Looking for a Haliotis rubra shell morphometric signature: contrasting geographic and age contributions to variation in shell morphometry

The shape of blacklip abalone Haliotis rubra shell is proposed to vary as a function of the quality of the environment in which an individual resides. The term ‘stunted’ is commonly applied to abalone from locations where growth is slower, and with smaller maximum size in comparison to other locations within a given fishery. It is hypothesised that in these slower growth areas, the shell shape is also divergent, with more rounded and taller shapes common place. The spatial variation in growth of H. rubra around Tasmanian is reasonably well understood. However, variation in shell shape is less well linked to geographic location, and is more commonly attributed to change in shell shape due to abalone age. For example as growth slows to a few mm/year, natural erosion of the shell edge combined with biofouling from sponges and polychaetes, and natural the continual laying down of nacreous layers, appears to alter the shape of abalone shells as they age. Here, we investigate geographic and age morphometric signature using univariate and multivariate techniques, and identify length based shape change parameters as a performance measure for the established Minimum Legal Size.