We can restore marine abundance by managing fish stocks at higher levels. Rescue Fish promotes managing fish stocks at 50% of its natural, unfished level. A fishery managed at 50% of its assumed natural size is considered to be a sustainable fish stock. The 50% level is international best practice. When a fish stock is at the 50% level it can provide for economical harvest whilst ensuring productivity and marine ecosystem services are maintained. In New Zealand many fish stocks are currently between 15% and 30% of their natural, unfished level. Rescue Fish policy.