Winter Survival, Movement, and Bio-energetics of Trout in Tailwater Habitat

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Winter Survival, Movement, and Bio-energetics of Trout in Tailwater Habitat

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1. Winter Survival, Movement, and Bio-energetics of Trout in Tailwater Habitat The Wyoming Game and Fish Department historically stocked large numbers of fingerling trout (< 6”) in various rivers in the state and particularly in tailwater habitats below dams on large rivers in the state. Periodic fish surveys revealed two trends – tailwaters were dominated by relatively large fish (>14”), and a relatively low return of stocked fish. Six different studies were done between We’ve now done 6 specific winter-oriented studies and have learned enough to talk about Winter survival behavior and bio-energetics of trout in tailwater habitat and unregulated streams The Wyoming Game and Fish Department historically stocked large numbers of fingerling trout (< 6”) in various rivers in the state and particularly in tailwater habitats below dams on large rivers in the state. Periodic fish surveys revealed two trends – tailwaters were dominated by relatively large fish (>14”), and a relatively low return of stocked fish. Six different studies were done between We’ve now done 6 specific winter-oriented studies and have learned enough to talk about Winter survival behavior and bio-energetics of trout in tailwater habitat and unregulated streams

2. Tailwaters are known for the big fish they commonly produce – which can be almost magical to anglers But there’s a problem with this picture in terms of the cost to get these fish and the potential to grow more, bigger fish.Tailwaters are known for the big fish they commonly produce – which can be almost magical to anglers But there’s a problem with this picture in terms of the cost to get these fish and the potential to grow more, bigger fish.

3. Contributors Dr. Wayne Hubert, University of Wyoming Dave Zafft, WGFD Darin Simpkins, UW Co-op Unit Lance Hebdon, UW Co-op Unit Christina Barrineau, UW Co-op Unit

4. Natural Winter Survival Strategy Trout seek slow, deep areas (pools) Stream caps with ice, covers with snow Trout wait for spring in a safe, dark environment We can draw on everything we’ve learned to this point to see how natural systems work and why they work Essentially fish park it in the winter – safe from predation, frazil ice, ice collapse With the lights off they don’t move and don’t even think about feeding and tolerate much higher densities of other fish than they would tolerate in the summer Minimize their energy expenditure and Wr doesn’t drop as much as in tailwaters where the cap is off, the lights are on and they feed actively Contrast this to what’s going on in tailwaters The ice cap is off, light is abundant, fish are actively feeding and burning energy faster than they can take it in. Losing more ground than their cousins sitting in the dark and cold mountain streams – and often dieing for their efforts We can draw on everything we’ve learned to this point to see how natural systems work and why they work Essentially fish park it in the winter – safe from predation, frazil ice, ice collapse With the lights off they don’t move and don’t even think about feeding and tolerate much higher densities of other fish than they would tolerate in the summer Minimize their energy expenditure and Wr doesn’t drop as much as in tailwaters where the cap is off, the lights are on and they feed actively Contrast this to what’s going on in tailwaters The ice cap is off, light is abundant, fish are actively feeding and burning energy faster than they can take it in. Losing more ground than their cousins sitting in the dark and cold mountain streams – and often dieing for their efforts

5. How does all of this relate to dams? In most situations, cold water (1C) enters the lake, Ice caps the lake Thermal inversion places warmest water at the bottom We release water from the bottom – and create long stretches of open water subject to ice processes we now know are detrimental The goal is to encourage a downstream ice cap as close to the base of the dam as possible that sets up as early in the fall as possible and stays there all winter This requires releases be as stable as possible since any change up or down can break the cap which opens up the river plus can cause significant problems with ice jams, channel scour, etc. This can be done by releasing water from the top of the reservoir – most dams aren’t designed to do this We recommend multiple penstocks to achieve this objective on all new dams in Wyo (High Savery) A fix is possible, but it’ll cost money How does all of this relate to dams? In most situations, cold water (1C) enters the lake, Ice caps the lake Thermal inversion places warmest water at the bottom We release water from the bottom – and create long stretches of open water subject to ice processes we now know are detrimental The goal is to encourage a downstream ice cap as close to the base of the dam as possible that sets up as early in the fall as possible and stays there all winter This requires releases be as stable as possible since any change up or down can break the cap which opens up the river plus can cause significant problems with ice jams, channel scour, etc. This can be done by releasing water from the top of the reservoir – most dams aren’t designed to do this We recommend multiple penstocks to achieve this objective on all new dams in Wyo (High Savery) A fix is possible, but it’ll cost money

6. Ice actually forms in the air as nucleated crystals that fall back to the surface of the river The crystals then may be pushed to the bottom of the river in turbulent sections or Float to the surface as small to large blocks Or remain in suspension Surface blocks stick together and form cap ice Frazil may form hanging dams if there’s open water upstream from the cap and there’s lots of frazil Frazil forms in super-cooled water = flowing ice. Once cap is formed temperature rises from –0.1C to about 1-2C Ice actually forms in the air as nucleated crystals that fall back to the surface of the river The crystals then may be pushed to the bottom of the river in turbulent sections or Float to the surface as small to large blocks Or remain in suspension Surface blocks stick together and form cap ice Frazil may form hanging dams if there’s open water upstream from the cap and there’s lots of frazil Frazil forms in super-cooled water = flowing ice. Once cap is formed temperature rises from –0.1C to about 1-2C

7. First need a basic understanding of ice concepts and processes Eskimos have over 100 words to describe ice. I’ll only use 3-4 in this talk Shelf ice forms in slow water along stream margins Frazil ice is the floating ice in the channel. It can be either slush or large floating “pans” = pancake ice Anchor ice is frazil ice that sticks to the bottom of the river First need a basic understanding of ice concepts and processes Eskimos have over 100 words to describe ice. I’ll only use 3-4 in this talk Shelf ice forms in slow water along stream margins Frazil ice is the floating ice in the channel. It can be either slush or large floating “pans” = pancake ice Anchor ice is frazil ice that sticks to the bottom of the river

8. This paper is derived from 4 studies done by or for WGFD between 1991 and 1997 Won’t do any of them real justice since each was very complex and contained much more data than I’ll deal with This paper is derived from 4 studies done by or for WGFD between 1991 and 1997 Won’t do any of them real justice since each was very complex and contained much more data than I’ll deal with

9. We began our studies looking at winter survival on the Green River We began our studies looking at winter survival on the Green River

10. We had long stocked over a quarter million small trout of all species (BRN, RBT and CUT) from near Pinedale to Green River But we’d also noted that most of these fish were never heard from again. We knew something was going on but didn’t know what. As good fishery biologists who know everything is related to habitat, we assumed it must be a habitat thing We had long stocked over a quarter million small trout of all species (BRN, RBT and CUT) from near Pinedale to Green River But we’d also noted that most of these fish were never heard from again. We knew something was going on but didn’t know what. As good fishery biologists who know everything is related to habitat, we assumed it must be a habitat thing

11. So we did what we knew best at the time to and that was to improve the habitat as we knew it by placing over 24K tons of rock in the river below Fontenelle Reservoir The rocks sort of worked by attracting large fish, attracting anglers but they didn’t increase numbers of trout. We were still losing lots of stocked fish and didn’t know why. So we launched a study So we did what we knew best at the time to and that was to improve the habitat as we knew it by placing over 24K tons of rock in the river below Fontenelle Reservoir The rocks sort of worked by attracting large fish, attracting anglers but they didn’t increase numbers of trout. We were still losing lots of stocked fish and didn’t know why. So we launched a study

12. Approach Sampled from 1991 to 1994 Three segments Fin clipped all stocked trout Intensive late summer and spring sampling Sampled for 4 years by marking every fish that went into the river and then going back and looking for them Ice processes were “natural” in the upper and lower sections But the tailwater remained open for almost 12 miles below the dam Ice processes did vary from year to year due to weather but we didn’t quantify the changes Sampled for 4 years by marking every fish that went into the river and then going back and looking for them Ice processes were “natural” in the upper and lower sections But the tailwater remained open for almost 12 miles below the dam Ice processes did vary from year to year due to weather but we didn’t quantify the changes

13. The basic result was that we saw lots of variability in fish loss (didn’t know what loss meant, though) We saw higher loss in years of high variability (92-93 We saw less loss in years of flow stability (93-94) We also noted that loss was always highest in the tailwater section This was a mystery since we assumed that this should be the most favorable place for trout due to warmer water (released from the hypolimnion of Fontenelle) We assumed the high loss was associated with flow The basic result was that we saw lots of variability in fish loss (didn’t know what loss meant, though) We saw higher loss in years of high variability (92-93 We saw less loss in years of flow stability (93-94) We also noted that loss was always highest in the tailwater section This was a mystery since we assumed that this should be the most favorable place for trout due to warmer water (released from the hypolimnion of Fontenelle) We assumed the high loss was associated with flow

14. So we looked at flow stability of releases Noted that losses were higher in years when there were 2 or more significant (20% increase or decrease of existing flow) during the winter Noted that losses were less when fluctuations were none or 1. Correlation explained about 60% of losses which we thought was good But we acknowledged that there was still much we didn’t know and needed to know about how river fluctuations might affect fish So we looked at flow stability of releases Noted that losses were higher in years when there were 2 or more significant (20% increase or decrease of existing flow) during the winter Noted that losses were less when fluctuations were none or 1. Correlation explained about 60% of losses which we thought was good But we acknowledged that there was still much we didn’t know and needed to know about how river fluctuations might affect fish

15. What’s going on when flows fluctuate? Loss of slow velocity waters (margins) Loss of aquatic plants (food and cover) Shelf ice can collapse Increased susceptibility to predation Physiological stress We were able to presume some possible sources of loss – some of which we had observed (shelf ice collapse) But most of these ideas were still just guesses and we needed more answers to just what fish were doing in the winter We were able to presume some possible sources of loss – some of which we had observed (shelf ice collapse) But most of these ideas were still just guesses and we needed more answers to just what fish were doing in the winter

16. What happened to the fish? (How do you lose 250,000 trout)? Sampling error ? Did they leave ? Did they die ? But nothing we had in hand explained what happened to the fish Many questions remained But nothing we had in hand explained what happened to the fish Many questions remained

17. Next step was to figure out the behavior and habitat use of the fish we were stocking Perhaps there was a clue there as to what was happening to the fish Next step was to figure out the behavior and habitat use of the fish we were stocking Perhaps there was a clue there as to what was happening to the fish

18. Methods Quantified habitat types Continuously monitored water temperatures (Nov – March) Documented frazil and surface ice formation daily Tracked fish with telemetry Measured habitat availability in fall and winter Measured temperatures Simpkins monitored frazil and surface ice daily – 5-7 a.m. since that’s when frazil is most likely present (often melts by the time most anglers hit the stream in late morning or afternoon) Measured habitat availability in fall and winter Measured temperatures Simpkins monitored frazil and surface ice daily – 5-7 a.m. since that’s when frazil is most likely present (often melts by the time most anglers hit the stream in late morning or afternoon)

19. Telemetry Implanted 20 hatchery and 20 wild trout Documented location every 2-3 days Followed fish for 4 months (November to March)

20. Available Habitat Types Habitat availability didn’t really change from fall through winter – not a real surpriseHabitat availability didn’t really change from fall through winter – not a real surprise

21. Both hatchery and wild trout sought out pool habitat where ever it occurred. They did not spend much time in faster moving water Both hatchery and wild trout sought out pool habitat where ever it occurred. They did not spend much time in faster moving water

22. This slide looks at velocity selection patterns. Different pattern for wild vs. hatchery fish when it came to selection of velocity Wild fish selected slower water as winter went on Hatchery fish showed no pattern This slide looks at velocity selection patterns. Different pattern for wild vs. hatchery fish when it came to selection of velocity Wild fish selected slower water as winter went on Hatchery fish showed no pattern

23. This slide looks at depth selection patterns Hatchery and wild fish showed similar pattern in terms of depth so lumped data Both sought deeper water as winter went on No real surprise here to know that trout generally seek out slower, deeper water as winter progresses – but good to have data that confirm what we suspected intuitivelyThis slide looks at depth selection patterns Hatchery and wild fish showed similar pattern in terms of depth so lumped data Both sought deeper water as winter went on No real surprise here to know that trout generally seek out slower, deeper water as winter progresses – but good to have data that confirm what we suspected intuitively

24. Temp recorders showed there were significant ice events on 8 occasions. Occurred in the middle of winter (Jan/Feb) Temp recorders showed there were significant ice events on 8 occasions. Occurred in the middle of winter (Jan/Feb)

25. Frazil ice events caused fish to: Move frequently Move long distances Remain in secondary habitats for long periods Frazil ice events to fish are like a dust storm to us Make fish move to get out of the abrasive ice – plugs gills, abrades scales and fins Frazil ice events to fish are like a dust storm to us Make fish move to get out of the abrasive ice – plugs gills, abrades scales and fins

26. Where did fish move? To frazil ice shelters Slow water margins – slow enough for shelf ice to form means that most water is flowing past, not through those areas Deep water habitat where frazil, being ice, floats over the top Unfortunately these habitats also are home to the biggest fish in the river too, and some of them may be large enough to eat an occasional smaller trout The largest fish, like the mink, may really like frazil ice events as a way to concentrate their food and minimize the energy they expend to find it – making live all the sweeter at the top of the food chain, and being just one more obstacle for the “have-nots” of the fish world to deal with. Where did fish move? To frazil ice shelters Slow water margins – slow enough for shelf ice to form means that most water is flowing past, not through those areas Deep water habitat where frazil, being ice, floats over the top Unfortunately these habitats also are home to the biggest fish in the river too, and some of them may be large enough to eat an occasional smaller trout The largest fish, like the mink, may really like frazil ice events as a way to concentrate their food and minimize the energy they expend to find it – making live all the sweeter at the top of the food chain, and being just one more obstacle for the “have-nots” of the fish world to deal with.

27. Similar mortality for both wild and hatchery fish Of 11 losses associated with ice events, 4 were killed by mink, 3 were trapped under ice and 4 were never seen again Similar mortality for both wild and hatchery fish Of 11 losses associated with ice events, 4 were killed by mink, 3 were trapped under ice and 4 were never seen again

28. Conclusions Wild fish winter habitat selection didn’t provide an advantage over hatchery fish. Hydraulic habitat isn’t the only thing going on – ice matters!

29. We had answered enough about habitat use and movement but we still didn’t know all we wanted to know about the fate of fish in winter So we launched two more studies. One that looked just at the Bighorn and Another that followed that study and added two more rivers to the analyses (Platte below Grey Reef and Shoshone) We had answered enough about habitat use and movement but we still didn’t know all we wanted to know about the fate of fish in winter So we launched two more studies. One that looked just at the Bighorn and Another that followed that study and added two more rivers to the analyses (Platte below Grey Reef and Shoshone)

30. Focus of this study was on surplus energy – indicator of fish health, well-being Surplus is a function of how much energy is assimilated minus the amount of energy used for basic bodily functions (maintenance energy) Focus of this study was on surplus energy – indicator of fish health, well-being Surplus is a function of how much energy is assimilated minus the amount of energy used for basic bodily functions (maintenance energy)

31. Approach Monthly invertebrate drift samples Described number, size, energy content Collected trout and pumped stomachs Calculated relative weight of trout

32. Monthly mean number of insects in the drift Insects declined through Dec Then increased Although the number of insects in Feb was greater than Sept, they were very small instars Insects declined through Dec Then increased Although the number of insects in Feb was greater than Sept, they were very small instars

33. Monthly mean number of zooplankton in the drift Zooplankton was nonexistent until Dec Then increased markedly as organisms left the reservoir As numbers increased so did their size – but only slightly Zooplankton was nonexistent until Dec Then increased markedly as organisms left the reservoir As numbers increased so did their size – but only slightly

34. Mean monthly energy value of the drift Total energy value declined along with numbers through Nov Increased through winter But most of energy in Dec-Feb was in very small organisms that trout probably couldn’t filter from the water very well Total energy value declined along with numbers through Nov Increased through winter But most of energy in Dec-Feb was in very small organisms that trout probably couldn’t filter from the water very well

35. Mean number of insects and zooplankton consumed This sort of shows up in the consumed data But this is numbers – not energy. While numbers consumed in Feb increased, these were mostly chironomids that didn’t show up in the drift but that were somehow becoming available to foraging fish. Still, these were fairly small and didn’t contribute as much energy as the fish really needed much of the time. This sort of shows up in the consumed data But this is numbers – not energy. While numbers consumed in Feb increased, these were mostly chironomids that didn’t show up in the drift but that were somehow becoming available to foraging fish. Still, these were fairly small and didn’t contribute as much energy as the fish really needed much of the time.

36. Mean monthly energy intake of juvenile trout Looking at energy intake tells more Wild trout got plenty of energy from the drift through Nov Hatchery fish didn’t forage quite as efficiently In Feb, trout did show increased energy consumption – and hatchery fish consumed more energy because they focused on Chironomids – not drift. Looking at energy intake tells more Wild trout got plenty of energy from the drift through Nov Hatchery fish didn’t forage quite as efficiently In Feb, trout did show increased energy consumption – and hatchery fish consumed more energy because they focused on Chironomids – not drift.

37. Why does consumption and energy intake go down when the number of insects goes up? Note that gills capture 2 things – oxygen and food. If inverts are too small to be filtered from the water with gill rakers, fish expend energy capturing them but get no reward for their effortNote that gills capture 2 things – oxygen and food. If inverts are too small to be filtered from the water with gill rakers, fish expend energy capturing them but get no reward for their effort

38. In terms of surplus energy, wild fish were in energy surplus to Nov, then in break-even mode Hatchery fish were in energy deficit until Nov. Then in break-even mode too (not significantly different than wild fish) In terms of surplus energy, wild fish were in energy surplus to Nov, then in break-even mode Hatchery fish were in energy deficit until Nov. Then in break-even mode too (not significantly different than wild fish)

39. Monthly Mean Relative Weight of Juvenile Wild and Hatchery Rainbow Trout Predictably, saw Wr decline through Nov and Dec Hatchery fish declined more and hit low point a whole month earlier than wild fish Decline of 48% is important because one study showed mortality set in at 50% drop in Wr Apparent increase in Wr after Nov/Dec may be misleading considering both groups of fish were in break-even mode at best and probably energy deficit Could be that smallest Wr fish were dieing/leaving which raised the average Wr of fish that survived No data to prove that – just a guess. Predictably, saw Wr decline through Nov and Dec Hatchery fish declined more and hit low point a whole month earlier than wild fish Decline of 48% is important because one study showed mortality set in at 50% drop in Wr Apparent increase in Wr after Nov/Dec may be misleading considering both groups of fish were in break-even mode at best and probably energy deficit Could be that smallest Wr fish were dieing/leaving which raised the average Wr of fish that survived No data to prove that – just a guess.

40. But did the fish starve to death? Efficiency of energy utilization/conversion drops as temps fall below 10C Just like the engine in a car functions less efficiently at cold temps than it does at warmer tempsEfficiency of energy utilization/conversion drops as temps fall below 10C Just like the engine in a car functions less efficiently at cold temps than it does at warmer temps

41. Laboratory study Split into fed vs. not fed groups Swam continuously for 5 months in 7 C water Fish swam at about 1 body length per second In spite of losing over 40% of their relative condition after 5 months without food, no fish died in either treatment during this experiment. If fish mortality occurs it is most likely due to secondary stressors – like moving to slow water habitats where they are unable to escape mortality from ice compaction or predators like mink.Fish swam at about 1 body length per second In spite of losing over 40% of their relative condition after 5 months without food, no fish died in either treatment during this experiment. If fish mortality occurs it is most likely due to secondary stressors – like moving to slow water habitats where they are unable to escape mortality from ice compaction or predators like mink.

42. Some Conclusions Frequency and magnitude of flow fluctuations is related to fish loss Frazil ice events cause trout to move . . . and some die Trout feed actively in open-water habitat all winter Energy expenditure may exceed consumption High rate of loss is common; “loss” usually = mortality Mortality is due to secondary factors – not starvation Effects are greatest on trout <10 inches

43. How does all of this relate to dams? In most situations, cold water (1C) enters the lake, Ice caps the lake Thermal inversion places warmest water at the bottom We release water from the bottom – and create long stretches of open water subject to ice processes we now know are detrimental The goal is to encourage a downstream ice cap as close to the base of the dam as possible that sets up as early in the fall as possible and stays there all winter This requires releases be as stable as possible since any change up or down can break the cap which opens up the river plus can cause significant problems with ice jams, channel scour, etc. This can be done by releasing water from the top of the reservoir – most dams aren’t designed to do this We recommend multiple penstocks to achieve this objective on all new dams in Wyo (High Savery) A fix is possible, but it’ll cost money How does all of this relate to dams? In most situations, cold water (1C) enters the lake, Ice caps the lake Thermal inversion places warmest water at the bottom We release water from the bottom – and create long stretches of open water subject to ice processes we now know are detrimental The goal is to encourage a downstream ice cap as close to the base of the dam as possible that sets up as early in the fall as possible and stays there all winter This requires releases be as stable as possible since any change up or down can break the cap which opens up the river plus can cause significant problems with ice jams, channel scour, etc. This can be done by releasing water from the top of the reservoir – most dams aren’t designed to do this We recommend multiple penstocks to achieve this objective on all new dams in Wyo (High Savery) A fix is possible, but it’ll cost money

44. Managing Winter Stream Habitat Maintain adequate flow for the channel Maintain stable flow Keep the water cold Minimize turbulence

45. Final Conclusions Winter habitat management is different than summer habitat management Open water fishing in the winter can be great for big fish but comes at a price Cold weather and ice are natural features But some ice processes are manageable

46. Why is this important to you? We tend to think of reservoirs and rivers and buckets and pipes, but that thinking can have significant negative effects if we don’t understand the consequences of how and when we manage water at all times of year. Sport fishing, especially in tailwaters, is worth almost a billion dollars a year to Wyoming. Water belongs to all of us and if we’re to maximize the benefits to the state, it behooves us all to understand natural processes and then to act on them to make sure we maximize all the benefits we can from our limited public trust water and fishery resources.Why is this important to you? We tend to think of reservoirs and rivers and buckets and pipes, but that thinking can have significant negative effects if we don’t understand the consequences of how and when we manage water at all times of year. Sport fishing, especially in tailwaters, is worth almost a billion dollars a year to Wyoming. Water belongs to all of us and if we’re to maximize the benefits to the state, it behooves us all to understand natural processes and then to act on them to make sure we maximize all the benefits we can from our limited public trust water and fishery resources.

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