Skip to main content
Last reviewed:

Bottom trawling summary facts

  • Around 30% of New Zealand’s exclusive economic zone (EEZ) is closed to bottom trawling. Trawling of all types is prohibited in about 21% of the territorial sea.
  • The trawl footprint (the total area trawled in a given year) has been declining over time. In 2019, it was 81,054 square kilometres.
  • The total area trawled from 1990 to 2019 is 460,627 square kilometres, or about 11% of New Zealand’s EEZ and territorial seas.
  • In the 2020/2021 fishing year, 68% of all fish caught commercially in New Zealand were caught using either bottom trawl gear or mid-water trawl gear within 1 metre of the seabed.

About bottom trawling fishing

Trawling is when a fishing net is towed by a boat. Nets can be towed either:

  • through the water column (mid-water trawl)
  • along the seafloor (bottom trawl).

Trawling is one of the most common methods of fishing. Large quantities of fish can be caught in a single tow. Many of New Zealand's popular fish live on or near the seafloor and are commonly caught by trawl fishing, like orange roughy, squid, and snapper.

Fishers report to us what type of fishing gear they use, the depth of the gear, and the depth of the seabed.

The gear used to trawl depends on the fish being targeted and the area being fished. Bottom trawling gear tends to be heavier and larger than mid-water trawl gear. Both types of gear can be used near the seafloor. But heavier bottom trawling gear can cause more damage to the seafloor.

When measuring the extent of bottom trawling in New Zealand, we include:

  • all fishing using bottom trawl gear, and
  • fishing with mid-water trawl gear where this is within 1 metre of the seafloor.

In the 2020/2021 fishing year, almost 250,000 tonnes, or 68% of the volume of all fish caught commercially in New Zealand was caught using bottom trawl gear or mid-water trawl gear within 1 metre of the seabed.

Graph: Estimated catch totals and number of bottom impact trawl events

This graph shows the amount of estimated catch from bottom impact trawl events for each fishing year from 2007/08 to 2020/21, including the number of events that relate to the catch for each year. Overall, the estimated catch and bottom impact trawl events have decreased slightly.

Why the seafloor is important

The seafloor is an important habitat for a number of marine species. It’s not entirely flat – some parts are made up of features like trenches, sea mounts, ridges, and rises. Some areas of the seafloor are made up of soft sediment. These areas are less likely to be impacted by bottom trawling.

The seafloor provides important habitats for many fish, invertebrates, and coral, particularly for juvenile life stages. Some seafloor species are long-lived. For example, deepwater coral can live for hundreds of years. Some species are also legally protected under the Wildlife Act 1953, or are defined as "threatened" or "at risk". Other areas support rare and special biological communities.

How fishing can impact the seafloor

The impacts of fishing on the seafloor depend on a range of factors, including:

  • the location of fishing
  • features on the seafloor
  • flora and fauna present
  • frequency and duration of fishing.

Trawling on the seabed results in contact of the fishing gear with the seafloor. Factors that influence the potential impact include:

  • gear design
  • weight
  • towing speed
  • tides and currents
  • seabed characteristics.

Some seafloor species can withstand bottom trawling due to their size, shape, and where they live. Species most sensitive to trawl activity are animals that live on the seafloor and are structurally fragile, like:

  • stony, gorgonian, and black corals
  • sponges
  • hydrocorals
  • bryozoans.

Bottom trawling can remove animals living on the surface of the seabed within the trawl path, reducing species richness, diversity, cover, and abundance. It can also affect the species richness, diversity, cover and abundance of these animals living on the surface of the seafloor.

Areas protected from bottom trawling

Around 30% of New Zealand’s exclusive economic zone (EEZ) is closed to bottom trawling. Trawling of all types is prohibited in about 21% of the territorial sea (the area within 12 nautical miles of the coast).

The effects of bottom trawling are managed through:

  • closing certain areas to trawling
  • limiting which sized vessels can fish in an area – for example, vessels over 46 metres in length are prohibited from trawling in the territorial sea.

The catch limits imposed under the Quota Management System also act to limit the amount of trawling that occurs in our waters.

Some closures to trawling were put in place to limit the effects of fishing on the seafloor environment, like seamount closures and benthic protection areas.

Download a map of marine protected areas [PDF, 7.1 MB]

The seafloor is also protected from bottom-impacting fishing with:

  • marine mammal sanctuaries
  • recreational areas
  • submarine cable closure zones.

The benthic protection area (BPA) proposal was brought into effect in 2007. It sets aside a broadly representative sample of seafloor habitats, in essentially pristine condition. BPAs were selected on the basis of 4 key criteria. They:

  • are large areas
  • are relatively unfished
  • have simple boundaries
  • are broadly representative of the marine environment.

Read more about benthic protection areas

Monitoring the impacts of fishing on the seafloor

We collect a range of information about impacts of fishing on the seafloor. This includes:

  • the trawl footprint
  • how much trawling is taking place in new areas
  • where and when trawling occurs.

The extent of bottom contact by commercial trawling and dredging in NZ waters, 1989–90 to 2018–19 [PDF, 29 MB]

Trawl footprint

The trawl footprint is the total area of the seabed that has or may have been contacted by fishing gear. This measurement includes all fish caught commercially in New Zealand using either bottom trawl gear, or  mid-water trawl gear within 1 metre of the seabed. 

In 2019, the trawl footprint was 81,054 square kilometres (km2). The total area trawled from 1990 to 2019 is 460,627km2. This is about:

  • 11% of the total area within the boundary of New Zealand’s EEZ and territorial seas
  • 33% of the area that can be fished (which is down to depths of 1,600 metres).

We have been estimating the trawl footprint since 1990 for deepwater fisheries and since 2009 for all trawl fisheries. How trawl effort is reported has changed over time. For example, in 1989 we began requiring some larger vessels (mostly those greater than 28 metres in length) to report start and end positions of trawl tows. Since 2007, smaller vessels have been required to report the start position of tows.

Table: Trawl footprint from 2006-07 to 2018-19

Fishing year

Estimated annual
footprint (km2)

Estimated annual
aggregated footprint (km2)

Newly trawled
footprint (km2)

2006–07

67,815

156,006

122.1

2007–08

93,220

153,356

782

2008–09

90,874

164,795

76.7

2009–10

95,489

157,466

55.5

2010–11

92,117

154,317

98.5

2011–12

88,931

148,136

27.8

2012–13

86,594

153,953

30.1

2013–14

91,430

150,830

25.8

2014–15

89,808

148,274

152.3

2015–16

87,220

156,040

72.8

2016–17

88,958

160,150

59.2

2017–18

89,432

143,502

27.4

2018–19

81,055

156,006

78.4

How much trawling is taking place in new areas

Since our records began in 1990, we measure how much trawling is taking place in new areas which have not been contacted by fishing gear. In 2019, 78.4km2 of the trawl footprint were newly trawled areas. Overall, the newly trawled area per year has been decreasing over time.

Where and when trawling occurs

The introduction of electronic position and catch reporting in 2018/19 has improved the level of detail about where and when trawling is occurring. We now have a more accurate measurement of where trawling is occurring. As a result the way we measure the trawl footprint has changed over time.

Some of the area in the footprint will have been trawled repeatedly. Overall, the frequency of areas being trawled has been reasonably steady over the past 10 years. The intensity of bottom contact is greater in some areas, like the central east of the North Island (FMA2) and the south-east of the South Island (FMA3). This is a result of greater levels of fishing in these areas, as well as the localised area of some species targeted.

How we measure trawl footprint

To estimate the trawl footprint, the reported start and end positions of each tow are plotted, and straight lines are drawn between them. The lines are then buffered by the standard width of the trawl doors to create a rectangle for each tow which represents the area of seabed contacted by the trawl gear, known as the swept area.

Before electronic reporting, for some vessels, end positions were not required to be reported and the coordinates reported were accurate to only 1 nautical mile. In addition, with only start and end positions available, we can only plot straight lines, whereas we know trawl tows are often not straight. As a result, the position of these plotted tow tracks is an approximation.

We continue to explore ways to improve our methods. A key improvement will be the transition from straight lines being drawn between start and end points of trawling events to calculate the trawl footprint, using GPS data, to define the area of contact with the seafloor more accurately.

Forum to manage the effects of bottom trawling in the EEZ

Fisheries New Zealand and the Department of Conservation have established a stakeholder forum on managing the effects of trawling in the EEZ. The forum includes members from:

  • environmental non-governmental organisations
  • the fishing industry
  • the National Iwi Chairs Forum.

The forum will provide recommendations in late 2022, which will inform public consultation on measures to reduce the impacts of bottom trawling.

Managing the effects of bottom trawling in the EEZ forum – Terms of reference [PDF, 200 KB]

Managing bottom trawl and Danish seine in the Hauraki Gulf

As part of the Revitalising the Gulf strategy, Fisheries New Zealand is further limiting Danish seining and bottom trawling activity in the Hauraki Gulf to carefully selected access areas or "trawl corridors". This will help protect the seafloor and its ecosystems.

These measures will help address the impacts of bottom trawling in the Hauraki Gulf in a way that sustains and supports the ecosystem. With input from mana whenua and stakeholders, Fisheries New Zealand will design, select, and designate areas or "corridors" within the gulf where bottom trawling and Danish seining can continue to occur but with less impact on biodiversity.

A research project commenced in 2022 to support this process and a Hauraki Gulf specific spatial planning tool is in place. Fisheries New Zealand will work to finalise options for trawl corridors in 2023, using the spatial planning tool that has been developed and with input from mana whenua, key stakeholders, and the Hauraki Gulf Fisheries Plan Advisory Group.

Find out more about the Revitalising the Gulf strategy

Who to contact

If you have questions about bottom trawling, email info@mpi.govt.nz

MPI business units