Density Dependent Responses in Greenlip Abalone

Rob Day, Cameron Dixon and Sylvain Hucette

University Of Melbourne, PARKEVILLE, AUSTRALIA

THEME: ASFB

Compensatory density dependent processes in fish stocks are critical for the sustainability of fisheries, yet density dependence in population processes is seldom investigated. We are experimentally manipulating density in populations of greenlip abalone to determine DD responses in growth, survival and fecundity. At each of 8 sites, six 3x2m boulder reefs were created, and tagged juveniles were placed on them at densities from 9 to 48 m-2. Growth, survival and migration are being monitored at 3 month intervals. Thus far all appear to be strongly density dependent. At a site with high adult densities, replicate patches have been tagged and thinned, with controls, to estimate effects of density on size at maturity, adult growth, and fecundity (which is strongly dependent on size). Estimating population level effects for management purposes requires information from the whole life cycle. We can complete the picture using work in abalone farms that has already estimated strong DD survival and growth of postlarvae. Simulation modelling will be used to investigate the implications of these DD processes. It appears likely that reduced production of larvae from fished down adult stocks would lead to much more successful and also more rapid recruitment of the available juveniles to adult stocks.