I have summarised recent reviews that show the behavioural capabilities of larvae of warm-water, demersal, perciform fishes to be well developed from relatively early in the pelagic larval stage, and have argued that, because these capabilities have the potential to influence dispersal trajectories, they should be incorporated into biophysical dispersal models. Recent research makes it clear that larvae of at least warm-water perciform fishes have behavioural capa bilities that can influence their dispersal trajectories. The present challenge is to determine if they use them for this purpose. In effect, this requires testing the simplifying assumption. Dispersal models can be used in this way where field data exist for comparison. The model can be run without larval behaviour and again with behaviour included, and these 2 predictions can be compared to the observed result. Other more direct attempts to test the simplifying assumption are few, and have had mixed results (Leis 2006).
I have developed the hypothesis of Hunt von Herbing — that behaviour should play a larger role in dispersal in warm seas than in cold ones—by presenting additional factors that support it and by extending it by implication to differences between warm seasons and cold ones. The historical factors of phylogeny and bio geography also make such regional differences likely. Testing this hypothesis requires care given the many, potentially confounding elements involved. If sustained, this hypothesis will have important implications both for dispersal in different regions and for attempts to model dispersal. At the very least, the elements presented in my development of the hypothesis provide a sound basis to treat with great caution any assumption that one size fits all with respect to dispersal of demersal fish larvae, not only with respect to regions, but also with respect to taxa.
Realistic biophysical models of dispersal are needed for a variety of important purposes, but, before realism can be achieved, we must gain an understanding of the behavioural capabilities of the larvae whose dispersal we seek to model and not just ignore these capabilities. Once the knowledge is gained, incorporation of behaviour into hydrodynamic models must take into account the issues raised above. All of these represent challenges, and many also confront the comfortable simplifying assumptions of the past, but, due to recent advances, none are completely out of reach. If realistic biophysical dispersal models of use to both researchers and managers are the goal, then we must deal with all these issues, perhaps not all at once, but certainly in the end.