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About conversion factors and calculating fish weight

Commercial fishers often process their catch at sea. This means licensed fish receivers (LFRs) often receive processed fish. Fishers and LFRs need to report the unprocessed weight (greenweight) of caught fish. To work this out, fishers and LFRs can multiply the weight of the processed fish by a conversion factor. This gives the unprocessed weight (greenweight) of the fish.

Conversion factors can ensure that all vessels that process fish at sea have a consistent and fair catch reporting process.

How to use conversion factors

Conversion factors depend on how much is removed from the fish during processing. When more is removed, the conversion factor is higher.

There are different conversion factors for different species and the states that they're processed into.

To calculate the greenweight of processed fish, multiply the weight by the correct conversion factor.

If fish are landed in 2 or more processed states, use the conversion factor for the one that weighs the most.

Find a conversion factor

FishServe (our partner for administering commercial fishing) has a conversion factor tool on its website.

Find a conversion factor – FishServe

To use that tool, you'll need to know the species code for the fish you're working with.

View fish species codes

You can also find conversion factors in the Fisheries (Conversion Factors) Notice 2014. It contains:

  • conversion factors for different species in different product states
  • descriptions and diagrams of product states (starting on page 12).

Remember – we may review and change conversion factors each year.

Fisheries (Conversion Factors) Notice 2014 – Gazette

Your responsibilities with conversion factors

Find out about responsibilities for:

Fisher responsibilities

Commercial fishing permit holders must use the greenweight information that the LFR gives them to complete landing returns.

Licensed fish receiver responsibilities

LFRs must provide fishers with documents that help record the:

  • species
  • landed state
  • greenweight of fish.

Learn more about what licensed fish receivers do

Vessel operator responsibilities

Vessel operators should ensure that:

  • conversion factor information onboard is up to date
  • crew follow and meet conversion factor requirements
  • production is monitored
  • operations comply with the Animal Welfare Act 1999
  • fish processing and production onboard meets product state requirements (they must have a risk management programme).

Find out about risk management programmes

Find out about risk management programmes and seafood processing

Ensuring conversion factor requirements are met on board

Operators should focus on:

  • head cuts (and whether fins are included or not)
  • the placement of any tail cuts (especially where there are requirements around tail removal)
  • making sure fillet products meet product state definitions
  • making sure the processed state matches the conversion factor.

Make sure that fishers know what they need to do, and how. Vessels that process at sea should have on board:

  • a list of conversion factors – for all species and processed state combinations that the vessel is likely to produce
  • copies of processed state definitions
  • diagrams relevant to all product states produced at sea (these are in the 2014 notice).

Factory managers and processing staff on board should be able to access the definitions and diagrams.

Apply to create and use your own conversion factor on your vessel

Vessel operators can apply to use a different conversion factor. They must show that that they can consistently get a higher yield for a species/processed state combination. This is called a "vessel-specific conversion factor". If we approve the request, the vessel will get a certificate to use the new conversion factor.

We will only issue a certificate after our observers have done at least one sampling trip on the vessel. Once we've issued a certificate, observers will need to check your conversion factor whenever they're onboard. They'll check it to ensure it works as intended. There are costs for having an observer on board.

Costs for having an observer on board

Observer fees are normally covered through annual cost recovery levies. Charges may also apply for the part of any trip where vessel-specific conversion factor sampling is done. To calculate this, observers will estimate how much time they spend sampling during a trip. That portion is then direct-charged. The rest of the daily observer fee is covered under the annual sea days plan.

Fisheries and conservation service levies

Find out more about observer services

How we calculate conversion factors

The conversion factors in the Fisheries (Conversion Factors) Notice 2014 are based on information collected by Fisheries New Zealand observers. They are averaged across:

  • geographic areas
  • vessel types.

The conversion factors in the 2014 Notice are the most current ones.

Who to contact

If you have questions about conversion factors, email info@mpi.govt.nz

MPI business units