Aquatic Environment and Biodiversity Annual Review 2012

7.1. Context
AEBAR 2012: Benthic impacts
For the purpose of this document, mobile bottom fishing methods include all types of trawl gear that
are used in contact with the seabed, Danish seines, and various designs of shellfish dredges. The
information available on the distribution and effects of Danish seining is poor relative to that on
trawls and dredges, so that method is not considered here in detail. The benthic effects of other
methods of catching fish on or near the seabed that do not involve deliberately towing or dragging
fishing gear across the seabed are thought to be considerably less than those of the mobile methods
(although not always negligible) and these methods are not considered in this version.
Trawls and dredges are used to catch a relatively high proportion of commercial landings in New
Zealand and such methods can represent the only effective and economic way of catching some
species. However, the resulting disturbance to seabed habitats and communities may have
consequences for biodiversity and ecosystem services, including fisheries and other secondary
production. The guiding sections of the Fisheries Act 1996 for managing the effects fishing, including
benthic effects, are s.8(2)(b) which specifies that “ensuring sustainability” (s.8(1)) includes “avoiding,
remedying, or mitigating any adverse effects of fishing on the aquatic environment” and s.9 which
specifies a principle that “biological diversity of the aquatic environment should be maintained”. Also
potentially relevant is the principle in s.9 that “habitat of particular significance for fisheries
management should be protected” (see the chapter on Habitats of Particular Significance for Fisheries
Management for more details).
One approach to managing the effects of mobile bottom fishing methods is through the use of spatial
controls. A wide variety of such controls apply in New Zealand waters (Figure 7.1). Some of these
controls were introduced specifically to manage the effects of trawling, shellfish dredging, and Danish
seining in areas or habitats considered sensitive to such disturbance (e.g., the bryozoans beds off
Separation Point, between Golden and Tasman Bays, and the sponge-dominated fauna to the north of
Spirits and Tom Bowling Bays in the far north). Other closures exist for other reasons but have the
effect of protecting certain areas of seabed from disturbance by mobile bottom fishing methods. These
include no-take marine reserves, pipeline and power cable exclusion zones, and areas set aside to
protect marine mammals (e.g., see Figure 7.2 for trawl closures introduced in 2008 to protect Hector’s
and Maui’s dolphins). Marine reserves provide marine protection in a range of habitats within the
Territorial Sea. Although marine reserves provide a higher level of protection by prohibiting all
extractive activities, most tend to be small. New Zealand’s 34 marine reserves protect about 7.6% of
New Zealand’s Territorial Sea; however, 99% of this is in two marine reserves in the territorial seas
around offshore island groups in the far north and far south of New Zealand’s EEZ (Helson et al.
2009). Until 2000, most closures that had the effect of protecting areas of seabed from disturbance by
trawling and dredging were in the Territorial Sea.
In the Exclusive Economic Zone, 18 seamount closures were established in 2000 to protect
representative underwater topographic features from bottom trawling and dredging (Brodie and Clark
2003, see Figure 7.1). These areas include 25 features, including 12 large seamounts >1000 m high,
covering 2% (81, 000 km 2 ) of the EEZ. The seamount areas are closed to all types of trawling and
dredging. In 2006, members of the fishing industry proposed the closure of about 31% of the EEZ to
bottom trawling and dredging in Benthic Protection Areas (BPAs), including the existing seamount
closures. The design criteria for the BPAs were they should be large, relatively unfished, have simple
boundaries, and be broadly representative of the marine environment. After a consultation process, a
substantially revised package of BPAs (including three additional areas totalling 13,887 km 2 , 10
additional active hydrothermal vents, and 35 topographic features) that complemented the existing
seamount closures was implemented by regulation in 2007 (Helson et al. 2009, Figure 7.3). BPAs
cover about 1.1 million km 2 (30%) of New Zealand’s EEZ and are closed to trawling on or close to
the bottom. Midwater trawling well off the bottom is permitted in the BPAs if two observers are on
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