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Seabed trawling in deep waters

To report on seabed trawling in deep waters the following two variables are measured:

Data collected from Trawl Catch Effort Processing Returns

Seabed trawling in deep waters is reported on using data collected from commercial forms called Trawl Catch Effort Processing Returns (TCEPRs) from 1990 to 2005. These returns are required from all commercial trawlers longer than 28 metres and some smaller vessels that are required to report their position.

Did you know?

  • Most small vessels do not have to complete TCEPRs, so an estimated 3.5 million dredges and trawls were not reported for 1990 to 2005.
  • In some inshore areas, the effects of dredging and trawling by small vessels can be significant.

 

Reporting on trawl effort

About 970,000 TCEPR trawls were reported in the 16 fishing years from 1990 to 2005. These include bottom trawling and trawling using mid-water gear close to the seabed. The area swept for each trawl is estimated using the reported start and end positions of the trawl, and estimates of the ‘doorspread’ (effective width) of the trawl gear.

To report on trawl effort, the area inside the Exclusive Economic Zone is divided into a grid of 25-square-kilometre cells. For each cell, the sum of the area swept (square kilometres) can be calculated. In a particular fishing year, a cell may have a total swept area of zero square kilometres (that is, it was untrawled) or, for example, 100 square kilometres, indicating that, on average, the area of the cell was trawled four times.

The trawl effort can then be analysed against the Demersal Fish Community Classification to see what types of fish community are likely to have been most affected by seabed trawling in New Zealand.

 

The above information has come from the latest national state of the environment report, Environment New Zealand 2007.

Last updated: December 2007