The populations of fish in the River Tees system on the Moor House National Nature Reserve, Westmorland

The age, growth, population densities and annual production of an isolated population of brown trout ( Salmo trutta L.) and bullhead ( Coitus gobio L.) were investigated over a 5 year period in Trout Beck in the northern Pennines. Additional data were obtained from two other sites; Great Dodgen Pot Sike and the River Tees.
Trout growth rates were low, particularly in Dodgen Pot Sike, but ages up to VIII were recorded. Bullhead growth rates were similar to those in the Tees at Cow Green (Crisp et al. , 1974), though the Moor House bullheads had a higher survival rate. Population densities of trout ranged from 0.10–0.22/m², with a fry contribution of 0.80%. The bullhead population in Trout Beck was sparse, generally 0.1/m², though an 0 group value of 0.46/m^a was estimated in 1967. At Tees Bridge values ranged from 2.5–7/8/m². Most trout matured by age III, though in Great Dodgen Pot Sike only half of the females were mature at age IV.
Annual production was estimated from Allen graphs. Trout production ranged from 1.02–3.50 g/m²/year, the fry contributing up to 51.5% of the total. A value of 0.48 g/m²/year was obtained for bullheads in the Trout Beck system in a year of good recruitment, whilst bullhead production at Tees Bridge was 7.43 g/m²/year, with fry and I group contributing 48.7 and 37.5% respectively. The high survival rate, irregular recruitment, and poor growth of these high altitude populations is discussed. Growth and reproductive peculiarities of the Great Dodgen Pot Sike trout are also discussed.     

Influence of water depth on dispersion of juvenile salmonids, Salmo salar L. and S. trutta L., in a Scottish stream

The dispersion of salmon and trout of 0 +, 1 + and 2 + age classes was examined by electrofishing 12 sections of a stream in Perthshire, Scotland at the end of the growing season in September to October in 1972 and 1976. In 1972 sections ranged in surface area from 21 to 122 m² and had volumes of 5.0–17.3 m³ and when surveyed in 1976 surface areas were 15–106 m² and volumes 2.1–6.7 m³. In 1976 widths and areas of sections were 63–87% of the values for 1972, depths were 39–68% and volumes 28–52% of the earlier values. These differences were due to 1976 being drier and warmer. In both years, all sections contained 0 + and 1 + age classes of salmon and trout and some sections contained 2 + age salmon and trout. The total density of fish in a section ranged from 1.9 to 3.9 m⁻² in 1972 and from 3.72 to 6.08 m⁻² in 1976. There was an inverse relationship, significant in 1972 only, between the density of 0 + salmon and that of 1 + trout in the different sections. Densities of both 0 + and 1 + salmon in the sections were inversely correlated, and those of 0 + and 1 + trout were directly correlated, with area of water deeper than 10 cm.     

Juvenile salmonid production in a Lake Erie nursery stream

Normandale Creek (2531m²) provides spawning and nursery grounds for lake-run rainbow trout, Salmo gairdneri Richardson, brown trout, Salmo frutta L. , and coho salmon, Oncorhynchus kisutch (Walbaum). Upstream movements are significantly correlated with peak stream discharge (P < 0.05). In 1973–1974, 59 adult salmonids constructed 86 nests of which 60% were disturbed by re-use or sand deposition. From a calculated deposition of 90 400 ova, 483 juveniles, 6 cm in fork length ( f.l. ), were resident in the stream when estimates by electrofishing first became valid. Estimated within-stream (i.e. all sections combined) monthly densities of wild juveniles >6 cm f.l. ranged from six to 22 fish (100 m²)⁻¹, and biomass from 1.3 to 3.1 gm⁻². The highest within-section biomass was 8.3 gm⁻² in November. Additions of hatchery-reared rainbow trout temporarily increased monthly within-stream juvenile density up to 23 fish (100 m²)⁻¹, and biomass to 8.2 g m⁻². Density and biomass were positively correlated (P < 0.05) with both instream and bank cover, and biomass negatively correlated (P < 0.05) with gradient. The importance of substratum and flow characteristics on juvenile density and biomass was strongly indicated although not statistically significant. Annual within-section production of juveniles > 6 cm f.l. ranged from 4.79 to 5.93 g m⁻² year⁻¹ in Sections III and IV, respectively. Inclusion of calculated probable numbers of fish < 6 cm f.l. increased within-section production from 5.93 to 18.65 g m⁻² year^−l in upstream Section IV.     

The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Yolk-sac pike fry were stocked at densities of 0.74 – 81.4 m⁻² in two ponds, each divided into eight sectors (mean area 155.8 m²). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size-range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density-independent but switched by late June/July to density-dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May-July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm⁻² and in Pond 2 was 3.49gm⁻².
Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m⁻².
Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m⁻² is advised if large, density-dependent mortalities are to be avoided.     

Stocking experiments with 0 + and 1 + trout parr, Salmo trutta L., of wild and hatchery origin: 1. Post-stocking mortality and smolt yield

Wild and hatchery-reared 8–12-month-old (5–8 cm) trout, Salmo frurta L., were stocked in tributaries of the River Gudenb. Mortality was examined by means of electrofishing. Repeated electrofishing and handling caused a small increase in mortality. The daily instantaneous mortality rate Z was high during the first 2 months after stocking, ranging from 0.0070 for wild trout to 0.0326 for domestic trout at a stocking density of one trout per m² and from 0.0206 (wild trout) to 0.0888 (domestic trout) at a stocking density of two trout per m². Two months after stocking, Z decreased drastically ranging from 0.0007 (wild trout) to 0.0067 (domestic trout). When stocked, first-generation hatchery trout showed Z equal to domestic trout. Wild trout resident in the experimental stream were negatively affected by the introduction of domestic trout and wild trout from another stream. at a stocking density above the carrying capacity. It is concluded that the higher mortality of domestic trout was caused by changes in food, feeding and exercise, possibly combined with the lack of selection in the hatchery. Smolt yield at age 2+ was 3.2% (0+ trout stocked in the fall)-7.0% (1 + trout stocked in the spring) of the domestic trout stocked (approx. one-sixth to one-third of natural populations) and 65.2–68.7% of the domestic trout present before the smolt run. For first generation hatchery trout of wild origin the corresponding figures were 7.3% (age 0 +) and 93.4%, and for wild trout introduced to the experimental stream they were 11.1% (age0 +)and39.8%.     

Density-dependent mortality of trout fry (Salmo trutta L.) and its relationship to the management of small streams

The natural mortality rate of trout fry and the impact of weed cutting and cleaning out of weeds, branches and twigs from the stream-bed upon the mortality rate of trout fry was studied on several reaches in small streams. Above an initial density of 3.1 fry m^–2 natural mortality rate was found to be density-dependent in the first few months of life. In reaches where weed cutting and cleaning out of the stream-bed had taken place the mortality rate was higher than that found under natural conditions in undisturbed reaches. The results support the suggestion that stream management works which make the stream more uniform will be in conflict with sound fishery management.     

Episodic exposure to acid and aluminium in soft water: survival and recovery of brown trout,Salmo trutta L.

Yolk-sac fry, swim-up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l⁻¹ (323 μg l⁻¹), minimum pH 4.5, total duration up to 54 h (yolk-sac fry) or up to 78 h (swim-up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l⁻¹ (0–8 mg l⁻¹) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk-sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk-sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.     

Quantitative Ultrastructural Investigations on Synaptogenesis in the Cerebellum and the Optic Tectum of Light-Reared and Dark-Reared Rainbow Trout (Salmo gairdneri Rich.)

The morphogenetic differentiation of synapses in the cerebellum and the optic tectum of darkand light- reared rainbow trout was investigated at critical stages of development. During normal differentiation the cerebellum is characterized by the appearance of 'indented', spinelike synapses. This type of synapses increases with age and prevails from day 60 on. At the same time the number of 'flat' synapses decreases. In the cerebellum the highest synaptic density (123 ± 12 synapses/1,000 μm²) is reached 30 days after hatching when the larvae begin to swim. The optic tectum is characterized by a preponderance of flat synapses in early postnatal and adult life; maximal synaptic density (66 ± 5 synapses/1,000 μm²) is reached 60 days after hatching when the larvae have reached optimal visual acuity.
Light deprivation causes a considerable and significant reduction in the number of synapses per unit area in the cerebellum and the optic tectum. The length of synaptic contacts do not change. If light-deprived, the density of synaptic vesicles decreases significantly in the optic tectum of a 25-day-old trout (74 ± 3 instead of 132 ± 7 vesicles/μm²). In the cerebellum this effect is absent.     

Benthic macroinvertebrates of a fluctuating reservoir

SUMMARY. Benthic macroinvertebrate distribution, abundance, and composition were observed in a fluctuating (7.7 m) central Wisconsin, U.S.A., reservoir during 1973–74. Chironomidae and Oligochaeta represented 98% of the total fauna by number. The chironomid, Chironomus plumosus , and an oligochaete, Limnodrilus , each averaged 36% of the total benthic biomass. Annual mean numbers and biomass in areas exposed to air, exposed to ice cover, or remaining inundated were 3025/m² (1.8g/m²), 4311/m² (4.5g/m²), and 8558/m² (16.0 g/m²), respectively. A substantial portion of the benthic fauna was stranded and subsequently decreased rapidly in drying and frozen substrates exposed to air. Total benthic numbers and biomass were greatest immediately below the drawdown limit.
Recolonization required 3 months (mid-March to mid-June, 1974) to attain pre-drawdown values for numbers and biomass, and subsequently both were greater after reinundation than before the substrate was exposed. Recolonization of areas exposed to the air was greater in substrates containing large amounts of organic matter than in sandy areas containing little organic matter. Sorting and transportation of sediments redistributed organic materials from the regulated zone to below the drawdown limit, and macrophytes were eliminated from the regulated zone. When compared to other reservoirs and lakes, the density of benthos in the Big Eau Pleine Reservoir is neither high nor low. However, when compared with non-fluctuating reservoirs the number of Ephemeroptera, Plecoptera, Trichoptera, Amphipoda, and Gastropoda was low.     

The production of brown trout, Salmo trutta in tributaries of the Upper Wye, Wales

The population density, age structure, biomass, growth and production of brown trout were investigated in four tributaries of the upper River Wye. The populations at each site were largely maintained by immigration from nursery areas. Abundance of separate year classes at sites on the three largest tributaries reached a peak at age 2+. On the smallest stream numbers reached a peak at 1+. Recruitment occurred throughout the year but decreased with age of year classes. Maximum O+ densities ranged from 0.04 to 0.89 m⁻², and >0+ densities from 0.13 to 0.59 m⁻². Average total biomass in 1975 ranged from 2.6 to 14.2 g m⁻². Within the study sites annual trout production in 1975 ranged from 2.9–19.7 g m⁻². Production values were dependent on age structure and population mobility at the study sites. In the three largest streams 2+ and 3+ fish contributed 66.3–88.3% of total production whilst 1+ and 2+ fish contributed 74.5–84.5 % of the total in the smallest stream. The mobile (non-resident) component of the population accounted for up to 60–70% of production at certain times of the year, but over the year (1976) accounted for =30 % of total production. The resident component of the highest annual production value (19.7 g m⁻²) was estimated to be between 15.0 and 18.2 g m⁻².     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

Reproductive and histopathological effects of long-term experimental exposure to bis(tributyltin)oxide (TBTO) on the three-spined stickleback, Gasterosteus aculeatus Linnaeus

Three-spined sticklebacks, Gasterosteus aculeatus Linnaeus, were exposed to 0, 0.1, 1.0, 2.5 and 10 μg bis(tributyltin)oxide (TBTO) 1⁻¹ for up to 7.5 months in a flow-through system of sea water. As early as 4 weeks after the start of the experiment, fish from the 10 μg TBTO 1⁻¹ group showed diminishing appetite, increasing lethargy and opaque eyes. The mortality in this group after 2 months of exposure was 80%. No significant differences between the control and the exposed groups were noted concerning fecundity, hatched fry and frequencies of malformed fry. The gonad somatic index (GSI) was determined before and during the spawning period. GSI in control fish increased significantly, while that in the exposed groups remained unchanged between the two sampling occasions. Structural examination of the gills from fish exposed for 2 months to 10 μg TBTO I⁻¹ revealed fusion between secondary lamellae and gradual cell degeneration. The chloride cells were characterized by degenerating mitochondria. Hepatocytes in fish exposed to 2.5 and 10 μg TBTO I⁻¹ contained an increased number of lipid-containing vacuoles and the nucleoli were disorganized and fragmented.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

The trout (Salmo trutta) population of the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales

Data are presented from a 10-year (1984 to 1993) study of a Salmo trutta population in the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales. The stream is a spawning and nursery area for sea trout. Growth of trout within the stream can be summarized by a von Bertalanffy growth coefficient ( K ) of 0·310, with asymptotic length (1∞) 21·6 cm and with length at age 1 of 7·6 cm. Mean population density in the whole stream varied from year to year between 0·05 and 0·60 0-group trout m⁻² and between 0·05 and 0·70 older trout m⁻². Mean biomass varied, between years, from 0·1 to 3·5 g m⁻² for 0-group and from 1·3 to 10·4g m⁻² for older trout. Loss between 3 and 5 months of age appeared to be proportionate at about 50 to 60% and instantaneous loss rate from 5 to 53 months of age varied from 0·04 to 0·10 month⁻¹ and was positively correlated with cohort number at 3 months of age. Production between 3 and 53 months of age varied between cohorts from 3 to 8 g m ⁻² live weight.     

The forest of Vorsø, Denmark: Succession towards a natural, decidous boreal forest influenced by breeding cormorants

The forest on the strictly protected island Vorsø in Horsens Fjord has since 1952 been examined every ten years to discover the number, basal area, wood volume and aboveground biomass of the species. This paper describes the results from 1982 and the development up to that. The dominating species are Fraxinus excelsior, Ulmus glabra and Fagus sylvatica. The two forests, "Vesterskov" (6.09 ha) and "Østerskov" (2.48 ha) respectively, were, in 1982, still immature. Their number of stems per ha were: 756 and 509; basal area: 38 m² and 45 m². volume: 544 m³ and 615 m³; biomass 207 t and 268 t. The annual increase 1972–1982 was respectively 8.8 m³/ha and 0.3 m³/ha. The impact of the cormorant ( Phalacrocorax carbo sinensis ) is especially in "Østerskov" increasing, since the colony here was established in 1976. The succession of the forest is discussed in relation to the disturbance by the cormorants.     

Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

The Abundance of Different Peritrich Ciliates on Stone Surfaces in Contrasting Lowland Streams Throughout the Year

ABSTRACT. Pentrich ciliates attached to small stones from the beds of two streams, one large with hard water, the other small with soft water, were enumerated throughout an annual cycle. Throughout the year, Platycola was the dominant peritrich in both streams, except for a brief period during the spring when Vorticella and Carchesium predominated. Vorticella reached peak levels of 89 ciliates cm² of stone surface, and up to 102 Platycola per cm² of stone surface were found. Mean volumes of samples of the main species were calculated, and used to estimate the standing stock biomasses. using a standard value of dry weight per unit volume. Published values of the growth rates of representatives of the main genera were used to estimate production values, which totalled about 6.5 g dry weight of peritrich cytoplasm/m² of stream bed per annum in the large stream (mean annual density = 8.3 peritrichs/cm² of stone surface), and 33 g dry weight/m² of stream bed per annum in the small stream (mean annual density = 47 peritrichs/cm² of stone surface). Food supply, temperature and predation were the primary factors determining peritrich abundance     

Recruitment control and production of market-size Oreochromis niloticus with the predator Lates niloticus L. in the Sudan

Experiments were conducted in earth ponds (242–1260m²) to evaluate the Nile perch (Lates niloticus L.) as a predator for recruitment control and the production of marketable Oreochromis niloticus L. in the Sudan. Supply of the predatory fish was maintained by induced spawning of L. niloticus brooders by raising the water level in a 1–0 ha earth pond. Lates niloticus fingerlings (7–5 cm total length) were then stocked with same size O. niloticus at the ratios 1:5, 1:10 and 1:15, Lates:Oreochromis , respectively. Over a period of 7 months Lates niloticus reduced young 50g) Oreochromis population and enhanced the production of preferred-size ( 200 g) Oreochromis. The ratio 1:5 Lates:Oreochromis was established to be the most desirable for Lates -with a total production of 0.2428 kg/m² of O. niloticus with 55.7% (by weight) at the target size averaging 287.5g. The ratios 1:10 and 1:15 produced 0.2106 and 0.2153 kg m² of O. niloticus , with 49.4% and 16.9% averaging 235.0 and 210.0 g, respectively.     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.