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Oceans Fishing activity Seabed trawling
Types of fish in areas trawled
Demersal fish live at or near the bottom of the sea. There are 16 classes in the Demersal Fish Community Classification.
Figure 1 - Cumulative trawled and untrawled areas by TCEPR vessels and Demersal Fish Community Classification, 1990–2008
Data source: Ministry of Fisheries and Leathwick et al 2006
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Figure 1 shows the geographic distribution of the 16 fish community classes in the Demersal Fish Community Classification. Each class represents a different demersal fish community characterising each area and is shown by a different colour. The dashed shades show where the various classes (and their fish communities) have not been trawled.
Current situation
Figure 1 shows the 16 fish community classes in the Demersal Fish Community Classification. Each class represents a different demersal fish community characterising each area and is shown by a different colour. The dashed shades show where the various classes (and their fish communities) have not been trawled. Note that the area trawled represented in figure 1 simply shows areas that have and have not been trawled, and does not show the intensity of trawling. For example, if a trawled cell had been trawled only once in the past 19 years, it would still appear as a trawled cell in figure 1.
Figure 2 - Cumulative area trawled by TCEPR vessels as a percentage of total area of each Demersal Fish Community Class, 1990–2008
Data source: Ministry of Fisheries and Leathwick et al 2006
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| Demersal Fish community class | Area trawled km2 | Total Area km2 | % of area |
|---|---|---|---|
| Northern Coastal | 42,007 | 45,725 | 92% |
| Southern Coastal | 19,468 | 27,725 | 70% |
| Northern Shelf | 75,080 | 79,237 | 95% |
| Central Shelf | 78,212 | 88,687 | 88% |
| Southern Shelf | 22,333 | 38,489 | 58% |
| Challenger Plateau 1 | 18,020 | 23,523 | 77% |
| Challenger Plateau 2 | 74,920 | 130,612 | 57% |
| Chatham Rise 1 | 33,748 | 35,238 | 96% |
| Chatham Rise 2 | 31,050 | 35,531 | 87% |
| Chatham Rise 3 | 108,571 | 132,106 | 82% |
| Campbell Plateau 1 | 33,409 | 39,150 | 85% |
| Campbell Plateau 2 | 87,077 | 126,692 | 69% |
| Campbell Plateau 3 | 118,800 | 191,838 | 62% |
| Northern Midslope | 72,157 | 213,641 | 34% |
| Southern Midslope | 48,301 | 153,813 | 31% |
| Deep Midslope | 25,177 | 517,165 | 5% |
Figure 2 shows the cumulative area trawled (the sum of the area of all trawls) as a percentage of the total area per demersal fish community between 1990 and 2008. In the main trawling hotspots trawls may have occurred multiple times in the same location over the past 19 years and so, while the total trawled area may be high this does not mean that the entire area of the fish community has been fished. For example, the cumulative trawled area may total 95 per cent of a demersal fish community class area, but all of this trawling can occur in one-third of the area, leaving the other two-thirds unfished.
Note that inshore fishing areas (coastal areas) are comparatively under-represented because smaller vessels that do not use TCEPRs are more likely to fish inshore and are not included in these analyses.
The Chatham Rise 1 fish community had the highest (96 per cent) percentage area trawled in the 19-year period 1990–2008. However, this is a fairly small demersal fish community class area. Fish caught in high volumes in this area are spiny dogfish, silver warehou, and occasionally hoki (Leathwick et al, 2006)2.
Northern Shelf and Northern Coastal fish communities also had a high percentage area trawled from 1990 to 2008 (95 and 92 per cent respectively). Fish species caught in high volumes in these areas include snapper, spiny dogfish, barracouta and tarakihi (Leathwick et al, 2006)3. The Chatham Rise 1, Northern Shelf and Northern Coastal fish communities all have relatively small areas compared to some of the larger demersal fish communities (eg, Campbell Plateau 3, Northern Midslope and Deep Midslope) and as a result small changes in fishing patterns in the vicinity can generate large local changes (B. Wood, NIWA, pers. comm., 21 December 2009).
The Deep Midslope fish community had the lowest percentage of its area trawled (5 per cent) in the 19-year period 1990–2008. However, the Deep Midslope fish community is the largest demersal fish community with a total area of 517,165 km2. Fish most commonly caught in small volumes in this area include lighthouse fish, spineback and Baxter’s dogfish, and occasionally smooth oreo are caught in large volumes (Leathwick et al, 2006)2. Despite the large size of this fish community, it is likely to be lightly fished as it is outside trawlable depths and the species that are listed are not target or Quota Management System or commercially viable species.
Trend
Figure 3 - Percentage change in average area trawled by TCEPR vessels between 1990–2005 and 2006–2008 by demersal fish community class
Data source: Ministry of Fisheries and Leathwick et al 2006
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| Demersal fish community class | Change |
|---|---|
| Northern Coastal | 1.2% |
| Southern Coastal | -36.9% |
| Northern Shelf | 16.7% |
| Central Shelf | -8.5% |
| Southern Shelf | -22.6% |
| Challenger Plateau 1 | -16.0% |
| Challenger Plateau 2 | -42.7% |
| Chatham Rise 1 | -37.5% |
| Chatham Rise 2 | -27.8% |
| Chatham Rise 3 | -38.5% |
| Campbell Plateau 1 | -34.0% |
| Campbell Plateau 2 | -49.2% |
| Campbell Plateau 3 | -63.2% |
| Northern Midslope | -31.2% |
| Southern Midslope | -16.4% |
| Deep Midslope | -29.2% |
Figure 3 shows a summary of percentage change in the average annual area trawled over the period 1990–2005 compared with the period 2006–2008 by demersal fish community. The average annual area trawled from 2006–2008 decreased in the majority of the demersal fish communities compared to 1990–2005.
The Campbell Plateau 3 fish community had the greatest decrease, with a 63 per cent drop in the average annual area trawled in 2006–2008 compared to 1990–2005. Campbell Plateau 2 and Challenger Plateau 2 also had large decreases (49 and 43 per cent respectively). Fish commonly caught in high volumes in these areas include hoki, javelin fish, ling, southern blue whiting, and occasionally orange roughy (Leathwick et al, 2006)2. As mentioned above, these trends reflect decreases in the total allowable catch of some target species such as hoki.
The establishment of protected areas also influence seabed trawling activity as some areas within a demersal fish community class may not be able to be fished or may have restrictions in place that have been brought in during the sampling period of 1990–2008. For example, 31 of New Zealand’s marine reserves were established after 1990 (Ministry for the Environment, 2008) and the Southern Shelf class has the second largest marine reserve in its area. This in turn has influenced fishing patterns since 1990.
Northern Shelf and Northern Coastal fish communities were the only two communities to have an increase in their average area trawled (17 and 1 per cent respectively) in 2006–2008 compared with earlier reporting. Fish species commonly caught in high volumes in these areas include snapper, barracouta, spiny dogfish, and tarakihi (Leathwick et al, 2006)2.
The above information has come from the latest seabed trawling snapshot report card.
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Last updated: April 2010
