The first and biggest steps

The first and biggest steps

Thursday, January 1, 2015

The main waterway that exits the Invermay deer farm (and itself drains directly into the Silverstream) does so at a site called the ‘Cattle Yards’, at a point at which the paddocks ‘Silage 1’, ‘Stag 1’ ‘Valley Hay’ and ‘Stag 2’ converge. Near this point there is a convergence of at least 4 smaller but permanent waterways that drain 90% of the deer farm area.

{Map 1}

It was decided that this site will be our main indicator of outcome of all our mitigations over the next 5 years.

Let me describe the state of this stream as of June 2014: it was a mess. Although only about a metre wide and half a metre deep in normal flow, you could not see the bottom. The level of sedimentation was so severe that water clarity was effectively zero. Electric fishing and invertebrate fauna surveys conducted several weeks later confirmed that the stream was in a very poor biological state. No fish (eels, galaxids), and only a handful of koura (freshwater crayfish) were found over a 50-metre stretch downstream from the deer farm exit point. The invertebrate fauna was impoverished, containing only those species able to survive in a highly degraded habitat.

Monitoring site 1 Cattle Yard Stream in September 2014.

Juvenile koura caught by electric fishing in September 2014.

Our priority task was to identify the main sources of contamination contributing to this state and eliminating them in order of the perceived severity of impact. This is what we did over a period of about 4 weeks:

  • The first decision was to completely retire 28 ha of the Invermay deer farm from deer grazing (some seasonal sheep grazing permitted). This was undoubtedly the single biggest step, and was not undertaken lightly. The fact is that some of our paddocks were predominantly swampy land heavily affected by deer (pugging and wallowing) and it was not cost-effective to re-fence to exclude the wet areas. Furthermore, drainage from these paddocks was directly entering the main creeks running through the farm …as can be seen on the map. The principle offending paddocks near the ‘Cattle Yards’ creek monitoring site were ‘Stag 2’, Stag 1’, ‘Crocodile’ and ’Roadside’. Fortunately, most of the actual creeks within the deer farm were already fenced along the riparian margins (e.g. below ‘Crocodile’) and it was just a matter of ensure that the fences along the riparian strip were fully deer-proof.

Invermay aerial map showing paddocks removed from deer grazing due to extreme water-logging (purple shading) and newly fenced deer paddocks (green shading).

  • 10 ha of new ‘safe’ deer paddocks were fenced into the deer farm around the western and northern margins to accommodate existing deer numbers and provide more options for deer fawning areas. These paddocks (e.g. 110, 127) were chosen based on their low risk in relation to waterways.
  • Two major deer wallows were fenced off for total exclusion, these being in paddocks ‘Hide 3’ and ‘Silage 1’. As these wallows were sited alongside existing fences, their exclusion simply required a single additional fence.
  • A number of smaller but draining wallows were infilled with rocks to deter further wallowing at these sites. However, wallows deemed as being ‘safe’ (non-draining) were left alone.
  • A large pond in ‘Silage 2’ was fenced off. This pond was heavily contaminated by deer and drained directly into the main creek. Exclusion required an extra 40 m of fencing.
  • 100 m of drain at the ‘Cattle Yards’, immediately outside the deer farm but above the main creek monitoring site , which had become heavily silted, was cleaned out by digger (under ORC supervision) and the riparian area bordering it was fully excluded from all livestock.

Silage 2 wallow pre-fencing in September 2014.

Silage 2 wallow two years after fencing.