Iron floc in streams is perfectly natural

 

Iron floc seeping from the stream bank

Floc is the fluffy material you see in some waterways, sometimes forming soft stalks. It is quite delicate and will break apart easily when disturbed so even though it may not be ‘aesthetically pleasing to the eye’ it is an important metabolic process that should be allowed to occur, and in fact is likely to be a very ancient process in the context of the development of life on earth (there is actually a good deal of research on different iron oxidizing bacteria, and it is a worldwide phenomenon). The harvested electrons by the bacteria provide energy for reproduction and other life-sustaining processes in the life of these single-celled organisms. A variety of species and sub-species of bacteria carry out this process. It requires oxygen, so these bacteria live and reproduce where iron-rich water flows out of the ground and is exposed to oxygen in the air. This is a completely natural process.

Interestingly enough, and it has not been worked out why, we find that giant kokopu are very fond of streams that have lots of iron floc, with good populations in some urban and perimeter urban Hamilton streams.

In this You Tube clip https://youtu.be/8w0kgAwv1Ps taken in the Gordonton arm (zone 3) of Mangaiti Gully stream you will see the iron floc floating about from the disturbance of the eels. A giant kokopu is visible at the end of the clip. Kōura / freshwater crayfish have been found a little downstream from this photo point. All indicating healthy stream fauna happily living among the iron floc.

Fishing prohibited signs to protect longfin eel / tuna

Several people that live on the gully feed eels in the stream below their properties. There are two types of eel: the shortfin, which is more common, and the longfin which has a DOC classification of “at risk – declining”. Eels have been written about before on this blog site. They have a remarkably interesting life cycle. The longfin grows up in the streams for 30 to 60 years, after which they leave the stream systems and migrate out to sea, swimming up to the tropics (around Tonga) to mate, spawn then die. The little glass eels drift back to NZ and find a stream to migrate up and so the cycle continues, unless someone fishes them out of the stream, often for no other reason than for “fun” leaving them to die on the stream bank.

Part of council’s project to develop the Gordonton arm (zone 3) is to cut a track to give access. Unfortunately, this also gave access to the public, and we have received a number of reports from concerned neighbours that fishing was going on and they feared for their “pet” eels. Once it was brought to council’s attention, signs were made and placed along the stream length.  

Unfortunately trying to protect our native fauna seems to be an ongoing battle.

Rat trapping trial

We have run a highly successful rat control community-based programme for the last ten years. This programme uses a bait block containing bromadiolone as an active ingredient. The design of these blocks was to have a very low, to no, secondary kill. In other words, if something ate a dead or dying poisoned rat it would not also be poisoned. We felt this was important because of domestic cats and dogs in the area. When you have a programme like this it is important that you have the majority of people in the area on your side and we would not get that if we were knocking off their cats and dogs. Incidentally, some baits, brodifacoum for example, are designed to have a secondary kill. This bait, which goes under a number of proprietary names, is freely available at most hardware stores.

Successive programmes around the country which have tried to get a good knock down of rat numbers using only traps, have never been successful. Remember it is not how many rats you catch, but the number of rats left. Rats are prolific breeders with one pair in spring potentially responsible for up to 2000 offspring by late autumn. Therefore, our aim has been to eradicate all resident / breeding rats and then knock out reinvasion to prevent the rats getting re-established. To date we believe we have been successful.  

So why look at traps? The use of toxins has never been ideal.

There are two motivations for this trial. One is that ruru / morepork owls nest in the gully. They catch mice. Mice also feed on the poison baits. Although the bait should have a low secondary kill, we do not know what effect it would have on chicks. Secondly Hamilton City Council has always been uncomfortable with our community-based programme.

Owl with mouse at nest in Mangaiti Gully 

Koi Carp not a problem in Mangaiti Streams

 

Koi carp are a very invasive and ecosystem destructive species so when a report was received of a sighting in the stream on the western side of Hukanui Road it was a concern that potentially, there was another invasive species that we had to contend with. Fortunately, this was found not to be the case after discussing the matter with Bruno David: SCIENTIST- water, science, and strategy, at Waikato Regional Council.

He said that while the odd koi carp may appear and may even move up into the wider system, the broader catchment is not an ideal habitat for koi to do well in (other than maybe the very lower reaches near the confluence with the Waikato River mainstem). Koi carp much prefer slower flowing, warmer water to cruise around and fossick among soft substrate (mud) etc. Koi carp only become a problem (and create measurable water quality changes) in systems when they get into densities that are >80-100kg/ha and he would be extremely surprised if this ever occurred up the Mangaiti. The odd fish, therefore, would be very benign.

Carp have been around in the lower Waikato system since the late 60’s and they are very dispersive so in most cases they have already infiltrated the places that they can reliably get to and want to get to. The fact that we do not see them routinely in the Mangaiti, indicates that they do not really want to go up there as they have much better options elsewhere.

So, all round it sounds as if we are safe from this pest species. On saying that if you do see one feel free to remove it from the stream notwithstanding the “Fishing Prohibited” signs around.

Nikau planting

14-year-old palms in 45Lt pots 

Nikau are very slow growers. It takes a good 15 years for them to form the beginnings of a trunk, so a two-metre specimen may be more than 30 years old. Our native nikau are prolific berry producers that are favoured by kereru / wood pigeon. Not only do kereru gorge themselves on the berries but they are very effective at seed dispersal, so once nikau are established and fruiting the cycle of distribution begins and they become self-sustaining.

Because of the long establishment time, we purchased twenty 14-year-old palms in 45Lt pots for this season’s planting. These have been planted in groves of five, in four different locations around the gully to supplement smaller nikau that have been planted over the years.