Management of SBT is greatly complicated by large uncertainties in the stock assessment. One key parameter is absolute spawning stock size, for which the only available estimates are highly uncertain and are driven entirely by fishery-derived data (e.g. Japanese CPUE, catches on the spawning ground). Hence, the management procedures being developed for SBt use relative, rather than absolute, abundance indices. Current concerns about historical over-catch, of uncertain magnitude and duration make the conventional stock aseessment even less certain. A fishery independent estimate of standing stock biomass (SSB) provides both a stand alone benchmark to compare with current catches, and a fixed reference point around which to rebuild future assessments. This cannot be done with current fishery independent approaches, such as conventional tagging. However, recent advances in genetic and statistical methods now permit a fishery-independent estimate, using identification of parent-offspring pairs in random samples of juveniles and spawners. The same approach can also provide information on age-specific fecundity and thus on appropriate definition of SSB (spawning stock biomass). This is another area of significant uncertainty for management because, as noted above, the different definitions of SSB have considerably different implications for stock projections and rebuilding times.

An absolute estimate of spawning stock biomass is particularly valuable given the estimated level of depletion of the SBT stock, and the high uncertainty about the productivity of the stock (i.e. the relationship between the parent stock and recruitment). Although this project will initially aim to provide an estimate of average SSB over 2002-2005, it will ultimately provide the methods to enable a time-series of SSB to be estimated if sampling continues. Furthermore, the statistical methods developed and applied in this project will have general applicability to a range of species.