Predicting suitability of cockle Austrovenus stutchburyi restoration sites using hydrodynamic models of larval dispersal

An important aspect of shellfish restoration projects is to evaluate whether potential sites are likely to be recolonised naturally once disturbances are removed and habitats are restored. Similarly, if active translocation or reseeding of juveniles or adults is undertaken, it is important to understand whether these introduced populations will be self-maintaining in future, and whether any seed they produce are likely to be retained within the restored area. We used a combined hydrodynamic and particle tracking model to predict larval dispersion patterns for the common cockle Austrovenus stutchburyi under different hydrodynamic scenarios for seven release locations in Whangarei Harbour, New Zealand. Our results implied that sites varied substantially in their potential for self-seeding and for exporting seed to other locations. For sites with more restricted dispersal, the model predicted that most larvae originating at these sites would settle inside the release region (68-94% for passive particle simulations), whereas relatively few larvae originating from the other release sites settled at these sites. In contrast, model larvae released from sites exhibiting high connectivity dispersed to all sub-regions in the harbour, and export outside of the model region was high. Forthcoming field validation of these model predictions will result in better integration of hydrodynamic connectivity in whole estuary restoration programs.