WFS 310 /
Habitat Suitability Index /
Salmo Trutta and Salvelinus Fontinalis /
Andy Leakey, Luke Haupt, Jason Hendershot and Jacob Bransky /
10/30/2008 /
Habitat suitability indexes serve to predict species occurrences, the relationship between differing species and habitats, and specific habitat requirements. The use of HSI models to predict species occurrence is an important tool for wildlife and fisheries managers. This lab provides an insight to the use, and data necessary to perform a statistical analysis of species occurance based on habitat. /

Introduction

The Brown Trout (SalmoTrutta) is the most widely distributed salmonid and was first propagated in the United States in the 1880’s, from two different European sites. The Brown Trout is highly adaptable and considered desirable by sportsmen. The Brook Trout (SalvelinusFontinalis) is actually a Char and is Pennsylvania’s only native salmonid. Since the introduction of the brown trout in PA’s cold water streams the range of the brook trout has diminished. However, the presence of the brown trout should not be considered the sole reason for the loss of brook trout habitation. The largest reason for the decline of the ‘brookie’ in PA’s waters is habitat degradation. (Behnke 2007)

Habitat Suitability Index models were developed by the U.S. Fish and Wildlife Service to provide biologists with a way to evaluate the effects of resource management practices on fish and wildlife. HSI models use only habitat information, providing researchers with quantitative relationships between the environmental necessities of a species and the habitat available (Grant 2008).

Methods and Materials

In this lab we were provided with all of the materials.

Materials:

  1. Data of Galbraith Gap Run
  2. The Brook and Brown Trout Habitat Suitability Index models

The methods involved using the correct HSI model to determine the value of a particular variable.

Results

These are the results from the data gathered from the HIS for the brook and brown trout. Statistical analysis was done to get the regression information. A comparative chart of Brook trout versus Brown trout was performed to compare population estimates for the ten sites.

Table 1, 2: Shows the statistics used for all of the regressions. Table 3 shows the residual output numbers used for the line fit plots of the trout in the following two graphs.

SUMMARY OUTPUT
Regression Statistics
Multiple R / 0.172335
R Square / 0.029699
Adjusted R Square / -0.09159
Standard Error / 0.033039
Observations / 10
ANOVA
df / SS / MS / F / Significance F
Regression / 1 / 0.000267 / 0.000267 / 0.244866 / 0.634016
Residual / 8 / 0.008733 / 0.001092
Total / 9 / 0.009
Coefficients / Standard Error / t Stat / P-value / Lower 95% / Upper 95% / Lower 95.0% / Upper 95.0%
Intercept / 0.001814 / 0.019566 / 0.092721 / 0.928405 / -0.0433 / 0.046932 / -0.0433 / 0.046932
X Variable 1 / 0.000418 / 0.000844 / 0.49484 / 0.634016 / -0.00153 / 0.002364 / -0.00153 / 0.002364
RESIDUAL OUTPUT
Observation / Predicted Y / Residuals
1 / 0.006408 / -0.00641
2 / 0.010585 / -0.01058
3 / 0.016432 / -0.01643
4 / 0.012673 / 0.087327
5 / 0.002649 / -0.00265
6 / 0.004738 / -0.00474
7 / 0.011838 / -0.01184
8 / 0.003902 / -0.0039
9 / 0.018938 / -0.01894
10 / 0.011838 / -0.01184

Graph 1

Graph 2

Graph 3: Shows the brown trout population estimate as well as the brook trout population estimate for the ten sites.

Discussion

Brooktrout estimates tended to be higher at most of the sites. This could be because of the limiting factors between the species. For the brook trout, the limiting factor was the percent of the stream that is shaded during the afternoon hours. For the brown trout the limiting factor was the levels of late summer nitrate/nitrogen. The brook trout limiting factor was a higher value that the brown trout limiting factor (0.15 compared to 0 on a scale of 0 to 1). That could account for the higher estimate in brook trout than in brown trout.

This goes well with a study that was done on brook and brown trout in Swedish headwaters where brook trout are an invasive species. They found that brook trout dominance was prevalent when environmental factors limited brown trout performance. Brown trout dominated otherwise through the streams. They also found that localities in the smallest watersheds that were dominated by brook trout hardly ever sustained a brown trout population. (Ohlund et al 2008)

If the results from that test are applicable here, then the sites where brook trout have a higher population must be sites where there is more shade on the stream during the afternoon hours and nitrate/nitrogen levels that are not adequate, or are too high, for brown trout, and the brook trout dominate. Otherwise, the brown trout would be more prevalent because when the sites are not limiting to brook or brown trout, brown trout will dominate.

Another interesting study was done on reproductive interactions between native and non-native species, namely brook trout and brown trout. Naturally these two species can reproduce and produce the hybrid tiger trout, but it is rare. It is slightly more common here in North America where the spawning seasons of these two species overlap by about four weeks. These two species interfere with each other’s reproductive success which could lead to one species dominating another in places where they both could exist. This negatively affects the population sizes of the species because survival rate of hybrids is very low. (Cucherousset et al)

So the competition between the species may not be all due to habitat, however, habitat is a large factor in determining the competition between these two trout species.

References

Ahmadi-Nedushan, Behrouz. "A review of statistical methods for the evaluation of aquatic habitat suitability for instream flow assessment." RIVER RESEARCH AND APPLICATIONS 22(2006): 503-523.

Grant, Jacqualine. "Habitat Suitability Index Models."WFS 310- Wildlife & Fisheries Measurements 7(2008): 1.

Behnke, Robert. About Trout. 1. Guilford, CT.: The Lyons Press, 2007.

Ohlund G (Ohlund, Gunnar), Nordwall F (Nordwall, Fredrik), Degerman E (Degerman, Erik), Eriksson T (Eriksson, Torleif), “Life history and large-scale habitat use of browntrout (Salmotrutta) and brooktrout (Salvelinusfontinalis) - implications for species replacement patterns,” CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES,Volume 65, Issue 4,Pages 633-644,Published APR 2008

Cucherousset J (Cucherousset, J.), Aymes JC (Aymes, J. C.), Poulet N (Poulet, N.), Santoul F (Santoul, F.), Cereghino R (Cereghino, R.), “Do native brown trout and non-native brook trout interact reproductively?” NATURWISSENSCHAFTENVolume 95,Issue: 7,Pages 647-654, Published JUL 2008