Largemouth Bass Habitat Suitability Index Technical Report

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APPENDIX D‐9 LARGEMOUTH BASS HABITAT SUITABILITY INDEX TECHNICAL REPORT<strong>Suitability</strong> <strong>Index</strong>10.90.80.70.60.50.40.30.20.100 10 20 30 40 50 60Chlorophyll a (ug/L)Figure 5. The relationship between chlorophyll a with the suitability index.b. Description of system being represented by the modelThis model predicts how suitable the habitat for largemouth bass is in a given cell per year. Itdoes not predict density or abundance. This model addresses aquatic habitat only and primarilyreflects the freshening or salinization of aquatic habitats. Although salinity is the principal driverof the model, the influence of salinity is modified by temperature and vegetation variables thatreduce habitat suitability when habitat is poor or temperatures are extreme, even if salinity issuitable. As suitability approaches 1, salinity is within tolerable ranges, vegetation andchlorophyll a, are appropriate, and temperatures are not extreme. Only salinity may drivesuitability to 0 and other variables may only force suitability to very low values.This model is dependent on temperature, salinity, chlorophyll a, and vegetation variables. Anyuncertainty in these input variables will be reflected in this model output. Additional discussionof uncertainty and model limitations is included in Sections 5 and 7.c. Analytical requirementsThe largemouth bass HSI has the following analytical requirements: 1) food availability asdescribed by emergent vegetation (SI 1 ) and chlorophyll a (SI 7 ); 2) cover as described byemergent vegetation (SI 1 ) and submersed aquatic vegetation (SI 6 ); 3) water quality as describedby temperature (SI 2 ), salinity (SI 3 ), and chlorophyll a (SI 7 ); and 4) reproduction as described bytemperature (SI 2 ). Because this HSI is based on Stuber’s (1982) HSI, 0 to 1 suitability indicesderived from the variables are actually incorporated in the HSI. Each 0 to 1 suitability index isderived from the variables following the decision rules associated with Figures 1 through 5 inthis document. The suitability index values for each variable are multiplied with the othervariables in the groups of food, cover, and water quality, and these products represents the rawsuitability of a given cell or polygon with regard to the variables. In the reproduction group, thesuitability index is simply the value from temperature. Because food, cover, water quality, andreproduction contribute equally to the HSI, each product of variable multiplication is weightedsuch that the products are equal. Unequal number of variables in each product unbalance theLouisiana’s Comprehensive Master Plan for a Sustainable CoastPage 11
APPENDIX D‐9 LARGEMOUTH BASS HABITAT SUITABILITY INDEX TECHNICAL REPORTmodel, therefore, exponents range from 1/4 for reproduction to 1/12 for water quality so thateach product comprises only 25% of the model.d. AssumptionsDuring HSI development, several key assumptions were made. First, although the final set ofvariables all were derived from data collected in Louisiana, supplemental data from neighboringstates was included to increase the sample size for deriving the variable‐suitabilityrelationships. Because largemouth bass are native, or thriving as an introduced species, acrossthis region, the assumption that data imported from neighboring states and territories wasrelevant to the HSI development was likely valid. Second, based on comparison of competingfunctions (e.g., linear and cubic) by chi‐square/degree of freedom fit statistic, it was assumedthat the polynomial or logit function employed to generate 0 to 1 suitability values were thecorrect non‐linear models. The author has published models selected by this method (e.g.,Kaller et al. 2011) and believed this assumption was valid. Finally, the relationship betweenvariables and largemouth bass in the literature were almost always relationships betweenvariables and density or abundance of bass. The HSI operates as a suitability index that predictspresence or absence rather than density or abundance. The author assumed that high predicteddensity corresponded to high predicted probability of occurrence or habitat suitability and viceversa. Because this assumption may not be true in cases where habitat could be suitable, butfish could not reach these habitats, it is important to acknowledge that high suitability implyingpresence is an assumption. However, given the natural dispersal capability of largemouth bassand widespread stocking, it is unlikely that barriers are a problem and the assumption of habitatsuitability implying presence is likely valid.e. Identification of formulas used in the model and proof that the computations are appropriateand done correctlyThe model decision rules that were coded are provided in section 2.a. above. Quality reviewwas performed by both the model coders and CPRA to ensure formulas and computations werecorrect.3. System Qualitya. Description and rationale for selection of supporting software tool/programming languageand hardware platformBuilding upon the ecological modeling application development performed for the Evergladesmodeling community, Java was used as the programming language inside the Eclipse RCPenvironment which supports plug‐in software development. This approach facilitated theconstruction of software suites which execute the specific decision rules provided by subjectmatter experts allowing an end‐user to choose which of the ecosystem services models to run.b. Proof that the programming was done correctlyAll software products are the result of multiple programmers working in concert. As part of thecode development process, code classes were either developed by teams which ensuredmultiple individuals were conducting real‐time code reviews or when codes were individuallywritten, spot checks were done prior to production builds and exports.c. Availability of software and hardware required by modelThe choice of Java as the development platform ensures the broadest execution platform.These software suites can run on desktops with the following operating systems: Windows XP, 7Louisiana’s Comprehensive Master Plan for a Sustainable CoastPage 12
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