Fishing in the Central South Island Region.

Graeme Hughes, Fish and Game Officer

Low water fishing creates a challenge.
The Central South Island region enjoyed a wet spring and early summer but recently dried abruptly and within a very short period norwest conditions and no rain had trout rivers down to precarious levels. Irrigation restrictions may have slowed their recession but levels continued to fall. Surprisingly trout numbers in the smaller rivers remained unchanged, however catching these at this time is very difficult. Low water trout are always a challenge and after such a long period of optimum levels and good invertebrate production the degree of difficulty for anglers increases markedly.

Fish salvage from drying pools in the Hakataramea, Ahuriri and Maerewhenua Rivers was imminent until life saving rain fell augmenting all waters of the region. The effects however have been short lived and levels have again dropped rapidly. Norwesterly weather patterns have returned a reminder of the undesirable El Nino conditions we have experienced before but fortunately this time, as the fishing season comes to an end.

Waitaki River Salmon run in top gear.
As the early closing of the salmon season looms the salmon catch has caused quite a commotion The Waitaki River has been running high and most days has been flowing at between 400 and 500 cumecs. High flows disadvantage anglers and most would prefer the river to be below the 300 cumec area especially during the salmon fishing period. After a slow start the salmon season in the last three weeks has “taken off” with limit bags not uncommon. More recently 30 to 40 fish are being taken per day. Despite reports of the fish being bigger and better than in previous seasons the salmon weights are consistent with the Waitaki River average of 7 to 8 kg. The largest salmon recorded so far weighed 11.5 kg Fishing for salmon in the Waitaki River is prohibited for the month of April, a regulation introduced to allow more salmon to reach their spawning grounds. There are some anglers who will see this as lost opportunities. Just when it appears that the numbers are up Fish and Game close the season a month early. Most however see this as a necessary move to ensure we don’t lose this valuable resource. If the run continues at this pace it will be to the anglers advantage, in three years time they will reap the benefits of an increase in the number of “Chinooks” spawning in the Waitaki River.

To the north the Rangitata and Opihi Rivers are still providing a regular supply of salmon to the angler. After a long period of low clear water norwest conditions have coloured the “Rangi” which should increase the catch rate while these conditions exist.

First Hatchery Releases of salmon due.
The restoration of the McKinnons Creek salmon hatchery has resulted in the successful rearing of about 40,000 Chinook salmon smolts. Some of these will soon be ready for release however before this can be done they will need to be fin clipped. Fish and Game may call on volunteers to assist with this mammoth task . If you have the time a call to the Temuka office registering your interest would be appreciated. The releases over the coming weeks will provide sufficient room in the raceways to allow the remainder to grow to a larger release size.

Didymo surveys ongoing.
Sampling of rivers within the region continue. Cells of didymo were collected in the lower Tekapo River however no blooms have been observed at this time. In all other rivers, samples returned negative results. A report from a fishing guide of didymo in a remote back country river in North Otago has not been confirmed however it was reported that he had taken samples of the algae. Hopefully it is one of the indigenous “look alikes”.

In conjunction with Southland and C.S.I. staff have been working with didymo and the effects of ground water on the algae. The work is supervised by NIWA scientists and it is not known how long this work will continue before any results are made public.

It is becoming more obvious that humans are the most likely vector of didymo and that felt soled wading boots or waders are a prime carriers of didymo cells. Soaking in bleach, detergent or saline solutions will not penetrate the dense felt to kill cells which have been forced into the felt while wading in affected rivers. Anglers who own felt soled fishing foot wear should dedicate these items to the affected river or rivers they fish, or dispose of them. Due to the difficulty of cleaning they should never be used in any other river or lake. The choice is not difficult, purchase a pair of waders, without felt soles, specifically for waters not affected with didymo or risk destroying a fishery. What value can you put on a fishery; the price of a pair of waders?

Sockeye Salmon. The best run for 25 years.
In the last issue of Reel Life it was reported that Sockeye Salmon had been seen and caught in the Haldon Arm of Lake Benmore. By late February thousands of Sockeye Salmon were migrating into the lower Ohau River to spawn.

Sockeye Salmon, Onchorhynchus nerka, were released into the tributaries of Lake Ohau in 1901. In early fisheries literature this species was thought to be Kokanee the lake dwelling form of Sockeye salmon. More recent studies of the New Zealand “Sockeye” indicate that the ova collected was from anadromous (sea going) Sockeye salmon, not lake dwelling Kokanee and that the resultant progeny failed to produce a sea going population. In their country of origin the nonanadromous progeny of anadromous Sockeye salmon are called “residuals”.

Sockeye salmon are plankton feeders and are seldom caught by anglers and it was thought that the species had failed to establish until in the 1960’s they were observed spawning in the newly constructed Aviemore spawning race. On further inspection this little known species was found spawning in several tributaries of the Waitaki Valley lakes from Lake Aviemore to Lake Ohau.

Larch Stream, a small spring fed stream at the head of Lake Ohau proved to be the most used spawning stream for “sockeye”. In the late 1970’s 16,000 were counted in Larch Stream. Research on Sockeye Salmon showed that there were two distinct populations, a Lake Ohau population and a Lake Benmore population. The Benmore Sockeye were larger and more coloured than the Ohau salmon. Many of the spawning salmon develop orange to red flanks, males are often more brightly coloured with a distinctive hooked snout They are aggressive fighters once in the spawning stream and especially during the egg laying period. At this time some of the population will strike at a small spinner or feathered lure

The resurgence of this little known species has surprised fisheries staff and anglers. The Sockeye salmon was thought to be almost extinct since its main migration route, the lower Ohau River was dewatered with the construction of the hydro canal which diverts the water to Ohau “B” and “C” hydro electric power stations. In 1982 thousands of salmon arrived at the Ruataniwha Spillway to find their upstream migration route permanently blocked. A huge relocation operation began and 8000 sockeye salmon were captured and transported to many streams within 50 km of the spillway. It appears that the relocation attempts were not successful as no returning salmon have been seen in any of the release sites.

Today where 70 cumecs once flowed, springs and seeps provide a small residual flow in the lower Ohau River, and it is this flow which has attracted the Sockeye Salmon. Recently Fish and Game and Environment Canterbury engineering staff embarked on a major clearing of a small spring fed tributary of the Lower Ohau which historically had been a well used spawning stream for salmon and trout. Sockeye salmon have moved into the enhanced stream and are spawning over its entire length wherever suitable gravels exist.
In March 2006, 752 salmon were counted in the lower Ohau River and 104 in the enhanced tributary.

Prior to their spawning run maturing sockeye salmon have been caught by anglers trolling for brown and rainbow trout in Lake Benmore around the river mouths or where tailrace of Ohau “C” flows into the lake. Although Sockeye salmon feature only occasionally in the anglers bag their presence in Waitaki Valley lakes is of great value to the fishery in that the juveniles, which drop back to the lakes after hatching, provide the trout fishery with a large and important food source. Large trophy trout in Lake Ohau disappeared soon after the demise of the migratory sockeye salmon run from Lake Benmore.

An aerial count of the rivers and streams which flow into the Haldon Arm of Lake Benmore was completed on the 19th March. In the lower Ohau River 7,400 salmon were counted, 1600 in the Tekapo River, 570 in the lower Twizel River, 300 in the enhanced tributary, 96 in Greys River and 14 in the outflow of the Maryburn Ponds. No salmon were observed in the Lake Ohau tributaries.

Within the region there are two recognised populations of Sockeye salmon, one in Lake Benmore the other in Lake Ohau. Sockeye salmon have been caught in Lake Ruataniwha however these are probably remnants of the Lake Ohau population.

It is not clear why there has been a resurgence in the Sockeye salmon populations however it is certainly good news for the trout fishery and indirectly the angler. The upper Waitaki Sockeye Salmon population is the only population in New Zealand and the only population in the southern hemisphere.