How we count fish

Find out about how we estimate how many fish are in the sea and how we use the data.

Getting the balance of fish numbers right

We aim to we keep fish numbers at healthy levels now and into the future. To do this, we need to collect a lot of data.

Fisheries scientists from Fisheries New Zealand and NIWA (the National Institute of Water and Atmospheric Research) work to estimate the size of fish populations. They compare the results with what we consider the ideal sizes. We can then work out:

  • how catch levels affect population sizes
  • where changes are required.

Fisheries research – NIWA

The state of New Zealand's fisheries resources [PDF, 2.3 MB]

Fish stock status

Monitoring commercial fishing catches

Commercial fishers must report:

  • what kinds of fish they caught, and
  • how many of each kind they caught.

We use this information to find trends. When there are more fish in an area, it's usually easier for commercial fishers to catch the same amount each year. When there are fewer fish, fishers need to work harder to catch the same amount. However, this information sometimes gives us a false idea of how many fish there are. If fishers started using new catch technology, we'd have to be careful how we interpreted the data.

Size and age of caught fish

In important fisheries, we also collect information on:

  • the sizes of the fish being caught
  • the ages of the fish being caught
  • how much of the fish are being caught.

Often, this is enough information to help us estimate how sustainable the fishing is for a particular kind of fish. This information sometimes comes from Fisheries New Zealand observers. Our observers join commercial fishing boats of fishing trips to collect data.

Find out about fisheries observers

Collecting data on recreational fishing

We do surveys of recreational fishing across New Zealand. This helps us to build a picture of what recreational fishers catch.

Find out about the national panel survey of recreational fishers

Research studies in valuable fisheries

With high-value fish species, there's often a desire to catch more fish. To collect better information, we use research vessels. These vessels do ongoing surveys and tagging studies. These are expensive, but they give us independent estimates on fish numbers.

Sharing and analysing information

Throughout the year, several fishery assessment working groups meet to discuss the latest research and fisheries catch information. These groups then:

  • update the status of different fish stocks
  • work to estimate the likely population size of each fish stock.

These groups can then compare the estimated numbers against the ideal target numbers.

Later, the working groups meet as a plenary. They discuss any major changes in:

  • stock status
  • methods for estimating stock status.

These groups are made up of:

  • fisheries scientists and researchers from across government
  • research institutes
  • industry organisations
  • universities
  • non-government organisations (NGOs).

The plenary meetings are open to the public.

Sustainable management

The more information we have, the more closely we can manage a fish stock at an ideal target size. When there’s little information, it's hard to determine how close a fish stock is to an ideal target size. This means we have to act cautiously, and set the catch limit at what we think is a safe level. However, information comes at a cost. New Zealand has the fourth-largest fishing zone in the world. So, we have to prioritise the science and research needed to manage New Zealand fisheries.

Ongoing research in deepwater fisheries shows that we're maintaining these at sustainable levels. However, we know less about some inshore species, and we aim to improve our understanding of these in the immediate future.

Find out about deepwater fisheries

Find out more

Fisheries science and research

Fisheries research publications, reports, and stock statistics

Who to contact

If you have questions about how we count fish, email

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