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Environmental Biology of Fishes 51: 245–256, 1998.  1998 Kluwer Academic Publishers. Printed in the Netherlands.

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario Scott McKinley1, Glen Van Der Kraak2 & Geoff Power1 1 Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada 2 Axelrod Institute of Ichthyology and Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada Correspondence to: Glen Van Der Kraak (e-mail: [email protected]) Received 10.3.1997

Accepted 7.8.1997

Key words: reproduction, radio telemetry, hydroelectric development, gonadosomatic index, sex steroid hormones Synopsis This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development.

Introduction Lake sturgeon, Acipenser fulvescens, populations have been seriously reduced or eliminated in much of their native range (Harkness & Dymond1, Brous1

Harkness, W.J.K. & J.R. Dymond. 1961. The lake sturgeon: the history of its fishery and problems of conservation. Ontario Department of Lands and Forests, Fish and Wildlife Branch, Toronto. 121 pp.

seau 1987). Life history traits such as late sexual maturity, high natural mortality of juveniles and sensitivity to fishing gear have not allowed rapid recovery of stocks following depletion from past commercial fishing practices (Houston 1987). Today in Ontario, lake sturgeon are common in only a few rivers within the Hudson Bay watershed. A potential threat to the remaining lake sturgeon populations is hydroelectric development of rivers. Water level fluctuations between dams leading to

Please indicate author’s corrections in blue, setting errors in red 148140 EBFI

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246 periodic flooding or de-watering of river margins have caused decreased production and the loss of fish species including the lake sturgeon from some reaches (Payne 1987). Control of upstream river hydrology, as a result of hydroelectric generation, may also create a stable flow/water level characteristic of a more lacustrine rather than riverine environment. Although no previous study has reported the seasonal migratory behaviour and reproductive patterns of lake sturgeon in a regulated, large river, such information is required to identify critical habitats and susceptibility to entrainment through hydroelectric facilities. In this study, we examined the migratory behaviour and abundance of lake sturgeon on the Mattagami River in northern Ontario over a three year period using radio telemetry. The study location on the Mattagami River was immediately upstream of four hydroelectric stations and represented their headpond. We also determined the seasonal reproductive patterns in sturgeon by measuring the gonadosomatic index (GSI) and circulating levels of reproductive steroids. These data were used to identify their susceptibility to entrainment at the initial hydroelectric facility (Little Long generating station) and to determine the reproductive behaviour of lake sturgeon.

Materials and methods Study site The study was conducted over a three year period (1989–1991) on the Mattagami River, approximately 75 km north-east of the town of Kapuskasing, Ontario (Figure 1). The Mattagami River, located within the Moose River Basin in northeastern Ontario, is 491 km in length and drains a basin area of 41 672 km2 (Brousseau & Goodchild 1989). Tributaries flowing into the Mattagami include the Groundhog and Kapuskasing rivers. Fish were collected in a 52 km stretch of the Mattagami River between the Little Long Generating Station and Cypress Falls and an area 7 km upstream of the confluence of the Mattagami and Groundhog rivers. These areas of the Mattagami and Groundhog riv-

ers are regulated by the operation of four, downstream located, hydroelectric stations. Water levels in these areas are controlled and varied less than a metre per year. Unregulated areas of the Mattagami and Groundhog rivers have been known to vary up to five metres within a calender year.

Sampling protocol – migratory behaviour Seasonal migratory behaviour was determined using both radio telemetry and conventional gill netting procedures. Because only a few adult lake sturgeon could be radio tagged, data from these fish were only used to approximate direction of movement within the calender year. Netting practices served to approximate the relative abundance of adult sturgeon at various locations within the study site over one calender year. Only adult lake sturgeon, approximately one metre in length, were radio tagged. These fish were collected alive using gill nets (15.2 m × 1.8 m panels – 20.3 cm stretched mesh). The radio telemetry procedures used in the present study followed the general protocol outlined in McKinley et al.2 A total of 29 adult lake sturgeon of both sexes (mean weight 10.12 ± 2.3 kg, length 121.1 ± 11.1 cm) captured in June (1989) and October (1989) were fitted with external mounted radio transmitters manufactured by Lotek Engineering Inc. (Newmarket, Ontario). Each of these uniquely coded transmitters broadcasted at frequency intervals of 10 kHz within an operating band of 50.000 to 51.999 MHz. Transmitters emitted signals once every second. In addition, ten of the radio tags also monitored water temperature. Transmitters weighed less than 1.5% of the weight of the fish. Movements of individual radio tagged sturgeon were monitored for approximately 28 months. Movement was monitored monthly during the winter, weekly during the spring, and bi-weekly during 2 McKinley, R.S., A.E. Christie, R. Evans & R. Sheehan. 1990. Seasonal distribution and movement of radiotagged walleye and lake sturgeon in the vicinity of the proposed Mattagami Hydroelectric Extension. In: Proceeding Canadian Electrical Association Annual Meeting, March 1990, Montreal (extended abstract).


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Figure 1. The study site. Grids 1 to 13 represent 4 km long segments of the study site which were fished using gill nets in order to estimate the distribution of lake sturgeon at various times during the open water period (May–November).

the summer and early fall using a radio receiver/data logger aboard a fixed wing aircraft. The scan rate for each radio frequency was four seconds. All detected frequencies were recorded on a map of the study area (scale 1:50 000) in Universal Mercator Units (UTM). The error associated with location determinations of detected radio signals using the aircraft was estimated to be ± 150 metres (McKinley et al.2). This estimate was determined under icefree conditions at water temperatures of 5 and 10° C. Relative abundance and location within the study site was determined from systematically netting 13 sampling blocks, each approximately 4 km long (Figure 1) during the open water period. Values were reported as a percent of the monthly catch per unit effort (CUE) in each sampling block. The majority of the 13 sampling blocks were on the Mattagami River; one additional sampling blocks was located on the Groundhog River. Sampling oc-

curred at monthly intervals and the entire study site was fished over a 5 day period. A minimum of three 15 m gill net panels with stretched mesh sizes of 7.6 cm (1 panel) or 20.3 cm (two panels) were set overnight at selected sites within each block. Each of these mesh sizes were adequate for sampling adult lake sturgeon. No collections were made from mid-July until September because of a concern that sturgeon would not survive in the gill nets overnight due to elevated water temperatures. Ice formation prevented collection of fish in blocks 10–13 in November. Data were expressed as catch per unit effort (CUE = number of fish per 24 h sampling).

Sampling protocol – GSI and steroid hormone analyses GSI determinations, gonad weight/total body weight × 100, were from individuals collected at


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248 monthly intervals (July to November) throughout the study site. Additional samples were also collected from fish in the area of a potential spawning site (Cypress Falls) during the spawning period over a two week period. Fish at this site exhibited spawning behaviour in terms of rolling on the surface, some males were ripe and some of the females were partially ovulated; these characteristics were not observed in fish from other sampling locations. A blood sample (3 ml) was collected from these fish by caudal puncture using heparinized syringes. Plasma was collected following centrifugation and frozen prior to hormone analyses. Plasma samples were extracted with diethyl ether prior to measurement of reproductive steroids by radioimmunoassay (RIA). The plasma content of 17β-estradiol and 11-ketotestosterone was determined using the methods described by Van Der Kraak et al. (1990) and Wade & Van Der Kraak (1991), respectively. Testosterone was measured using an antiserum purchased from ICN Biomedicals (St. Laurent, Que.) according to the protocol described by Van Der Kraak et al. (1984). This antiserum cross-reacts 100% with testosterone, 19% with 5α-dihydrotestosterone, 4% with 11-ketotestosterone, 0.6% with androstenedione and less than 0.1% with 17β-estradiol. Serial dilutions of extracted sturgeon plasma sera were parallel to the standard curves in each of the steroid assays (data not shown). Intra-assay and inter-assay variability as determined by repeated measurement of an extracted serum pool were less than 5% and 15%, respectively, for each of the assay systems. All serum samples were assayed in duplicate.

Statistical analyses Reproductive data were pooled over the three years and differences in GSI and steroid hormones among sampling intervals were tested using ANOVA. Assumptions of constant variance and normality of errors were examined and appropriate transformations (log) were made if these assumptions were not satisfied. Significant differences (p < 0.05) were detected using the LSMEANS test (Steele & Torrie 1980).

Results Seasonal migratory behaviour Lake sturgeon initiated an upstream migration in January (Figures 2, 3). This pattern continued through to May. The initial upstream movement was directed at Whist Falls, located on the Groundhog River, and Cypress Falls, located on the Mattagami River. Spawning activity, an accumulation and rolling of adult lake sturgeon in shallow water, was only observed at Cypress Falls. Similar habitat characteristics (i.e. substrate, water velocity) are found at Whist Falls and may represent a second spawning site. There was also no evidence that sturgeon migrated to different spawning sites (Cypress or Whist Falls) in alternate years. The appearance of sturgeon at these locations in May coincided with a water temperature of 8–10° C. Lake sturgeon dispersed downstream toward the Little Long Generating Station as water temperatures approached 13° C (Figures 2, 3). The downstream dispersal of sturgeon continued throughout the summer where the majority of individuals could be found in the forebay of the Little Long Generating Station. These fish began a second annual upstream migration in September towards their initial point of movement back in January. The area where sturgeon preferred to ‘hold-up’ for the late fall period was located on the Groundhog River. This stretch of the Groundhog River had an average depth of 10 m and a sand/silt substrate. Estimates of relative abundance and location of fish throughout the study site, based on CUE (Figure 4), were similar to the movement of sturgeon using radio telemetry. The highest number of fish were caught at Cypress Falls in May. In June, fish were evenly distributed among the sampling blocks. By July, sturgeon had concentrated towards the northern boundary of the study site (blocks 1–7), within 10 km of the forebay of the Little Long hydroelectric station. By the fall, sturgeon were concentrated in the southern most study blocks on the Groundhog River; this was consistent with the localization of fish as determined by radio tracking.


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Figure 2. The rate of movement of radio tagged lake sturgeon in relation to their presumed spawning sites at Cypress Falls and Whist Falls. Values are reported as the monthly mean distances (km per day ± SEM, N) travelled by individual fish in an upstream or downstream direction relative to either Cypress Falls or Whist Falls.


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Figure 3. Summary of the annual migratory patterns of lake sturgeon in relation to their presumed spawning sites at Cypress Falls and Whist Falls. Arrows indicate the general direction of radio tagged individuals throughout the year.

Reproductive pattern Reproductive hormone levels and the gonadal condition of adult male (mean weight 7.9 ± 1.5 kg, length 109.3 ± 10.0 cm) and female (mean weight 12.4 ± 3.3 kg, length 120.6 ± 13.1 cm) lake sturgeon collected over a 3 year period are shown in Figures 5 and 6. Preovulatory female and spermiating male lake sturgeon were caught on the spawning grounds (Cypress Falls) shortly after ice breakup (mid May). The actual spawning period was short as fish caught in late May were in post-spawning condition. The GSI and plasma testosterone and 11- ketotestosterone levels in male lake sturgeon were highest in pre-spawning fish and had declined to low levels in post-spawning fish by late May. Samples collected throughout the summer and fall were likely from a mixed population of potential spawners and regressed individuals. In this mixed population, male lake sturgeon GSI’s were generally higher

than those of spent fish and the September sample GSI was not significantly different than that of the pre-spawning fish sampled. A similar pattern was observed in the plasma levels of testosterone and 11-ketotestosterone which were at near pre-spawning levels in the mixed population most of the summer but were lower in October. Circulating levels of 17β-estradiol were low in male lake sturgeon and did not change on a seasonal basis. The GSI and reproductive hormones (testosterone, 11-ketotestosterone, 17β-estradiol) in female lake sturgeon decline abruptly from their highest levels in prespawning fish to low levels in post spawned fish. In August and September there was an indication that plasma testosterone and 17β-estradiol levels were higher and this matched a slight but a nonsignificant increase in the GSI.


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Figure 4. Relative distribution of lake sturgeon throughout the study site based on monthly collections of fish using gill nets. Values are reported as the % of the monthly catch per unit effort (CUE) in each of 13 sampling blocks described in Figure 1. The N values represent the total number of fish collected in each monthly sampling period.


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252 Discussion Information on lake sturgeon movements has been vague. The two procedures used in our study, radio telemetry and conventional netting practices, indicated that lake sturgeon utilized the entire study site extending from Whist Falls on the Groundhog River and Cypress Falls on the Mattagami River to the forebay of the Little Long Generating Station. The distribution of fish throughout the study site varied on a seasonal basis and was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River. In general, this migratory pattern was similar to that reported for other northern Ontario lake sturgeon populations based on previous mark-recapture studies (Threader & Brousseau 1986, Nowak & Jessop 1987, Sandilands 1987). Priegel & Wirth3, based on capturemark-recapture survey in Lake Winnebago, Wisconsin, found that sturgeon travel widely but have a home basin. Mosindy & Rusak4, using radio telemetry, indicated that sturgeon in Rainy River, Ontario, travelled between 5 and 25 km during the spring and summer. Hay-Chmielewski5, using radio telemetry, concluded that lake sturgeon did not exhibit a home range in Black Lake, Michigan, but exhibited a wide range of daily movements. Threader & Brousseau (1986) found that most sturgeon in the Moose River remained within 5 km of the tagging site whereas Sandilands (1987) reported movement of 130 and 180 km for fish in the Kenogami River in northern Ontario. Nowak & Jessop (1987) reported

3

Priegel, G.R. & T.L. Wirth. 1971. The lake sturgeon. Its life history, ecology and management. Wisconsin Department of Natural Resources, Publ. 270-70, Madison. 20 pp. Figure 5. The gonadosomatic index of male and female lake sturgeon collected during the open-water period. Values are reported as the mean ± SEM with the n values indicated and represent pooled data from fish collected during the 1989–1991 field seasons. Sampling times with similar GSI values, as determined by the LSMEANS test (p > 0.05), are identified by the same superscript.

4

Mosindy, T. & J. Rusak. 1991. An assessment of lake sturgeon populations in Lake of the Woods and the Rainy River 1987– 1990. Lake of the Woods Fisheries Assessment Unit Report 1991:01, Ontario Ministry of Natural Resources, Toronto. 66 pp. 5

Hay-Chmielewski, E.M. 1987. Habitat preferences and movement patterns of the lake sturgeon (Acipenser fulvescens) in Black Lake, Michigan. Michigan Department of Natural Resources, Fisheries Division, Fisheries Research Report No. 1949, December 1987. 39 pp.


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Figure 6. Plasma sex steroid levels in male and female lake sturgeon during the open-water period. Values are reported as the mean ± SEM and represent pooled data from fish collected during the 1989-1991 field seasons; the numbers of samples at each time point are as reported in Figure 1. Sampling times with similar steroid levels, as determined by the LSMEANS test (p > 0.05), are identified by the same superscript.

movement of 6-20 km for sturgeon in an area just south of the present study site. Defining the migratory behaviour of lake sturgeon within our study site was complicated by movement of fish towards two different sites in the spring. The periodicity, relative speed and direction however, was similar between the two sites. Spawning behaviour was only observed at Cypress Falls. The physical characteristics of Cypress Falls, including a cobble/bedrock substrate, substantial back-eddy area and a water velocity exceeding 0.5 m s−1 also occurred at Whist Falls. At Cypress Falls, sturgeon were most abundant just outside the main channel at depths of < 2.5 metres. Optimum spawning temperatures for lake sturgeon have been reported to be between 13–18° C (Scott & Crossman 1973). Sturgeon dispersed downstream after a very short stay at Cypress Falls (3–4 days). We found that water temperature changed rapidly during the spring freshet and that

adults had left Cypress Falls area before water temperatures rose above 13° C. The downstream dispersal of sturgeon following suspected spawning is likely a feeding migration since sturgeon do not feed during spawning (Houston 1987), relying instead on lipid stores. Most movement occurred outside the summer season. The decreased rate of movement observed during the summer in the present study was likely due to the high water temperatures (17–23° C) recorded in July and August. Locomotory activity of lake sturgeon in the field has been shown to decrease dramatically as water temperature approaches 19° C (McKinley & Power 1991). Furthermore, Ono et al. (1983) reported that lake sturgeon are not usually found in waters much above 23° C. We found lake sturgeon were easily stressed, hemorrhaging about fins and eyes, when handled during the summer months. The only mortality occurred during collection events in July and August.


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254 It is generally perceived that sturgeon are intermittent spawners (Roussow 1957, Magnin 1966). Studies in northern Quebec suggest that females spawn every four to six years and males every two to three years (Magnin 1966). Evidence for spawning periodicity appears to stem from the spacing of the annuli in the pectoral fin ray cross sections. According to Roussow (1957), the growth in the years just prior to spawning is quite slow, resulting in a series of annuli located very close together. After spawning, growth rate is increased as well as the spacing of subsequent annuli. The pattern is repeated once the fish resumes the production of sex products. Evidence for this pattern is reported to vary with locality (Houston 1987). The failure of some fish to mature may be related to the level of somatic depletion suffered during the previous period of recrudescence as well as factors such as food availability and general health. On the basis of the systematic fishing of the study site on the Mattagami River, it appears that about 50% of adult sturgeon collected in May were found in the vicinity of a potential spawning location (Cypress Falls). In a related study, we found that 16/18 males and 13/16 females collected at Cypress Falls during early May were in prespawning condition (Van Der Kraak & McKinley unpublished). Collectively, these data suggest that once they have attained maturity, sturgeon in the Mattagami River may spawn in alternate years. In this respect, this population of sturgeon on a highly regulated river may differ from other populations described in the literature which are believed to spawn at 4–7 year intervals (Goyette et al.6, Fortin et al.7. There may be an underlying nutritional basis to this difference 6

Goyette, D., S. Gueńette, N. Fournier, J. Leclerc, G. Roy, R. Fortin & P. Dumont. 1988. Maturite´ sexuelle et pe´riodicite´ de la reproduction chez la femelle de l’Esturgeon jaune (Acipenser fulvescens) du fleuve Saint-Laurent. Que´bec, Ministe`re du Loisir, de la Chasse et de la Peˆche, Service de l’ameńagement et de l’exploitation de la faune, Montreál, Rapp. trav. 06-02. 84 pp. 7 Fortin, R., S. Gueńette & P. Dumont. 1992. Biologie, exploitation, mode´lisation et gestion des populations d’Esturgeon jaune (Acipenser fulvescens) dans 14 re´seaux de lacs et de rivie`res du Que´bec. Que´bec, Ministe`re du Loisir, de la Chasse et de la Peˆche, Service de l’ameńagement et de l’exploitation de la faune et Service de la faune aquatique, Montreál et Que´bec. 213 pp.

as lake sturgeon from this location had significantly higher plasma nonesterified fatty acid levels which could be used as an energy substrate than sturgeon from downstream locations (McKinley et al. 1993). This study revealed a marked difference in the pattern of gonadal recrudescence in male and female lake sturgeon. Female lake sturgeon exhibit a prolonged period of gonadal regression following spawning. Resumption of ovarian development was not evident until September. This pattern is consistent with the majority of spring spawning, cold temperate freshwater species in which gonadal recrudescence begins in the fall and continues through the winter and early spring (MacKinnon 1972, Craig 1977, Diana & Mackay 1979, Peter & Crim 1979). In contrast, testicular recrudescence began within one month of spawning and the gonadosomatic index was at the prespawning level by September. Other exceptions include mooneye, Hiodon tergisus (Glen & Williams 1976) and goldeye, Hiodon alosoides (Pankhurst et al. 1986) which exhibit a similar pattern of rapid gonadal recrudescence following spawning with much of the gonadal growth completed by October. Measurement of circulating sex steroid levels provided additional evidence for a divergent pattern of ovarian and testicular development in lake sturgeon. In male sturgeon, circulating androgen levels were high in pre-spawning fish and decreased dramatically by the end of May. In the mixed population, elevated testosterone and 11-ketotestosterone levels through the period from June to September paralleled the pattern of testicular recrudescence. The histological appearance of the testis was not assessed so it is not possible to comment on the status of testicular development, although both of these hormones are known to regulate spermatogenesis in teleosts (Fostier et al. 1982). The observation that circulating levels of both hormones were reduced in October raises the possibility that male sturgeon may experience two distinct periods of elevated androgen levels. The high levels in summer may be associated with the initiation of spermatogenesis and high levels at spawning may be associated with spermiation. Resolution of this issue will necessitate the collection of samples in winter months.


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255 The hormone changes in female lake sturgeon parallel what has been described in a large number of freshwater teleosts. The high levels of androgens in female sturgeon during the prespawning period is consistent with studies on a wide array of teleost species including rainbow trout (Scott et al. 1983), coho salmon (Van Der Kraak et al. 1984), white sucker (Scott et al. 1984, McMaster et al. 1991) and goldeye (Pankhurst et al. 1986). Although the precise role of high androgen levels is not well understood, they may function in a positive feedback loop leading to the increased gonadotropin secretion at ovulation (Kobayashi et al. 1989). Levels of 17β-estradiol were elevated in pre-spawning fish and in recrudescing fish in September. The involvement of 17β-estradiol in the stimulation of vitellogenin biosynthesis is well established which suggests that the increased GSI in females in September may reflect the accumulation of yolk by developing oocytes. Hydrologic manipulation of rivers should be planned so as to minimize the risk of entrainment and seasonal disruptions in habitat or food availability. The latter point may be particularly important for lake sturgeon in the Mattagami River since there is only a limited period of gonadal regression and especially in males which exhibit gonadal development throughout much of the year. However, sturgeon in this upstream area of the Mattagami River have enhanced nutritional status (McKinley et al. 1993) and reproductive development (McKinley & Van Der Kraak unpublished). The migratory behaviour of lake sturgeon within the study area makes the species particularly prone to impingement or entrainment, either through the generating station or through the spillway into Adam Creek, during the summer months. The potential for the loss of individuals from the Mattagami River is greatest however during the spring freshet when the station is continuously operated and any excess water is spilled into Adam Creek. Fortunately, both the radio tracking and netting data suggests that the majority of sturgeon are well upstream during freshet and therefore unlikely to be entrained in the spring. Their vulnerability to entrainment may increase if the spring freshet is prolonged into late June when sturgeon are moving towards the station.

Acknowledgements Funding for this study was provided by Ontario Hydro. We are indebted to H.E. Kowalyk and R.W. Sheehan of Ontario Hydro for their assistance in the collection of samples. We also wish to thank J.S. Griffiths and R. Evans of Ontario Hydro for critical reviews of this manuscript.

References cited Brousseau, C.S. 1987. The lake sturgeon (Acipenser fulvescens) in Ontario. pp. 2-9. In: C.H. Olver (ed.) Proceedings of a Workshop on the Lake Sturgeon (Acipenser fulvescens), Ont. Fish. Tech. Rep. Ser. No. 23, Maple. Brousseau, C.S. & G.A. Goodchild. 1989. Fisheries and yields in the Moose River Basin, Ontario. pp. 145–158. In: D.P. Dodge (ed.) Proceedings of the International Large River Symposium, Can. Spec. Publ. Fish. Aquat. Sci. 106. Craig, J.F. 1977. The body composition of adult perch, Perca fluviatilis in Windermere, with reference to seasonal changes and reproduction. J. Anim. Ecol. 46: 617–632. Diana, J.S. & W.C. MacKay. 1979. Timing and magnitude of energy deposition and loss in the body, liver, and gonads of northern pike (Esox lucius). J. Fish. Res. Board Can. 36: 481–487. Fostier, A., R. Billard, B. Breton, M. Legendre & S. Marlot. 1982. Plasma 11-oxotestosterone and gonadotropin during the beginning of spermiation in rainbow trout (Salmo gairdneri R.). Gen. Comp. Endocrinol. 46: 428–434. Glen, C.L. & R.R.G. Williams. 1976. Fecundity of mooneye, Hiodon tergisus, in the Assiniboine River. Can. J. Zool. 54: 156– 161. Houston, J.J. 1987. Status of lake sturgeon, Acipenser fulvescens, in Canada. Can. Field Nat. 101: 171–185. Kobayashi, M., K. Aida & I. Hanyu. 1989. Involvement of steroid hormones in the preovulatory gonadotropin surge in female goldfish. Fish Physiol. Biochem. 7: 141–146. MacKinnon, J.C. 1972. Summer storage of energy and its use for winter metabolism and gonad maturation in American plaice (Hippoglossoides platessoides). J. Fish. Res. Board Can. 29: 1749–1759. Magnin, E´. 1966. Recherches sur les cycles de reproduction des esturgeons (Acipenser fulvescens Raf.) de la rivie`re Nottaway tributaire de la baie James. Verh. intern. Verein. Limnol. 16: 1018–1024. McKinley, R.S. & G. Power. 1991. Measurement of activity and oxygen consumption for adult lake sturgeon (Acipenser fulvescens) in the wild using radio-transmitted EMG signals. pp. 307-–318. In: I.G. Priede & S.M. Swift (ed.) Wildlife telemetry – Remote Monitoring and Tracking of Animals, Ellis Horwood Limited, West Sussex. McKinley, R.S., T.D. Singer, J. S. Ballantyne & G. Power. 1993. Seasonal variation in plasma nonesterified fatty acids of lake


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