The issue of how best to survey abalone populations to obtain estimates of abundance has been the subject of debate among fisheries biologists for many years.  In an attempt to resolve this issue we compared and evaluated abalone abundance estimated by the following methods: Transect survey, Timed-collection surveys, Mark-Recapture, Change-in-Ratio and Leslie (catch-effort) estimates. This study involved a fish-down of an abalone reef by commercial abalone divers.  Estimates of abalone abundance were made by applying the different methods before, during and after the fish-down.  The total catch (number of abalone harvested) was used as a bench-mark against which the differences between the before and after abundance estimates for each method could be compared.  In addition the precision for each method was estimated and compared.

Previously, the use of area-based transects was thought to be limited for estimating the abundance of spatially aggregated animals such as abalone.  However, the outcome of this study was that transect surveys are the preferred method because they accurately reflected absolute abundance, required a relatively small number of sampling days and were reasonably precise.  It is recommended that a stratified random approach be adopted when using transect sampling.  Timed-collections gave precise but inaccurate estimates of abundance which were somewhat more sensitive to diver (operator) effects.  CIR methods using transect data to estimate proportions can be as efficient as transect-based abundance estimates, however they require more intensive data collection.  If a cost-effective and quick tagging method can be identified, then a mark-recapture study will also work well, although a test for equal catchability of tagged and untagged animals should be included in the design of the experiment.  CIR analysis using timed collection data is less certain due to possible violation of equal catchability of two animal types, but will still give a workable result.  The use of catch and effort data as an index of abundance is not recommended for monitoring abalone abundance because, despite the controlled conditions during this study, estimates of abundance using these data could not be obtained in two out of three instances.

Future research should be directed towards a better understanding of the importance of aggregating behaviour in determining the impact of harvesting on blacklip abalone populations.  The involvement of commercial abalone divers is crucial to the success of these types of studies.  For this project, co-operation between managers, researchers and commercial divers was beneficial to all parties involved and it is hoped this will become a common occurrence in future research of the Victorian abalone fishery.