Stream Tender Magazine

June 2015 Issue

Great Trout Hatch on the Upper Spring Creek This Year

    In the first week of May this year I visited the Upper Spring Creek to see if I could find any newly hatched trout. It turned out that there were plenty to see in the areas in and just downstream of the spawning beds.

    I checked out some of the same small quite water habitats along the edge of the stream as I did in the previous year’s monitoring program. Once again I found trout fry holding in the same spots as in the spring of 2014.

    However, this year there were a lot more than in last year’s survey. This will be great news for the Bighill Creek’s trout populations, with lots of new trout repopulating areas of the stream on the upper reaches.

    Both Millennium Creek and the Upper Spring Creek produced a good hatch of brook trout this new year and this will help make up for the loss of no spawning activity on Ranch House Spring Creek.

    Due to the surplus water

that was pumped into Ranch House Spring Creek last year, from the Cochrane Lake, there was no spawning in the tributary. The loss of a total year’s recruitment from Ranch House Spring Creek is a tremendous set-back for the restoration of the BH Creek fishery.

    Having three primary spawning tributaries to the Bighill Creek is a real positive asset to any small trout stream. So looking after these creeks is very important.

Lateral Margin Habitats are Very Important Micro Habitats for Juvenile Trout !

    When I am on the hunt for finding newly hatched trout on any spawning tributary, I always search the small little backwaters and current breaks found along all flowing streams. This is where trout fry will end up after they are washed downstream from there gravel egg nests, after emergence.

    These lateral habitats are also usually full of organic materials covering the bottom, including plant debris and other growing aquatic

weeds. This makes for perfect cover for hiding trout fry and usually provides an abundant invertebrate population for a food source for small fish.

    Once the fry become better swimmers and more confident in wandering further for food and habitat, they will travel upstream or downstream in the main stem of the stream. However, this will take a few weeks to happen. Density dependency will also force fry to move to other  

lateral habitats along  the stream.

    Density dependency is when the competition for food from other trout forces the less aggressive fish to move to new habitat. This migration will leave the trout that are forced to move, vulnerable to predation from more mature fish and other predators.

    Usually, by the end of May, it will be very hard to find juvenile trout along the stream banks of the creek.

Trout fry will feed on a variety of aquatic invertebrates such as the midge larva and pupa (right photo).

 

When may fly nymphs and caddis larva are very small in their life stage, they are also a prime target of juvenile trout.

May Fly Nymph

Caddis larva will build a protective case from pebbles or plant material  (like the photo to the right), or some will have no case for protection.

Juvenile Shrimp or Gammarus, (like the photo to the right), are a prime source of food for early stage trout.

Juvenile Trout Food

How Large are These Trout  -  Just After They Emerge ?

    It is hard to get an idea of how large these juvenile trout are from the photos that you have seen in this article. So I looked back in my files from the 2008 and 2009 fisheries study that Bow Valley Habitat completed in 2009.

    I found one that shows a juvenile trout just after it had emerged from a spawning bed and was captured in a bottle trap for processing. In the background you can see the centimetres marked on the viewing glass. This trout has just finished feeding off of the egg sack that it had for initial survival while living in the gravel before emergence.

    At this stage in their lives, trout fry have very under developed fins and on some of the trout fry that I captured, the caudal fin was almost worn completely down, from the trout struggling to free itself from the spawning bed. However, this trout in the photo was in pretty good shape.

    The newly hatch trout are very delicate creatures and it will take a while before they become strong enough to swim in the faster flowing waters of the main stem of the creek. It is very important that there is a good supply of micro invertebrates for the next weeks of their lives.

This Juvenile Brook Trout was captured during a fisheries study on Bighill Creek in 2009. The trout had just emerged from the gravel redd and it measured 27 mm in length.

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