Assessing the effect of intra-haul correlation and variable density on population estimates from marine surveys
Original version
This report is not to be cited without prior reference to the authorsAbstract
In a previous paper (Pennington and Vølstad, Biometrics 47, 1991) it was suggested
that reducing the size of the sampling unit generally used in marine surveys could
increase the precision of abundance estimates. But if unit size is reduced, fewer animals
would 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
mean fish length, 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 population estimates. Based on an examination of some survey data, it
appears that reducing the size of the sampling unit generally employed and using the
time saved to take samples at more locations could also yield more precise population
estimates.