Stream just stocked? Skunked again? Blamed it on the “locals”? Or is something more sinister at work? A gang of rowdy blue herons?
Stockers have been driving fisheries professionals insane for years with their central questions being the same as ours, “What happened to all the fish? Were they caught? Did they die? Did they leave?” Understanding the answers is crucial to their mission to provide a good angling experience that, in turn, stimulates license sales supporting hatchery programs. The problem was succinctly stated in a Wyoming Fish, and Game presentation on tailwater trout survival as “How do you lose 250,000 trout?”[i] Many experts puzzled through the problem producing studies focused on answering these compelling questions that, if understood and lessons applied, will improve your day on the stream. It’s even better the studies all reach the same general set of conclusions; an academic event as rare as your teenager offering to take out the garbage.
You may think a stream is cleaned out, but unless fishing with hand grenades is legal, you are wrong. A comprehensive British study discovered that only 40% of the stockers planted were reported caught by fishermen.[ii] Of that 40%, 65% were caught within five weeks of the stocking.[iii] Even when you factor the 40% number upwards for poaching and the heron gang, there are plenty of fish cruising the stream after the localized slaughter following the publication of the daily stocking report. So, if there are so many uncaught fish, why do you get skunked?
A freshly stocked trout takes time to learn what to eat when taken off a diet of fish pellets. Understanding the timeline is critical as we rely on fooling trout with replicas of natural food. Brown trout present the worst case scenario taking up to 50 days to completely adapt to natural foods.[iv] The good news is rainbow trout, a hatchery favorite, begin their slow adaptation to a wild diet in about a week.[v] But, even their learning curve can still be slow. The Oklahoma Department of Wildlife Conservation confirmed this in April 2005 when they examined the stomach contents of rainbow trout stocked in January.[vi] In Oklahoma study-speak, “Non-food items were the dominant prey item.”[vii] However, by June, non-food items composed a significantly smaller portion of the fish’s intake; dropping from 27% in April to 11%.[viii] While the actual food items in the Oklahoma trout diet were primarily snails and invertebrates[ix], you should not extrapolate that mix directly to local water since your environment is probably different.
All this implies the advantage slowly tips in favor of the flyfisher. If you put your faith in the fact that 60% of stocked trout were unaccounted for, you can afford to wait for the fish to adapt to the wild. The longer a stocker is a resident in a stream, the more it will learn how to feed. You should see their interest in dry flies and nymphs pick up in direct proportion to time in the water as they adapt and learn through trial and error. On the flip side, if you remain convinced that you need to hit the stream soon after stocking to have a shot at catching anything, you should focus on bright streamers to provoke reaction strikes or a fly that looks like a pellet rather than using traditional dries or nymphs a stocker may not recognize. The transition to natural food is not the end of the story. By waiting for a stocker to develop a taste for stream fare, you give them time to disappear. Where do they go?
Finding the answer is precisely what motivated the Pennsylvania Fish and Boat Commission to do a series of studies between 2003 and 2006 in reaction to complaints from anglers asserting the fish were gone by opening day.[x] It turns out the anglers were right. The Pennsylvania studies concluded that rainbow trout will hold where stocked for 3 days, browns for 7 and brookies for 10.[xi]
Once the fish adapt, they move. They move downstream. Some even take giant steps. The Pennsylvania study reports that one radio-tagged rainbow was found a staggering 123 miles from its stocking location while the most adventurous brown moved 6 miles and the comparable brookie, 7.5 miles.[xii] Although the study was silent on how far a stocker typically runs since it limited recapture efforts to an arbitrary 300 yards, a South Dakota study of Rapid Creek pegged the average distance at 224 yards.[xiii] The British Study reinforced this by discovering that 90% of the fish recaptured by electro-fishing were within 656 yards of the stocking site 5- 13 days later.[xiv] South Dakota was the outlier to the downstream imperative and reported some upstream movement during periods of lower flow.[xv] While the actual distance moved depends on the specific characteristics of the particular streams studied, the point is that the fish “get out of Dodge” and most board the downstream train heading to a pool or run.[xvi]
Interestingly, there was no statistical significance related to the presence or absence of environmental factors. While stockers hang longer in the presence of good structure – logs, boulders, stable banks – they still eventually migrate.[xvii] In total, Pennsylvania considered 20 different variables to determine if any was the prime motivator spurring movement. For those who watch the environment, an immediate assumption might be that water chemistry and temperature would be key drivers. After all, if the water is too acid or too warm, trout should move immediately to seek out better habitat.
Regarding temperature, the 2006 Pennsylvania study did not see this behavior since there was no significant difference between the water temperature of the hatchery, stock truck, and destination streams.[xviii] They did discover a weak pH correlation with more trout being recaptured in the 300-yard footprint in less acid areas.[xix] In general, fish moved at the same rate regardless of the water characteristics.[xx]
What about flow? In the Rapid Creek study, fish immediately migrated downstream when placed in water flowing more than 100 cubic feet per minute.[xxi] You might think a flood would influence the downstream dispersion as in “all the fish were washed downstream by the big storm,” but that is not the case. Radio-tagged trout held in position during two Pennsylvania floods in 2005.[xxii] This makes sense. A stocked fish may not be accustomed to strong flows and drift with the current when deposited in a stream running at high volume. Once acclimated and comfortable, fish find protected holding positions where they can deal with high water conditions. So, our common assumption that fish wash downstream after a storm is terrible.
This is the last piece of the puzzle. Since you must wait a week or more for the fish to recognize standard fly patterns mimicking natural food, you can assume the stockers will no longer be lying next to those easy spots on the road used by the stocking truck. Knowing the trend is to migrate downstream, lay in a simple strategy for success. Start between 300 and 600 yards downstream of the stocking points and work up; targeting the pools and runs. Since the most intense pressure is in the several days immediately after stocking, by waiting you will probably have the stream to yourself. After all, the stock truck chasers assume the stream is cleaned out when, in fact, the trout have just moved out. To catch fish, you must fish where the fish are. Pretty simple advice and, with the knowledge of when to fish (wait a week or more) and where to fish (downstream in pools), you can have a good day on the stream – even a stocked stream.
Footnotes – for more reading:
[i] Wayne Hubert, Dave Zafft, Darin Simpkins, Lance Hebdon, and Christiana Barrineau, “Winter Survival, Movement, and Bio-energetics of Trout in Tailwater Habitat” (presentation , Wyoming Game and Fish Department, March 2007, 16.
[ii] R.C. Cresswell, G.S. Harris and R. Williams, “Factors Influencing the Movements, Recapture and survival of Hatchery Reared Trout Released into Flowing Waters and their Management Implications”, Food and Agriculture Organization of the United Nations, http://www.fao.org/docrep/009/ae996b/AE996B13.htm.
[v] T. A. Lasenby and S. J. Kerr , “Brown Trout Stocking: An Annotated Bibliography and Literature Review”, Ontario Scholars Portal, 17
[vi] Randy Hyler and Paul Blakenbush, “Assessment of Impacts to Spring Creek from Introductions or Rainbow Trout in 2004 and 2005”, Spring Creek Coalition and Spring Creek Conservation Coalition, 4
[viii] Ibid. 13-14
[x] PFBC Staff Report, “Factors Influencing the Post-Stocking Movement of Hatchery Trout in Streams”, Pennsylvania Fish and Boat Commission, 1
[xi] Ibid., 2
[xiii] Greg Simpson, “Rainbow Trout Movement after Stocking in Rapid Creek”, South Dakota State Government, 13
[xiv] Cresswell et al,” Factors Influencing”
[xv] Simpson, “Rainbow Trout Movement”, 11
[xvi] Ibid., 12
[xvii] PFBC Staff. “Factors Influencing”, 3
[xviii] Daryl Pierce, Michael Kaufman, Russell Green, Robert Wunk, “2006 Preseason Stocked Trout Residency Study”, Pennsylvania State Government, 10
[xix] Ibid., 10
[xx] PFBC Staff. “Factors Influencing”, 3
[xxi] Simpson, “Rainbow Trout Movement”, 11
[xxii] PFBC Staff, “Factors Influencing”, 3