Saving our Snapper fishery

07 October 2013
cl-snapper-brady-doak
Image courtesy of Brady Doak

Throughout much of the north-eastern coast of New Zealand our kelp forests have vanished. They have been mowed down by hordes of hungry sea urchins or kina, which are no longer kept in check by their arch enemies - large snapper and crayfish. The barren kina wastelands are around 75 times less productive than the lush kelp forests they have replaced. The massively productive coastal kelp forests are vitally important for supporting a myriad of creatures, especially a rich diversity of fishes and shellfish, many of them important to our fisheries. Unfortunately, a great deal of this kelp productivity on our north-eastern coasts has disappeared along with our largest snapper and crayfish.

Mussel beds once carpeted the seafloor of the Hauraki Gulf over a total area larger than Wellington City. These mussels pulled nutrients out of the water column and made them available to the rich variety of animals living amongst the mussels, especially baby fishes, such as snapper. Last century these mussel beds were almost entirely fished out due to poor fishing controls. The mussel beds have failed to recover and this vast nursery area for fishes has now been lost.

Other vital nursery habitats for juvenile fishes have also been destroyed, such as the vast areas of sea grass beds which were wiped out in the Whangarei Harbour by the 1960s due to sediment discharges from land. Baby snapper love hiding in sea grass and feeding on the rich food sources this unusual plant provides.

Seabed dredging and some types of bottom trawling for fish, have also been shown to remove the structure and diversity of the seabed, by knocking over sea sponges and breaking up horse mussels which poke up into the water column. These seabed features are vitally important nursery habitats for juvenile snapper. A great deal of our coastal environment is open to these kinds of seabed changing activities, managed through fisheries controls.

Marine species such as snapper maintain a high degree of genetic diversity throughout their large populations in order to help them adjust to environmental changes such as loss of nursery habitats and climate change. However, when fish stocks are heavily fished this important genetic reservoir is eroded. Recent research has shown this to be the case for snapper populations in New Zealand. Scientists have advised that maintaining adequate size of fish populations in these situations is an important management consideration.

Despite this extensive profile of environmental concerns for improving the management of our most valuable coastal fishery, the Ministry of Primary Industries recently released a discussion document for our largest snapper fishery that largely overlooks this. Instead it concentrates almost solely on who should get what share of the fish and does not even mention the environmental performance of the snapper fishery.

This is remarkable because in 2009 the Minister of Fisheries made a major commitment to maximise the benefits from our fisheries but with careful regard to the environmental limits. This was the foundation for the excellent Fisheries 2030 policy which promised to maintain our world-leading track record in fisheries management by better managing fish stocks within the context of the environment on which they rely.

A major promise of the policy was to deliver environment outcomes by ensuring “the capacity and integrity of the aquatic environment, habitats and species are sustained at levels that provide for current and future use. This means

  • Biodiversity and the function of ecological systems, including trophic linkages, are conserved
  • Habitats of special significance to fisheries are protected
  • Adverse effects on protected species are reduced or avoided
  • Impacts, including cumulative impacts, of activities on land, air or water on aquatic ecosystems are addressed.”

It is critical that going forward the public discussion on our snapper fishery should not just be about how to divvy up the existing fish, but also about how we best manage our environment to protect our fish into the future.

A great deal of research by the University of Auckland is focused on improving our understanding of how we can better manage marine organisms within their environment. Our snapper-related research has shown how important large snapper are for maintaining kelp habitats; how key habitats, like sea grass and horse mussel beds, are critical as nurseries for snapper; and how the reproduction of snapper living within marine reserves can help restock snapper on surrounding coasts.

It is not only about learning more, but taking positive action is also important. For example, University students and scientists are working with a community group and members of the mussel farming industry to restore mussel beds in the Hauraki Gulf, in an attempt to get back the fish nurseries they once provided.

See reviveourgulf.org.nz

Professor Andrew Jeffs
Institute of Marine Science