Different rates of mortality (M) and growth (K) will produce different expected body size distributions in natural populations. In fact, the M/K ratio is the major determinant of the body size distribution shape, as well as population’s resilience to exploitation. Yet, for most species around the world M and K values remain unknown, because determining them requires ageing data. It has been suggested that M/K ratio is fairly consistent across species, but this remains to be tested. Here we assess whether M/K ratios, asymptotic size and other population parameters can be estimated using Bayesian approaches from underwater visual census (e.g. Reef Life Survey, RLS) datasets. These datasets include thousands of diverse coastal species, but include observation selectivity and specified size bins. Using a Von-Bertalanffy growth-based model, we simulate datasets with different M/K, asymptotic size, recruitment and size variability parameters, as well as different sampling and length binning regimes. We then apply the estimation procedure to a range of RLS fish species and, where available compare their M/K estimates with those from earlier studies.