (0.77to 0.90). These trends were statistically significant despite variable sample sizes (P < 0.0005). Fry collected during the outmigration period in March 1999 all tested negative forM. cerebra/is (n = 36) but by June 1999, 83% ofage-0 kokanee in the reservoir were infected by M. cerebra/is and I 00% were infected by August 1999. In 2000, the majority of age-0 kokanee were not infected until after they entered the reservoir in the spring. In March and April2000, during the fry outmigration, 11 6 (95%) of the fish collected were not infected by M. cerebra/is. However, five fish tested weakly positive !Tom the reservoir net pen experiments in April, and all fish collected !Tom the reservoir in May-September were infected by M. cerebra/is. The PCR signal rariking, which indicated the amount of M. cerebra/is DNA fo und in the heads of age-0 kokanee, increased through time for both years. indicating a possible increase in severity of infection . Degree-days were estimated for the period between potential exposure when the majority of age-0 fis h entered the reservoir and when they were collected for pathogen testing in subsequent months (Figures 3-14 and 3-15). Because of warmer reservoir temperatures, degree-days accrued more quickly in 2000. For example, fish collected in June 2000 had experienced an estimated 642 degree-days compared with 373 degree days in June 1999. By the end of September, age-0 fish had experienced 1,537 degree- 80 70 .sE 60 .c 0, c 50 Q) ....J ~ ~ 40 30 -<>-- 2000 20 ?:- ?:- >. ., >. 1;) · ~ .. c :; ::J .. .. ~ :; ::J .., ~ ::J Figure 3-1 3.-Growth cUJves for age-0 kokanee at Porcupine Reservoir during the 1999 and 2000 growing seasons. Data points denote the mean length for each month and error bars denote the 95% Cl. 79 300000 . 250000 UJ rJi 200000 "'tJ ~ ..l! 150000 c ! .a"" < 100000 ~ .....0 50000 ' t (n::3e) 100 b ., 80 l! (n=70) ~ 60 <1:"* (n-) " (n=28) ~ 40 ~ 20 u. }A ~ ~ i ~ • - Negative ~ ~ "~ We'MPca (373) « C=:l (1 148) - PoStM Month l = Streng Poe (1537) (Degree- Figure 3-14.- Monthly total abundance (± 2 SE) estimates (a) and results ofPCR testing for the presence of Myxobo/us cerebra/is for age-0 kokanee at Porcupine Reservoir during summer 1999. Age-0 kokanee were not captured during April, May, and July. Estimated degree-days were calculated based on collection date. 80 100000 . 80000 uJ vi ! "'+I 80000 ~ .,~ .B 40000 < ]i 0 t- 1 20000 ! 0 100 (n::63) b (n=SII) (n=S!I) (n=32) (n::21) 80 (n=22) (n=13) l: (n=23} ~ v 60 a:"~ 4ll ~£ 20 h I I ~ I• I! J t i .r... i l ~ " • i z (302) (842) 1~75 ) i ! c:::::l- Neg-Wfllkp05itiW: (131) (1 435) ~ -pot:itt\18 1181l8) C:=J llrong potitNe Month -verystrcr~gpos (Degree- Figure 3-15.- Monthly total abundance(± 2 SE) estimates (a) and results ofPCR testing for the presence of Myxobolus cerebralis for age-0 kokanee at Procupine Reservoir during summer 2000. Estimated degree-days were calculated based on the collection date. 81 Polelllia/ No11leihal Effects ofM cerebra/is 011 Kokanee Lengths, weights, and condition factors were analyzed among fish with varying infection levels for each month but no relationship existed between these indices of age-0 kokanee growth and re lative severity of infection. Small sample sizes, equipment or diagnostic technique limitations, and the possibility that M. cerebra/is did not affect the growth of age-0 kokanee at Porcupine Reservoir in 1999 and 2000 may explain the lack of any type of relationship. In older cohorts (age-l +), M. cerebra/is infection and the presence of clinical deformities varied between years (Table 3-5). Infection prevalence was highest (93%) in fish collected during the 1999 spawning run and lowest in fish collected during the previous year's spawning run {68%). Although spawners showed the lowest prevalence in 1998, they also had the highest percentage of fish with observed deformities (48%). Average spore counts were highly variable between years, ranging from 34.8 (SE = 12.2) in fish collected during the 1998 summer and 200.4 (SE = 21.7) in fish collected during the 2000 summer. The deformity ranking, a measure of the severity of deformities, remained relatively stable throughout all years and collection periods. Prevalence of infection and spore counts from indhidual fish varied by age and year (Table 3-6). Prevalence declined between age-2 and age-4 kokanee in 1999. In 2000, age- l and age-2 fish had identical prevalence percentages (83%), but prevalence declined from 72% in age-3 fish to 50"/o in age-4 fish. In both years, spore counts decreased by fish age; however, this decrease was not statistically significant because of small sample sizes of some age classes and the high variance between spore counts of individual fish . Interestingly, age-2 fish in 1999 averaged 95.43 spores I I 00 fields I fish (SE = 53 .3), but by 2000, the same cohen averaged 65.03 spores I 100 fields I fish (SE = 21.6) yet prevalence of infection in the cohort remained constant between the two years. Predalion ofage-0 Kokanee Kokanee were observed in the stomach contents of brown trout during all sampling periods but were only observed in the diets of cunhroat trout during July and August (Table 3-2). Older age classes of kokanee were more prevalent in the diets than age-0 kokanee and age-0 kokanee did not appear in cutthroats diets at all in 2000. Similarly, age-0 kokanee were not observed in the diets of brown trout until Table 3-5.-Sum of observed ranked deformities, percent fish with deformitites. deformity ranking, infection prevalence, and average spores per 100 fields for kokanee collected during the summer and spawning runs at Porcupine Reservoir, 1998-2000. Percent of fish with observed deformities and deformity ranking are higher during spawning runs, after fish have undergone morphological changes associated with sexual maturity in kokance. 1998 1998 1999 1999 2000 2000 Summer Spawn Summer Spawn Summer Spawn Deformity type (n=59) (n=60) (n=59) (n=60) (n=85) (n=60) Vertebral 0 0 0 0 2 Mandibular 18 32 4 IS 8 23 Cranial 9 12 6 9 7 18 Opercular 12 10 2 2 7 8 Fins 0 0 0 0 0 Raker 0 7 0 4 0 4 Other 0 0 0 0 0 0 % Fish with deformities 37"/o 48% 18% 25% 22% 43% Deformity ranking• 8% 10% 6% 10% 5% 10% Prevalence 73% 68% 71% 93% 79% 82% Average spores per 34.8 (12.2) 51.7(18.0) 79.6 (23.1) 40.6 (5.2) 200.4 (21.7) 87.6 (11 .3) 100 fields SE •Deformity ranking = (no. deformed fish I no. dcfom>ed fish • 21) • I 00 00 "' Table 3-6.- Average spores I 100 fields for age I and older kokanee collected during 1999 and 2000 summer vertical gi llnetting and spawning runs. Fish were processed using the pepsin-trypsin digest . No age-l fish were collected in 1999 because of problems with gear selectivity. 1999 2000 Age- l+ Age-2+ Age-3+ Age-4+ Age-l+ Age-2+ Age-3+ Age-4+ N (sample size) 21 85 6 40 58 32 6 Prevalence 71% 59% 33% 83% 83% 72% 50% Avg. spores / tOO fields 95.43 58.34 2.33 303.03 125 .63 65.03 29.67 Standand error 53.3 16.1 1.8 96.1 31.0 21.6 14.3 ....., 84 August, but then only represented 9. 1% of the total kokanee biomass consumed. Consequently, model simulations indicated that the consumption of age-0 kokanee was negligible until July-August (simulation days 90-120) when an estimated 24,168 g or 19,487 age-0 kokanee were consumed by I ,000 brown trout (age-3 to age-7; Table 3-7). During August-September (si mulation days I 20- I 50), an estimated 35,794 g or 18,988 individual age-0 kokanee were consumed per 1,000 age-3 to age-7 brown trout. During these periods, bioenergetic model simulation days (days 90, 120, and 150) closely coincided with dates on which hydroacoustic estimates of age-0 kokanee abundance were obtained (days 89, 118, and 150). Between July and August2000, model estimates suggested that up to 45% of the observed decline of age-0 kokanee abundance could be attributed to predation by I 000 age-3 and age-7 brown trout whereas 98% of the observed decline between August and September could be accounted for by brown trout predation. Discussion The rapid decline in age-0 kokanee observed in 1999 and 2000 may be attributed to a number of facto rs. Infection by Myxobolus cerebra/is may result in whirling disease, which has been linked to declines in other wild salmonid populations in the western U.S. Whirling disease may influence a host 's ability to survive by reducing abilities to cope with environmental stressors such as low food and warm temperatures. Infection may also influence host behavior and reduce survival by compromising the ability to feed or avoid predation. Another possible reason for the decline is Joss due to entrainment, which has been documented in many kokanee populations throughout the west (Stober et al. 1983; Skaar et al . 1996; Maiolie and Elam 1998). The onset and severity of whirling disease are influenced by fish host species, size and age of fish at first exposure, parasite dose, and ambient temperature. Temperature is a particularly imponant fuctor because it influences the development and release of triactinomyxons from within T. lllbifer and affects the rate of development and severity of the disease within the fish. Halliday (1973) conducted laboratory experiments in which rainbow trout held at 17 •c had developed mature myxospores afler 52 days post exposure to the parasite while fish held at 12 •c had developed mature myxospores 10 I days post exposure. The optimal temperature for parasite development and growth was 15- I 1•c (Halliday I 976). Table 3-7.- Monthly consumption ofkokanee (kok} by all cohorts of salmonids for 2000 summer. Population structure for 1,000 individuals was calculated fi-om survival rates obtained fi-om a regression of age fi-equencies fi-om fish fully recruited to gillnets for brown trout. Because age frequency data were incomplete for cutthroat trout . we assumed that the population structure for both species was the same for purposes oft he model. The population of 1,000 predators was partitioned into 354 age-3. 251 age-4, 178 age-S, 127 age-6, and 90 age-7 indi viduals for both brown trout and cutthroat trout. Individual ~tor Po~ula t ion (n = 1000) Simulation Total Age--0 kok Numbcrag,e-0 Age-0 kok Nwnberage..O dar Month Tern~ kok (!!) oonsum rainbow trout, and cunhroat trout developed clinical signs of whirling disease 40-60 days post-exposure in the Colorado River (Thompson et al. 1999). In these experiments, rainbow trout exposed in June immediately after hatching began developing clinical signs of the disease and mortality by September. Younger and smaller fish develop more severe clinical signs and monality than do fish that were exposed to the parasite at older ages, even though the age difference was only in weeks (Markiw 1991 , 1992a; Thompson et al. 1999). Environmental stressors, such as warm temperatures, low food, competition, low oxygen levels, and bacterial infections, may act in concert with M cerebra/is infection to cause population level effects on fis h (Schisler et al. 1999). Infected fi sh held at 17 •c suffered substantially higher mortality than non infected fish and infected fish held at 12.5 •c (Schisler et al. 1999). In these experiments, compounded stressors (M cerebra/is infection , warm water temperatures, and secondary bacteriaJ infection) increased mortality in a linear fashion. Increased water temperature did not have a profound effect on clinical signs of whirling disease. Schisler et al . ( 1999) stated that warmer temperatures increased mortality in infected fi sh and may be due, in part, to an increase in the metabolic rate of both fish and parasite. Although 0. nerkn were known to be susceptible to the parasite under laboratory conditions (0 ' GTodnik 1979), potential impacts on the abundance and survival of the species in the wild were not known. Determining the age at first infection is an imponant indicator of whether or not an M. cerebra/is infection will result in death. ln this study, it was demonstrated that the majority of age-0 kokanee were not infected until after they reached the reservoir, at which point they may already be > 3-4 weeks old (post hatch). Ryce et al. (1999) demonstrated that older fish (rainbow trout), when first exposed toM cerebra/is, took longer to develop clinical signs of infection. No significant differences in survival were observed between fish exposed with I 00, I 000, and I 0,000 TAMs I fish after 7 weeks post hatch. ln addition, fish exposed after II weeks post hatching developed no clinical signs, regardless of parasite dose. Wild rainbow and cutthroat trout hatch in mid-late July and early August when temperatures are warm and triactinomyxon releases should be at their peak. Therefore, they are at their most susceptible stage, in terms of age and size, when parasite levels are at their highest. In comparison, kokanee hatch in mid winter and early spring when temperatures, and thus parasite levels may be lower. 87 Degree-days until onset of clinical signs associated with M. cerebrali. parasite dose and temperature in various published studies (Table 3-8). Comparisons should be made with caution because parasite doses used in most laboratory studies far exceeded what fish probably experience in the wild. The earliest that clinical signs such as black tail and whirling behavior were observed in examined lit erature, was 630 degree-days. The presence of clinical signs, such as whirling behavior, black tail, and sloped heads, may be indicative of a reduction in the fish host 's ability to survive, perhaps due to an inability to forage or avoid predators. Halliday ( 1973) observed mature myxospores in the heads of rainbow trout after 840 degree-days post exposure. Since trophozoites are the stage that lyse canilage, the presence of mature myxospores suggests that much of the damage to a fish during the development of the parasite has already occurred. Because it is unlikely that age-0 kokanee experienced the high parasitic doses used in most aboratory studies, it was concluded that 900 degree-days post exposure may be a good estimate of when clinical signs may be established, if they appear at all. This would mean that if age-0 kokanee were to develop clinical signs fi'om natural M. cerebra/is infection at Porcupine Reservoir, they would have not likely occurred until August 1999 or July 2000, based on when fish were collected for pathogen testing. It should be noted that at a low exposure dose (10 TAMs I fish), Hedrick et al. (1999a) observed that only one fish developed black tail, and it took 2,325 degree-days for the abnormality to arise. One age-0 fish was collected in July 2000 (975 degree-days), with a severe cranial deformity and subsequentl y tested positive forM. cerebra/is. This suppons comparisons between degree-days and the onset of clinical signs and the potential link to survival. In 1999, infection increased in both prevalence and PCR signal strength, and all of the fish we collected in August were infected by M. cerebra/is. In 2000, only a small percentage of kokanee fi'y were infected during the downstream migration, but they apparently became infected very quickly after they entered the reservoir. By May 2000, all fish we collected were infected by M. cerebra/is, as were all fish we collected during subsequent months of that year. These results demonstrate that both prevalence and severity of infection in age-0 kokanee increased with time, up to the point where the large majority of age-0 fish are infected. Fish appear to have been infected much earlier in 2000 than in 1999. Warmer reservoir temperatures in 2000 compared to 1999 may have contributed to earlier infection, but the reservoir draining during full 1998 may have also played a role. The draining of the reservoir to the small conservation pool Table 3-8.-Various estimates of degree-days until onset of clinical signs associated with M. cerebra/is in various laboratory studies. Parasite dose Temperature Observed Degree-days Source Fish species (avg. TAMs I Fish) (oCJ Days clinical sign at onset Halliday 1973 rainbow trout 17 52 mature spores observed 884 12 10 1 mature spores observed 1,212 7 120 mature spores observed 840 Hedrick ct al. 1999a rainbow trout 1000-2000 15 42 black tail and whirling 630 cutthroat trout 1000-2000 IS 42 black tail 630 Hedrick et al. 1999b rainbow trout 10 IS 155 I fish with black tail 2,325 100 IS 63 black tail 945 1000 IS 56 black tail and whirling 840 10000 15 42 black tail and whirling 630 Rose et al. 2000 rainbow trout 485 12.5 60 black tail and whirling 750 *Study was conducted prior to knowledge ofT. tubifer as the alternate host of M. cerebra/is. Mud from infected aquaria was used to expose fish to the parasite. 00 00 89 would have surely affected the abundance ofT. lubifex, the alternate host ofM. cerebra/is. T. wbifex have the ability to survive drought cond itions for up to 5 months by forming cysts (Anlauf 1990), but it is quite reasonable to suggest that there was a lag between when the reservoir refilled and when the oligochaetes repopulated the sediments, became infected, and began releasing TAMs. In tota~ 495 age-0 kokanee were examined for clinical signs ofM. cerebra/is during 1999 and 2000, but clinical signs were never observed at any time in 1999 and only one fish collected in July 2000 displayed a cranial abnormality often associated with M. cererbalis. This fish scored "+++" in signal strength by PCR, but no other fish wit h similar deformities were collected during our study. However, because of extreme reservoir drawdown, we were not able to collect age-0 kokanee past October each year. Age-0 kokanee may have developed deformities, after we could collect fish. Clinical lesions could have al so caused behavioral changes that prevented affected fish !Tom inhabiting the pelagic areas of the reservoir that were sampled by collection gear. Low survival rates from July through September were similar between 1996 (17%) and 2000 (22%); however, the low survival in 1999 occurred July to August followed by an 88% survival during August tO September. In 2000, survival remained constanl between these months, with 43% surviving from July to August and 40% surviving from August to September. Survival rates of age-0 kokanee at Porcupine Reservoir were low but fell within the range reported for other western populations ofkokanee (Table 3-9). Published survival rates for age-0 kokanee are sparse and differences in sampling methodologies, and the large variances associated with these sampling methodologies may limit comparisons. However, annual survival (2.3%) at Odell Lake, Oregon, and survival of age-0 kokanee at Lake Billy Chinook in 1998 (8.2%) and I 999 (8 .3%), which were measured over very si milar periods to our estimates at Porcupine Reservoir, suggest that low survival may be more common than one might expect. Although comparisons with other western kokanee populations suggest that age-0 survival rates at Porcupine Reservoir are not extreme, the survi val of age-0 fish from July to August 1999 (22%) can still be considered inordinately small for a I -month period. Mortality coincided with a high prevalence of infection by M. cerebra/is and increased severity of infection based on PCR analysis of August fish. By July-August, kokanee fry that outmigrated in April would have resided in the reservoir for 3-4 months. Table 3-9 - Various survival rates for age-0 kokanee and time periods over which survival was measured. When possible, an error was calculated from published data using two standard errors. Locale Time~riod Survival (%) Error Porcupin e Reservoi r July to September 1999 20"/o 18-22% (2 SE) Porcupine Reservoir Jul y to September 2000 17% 14-20"/o (2 SE) Dworshak, ID' Annual, 1988- 1994 71.9% 32% (lower o nly; 2 SE) Pend Oreille, ID' Annual, 1976-1993 44.4% 33-59% (2 SE) Cowichan. BC' Annual, 1984-1 987 13 .5% I% (lower only; 2 SE) Kootenay, BC' Annual, 1988-1997 22.7% 17-30"/o (2 SE) Odell, OR' Annual, 1972-1974 2.3% 1-5%(2 SE) Pend Oreille, m• June to September 1987 13.6% 8.2-19% (2 SE) Pend Oreille, m• June to September 1988 28.7% 11 .5-45% (2 SE) Pend Oreille, I o• June to September 1989 19.1% 7.6-30.6% (2 SE) Pend Oreille, ro• June to September 1990 20.0"/o 0-40"/o (2 SE) Pend Oreille, ro• June to September 199 1 20.7% 0-41.4% (2 SE) Pend Oreille, rn• June to September 1992 38.5% 0-92%(2 SE) Lake Billy Chinook, OR' July to October 1998 8.2% 8.0-8.3% (95% Cl) Lake Bill:z: Chinook, OR' Jul :z: to October 1999 8.3% 7.2-9.2% (95%CI) ' McGurk 1999 •Paragamian and Bowles 1995 'Thiede et al. 200 I 91 Pathogenic testing forM cerebra/is in 2000 showed that fish were infected relatively soon after entering the reservoir. Degree-day analysis suggested that mortality also occurred during a period when clinical signs normally developed in fish exposed in laboratory settings. However, the data do not imply that the mortality between the months of July and August 1999 can be attributed solely toM. cerebra/is. During this period, reservoir water temperatures warmed considerably from an average temperature of 11.8 'Con II July to 16.0 'Con II August. Interestingly, these water temperatures correspond to favorable ranges for both host and parasite (Brett 1971 ; Halliday 1976). Dissolved oxygen levels were within acceptable limits for salmonids during this period. Zooplankton abundance was quite low throughout the summer because of entrainment losses both during the draining period of the previous winter, and during normal summer drawdown. ln addition, during the 1999 winter, ephippia may have frozen or been dessicated, which would have decreased the recruitment of dormant Daphnia from sediments in the spring after the reservoir had refilled . Abundance of the age-0 year class should have been larger than normal due to the record spawn (see Chapter 2) and it is possible that competition within the age-0 year class may have compounded problems associated with low food levels. However, the fish appeared to grow adequately throughout the summer, suggesting that low food levels were not a likely cause of the high mortality rate. Model simulations suggested that predation could account for a significant amount of the observed mortality of age-0 kokanee during the summer. The results from the bioenergetic models may be suspect because of small sample sizes and the use of model parameters borrowed from surrogate species. However, the objective for using the bioenergetics model in this study was to assess the degree to which predation could influence age-0 kokanee abundance in Porcupine Reservoir. Consumption estimates from the brown trout bioenergetic models suggest that an arbitrary population of I ,000 brown (ages 3-7) could have affected abund ance of age-0 kokanee in 2000. During the period between July and August when the most dramatic decline in age-0 kokanee abundance occurred, bioenergetic models suggest that although predation contributed to losses, piscivory cannot be held entirely accountable. Assuming predation pressure between 1999 and 2000 were similar, although age-0 kokanee abundance was much higher in 1999, it is likely that additional sources of mortality accompartied predation. Porcupine Reservoir is managed primarily for irrigation and consequently experiences an average annual drawdown of 22 m. Reservoir volume decreased by almost 50"/o between June and September 1999 92 and 2000 (Figure 3-16). These extreme and rapid draw downs could cause losses ofkokanee by entrainment through the dam. Skaar et al . {1996) estimated that 27% of the kokanee population at Libby Reservoir, Montana, were lost through entrainment, and the majority of these fish were age-0. An estimated 90% of all kokanee were lost to entrainment during late winter and early spring flood control discharge in 1996 at Dworshak Reservoir. Idaho (Maiolie and Elam 1996). In addition, Stober et al . ( 1983) estimated that kokanee at Banks Lake, Washington, experienced an average loss of64% through entrainment. Given the extreme annual loss of water during both summers, it is not unreasonable to suggest that entrainment was responsible for some of the loss in age-0 kokanee abundance. !mer-annual differences in observed defonnities between older fish collected in the summer and during spawning runs may reflect the fact that a different observer conducted the defonnity index for all spawning runs. However, mandibular and cranial defonnities, which are the two most common types observed in kokanee at Porcupine Reservoir, are generally quite pronounced, and it is unlikely that these types of deformities went unnoticed. Although previously undocumented, one possible cause would be changes in the skeletal tissue caused by the parasite and the influence those changes may have had on the development of secondary sexual characteristics such as when the jaws hypertrophy into a kype in males prior to spawning. Literature on these morphological transformations is scarce, but Kacem et al . ( 1998) demonstrated that sl.:ull morphology changes considerably in Atlantic salmon (Salmo salar) during the spawning period. Bones such as the dentary, premaxillary, maxillary, vomer, and supra-<>thmoid grow allometrically between males and females during a spawning run, and other bones such as the posterior and middle portions of the neurocranium grow isometrically between sexes. Damage or alterations to these bones, caused by the parasite prior to ossification, may affect the growth and transformation of these tissues during the normal morphological changes that are characteristic of spawning kokanee. The observed decline in average spore counts with age may simply be an ani fact of the pepsin-trypsin diagnostic procedure, in which fewer spores are liberated from the bone tissue of older fish because the enzymes may not be given enough time to fully digest the denser tissue of older fish. There may also be a dilution effect by which older and larger fish yield more post digest residue, but only 0.5 rnl of residue is examined and enumerated from each fish_ Some researchers have suggested that living salrnonids may be capable of expelling mature myxospores (Uspenskaya 1957; Nehring et al. 2001), but the pathways for potential 93 18000000 16000000 .., .. 1999 .s 14000000 ·0 2000 Ql E :J 12000000 ~ ·....a c: 10000000 Ql rJl Ql cr 8000000 6000000 '0 4000000 June July August September Month Figure 3-16.-Porcupine Reservoir volume for June through September 1999 and 2000 The reservoir experiences an average drawdown of 22 m or 50"/o of the full volumetric capacity during the four prime irrigation months. 94 expulsion are unknown and the evidence thus far is suspect. Another possibility is the internal destruction of spores within the bone tissue during the development and growth of a fish. A major problem in conducting research on a pathogen's effects on a wild population is that often only the survivors are sampled. Although results of PCR testing on age-0 kokanee showed an increase in prevalence and severity, fish coll ected for pathogen testing may have been the surviving "healthy" fish that escaped some type of environmental or epizootic bot1leneck. During the 1999 summer, attempts to collect age-0 kokanee were unsuccessful during the period in which the mortality apparently occurred. However, the large mortality that was observed from July to August 1999 appears to have been an isolated event, which is su pported by the August to September 1999 survival rate and the observed survival rates in 2000. At1empts to associate the relatively low age-0 kokanee survival rates at Porcupine Reservoir with M cerebra/is were somewhat unsuccessful, particularly because of the presence of other factors that likely contributed to the declines. However, high levels of infection were observed while age-0 fish were still developing and clinical deformities in older fish were regularly observed during the 1996-2000 spawning runs. Given the strong presence of the parasite within the population and the low survival of age-0 kokanee during both 1999 and 2000, we suggest that the parasite is likely influencing the abundance of age-0 kokanee in concert with other environmental stressors. References Agresti, A. 1984. Analysis of ordinal categorical data, 1• edition. John Wiley and Sons, Inc., New York. Andree, K.B ., and E. MacConnell, and R.P. Hedrick. 1998. A nested polymerase chain reaction for the detection of genomic DNA of Myxobalu .~ cerebra/is in rainbow trout Oncorhyt~chus mykiss. Diseases of Aquatic Organisms 34: 145-154. Anlau£; A. 1990. Cyst formation of Tubifex tubifex (Muller)-an adaptation to survive food deficiency and drought. Hydrobiologia 190:79-82. Baldwin, C. M., D. A Beauchamp, and J. J. Van Tassell. 2000. 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Science 225: 1449- 1452. 100 CHAPTER 4 CONCLUSIONS Prior to this study, much was unknown about the effects that Myxobolus cerebra/is have on kokanee, panicularly at the population level. In addition, few studies have addressed how the parasite may function within a standing body of water such as a lake or reservoir. We were able to describe changes in infection severity and prevalence in spawning kokanee between 1996 and 1999. Infection in other age classes of kokanee was also quantified in 1999 and 2000. Imponantly, we discovered that age-0 kokanee were not infected by M. cerebra/is unt il after they entered Porcupine Reservoir and both prevalence and infection severity rapidly increased during the following months. In 1999 and 2000, a significant monality event occurred in age-0 kokanee that coi ncided with increases in infection severity and prevalence. However, we were unable to attribute monality directly toM cerebra/is infection because environmental conditions were unfavorable to kokanee survival during the same period. The low survival rate of age-0 kokanee in Porcupine Reservoir is likely the result offish being unable to cope with both parasitic infection by M cerebra/is and environmenta.l stressors. The following is a summary of the major findings of our study In spawning kokanee, prevalence of Myxobolus cerebra/is infection, spore counts, and clinical signs varied between 1996 and 1999. However, prevalence does appear to be increasing since 1996. A reliable estimate of total spawner abundance (within ± 25% of true abundance} can be generated by applying an expansion factor of5.8 times the I -day spawner count during the peak of the run (around 19 September). Age-0 kokanee were primarily infected after they entered the reservoir and both prevalence and severity increased rapidly throughout the summer and nearly all age-0 kokanee were infected by August of both years. Low survival rates of age-0 kokanee from July through September coincided with increased prevalence and severity. 101 Comparison of degree-days until development of clinical signs between previously published laboratory and thermal experience of age-0 kokanee suggested that clinical signs could develop as early as July. However, only one fish (out of 495) was observed to have a lesion that was associated with M cerebra/is infection. Results of bioenergetic simulations suggest that piscivory by brown trout and cunhroat trout were a major source of direct monality in age-0 kokanee. ln age-l and older kokanee, we did not find any evidence that M cerebra/is had an effect on growth and overall condition of fish . Infection severity and presence of clinical signs varied between years and were likely more related to limitations of diagnostic techniques.