Fishing in the Central South Island Region.

Graeme Hughes, Fish and Game Officer

River flows hamper anglers.
The last 6 weeks of the season have been extraordinary! At this time in most years, staff area checking nets charging Electric Fishing Machine batteries in preparation for inevitable fish salvage from rivers suffering from drought. This season has been the wettest for many years and continual rain events have seen almost all our rivers in high flow, many too high and discoloured for most anglers to fish. The timing has been unfortunate as most weekends flows have been at best marginal, but improving by mid-week which has been good for those able to fish at this time. Rain then falls and by the following weekend rivers are high and discoloured again.

High flows have positive effects.
While these conditions have been frustrating for anglers who can only fish weekends there have been some positive effects. The higher flows in the salmon rivers may have allowed for increased escapement of salmon in the Rangitata and Waitaki Rivers.  As far as can be ascertained 51 salmon have been landed by Rangitata anglers and one confirmed in the Waitaki. It is reasonable to assume that had rivers been at low flow more salmon would have been caught. Recent salmon seasons have been poor and most anglers would agree that the more salmon that successfully run the gauntlet of lower river anglers to reach the safety of natal spawning tributaries the more chance there will be of better returns in later years. Significant numbers of salmon are being taken from the Otago heads by trollers and it has often been assumed but never proven, that these fish are migrating northwards to the Waitaki River. Many will be optimistically waiting and hoping that some will make a “hard left” on their arrival at the Waitaki Mouth. The Waitaki River mouth is well north of the north bank fishing camp. From the South mouth car park it is a long walk, estimated to be 3 kilometres. While most have “4 wheelers” to travel the shingle dune for those who don’t, the north bank is a better option.  

The high flows have been useful in clearing “didymo” from several rivers, albeit temporarily. The Twizel, Ahuriri and to a lesser extent the Waitaki have shown that the high flows and moving bed material have abraded the growth from the substrate. In those streams where “didymo” has not established, river debris and macrophytes have been cleared giving the stream beds a much needed spring clean.

Progress on “Didymo”
NIWA research has shown that Didymosphenia geminata can be controlled, at least in its early colonisation, by a copper compound the scientists have name “Gemex”. Unfortunately where “didymo” is well established, it is doubtful if “Gemex” will be able to penetrate and destroy all the algae when it is in a dense carpet as found in the Waitaki River. It appears that as a first response to new infestations “Gemex” could be a stream saver. “Gemex” is a major break through; it will kill “didymo” but is non toxic to important algae, fish, and aquatic invertebrates.

Early in the history of “didymo” in New Zealand, observers of infected rivers in Southland noted that where groundwater inflows joined, there was an apparent deleterious affect on “didymo”. “Didymo” appears not to grow where the inflows meet, it struggles in the mixing zone and will not flourish until the flow is well diluted a short distance downstream. Several excellent examples of this phenomenon can be found along the Waitaki River. Accompanied by a Southland Fish and Game colleague several artificial substrates have been anchored in infected braids of the Waitaki upstream of some of these spring fed tributaries. When “didymo” has established on the substrates they will carefully be moved downstream into the confluence areas to see what the effects of the groundwater will be on the portable “didymo” plots.

Boaters Beware.
Boating the Waitaki River is quite different to other east coast rivers. Flows are controlled artificially by hydro power controllers and their dams, dictated by demand for electric power. There are few floods to keep beds clear of willow and scrub as occurs in rivers to the north. For example, in the Rangitata or Rakaia, when norwest rain events occur, unimpeded floods scour the riverbed removing any plants which grow in the flood plain. In the Waitaki this is not the case. Willows, standing and semi submerged are a constant threat to jet boaters. “Didymo” compounds the willow risk. Already reports have been received indicating how simple it is to render a boat helpless with a grill jammed solid with “didymo”. In the big willow studded flows of the Waitaki, a jet boat has little chance of surviving long without power or steerage. Overheating and seizing of jet boat engines has also been reported. “Didymo” is not only a danger when landing or leaving the shore line, the most common place to block the intake grill, but “didymo” will also be picked up as drifts in the water column. “Didymo” can have an accumulative effect, due to its fibrous nature, unlike indigenous algae which easily break up; “didymo” can build up on the intake as small particles.
Large mats of “didymo” torn off the substrate by river current can be sucked into the grill. Boaters will need to keep a watchful eye on the  water ahead and avoid downstream drifting algae. As engine cooling can be affected, constant monitoring of the temperature gauge is necessary. Boating anglers wii need to choose their landing and departure points on the river very carefully. Deeper backwaters or silted areas where “didymo won’t grow are recommended. Far better a short walk to the preferred fishing spot than sucking up a grill full of hard to remove “didymo”.  A weed rake is essential equipment, along with plenty of rope and some form of communication.  Tell some one where you are going, stick to your travel plan and have an ETA at your point of departure. 

Check, clean and dry message to continue.
Fish and Game Staff and Honorary Rangers will be distributing spray bottles with the required amount of detergent to kill “didymo” to any anglers they meet during the holiday period. Rubber waders are easy to clean, nets and lines feathered lures are no problem and easily disinfected. Neoprene takes a little more time as they tend to hold water. The main offenders are felt soled wading boots or felt soled waders. The soles cannot be successfully sprayed, they must be soaked preferably “stomped “ up and down in a bleach solution, i.e. Janola or a nappy cleaner to ensure the interior of the felt is thoroughly wetted. Anglers’ who in the warmer weather prefer to “wade wet” often wear their old hunting boots, too worn for the hill but very comfortable while fishing. They face a similar problem. To completely “de-didymo”, plunging them and allowing them to soak should do the job. Dedicating one pair of foot wear for each particular river fished is the ideal, however it depends on the individual and how many pairs of fishing boots are available. 
DOC have a team of staff dedicated to educating river users about “didymo” during the holiday season. If travelling in the MacKenzie high country don’t be surprised to see the “Rock snot rangers”, a title far from flattering, but one which I’m sure will stick. They are doing an important job, give them some encouragement and not a hard time, we need them out there!

Report on the 2005/06 Angler Diary Scheme
Hamish Stevens, Fish and Game Officer.

The following report summarises information from all diaries returned for the 2005/06 season, the second year of diary scheme, and also has a personal report of the fishing anglers  recorded over the two years.

The information gathered from diarists covers rivers and lakes fished, the catch and catch rates for both salmon and trout. A wide range of other data is also gathered which includes specific reach or area information, various environmental conditions and river levels. This gives us the opportunity to see possible effects on catch rates. That information is not presented here but we are happy to present any analysis you wish, just let us know.

Table 1: Your fishing over the last two seasons.

We provided diaries to 140 anglers in early October 2005. One hundred of those were returned at the end of the season although seven were incomplete or with an apology and promise to do better or fish more next season. The 93 diarists who completed daily records of their fishing activities visited 66 rivers or lakes and recorded landing 179 salmon and 1,638 trout for 7,227 hours spent fishing.

Comparing 2005/06 to the 2004/05 season, the total number of salmon landed was less than half that of the season before (down by 295) and the total fishing hours were also down on the previous season (down by 2,698 hours). However the total number of trout caught increased in 2005/06 with 212 more trout caught than in the previous season. The trout fishery’s gain was the salmon fishery’s loss with 16% more anglers targeting trout in 2005/06 than in the previous season and 11% fewer anglers targeting salmon.

Rivers sustaining sea-run salmon fisheries, such as the Rakaia, Opihi and Waimakariri were visited by 66 anglers who targeted salmon. These anglers landed 82 salmon in 4,130 hours with a success rate of 1 salmon every 50 hours. The average weight for salmon was 6.22kg. Salmon anglers also landed 100 trout, 75% of which were rainbows, with an average weight of 1.4kg. 

Land-locked salmon fisheries such as lakes Coleridge, Heron and the hydro canals were fished by 13 anglers. They caught 97 salmon at a catch rate of 5.2 hours per fish and 21 trout at 24 hours per fish.

Sixty four anglers targeting trout fished 65 different rivers or lakes and caught 7 perch and 1,521 trout at 1 trout every 1.5 hours. The catch was evenly split between browns and rainbows with 52% being brown trout.

On the following page is a summary of the 2005/06 fishing seasons activity for all anglers. Anglers fished for T = trout, S = Salmon and T/S = trout and salmon. In addition to this table, there were 31 river or lake fisheries that were visited by only one diarist. These fisheries accounted for another 80 days of fishing and 80 trout landed.