New Zealand’s Quota Management System has been viewed internationally as successful. This is particularly in comparison with many of the world’s fisheries where there is still an open-season approach (whereby regulations are placed on fishing days and equipment, rather than on limiting the total catch). Although some fish stocks have been over-exploited, New Zealand has (so far) largely avoided the significant stock collapses that have occurred in fisheries overseas. In the early 2000s the Ministry of Fisheries had records on the status of 60–70% of stocks. Of these, about 80% were at or near target levels for sustainable harvest, and the total allowable catch for some fish had even increased.
The remaining 20% of fish species are in decline or remained depleted. This does not necessarily mean that these fisheries are collapsing – a stock is often ‘fished down’ to a level that produces the maximum sustainable yield. A stock of fish that has never been harvested is dominated by older, larger fish. When a stock is first fished, the removal of the large fish allows more food for younger fish, and as they grow faster, the total biomass (weight) of the harvestable stock increases. This process is termed ‘fishing down’ as the stock is reduced to a level that allows the maximum weight of fish to be harvested while still retaining enough individuals to allow a similar level of harvest in future years. ‘Fishing down’ alters the population structure from one which is old and slow-growing to one dominated by young, fast-growing individuals.
Despite the relative success of the quota system, difficult issues remain.
How many fish should be caught?
Setting quotas for individual species is problematic. To determine how many fish can be taken from a population, scientists have to estimate how many fish there are and how quickly they reproduce. They then attempt to determine the maximum sustainable yield, which is an estimate of how many individual fish can be removed from a population without the stock going into an ongoing decline. If numbers fall too low, then quotas are immediately cut.
Populations and quotas are determined using various methods, such as research surveys, catch monitoring, ships’ logs, landed catches and computer modelling. However, these calculations are not always reliable, as declines in some oreo and orange roughy stocks have proven. This is particularly true with deep-sea stocks. Little is known about some species, and their populations can be overestimated.
In 2004 the New Zealand fishing industry employed some 26,000 people and was worth a billion dollars in export revenue. With so many jobs and investments at stake, fisheries management, including the quota system, can be political, and major disagreements are often only settled in court.