Application 124771 - Ministry of Fisheries

CAWTHRON INSTITUTE | REPORT NO. 2134 MAY 2012
5. RESULTS
5.1. Sediment physical and chemical properties
Sediments sampled from within the eight reference farms and six control sites
contained varying amounts of silt and clay (< 63 µm), sand (< 2 mm and > 63 µm) and
gravel-sized (> 2 mm) components (Figure 4, see Appendix 2 for raw data). No clear
patterns in sediment particle grain-size components relating to area (north or south of
Coromandel Harbour) or site type (‘control’ versus ‘farm’) were evident. The majority
of sites within the region had only small gravel components, and only four sites had an
average gravel component of 20% or more (Control sites 1 and 4 and Farm sites 1
and 6). A different suite of sites had sand components greater than 30% of their total
dry weight (Control sites 2 and 4 and Farm sites 2, 6 and 7), and it was these same
sites that had silt components that were less than 50% of their total dry weight. At all
other sites, the majority of the sediments (> 50%) were comprised of fine muddy silts
(< 63 um).
Observations made from video footage (see Section 5.4), were consistent with these
results, where fine silt/mud was the most common substratum, even at control sites.
Sand/shell dominated substrata were only observed at a small number of control and
farm sites. Sediment cores at the majority of reference farm and control sites were
characterised by a fairly uniform light grey/brown colour and appeared well
oxygenated, with poorly defined aRPD layers that ranged between 40 and 60 mm
below the seafloor (see Appendix 2 for images). No sulphide odours were detected.
Total nitrogen (TN) was significantly higher in sediments collected from under farms
than at control sites (site type, F1, 38 = 7.98, p