Simultaneous enhancement of rock lobster fisheries and provision of puerulus for aquaculture

Rock lobsters have a number of attributes that suggest potential for aquaculture, such as high market demand and gregarious behaviour. However, commercial hatchery production of seed is not feasible due to the long larval period so juveniles must be sourced from the wild. Harvest of puerulus potentially increases exploitation of the resource and fishery managers have sought compensatory mechanisms to achieve “biological neutrality”. Two options are compared here. “Quota lease” involves the lease and retirement of units of fishery quota so that fishing harvest is reduced to compensate for the removal of puerulus. “Reseeding” involves the release of a portion of cultured juveniles after 1 year to compensate for those that would normally have survived. Costs for aquaculture operations were similar for each option although increasingly favoured reseeding where survival in culture was high, lease price high, and production costs low. The reseeding option was considered superior for management of puerulus harvest in Tasmania because: there was no removal of egg production by sub-legal females; survival was estimated for only 1 year rather than from settlement to recruit, so uncertainty was reduced; the total fishing catch was not reduced so there was no negative socio-economic impact; and there was no displacement of fishing effort into over-exploited regions (juveniles were reseeded to the same location as puerulus harvest whereas quota lease is spatially decoupled from puerulus harvest). Conversion ratios for both options were strongly influenced by estimated survival in the first year post-settlement. This parameter was poorly understood so management assumed a highly conservative value for natural survival. This conservative value was intended to provide a high probability that the juveniles released with the reseeding option not only compensate for puerulus harvest, but also enhance the wild fishery.