Commercial coastal seabed trawling and dredging

  • Image, Commercial caostal seabed trawling.

    Seabed trawling and dredging, when fishing nets or dredges are towed near and along the seabed, can physically damage seabed (benthic) habitats and species. It can also stir up sediment from the seabed, shading (in shallow waters) or smothering marine species. This measure focuses on coastal areas (waters shallower than 250m). Focusing on coastal benthic habitats is important as these face multiple threats (for example from land-based activities) in addition to fishing.

    We classified Commercial coastal seabed trawling as supporting information.

    Key findings

    Seabed trawling and dredging are widespread in New Zealand coastal waters.

    • 64 percent of our inshore and shelf seabed environments identified in the Benthic-Optimised Marine Environment Classification (BOMEC) had at least 50 percent of their area trawled
    • seabed bottom trawling covered 48 percent (112,423 km2) of the BOMEC coastal environments (shallower than 250m).

    Figure 1

    Note: Commercial fishers report dredge tow numbers on CELR (catch effort landing return) forms.

    Figure 2

    Note: BOMEC = Benthic-Optimised Marine Environment Classification. Data are from trawls by coastal vessels fishing at depths shallower than 250m. A–E = inshore and shelf, F–H = upper-slope, I–J = northern mid-depth, K = lower-depth steep slopes, L = southern mid-slopes. The trawl areas for classes F, I, J, and L are too small to display. See Marine environments for a map of where BOMEC classes occur.

    Figure 3


    Definition and methodology

    This supporting information covers only the area of coastal seabed (depth less than 250 metres) trawled by commercial fishing vessels. This area is broken down by Benthic-Optimised Marine Environment Classification (BOMEC) seabed environments and by depth class.

    There is some overlap with the information reported on the Commercial seabed trawling webpage.

    The data are derived by overlaying the combined TCER and TCEPR 2007–08 to 2011–12 fishing years trawl footprint on BOMEC and depth classes for depths shallower than 250 metres (Baird et al, 2015). There are three depth classes: less than 50 metres, 50 to 100 metres, and 100 to 250 metres. There is some overlap with the Commercial seabed trawling and dredging case study.

    The BOMEC (Leathwick et al, 2008) includes five inshore and shelf classes (A, B, C, D, and E), three upper-slope classes (F, G, and H), two northern mid-depth classes (I and J), and one southern mid-slopes class class (L). BOMEC classes are broad surrogates for the different habitats affected.

    The commercial fishing year for most fish stocks goes from 1 October to 30 September, but some fish stocks have a fishing year of 1 April to 31 March.

    Data quality

     Topic Classification   Relevance Accuracy 
    Resource use and management, and other human activities Supporting information



    See Data quality information for more detail.


    Baird, SJ, Hewitt, J, & Wood, BA (2015). Benthic habitats and trawl fishing disturbance in New Zealand waters shallower than 250m (PDF, 11MB). New Zealand Aquatic Environment and Biodiversity Report 144. Retrieved from

    Leathwick, JR, Rowden, A, Nodder, S, Gorman, R, Bardsley, S, Pinkerton, M, …  Goh, A (2012). A Benthic-Optimised Marine Environment Classification (BOMEC) for New Zealand waters. New Zealand Aquatic Environment and Biodiversity Report No. 88. Available from

    Archived pages

    See Commercial coastal seabed trawling (archived October 2016).

    Updated 27 October 2016

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