Application 124771 - Ministry of Fisheries

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CAWTHRON INSTITUTE | REPORT NO. 2134 MAY 2012 usually difficult to detect within 20-50 m away. A similar conclusion was reached in a recent study under mussel farms in the Hauraki Gulf (Wong & O’Shea 2011), who suggested that the extent of mussel clumps on the seabed was the best indicator of the extent of benthic effects. The most important factors influencing the area and magnitude of effects surrounding mussel farms are water depth and current speeds (Hartstein & Stevens 2005); hence severity of effects is very much site-specific and effects are minimised by locating farms in well-flushed areas, where species and habitats of special value are not present. Enrichment from farm-derived biodeposits is the primary cause of seabed effects in soft-sediment habitats and the type of effects are reasonably well described (Keeley et al. 2010), as such they can be placed on an enrichment gradient ranging from natural to azoic (Figure 3). Using biological and physico-chemical data from benthic enrichment studies under finfish and mussel farms throughout New Zealand, the gradient has been described numerically with enrichment stages (ES) 1 to 7 (Figure 3). This method can now be assigned to benthic grab samples to allow comparison of enrichment effects from sites around New Zealand (Keeley et al. 2012, Keeley et al. In press). Figure 3. Stylised depiction of a typical enrichment gradient experienced at low flow sites, showing generally understood responses in commonly measured environmental variables (species richness, infauna abundance, sediment organic content and sulfides and Redox). Apparent Redox Potential Discontinuity depth (aRPD) and prevalence of bacteria (Beggiatoa spp.) mats and methane/H2S out-gassing also indicated. The gradient spans from natural or pristine conditions on the right (ES = 1) to highly enriched azoic conditions on the left (ES = 7). 5
MAY 2012 REPORT NO. 2134 | CAWTHRON INSTITUTE 6 3.2. Water column effects Effects of mussel cultivation on the water column are less well defined than for the seabed, because water column characteristics are more dynamic and inherently harder to quantify. The physical presence of farms can alter and reduce current speeds, which affects water residence times and has implications for associated biological processes. Farm structures can also attenuate short-period waves (Plew et al. 2005), which can affect inshore ecology, but these issues are not considered significant at the present scale of development in New Zealand. Bivalves and other associated fauna release dissolved nitrogen (e.g. ammonium) directly into the water column, which can cause localised enrichment and stimulate phytoplankton growth. Toxic microalga blooms may lead to ecological or health problems, but there is no evidence of this being exacerbated by mussel farming in New Zealand waters. Filtration pressure by mussels is sufficient to potentially alter the composition of the phytoplankton and zooplankton/mesoplankton communities through feeding, but the extent to which this occurs and its ecological consequences are poorly understood. Despite the recognised knowledge gaps, the fact that no significant water column related issues have been documented, suggests that effects associated with traditional inshore farming practices are minor (Keeley et al. 2010).
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CAWTHRON INSTITUTE | REPORT NO. 213
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To: Waikato Regional Council Privat
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Contents 2 Contents ...............
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4 marine farm (which expires on 1 J
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6 2011) identified that the aquacul
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8 Goodwin E, 2012. Assessment of Be
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10 4.5.8 The capacity of the wharf
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12 in Appendix 1 and designed in ac
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7. Relevant Planning Provisions 14
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16 the applicant is a member of the
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7.18 Policy 6.1.3 - (Integrated Man
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Appendix 1: Survey plan showing loc
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REPORT NO. 2167 COROMANDEL MUSSEL F
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Application 124771 - Ministry of Fisheries

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