While S. biaculeatus has been reported by many authors in its range, there is no information available to our knowledge about population structure or sizes. Takahashi et al. (2003) (and earlier thesis Takahashi 2000) report on index of population size (CPUE) and seasonal changes in Moreton Bay, Queensland. Work in Bootless Bay, PNG (Barrows, Baine and Martin-Smith unpub. data) shows they are very common (found at all seagrass sites) in moderate abundance (2-6 individuals/100 m²) with no systematic changes across the year.