Fit length weight relationship to species data from SVDBS

Fits a length weight relationship for use in catch expansion

fit_length_weight(
  lengthWeightData,
  speciesName,
  speciesRules,
  outputDir = NULL,
  logfile = NULL,
  suppressMessages = F
)

Arguments

lengthWeightData: Data frame. length-weight pairs. Each row represents an individual fish
speciesName: Character string. Common name for species
speciesRules: List. Obtained from get_species_object
outputDir: Character string. Path to output directory (Default = NULL, no output written)
logfile: Character string. Specify the name for the log file generated describing all decisions made. (Default = NULL, no output written)
suppressMessages: Boolean. Suppress all messages

List of model fit objects

The Weight-Length relationship is defined as

$$W_{ij} = \alpha L_{ij}^{\beta_j} e^{z_{ij}}$$

where,

$W_{ij}$ = Weight of fish i in season j, $i = 1, ..., n, j = 1, ... J$

$L_{ij}$ = Length of fish i in season j,

$z_{ij}$ ~ $N(0,\sigma^2)$,

and $\beta_j$ is effect of season j

On the more familiar log scale the model is

$$log(W_{ij}) = log(\alpha) + \beta_j log(L_{ij}) + {z_{ij}}$$

To test for a seasonal effect, we test the Null hypothesis:

$${H_0}: \beta_j = \beta$$

against the alternative,

$${H_1}: \beta_j \neq \beta$$

The test statistic is the standard F statistic

$$F = \frac{(RSS_{H_0}-RSS_{H_1})/(J-1)}{RSS_{H_1}/(n-J-1)}$$

which will have an F distribution with (J-1, n-J-1) degrees of freedom

where RSS= Residual Sum of Square s