Application 124771 - Ministry of Fisheries

MAY 2012 REPORT NO. 2167 | CAWTHRON INSTITUTE
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The sediment at the southern edge of the farm was primarily gravel (57.6% silt and
clay) with some sand (19.7%) and silt and clay (22.6%) present (Figures 2 and 3). The
high gravel content is consistent with the fine covering of shell hash observed in some
areas around the farm. The sediment core was a uniform grey brown colour with shell
hash/gravel visible and no obvious apparent redox potential discontinuity (aRPD)
layer (Figure 3).
Figure 3. Photograph of the sediment core from mussel farm Li 373.
2. CONCLUSION
The benthic environment observed under the current farm and the proposed
extension was typical of the modified benthic habitats found beneath inshore mussel
farms throughout the Coromandel (Taylor et al. 2012). The area was characterised by
areas of increased mussel shell cover and greater abundances of associated
epifauna. Site-specific factors such as water currents and substratum type are known
to influence the depositional effects of mussel farms on the benthic environment
(Hartstein & Stevens 2005, Giles et al. 2006), but the extent of effects can largely be
determined by the limits of the mussel shell drop-off (Wong & O’Shea 2011).
The main findings of the benthic assessment were:
1. Mussel clumps and shell drop-off were the most conspicuous changes to the
benthic environment. This extended approximately 50-115 m north and south of