Stock structure, mortality and growth of the decorated goby, Istigobius decoratus (Gobiidae), at Lizard Island, Great Barrier Reef

Gobiids are an abundant component of coral reef ichthyofauna, yet little is known of their life histories. I examined population structure, mortality and growth of the decorated goby, Istigobius decoratus, a common gobiid of shallow patch reefs on the Great Barrier Reef. Presumed daily increments in sagittal otoliths were used as a proxy for age. The upper age estimate was 266 days suggesting at most an annual life cycle. Instantaneous natural mortality rate estimates were 5.92 year⁻¹ and 7.92 year⁻¹ using two estimators, both corresponding to less than 1% annual survivorship. Specimens ranged from 12 to 84 mm total length. Analysis of size-at-age data indicated linear growth at a rate of 0.33 mm day⁻¹. The linear relationship between size and age meant the population size structure mirrored the age structure with both skewed toward the smallest and youngest classes. High mortality over a 1-year longevity and linear growth suggest high population turnover and, therefore, that I. decoratus and ecologically similar species serve a potentially important role as prey species. This suite of traits is rarely reported for coral reef fishes, which is probably due to the limited attention paid to small-bodied species rather than the rarity of such a life history in these communities