This simplified food web for the subantarctic area of New Zealand shows the estimated transfer of energy between the different parts of it.

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. This includes the main hoki, hake, ling, silver warehou, squid and 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 (eg hake, hoki, ling, silver warehou).

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.

Longer term weather cycles like El Niño and La Niña not only affect New Zealand's farmers; they also affect our fisheries.

Chart showing snapper recruitment against surface water temperature in the Hauraki Gulf. More baby snapper are produced when water temperatures are higher.

Scientists have found links between these weather patterns and fish abundance in a number of important fisheries. These include snapper, scallop, red cod, hoki, and rock lobster.

La Niña years favour the production of young snapper and scallops in the Hauraki Gulf and Coromandel.

Some climate scientists think New Zealand is coming into a time of more frequent La Niña years. This could be good news for our northern snapper fisheries, but it might not be so good for some other species, like hoki (where more young fish seem to be produced in El Niño years).

Learning more about the natural cycles that affect fish abundance will help us predict good years and bad years for fisheries. This would help in their management, and could help fishing companies in planning ahead.

Trawling on or near the sea floor during the 1990s.