Fish from the Researcher Perspective (2-D Processes)

In InterWET, the fish (brown trout) from the researcher perspective gives a two dimensional view or process level view of fish using the Habitat Suitability Index Method.
1. Fish Calculators.

Click the button below to load the Fish Calculator.

The calculator can be resized to fit your screen.
The fish calculator is designed to predict the habitat suitability index (HSI) for four life stages and overall for brown trout. The HSI is used by scientists to rate how well a given body of water can support a particular fish life stage and species. The index goes from 0 for totally unsuitable to 1 for completely suitability. An index near 1 does not guarantee large fish populations at a particular site, just that the site has the good potential to support large populations.
The four stages listed in the calculator refer to the growth stages of a brown trout. Starting with the spawning, an egg is laid in a nest or redd, the trout egg hatches a fry, which grows into a juvenile and then an adult, which spawns and the cycle is repeated. At each life stage, brown trout require specific habitat requirements. One site can not fulfill the requirements for all life stages. The overall HSI gives the most limited HSI for all four life stages.
There are several different types of HSI methods that can be used. The Fish Calculator makes use of a method that only requires five factors. These factors primarily deal with stream water quantity or quality. More complex methods employ many more specific factors.
2.Effects of Water Quantity
In the fish calculator, set the Stream Velocity to 1.0 ft/sec, Stream Depth to 1.0 ft, Stream Bottom to Gravel, Stream Shade to 20%, and Stream Temperature to 50 degrees F and click calculate. Note that each input indicates a range of possible values.
Notice the HSI values for overall and each life stage. This particular habitat is best suited to spawning and eggs and least suited for adults. Therefore, the overall suitability is the same as the adult suitability, the most limited of the four life stages. The two factors which indicate water quantity or stream flow are the stream velocity and stream depth. Experiment with different velocities and depths.
Notice how changing these values has different effects on each life stage. Just as the overall HSI indicates the most limited of the HSI for each life stage, so too does each life stage HSI indicate the most limited of the HSI for each factor. Notice that the adult HSI never gets better than 0.54. This indicates that one of the other factor's HSI is at 0.54. Varying the stream velocity and depth can make lower HSI values. But when the values associated with stream velocity and depth are higher than 0.54, then 0.54 is most limiting HSI for the adult life stage.
Each life stage has an optimum range of stream velocity and depth. Usually, the range for velocity goes from slightly above 0 to 3 ft/sec. Between 1 and 2 ft/sec, the HSI for each life stage is especially sensitive to change. For most life stages, the depth range begins at slightly over 0 and reaches some minimum HSI for depths greater than 4 ft. If you keep increasing the depth, the fry stage HSI will go to zero, while all of the other will reach some constant value.
3.Effects of Water Quality
The other three factors can be grouped under water quality. First, experiment with the stream shade factor. Notice that the spawning/egg stage is not affected by stream cover, and that stream cover only changes HSI values for the other stages for shades between 0 and 30%. For stream shading greater than 30%, other factors are more limiting than stream shade.
Now vary the stream bottom choices. Notice how sensitive each life stage is to stream bottom type. The spawning/egg stage must have gravel. The fry stage and juvenile stages are best for gravel, but can endure other bottom types. The adult stage is best with sand bottom. This reinforces the fact that one site can not meet all of the life stage needs for brown trout.
Finally, experiment with temperature. The lower limit is the freezing point. The upper limit ranges from 45 to 75 degrees F, depending on the life stage. The spawning/egg stage bottoms out at only 55 degrees F. The other stages' HSI values go to zero in the high 60's and low 70's.

4.Isolating the ranges for each life stage
As mentioned earlier, there is no "magic" set of factors which is good for every life stage. However, there are specific ranges of factor values for each life stage which are best. To discover what these ranges are, first choose a particular life stage to study and some starting set of values. Then go through each factor and experiment with different values until the HSI is at a maximum. Since all factors act independently, you should be able to determine the set of factor values which produce the highest HSI values for each life stage. The highest HSI value for each stage should be somewhere between 0.9 and 1.0.

Summary
1. Each life stage responds differently to changes in water quantity and quality factors. There is no single set of values which is perfectly suited for all life stages.
2. Each life stage has an unique range of water quantity factors (stream velocity and depth) which are optimum. The velocity range goes from slightly above 0 to around 3 ft/sec. The depth range goes from slightly above 0 to about 4 ft.
3. Each life stage also has a unique range of water quality factors (stream shade, stream bottom, and stream temperature.) Stream shade affects suitability only between 0 and 30% shade. Most life stages are best suited by a gravel bottom. All temperature ranges have a lower limit of the freezing point. The spawning/egg life stage requires temperature below 55 degrees F and the other life stages require temperature below about 75 degrees F.

More Details?
Check out the on-line dissertation on InterWET for more information behind the theory and techniques used to make this calculator.

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Questions or Problems? Let me know at parson@andassoc.com.
Last revision 9/9/01.
Created by Shane Parson, Copyright 1999.


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