New Zealand aquaculture produces 93,000 tonnes/year of Greenshell mussels, worth NZ$420 million. The industry has relied over the past 50 years for its seed stock, on a natural resource. The resource is “Kaitaia spat”, a mix of seaweed and debris encrusted with seed mussels that washes up on one beach in the far north, and is gathered to supply to mussel farmers. From initial hand-gathering in the 1970s, a mechanized local industry developed that has harvested over 100 tonnes of Kaitaia spat in most years since 1990. This material provides upwards of 80% of the industry’s seed. Only in recent years has the origin of this material been identified, using a combination of biophysical and genetic modelling. This knowledge should enable environmental protection and harvesting management of the Kaitaia spat resource. Wild spat catching in some farming areas provides some seed, but the most likely alternative to Kaitaia spat will be from hatchery production. “SpatNZ” has, since 2015, been developing selective breeding and seed production technology, which is now capable of supplying sufficient spat for growing 30,000 tonnes of mussels. Will the advantages of hatchery spat, such as certainty of supply, outweigh the added cost when compared to Kaitaia spat?