surveyfit {fishmethods}

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)

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.

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.

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.

Author(s)

Gary A. Nelson, Massachusetts Division of Marine Fisheries [e-mail]

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)