A range of marine intertidal and subtidal invertebrates are recreationally and/or commercially fished along the coast of NSW, in fisheries that are often poorly or unregulated. Modelling of populations of these species to assist the development in plans to manage these fisheries must take into account the scales at which these species vary in space and time. Much of the variation in their densities occurs at small scales and changes unpredictably through time. Yet most fisheries-based modelling does not take such small-scale and interactive variation into account. Variation in densities of sea-urchins from scales of metres to hundreds of kilometres illustrates strong and presently poorly-understood habitat-specificity of urchins. Many models also assume recruitment is relatively consistent among places (although not necessarily from time to time), but research has shown that for many species (illustrated for the cats-eye snail, Turbo undulatus), it varies markedly at scales of metres within shores. This partly gives rise to the large small-scale variation in densities. Patterns of abundance of predators is also not predictable from patterns of abundance in prey, either is a spatial or temporal context (Illustrated using the intertidal whelk, Morula marginalba and the barnacles that they eat). Finally, the range and amounts of invertebrates fished in NSW was summarized with the degree to which they are being exploited (largely unknown). Any modelling that plans to predict changes in populations in response to fishing pressure will only be realistic if it can incorporate the spatial and temporal scales at which these organisms vary and the scales of variation in habitats to which they respond.
