fishmethods (version 1.12-1)

surveyfit: Estimating the Relative Abundance of Fish From a Trawl Survey

Description

This function applies the time series method of Pennington (1986) for estimating relative abundance to a survey series of catch per tow data

Usage

surveyfit(year = NULL, index = NULL, logtrans = TRUE, graph = TRUE)

Value

List containing summary statistics (sample size (n), the first three sample autocorrelations (r1-r3) for the first differenced logged series) and parameter estimates (theta, theta standard error, and sigma2), the observed log-transformed index and fitted values, and the ARIMA function output.

Arguments

year

vector containing the time series of numeric year labels.

index

vector containing the time series of mean catch per tow data.

logtrans

a logical value indicating whether the natural log-transform should be applied to the mean catch per tow values. Default is TRUE.

graph

a logical value indicating whether a graph of the observed and model fit should be drawn. Default is TRUE.

Author

Gary A. Nelson, Massachusetts Division of Marine Fisheries

Details

Parameters for a first difference, moving average model of order 1 are estimated from the trawl time series using function arima. Following Equation 4 in Pennington (1986), fitted values are calculated from the model residuals and the estimate of theta.

References

Pennington, M. P. 1986. Some statistical techniques for estimating abundance indices from trawl surveys. Fishery Bulletin 84(3): 519-525.

See Also

surveyref

Examples

data(yellowtail)
surveyfit(year=yellowtail$year,index=yellowtail$index)