FISHERIES & THEIR ECOSYSTEMS
Incredible marine habitats and ecosystems
New Zealand’s 200 nautical mile Exclusive Economic Zone (EEZ) covers around 4.4 million km2, and is the fourth largest in the world.
Within this lies a rich and complex seascape with a huge variety of marine habitats and life forms. There are undersea plateaus and mountain ranges, volcanoes, coastal estuaries and the 10,000-metre deep Kermadec Trench – the second deepest point on Earth.
Over 15,000 marine species have already been found living in these seas. And scientists think that another 50,000 may yet be found here. This could represent about 10 percent of the world’s known marine species.
Also, our isolation in the south-west Pacific means that there are many species unique to New Zealand.
Many migratory species also visit our waters. In fact, some marine mammal and seabird species depend on New Zealand breeding areas and feeding grounds for their existence.
Oceans and productivity
New Zealand’s ocean productivity results from a combination of its location in the Pacific, its undersea landscape, ocean currents, and climate.
Warm subtropical surface waters bathe the North Island and the west coast of the South Island. Much colder subantarctic surface waters surround the rest of the South Island and offshore islands to the south and east. These warm and cold waters meet to create the Subtropical Front, an ocean feature that circles the Southern Hemisphere.
Here, nutrient rich waters from the south mix with the warmer northern waters. These create ideal conditions for plankton and the animals that feed on them. This is good news for our fisheries. On the Chatham Rise and in the Subantarctic, the undersea landscape and currents enhance these conditions.
NEW ZEALAND ’S FISH CATCH
The Chatham Rise and Subantarctic fishing grounds provide 60 percent of New Zealand’s fish catch. Most of this comes from areas near the Subtropical Front, and includes the main hoki, hake, ling, silver warehou, squid, orange roughy and deep sea (oreo) dory fisheries.
New Zealand’s west coast (mostly off the South Island) provides around 30 percent of our fish catch. Much of this occurs when fish gather there to spawn in winter and spring (e.g., hake, hoki, ling, silver warehou).
WEATHER EFFECTS ON PRODUCTIVITY
Westerly winds affect our ocean currents and the temperatures of surface waters. These vary between seasons and between years, and so affect the patterns of upwelling and nutrient mixing in our seas. This in turn affects how much food is available and how many fish are produced.
Like El Niño and La Niña, scientists have found links between these weather patterns, and fish abundance in a number of important fisheries. These include snapper, scallops, red cod, hoki, and rock lobster.
During La Niña years, westerly winds are weaker and plankton food sources more abundant in the Hauraki Gulf and Coromandel. These years bring the best production of young snapper and scallops in these areas.
Climate scientists think New Zealand is coming into a time of more frequent La Niña years. This may be good news for our northern snapper fisheries, but it might not be so good for other species.
Learning more about the natural cycles that affect fish abundance may help us predict good years and bad years for fisheries. This would help in their management, and could help fishing companies in planning ahead.
Keeping within environmental limits
Children born in 2006 will be starting to plan for their future by 2020. What kind of world will they inherit?
Globally, the omens do not look good. Everywhere, there are signs of the environment’s limits being stretched. The global fish catch has now reached the limits of our ocean’s fisheries. And these limits are being stretched as some marine ecosystems and habitats are damaged or destroyed by fishing and pollution.
Our oceans and their ecosystems are hugely complex affairs, and we struggle to understand a tiny fraction of them. So the government is naturally cautious whenever it sets catch limits for fisheries. It is also naturally cautious when it deals with the effects of fishing on threatened seabirds and marine mammals, or on habitats and ecosystems.
To get better at managing such things, we must learn more about the marine life in our seas. We need to know more about how these ecosystems function. And also what effects fishing, pollution from the land, or changes in ocean and weather patterns have on them.
When setting limits around the effects of fishing, three questions are asked: Can the environment handle the effects? What does society think about the effects? And what are we leaving for future generations?
WORKING TOGETHER TO MANAGE THE EFFECTS
To answer the first question, the Ministry of Fisheries’ science group draws on international experience, as well as scientists from research agencies like the National Institute for Water and Atmospheric Research. Answering the other questions involves a wider range of people, including government agencies like the Department of Conservation, tangata whenua, environmental interest groups, and fishing companies. Together, we are making progress in many areas.
The government and industry have recently worked hard to reduce seabird deaths in our fisheries. As a result, we have seen huge drops in seabird deaths in the tuna and ling auto-line fisheries. We expect to soon see a drop in seabird deaths in our squid and hoki fisheries, through some recent actions by the government and industry.
There has recently been growing concern about the effects of bottom fishing on seafloor habitats. Fragile bryozoan beds on the sea floor in Tasman Bay and Spirits Bay have already been closed to bottom fishing, as have some 19 deep-water seamounts. The government is now looking at the effects of bottom fishing on other habitat types.
Many other types of human activities can potentially damage the marine environment. One of the greatest threats is runoff from the land. This includes sediment and nutrients being carried down rivers from farmland, forestry and other land development. In some coastal areas, these effects may be greater than the effects of fishing.
Another potential threat to our marine environment is the introduction and spread of marine pests, like the seaweed undaria and the clubbed tunicate sea squirt.
Impacts of bottom fishing
About 35% of our EEZ lies in trawlable depths (0–1500 m). Much of the shallower parts will have been fished at some point, but some depths and certain fishing grounds are fished often. In places like these, the sea floor today will likely be different to what it once was.
One heavily modified stretch of sea floor is Foveaux Strait, where oyster boats have dragged their dredges for over a century. The sorts of plant and animal communities that develop on the sea floor there are those that can survive this sort of regular disturbance.
In shallow waters, some types of sea floor communities can recover quite quickly from the effects of dredging or trawling. But fragile deepwater habitats may take hundreds of years to recover from such effects.
The government has already closed a number of areas to bottom fishing.
Other areas of our sea floor may also need protection. So the Ministry of Fisheries and Department of Conservation are working together working to learn more about the effects of bottom fishing on a range of sea bed communities.
Using resources wisely is a delicate balancing act. It means meeting today's needs without compromising those of tomorrow. We want to leave future generations with at least as many options for using marine resources as we ourselves enjoy.
The catches in most of our major fisheries are set close to the maximum sustainable level. But we know it is not enough to just manage catches sustainably. We must also consider the effects fishing has on the wider environment - fish and other creatures caught or killed during fishing, habitat damage, and the flow-on effects of all these things on marine ecosystems.
To manage fishing's "footprint" on other species, and on our marine habitats and ecosystems, we must set limits around what level of effect is acceptable, and what is not.
In 2005, the Ministry of Fisheries set out a Strategy for Managing the Environmental Effects of Fishing (SMEEF), which describes how such limits will be set.
Three key factors will be considered when setting environmental limits:
- weighing up whether effects on species or habitats are sustainable in the long-term;
- what society feels is the right balance between use and protection; and
- what the needs of future generations might be.
Threats from the land
Soil and nutrient run-off from the land can have huge effects on our coastal ecosystems.
Recent research, done by NIWA for the Ministry of Fisheries, shows that with more sediment in the water, fewer baby paua and kina survive. It also shows that sediment affects the tiny animals living on kelp. As these are a major food supply for other rocky reef species, it seems that high sediment levels will reduce the productivity of whole rocky reef ecosystems, and affect catches of important recreational, customary, and commercial species.
Future studies will look at the effects high nutrient levels are having on the marine environment. One of these will be done this year in Southland, and will examine the effects of runoff from agriculture and intensive dairy operations on coastal ecosystems.