Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Benthic impacts
Figure 7.13: Maps from Baird and Wood (2010) showing BOMEC classes I (left) and M (right) overlaid with the
footprint of trawls on or near the seafloor reported on TCEPR forms to 2004–05 for each 25-km 2 cell.
7.3.4. Studies of the Effects of Mobile Bottom Fishing Methods in
New Zealand
The widespread nature of bottom trawling suggests that fishing is the main anthropogenic disturbance
agent to the seabed throughout most of New Zealand’s EEZ. Wind waves are certainly very
widespread, but both field studies and modelling (Green et al. 1995) suggest that erosion of the
seabed deeper than 50 m by waves occurs only very rarely in the New Zealand EEZ. Despite their
widespread distribution at the surface, therefore, wind-waves are not a dominant feature of the longterm
disturbance regime throughout most of the EEZ. In some places, especially in the coastal zone
and in areas close to headlands, straits, or islands, currents and tides may dominate the natural
disturbance regime and a community adapted to this type of disturbance will have developed.
However, over most of the EEZ between about 100 and 1000 m depth, especially in areas where there
are few strong currents, fishing is probably the major broad-scale disturbance agent.
Several studies have been conducted since 1995 in New Zealand, focussing on the effects of various
dredge and trawl fishing methods on a variety of different habitats in several geographical locations
(Table 7.4). Despite the diversity of these studies, and their different depths, locations, and habitat
types, the results are consistent with the global literature on the effects of mobile bottom fishing gear
on benthic communities. Generally, there are decreases in the density and diversity of benthic
communities and, especially, the density of large, structure-forming epifauna, and long-lived
organisms along gradients of increasing fishing intensity. Large, emergent epifauna like sponges and
framework-forming corals that provide structured habitat for other fauna are particularly noted as
being susceptible to disturbance by mobile bottom fishing methods (Cranfield et al. 1999, 2001, 2003,
Cryer et al. 2000), especially on hard (non sedimentary) seabeds (Clark & Rowden 2009, Clark et al.
2010a&b, Williams et al. 2011). Even though large emergent fauna seem most susceptible, however,
effects have also been shown in the sandy or silty sedimentary systems usually considered to be most
resistant to disturbance (Thrush et al. 1995, 1998, Cryer et al. 2002). Also typical of the international
literature is a substantial variation in the extent to which individual New Zealand studies have shown
clear effects. For instance, in Foveaux Strait, Cranfield et al. (1999, 2001, 2003) inferred substantial
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