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Seabed trawling in deep waters

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

Reporting on trawl effort

Between 1990 and 2008, three different data return forms were used to collect trawl effort data from commercial fishing vessels operating in New Zealand waters. The Trawl Catch Effort Processing Return (TCEPR) was used primarily by vessels longer than 28 m operating in waters deeper than 200 m. TCEPR forms report individual trawl positions, and data reported here include bottom trawls and mid-water trawls close to the seabed (referred to here as ‘seabed trawling’). The Catch Effort Landing Return (CELR), which does not report individual trawl positions, was used by vessels smaller than 28 m fishing in shallow inshore waters up until 2008. In 2008, a new form, the Trawl Catch Effort Return (TCER) was introduced for small trawl vessels (6–28 m long), to allow individual trawl reporting, and the use of CELR is being discontinued.

The amount of seabed trawling has therefore been determined from the TCEPR forms, and is reported here for 1990 to 2008. The seabed area of each TCEPR trawl was calculated using the reported start and end positions of the trawl and estimates of the ‘doorspread’ (effective width) of the trawl gear. Although individual trawl positions for smaller vessels are not known, the number of CELR/TCER trawls is also reported to provide some estimate of effort by these vessels (see number of trawls by commercial fishing vessels).

To summarise the geographic distribution of trawl effort, the area inside the EEZ has been divided into a grid of 25 km2 cells. For each cell, the cumulative area trawled by TCEPR vessels was calculated. To report on recent changes in total trawl effort over time, we have compared the average area trawled for the three new years of data (2006–2008) against the average area trawled since we last reported (1990–2005). (Note that this comparison only shows recent changes and not long-term trends). For the purpose of this snapshot report, a trawled cell is defined as a cell that has undergone at least one trawl.

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 seabed trawling snapshot report card.

Last updated: April 2010