Abstract
The .DELTA.-distribution has been suggested as a useful model for the distribution of catch-per-tow data from trawl surveys for fish and plankton (Pennington, 1983, Biometrics 39, 281-286). Previously the efficiency of the .DELTA.-distribution mean estimator .cxa..kappa. with respect to the sample mean had been evaluated by using a large-sample approximation for the variance of .cxa..kappa.. The exact form of the variance of .cxa..kappa. is derived here and used to study the efficiency for the small sample sizes typical of trawl surveys. Actual data from a recent trawl surveys are used to assess the expected gains in precision from using .cxa..kappa. in practice.

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