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Oceans Fishing activity Seabed trawling
Area swept by commercial trawlers
Current Situation
Trawling on or near the sea floor is the most widespread fishing activity in the New Zealand marine area that physically affects the seabed. There were 85,222 km2 trawled by commercial vessels in the 2008 fishing year. (Note that this is the total area of all trawls added together, and is not a measure of actual seabed area covered by these trawls because many trawls overlap.) The Fish Stocks Environmental Snapshot (Ministry for the Environment, 2009) showed that middle-depth fish (ie, hoki, hake and ling) made up almost a quarter of total commercial catch in 2008. Eighty-two per cent of the middle-depth fish catch was hoki. Some of these fish would have been caught during seabed trawling.
Figure 1- Total area trawled by Trawl Catch Effort Processing Return (TCEPR) vessels (sum of all overlapping trawls), 1990–2008
Data source: Ministry of Fisheries (data groomed by NIWA)
Note: Effort data is reported by ‘fishing year’, which for most species runs from 1 October to 30 September. A fishing year takes its name from the second of the two calendar years because this is the year in which most of the fishing year lies.
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| Fishing year | Swept area |
|---|---|
| (1000 km2) | |
| 1990 | 85.448 |
| 1991 | 111.091 |
| 1992 | 124.493 |
| 1993 | 123.883 |
| 1994 | 100.684 |
| 1995 | 124.764 |
| 1996 | 137.251 |
| 1997 | 147.513 |
| 1998 | 166.233 |
| 1999 | 151.592 |
| 2000 | 146.347 |
| 2001 | 152.049 |
| 2002 | 155.413 |
| 2003 | 155.116 |
| 2004 | 130.527 |
| 2005 | 111.104 |
| 2006 | 105.993 |
| 2007 | 99.091 |
| 2008 | 85.222 |
Figure 2- Area trawled by TCEPR vessels, 1990–2008
The animation in Figure 2- Area trawled by TCEPR vessels, 1990–2008 shows the geographic distribution of commercial trawling effort by Trawl Catch Effort Processing Return (TCEPR) vessels in New Zealand waters from 1990 to 2008, expressed as the total area trawled for each year in each 25 km2 (5 km by 5 km) ‘cell’. Around 67,000 of these cells are in fishable depths (less than 1600 m deep).
Many areas in the Exclusive Economic Zone (EEZ) are not fished by trawling, usually because they are too deep, or the sea floor is too rough, or because they do not support commercially viable fish catches. Overall, about 20 per cent of fishable cells (between 200 m and 1600 m deep) were trawled at least once1 by these large commercial vessels in the 2008 fishing year.
Figure two shows that trawl effort is highest in the eastern (on the Chatham Rise) and southern (on the north west edge of the Campbell Plateau) areas of the EEZ and is also high off the west coast of the South Island at the edge of the Challenger Plateau. Other trawling hotspots include areas off the Wairarapa coast and east of the Coromandel Peninsula. These are areas where the main target species of hoki, squid, orange roughy, southern blue whiting, barracouta, scampi and hake can be found.
Long-term trend
Figure 1 shows that the estimated total area trawled by TCEPR vessels increased from 85,448 km2 in 1990 to a peak of 166,233 km2 in 1998. Since 1998, the total trawled area has almost halved to 85,222 km2 in 2008. The percentage of fishable cells trawled at least once1 per year rose from around 18 per cent in 1990 to a peak of about 28 per cent in 2002, and decreased to around 20 per cent in 2008. Overall, 54 per cent of cells at fishable depths were trawled at least once1 in the 19 years for which there is data.
Recent trend
Figure 1 shows that the trawled area by TCEPR vessels steadily decreased from 111,104 km2 in 2005 to 85,222 km2 in 2008 (see ‘new data’ line). The percentage of fishable cells trawled at least once1 also decreased, from 23 per cent in 2005 to 20 per cent in 2008.
Figure 3 - Percentage change in average annual area trawled per cell by TCEPR vessels between the periods 1990–2005 and 2006–2008
Data source: Ministry of Fisheries (data groomed by NIWA)
Notes: (1) Cells trawled for the first time in 2006–2008 are displayed in burgundy. These cells have undergone an increase in trawled area but it is not possible to quantify the percentage change as the original area trawled is nil. (2) Cells with decreasing trawling effort may include cells that have been intermittently trawled over the 16-year period, but that have not undergone any fishing in the past three years.
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Figure 3 shows the geographic distribution of the percentage change in the average annual area trawled over the period 1990–2005, compared to the period 2006–2008.
Figure 3 shows the percentage change in the average annual area trawled over the period 1990–2005, compared to the period 2006–2008. On average, over the past three years (2006–2008), 41 per cent of fishable cells had decreasing trawling effort, with the majority of these cells decreasing by more than 50 per cent. Twelve per cent of fishable cells had increasing trawling effort compared with earlier years and 46 per cent of cells in less than 1600 m remained untrawled over the entire 1990–2008 period.
Figure 3 shows that, on average in the past three years (2006–2008) trawling effort in most of the areas in the main trawling hotspots decreased by more than 50 per cent compared with earlier years (1990–2005). This is also evident in the animation in figure 2. In contrast, trawling effort increased around other trawling hotspots including areas around the Coromandel, East Cape and Wairarapa. Trawling effort has also increased off the coast of Taranaki. As previously mentioned, the main target species found in the areas listed above include hoki, squid, orange roughy, southern blue whiting, barracouta, scampi and hake.
Trawling effort over these two time periods is dominated by the catch of middle-depth fish (ie, hoki, hake and ling) (Ministry for the Environment, 2009). Eighty-two per cent of the middle-depth fish catch was hoki. Middle-depth fish catches have declined from 203,140 tonnes in 1990 to 112,513 tonnes in 2008. Total allowable catches have been reduced for target species such as hoki from 200,010 tonnes in 2003 to 90,010 tonnes in 2008. This combination of fish catch declines and active management to reduce catch of target species has contributed to changes in the distribution of fishing effort over these time periods.
Number of trawls by commercial fishing vessels
Trawl effort by commercial fishing vessels increased from 112,822 trawls by 495 vessels in 1990 to a peak of 145,306 trawls by 481 vessels in 1997, followed by a steady decline to 84,800 trawls by 251 vessels in 2008 (figure 4). The increase in the number of trawls reported up to 1997 reflects increasing effort in a number of target fisheries, particularly hoki for the TCEPR vessels and inshore species such as flatfish and red cod for the CELR vessels. The drop in the number of CELR trawls after the mid-1990s reflects the change in form use to TCEPRs by some vessels. In 2008, the number of trawls by CELR vessels was almost nil as these forms were replaced by the new TCER forms.
Figure 4 - Total number of trawls by TCEPR and CELR/TCER fishing vessels, 1990–2008
Data source: Ministry of Fisheries (data groomed by NIWA)
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| TCEPR | CELR | TCER | |
|---|---|---|---|
| 1990 | 37.02 | 75.802 | 0 |
| 1991 | 44.754 | 83.112 | 0 |
| 1992 | 48.969 | 84.664 | 0 |
| 1993 | 51.716 | 91.592 | 0 |
| 1994 | 51.66 | 81.523 | 0 |
| 1995 | 57.293 | 78.739 | 0 |
| 1996 | 66.185 | 69.571 | 0 |
| 1997 | 70.004 | 75.302 | 0 |
| 1998 | 76.652 | 68.37 | 0 |
| 1999 | 70.113 | 69.9 | 0 |
| 2000 | 64.783 | 62.137 | 0 |
| 2001 | 63.096 | 58.81 | 0 |
| 2002 | 64.011 | 54.432 | 0 |
| 2003 | 62.447 | 57.319 | 0 |
| 2004 | 57.18 | 54.65 | 0 |
| 2005 | 53.981 | 58.319 | 0 |
| 2006 | 49.012 | 54.793 | 0 |
| 2007 | 44.912 | 52.341 | 0 |
| 2008 | 38.648 | 1.228 | 44.924 |
The above information has come from the latest seabed trawling snapshot report card.
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Last updated: April 2010
