Balancing cost and precision of estimating age composition using a proportional two-stage sampling method

Age composition provides basic information for age-structured stock assessment of many marine finfish species in the coastal states.  However, because of financial and labor constrains, fisheries managers always face the challenge on balancing the cost with the precision of age composition estimation. In Virginia, we have been using a proportional two-stage sampling method to estimate sample sizes for ageing 10 marine finfish species.  This method allows us to minimize cost for a specified level of precision.  The specified precision is determined beyond which ageing 100 more fish will no longer result in a precision increase of 1% (or CV decreases 1%).  The costs on collecting specimens and ageing calcified structures have been reduced significantly while the precision is kept at reasonable levels since we started estimation of sample size for ageing in 2007.  We believe that this work is particularly important to state-level fisheries management when many state governments have budget difficulties due to the current downside economy.