5.1 Status of the stocks and marine environment
Approaches to fishery management continue to evolve as understanding of the marine environment increases and attitudes change. There is recognition that fisheries are part of an ecosystem and should not be managed in isolation. Growing awareness of the need to maintain wider ecosystem viability is moving us towards an integrated approach to fisheries and environmental management.
While both Mfish and the industry put significant resources and time into monitoring stock status, the nature of fish populations and the limited available information makes evaluating the state of New Zealand’s marine ecosystems difficult.
Coastal fisheries were heavily depleted in the two decades prior to 1985. Since 1986, most QMS stocks for which biomass and productivity data are known are thought to be above sustainable levels. However, for most of the species managed under the QMS, too little is known to be able to assess stock status.
For several species where information is available, stocks have been depleted below levels judged to produce maximum sustainable yields1, but management strategies are in place to rebuild these stocks to sustainable levels. The 14 fish stocks that are known to be below maximum sustainable yield [Maximum sustainable yield is defined as "the greatest yield that can be achieved over time while maintaining the stock’s productive capacity, having regard to the population dynamics of the stock and any environmental factors that influence the stock”.] include oyster, gemfish, orange roughy, paua, snapper and rock lobster stocks. In all cases a rebuild strategy is in place allowing the stock to rebuild over time to maximum sustainable yield.
Shellfish and some other marine invertebrates remain vulnerable to over-harvest and habitat degradation, caused by sediment from rivers, pollution, changes in sea temperature, and fishing activities. Although our coastal waters and habitats are generally held to be of high quality by international standards, they are under stress in some areas, particularly near large estuarine towns and cities and the mouths of large rivers. Estuarine and marine ecosystems are also threatened by the invasion of exotic species; a problem aggravated by vessels transporting ballast water and hull encrustations.
Little is known about the composition of benthic species, the resilience and regenerative capacity of deepwater seamount habitat, or the actual nature and extent of damage by trawling. The history of seamount fisheries in the northern hemisphere is one of sequential collapse, and concerns about rapid decline of deepwater fish stocks in seamount fisheries in New Zealand and Australia suggests such habitat could be quite fragile, and trawling may have an effect on long term productivity.