ASSESSING THE EFFECT OF INTRA-HAUL CORRELATION AND VARIABLE-DENSITY ON ESTIMATES OF POPULATION CHARACTERISTICS FROM MARINE SURVEYS

In a previous paper (Pennington and Volstad, 1991, Biometrics 47, 717-723); it was suggested that reducing the size of the sampling unit currently used in marine surveys could increase the precision of the resulting density estimates. But if unit size is reduced, fewer animals will be caught during a survey. Concern has been expressed that this reduction in total catch would lower the precision of estimates of population characteristics, such as age and length frequency distributions, of importance for stock management. In this paper we examine the effect of sampling unit size, intra-cluster correlation, and variable density on the precision of estimates of population characteristics. An examination of some survey data indicates that reducing the size of the sampling unit employed and using the time saved to take samples at more locations could also yield more precise estimates of population parameters.