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Stocked Trout Behavior

It is amazing how much energy we put into trying to outsmart a creature with a 1 ounce brain.  Recognizing the accurate calculus embedded in Jimmy Moore’s humorous article titled, “How Smart is a Trout?” led me to conclude that, on a pound for pound basis, a trout has the angler beat.  Since I can't compete, I have to sneak. 

Jumping immediately to Sun Tzu's classic quote - "Know your enemy and know yourself and in a thousand battles you will never be in peril", I realized that I did not know much about stockers - the breed of trout that I encounter most on the streams in the middle Atlantic.  I needed to get inside the mind of the creature and determine some aspect of behavior that I could leverage to improve my success.

Thankfully, there are a number of credible studies which provide us “actionable intel” on a stocked trout’s behavior patterns.  Even more amazing, these studies, which span 30+ years, all reach the same general set of conclusions.

Here’s the bottom line, if you do not want to delve into the trivia of my notes on each study.

  • Stocked trout will only remain where stocked for a small number of days and then they move.  According to the PA Fish and Boat Commission, brown trout move in 7 days, rainbows in 3 and brookies in 10.
  • When trout move, they move downstream with few exceptions.  How far they move depends on the nature of the stream or river.  A study done in South Dakota pegged the movement at 224 yards while a British study discovered trout moved 656 yards.  The PA study discovered one wandering, radio tagged trout 123 miles from the stock point.
  • Unless the stocker is plopped into a raging torrent, trout do not “wash” downstream.  They move with a purpose.  The PA study demonstrated that radio tagged trout held their position through 2 major floods in 2005.  So, fish move when they want to move.
  • It takes a stocker a long time to completely adapt to eating in the wild.  Several of the studies demonstrated that stockers were not fully adapted to wild forage even after several months had elapsed.  They did this by examining and measuring the amount of “non-prey” items found in the stomachs of the fish.  The good news is that a rainbow will start to adapt to the wild after a week. It can take a brown trout up to 50 days to make the change.
  • The final bit of trivia is that the British study found that only 40% of the fish stocked are caught. Good news!

Conclusions:

If fly fishing, we need to wait a week or so for the transition to natural food to start.  If we fish sooner than that, we should use streamers whose jerky movement will attract reaction strikes in the same way a spinner will.

If you hit the stream a week or more after stocking, start as far downstream as you can to catch the fish that have moved away from the easy holes next to the road.  This also produces a better fishing experience as you will be away from the road-bound crowd who are fishing where the trout used to be.

We can afford to wait the week or so for the transition and the movement since 60% of the trout stocked should still be around (minus predation).  No need to track the movement of the stock truck on a daily basis...

Purchase Switchfisher's books using the links to Amazon below for:

  • Wade Fishing the Rappahannock River of Virginia (more info)
  • Wade Fishing the Rapidan River of Virginia (more info)
  • Wade and Shoreline Fishing the Potomac River for Smallmouth Bass (more info)
  • Trout and Smallmouth Fishing on the North Branch of the Potomac (more info)

 




Here are my notes (I wrote all this up in a formal article and submitted it for publication) with links to the source material:

PA Study Facts (Full Study or 4 page summary)

  • Considered over 20 variables; none correlated to trout residency; fish would hold longer where there was good physical habitat – logs, banks, rocks
  • Rainbows hold for 3 days
  • Brown hold for 7
  • Brook hold for 10
  • One tagged rainbow was found 123 mi from its stocking point; farthest traveling brown went 6 mi; max brookie movement was 7.5 mi, but most did not move that far
  • More trout captured near structure and stable bank
  • Water temp, pH did not make a difference – fish bred in warm water exhibited no preference to finding those same conditions
  • Admits to sources of error – poor fish counts, lack of distinction between species, recognized the need to improve ability to measure habitat
  • Quoted other studies where trout stay put during floods and take shelter; radio tagged trout did not move during the two floods in 2005
  • Freestone / limestone – no difference in trout residency.  Being in one or the other did not spur movement.

OK Study Facts

  • Fish move downstream of initial stocking locations; conditions would permit movement in both directions
  • Move short distance
  • Significant non-food items consumed early after stocking, switching to food items 3 months later
  • Fish body mass decreased the longer they were in the water

South Dakota Study Facts

  • Early studies concluded that fish did not move much   
  • Browns made only small movements during storm events (urban setting)
  • Browns major movement only associated with spawning
  • Low flows drove rainbow movement in British Columbia streams (Mellina 2005)
  • 1999 study showed stockers moved out of area that contained wilds (Bettinger and Bettoli 1999)
  • Fish that moved headed to pooled or run sections
  • Few fish remained in high flow areas
  • High flow behavior (100 cfs) – fish moved downstream
  • Low flow behavior – some fish moved upstream to a pool or run environment
  • “Founder effect”  (Mayr 1942) - some individual fish moved away from the stationary body – limits risk to the species to a few, but still allows group to spread to new areas
  • Average total distance moved was 205m – proved that stocking at bridge crossings, if numerous, is adequate for good dispersal and access to private property is not required to achieve an even stocking in a section

British Study (Starts on page 129)

  • Fish moved principally downstream less that 1000m
  • More dispersal in fast water; less in slow
  • Acclimation to fast water prior to stocking had little impact on dispersion
  • Presence of a wild population was not a factor at all
  • Of the fish that were caught, 65% caught within 5 weeks; on one river more than 80% caught within 3 weeks
  • Stockers did not begin feeding for several weeks
  • Brook and rainbow move more than brown and head downstream
  • Greater dispersion of fish who overwinter
  • Majority of fish caught where stocked
  • 90% captured within 600m of stocking location
  • Only 40% of the stockers were caught
  • Only 1% of stockers were caught the following year indicating a poor ability to holdover
  • Brown stockers did not start to feed for several weeks; lower food consumption than wild trout for 50 days after stocking
  • Stockers are more visible to predators – silvery appearance – persisted for 2-3 months
  • Acclimation to flow contributes to survival
  • Fish move more if there is limited structure/cover

Misc facts

  • It will take up to a week for trout to learn which items are edible
  • Browns may take weeks
  • Browns stocked at the lowest end of the tailwater move upstream
  • Montana study – trout seek pools; did not spend much time in fast water


Unless stated otherwise, this article was authored by Steve Moore

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