Application 124771 - Ministry of Fisheries

MAY 2012 REPORT NO. 2134 | CAWTHRON INSTITUTE
The differences in infauna communities between the reference farm and control sites were
indicative of a mildly enriched benthic environment beneath farms resulting in greater
abundances of opportunistic species. However, in most cases the subtle differences
observed were in the abundance of species, rather than their presence or absence,
suggesting that infauna communities in the wider environment are already exposed to mild
enrichment. This conclusion was supported when the biological and physico-chemical data
were used to calculate enrichment stage (ES), and no significant difference between the ES
of control and farmed sites was found.
Epibiota communities at the reference farm sites were characterised by mussels and large
numbers of sea stars, sea cucumbers and ascidians, and were relatively diverse compared
to the sparse epifauna observed at most control sites (see Section 5.3). Scallops and horse
mussels were observed inshore of some reference farm and control sites, particularly on
sand- and shell-dominated substrata.
A snap-shot of water column properties at the reference farm and control sites using
replicate CTD casts showed a well-mixed water column at some reference farms and control
sites, but a thermo- and halo- cline (stratification of temperature or salinity) was observed
between 5-10 m at several reference farm sites and control sites (Section 5.4). The greatest
inter-site range in salinity and temperatures was observed in the top 5-10 m of the water
column. Chlorophyll-a (chl-a) was similar between reference farms and control sites
throughout much of the water column. Water column turbidity was similar between the
reference farms and control sites in the top 1-2 m of the water column; but there was less
turbidity between 3-5 m at farm sites. At depths of 5-7 m, farm sites were more turbid, but at
depths greater than 7 m, turbidity was generally lower at farm sites.
All of the 32 mussel farm sites and their proposed extension areas (Appendices 7-39) appear
to have been placed away from significant inshore reef and other sensitive habitats and were
mainly over muddy substrata. Consequently, effects to the benthic environment were
restricted to changes in infauna and epifauna abundances, related mussel drop-off and mild
enrichment from the farms.
Conclusions:
iv
1. Our assessment of the environment beneath the reference farms in the north and
south of Coromandel Harbour (from Wilsons Bay to Colville Bay) found differences
in the physical and biological characteristics of benthos, when compared to control
sites. Effects included minor enrichment and increased diversity of epibiota, and
were equivalent to those observed beneath mussel farms elsewhere in New
Zealand.
2. Farm-related effects of mild enrichment, and increased abundances of infauna
and epibiota were attributable to mussel drop-off and other farm-related deposition
that are not necessarily negative and would be reversible over time. The