Fish and Game report to Hurunui Zone Committee

Hurunui Waiau Zone Committee

Response by North Canterbury Fish and Game 11.04.16

 

Background:

 

Following the March HWZC meeting, Fish and Game was asked to provide justification for the closure of all North Canterbury Rivers below SH1 to the mouth, for the upcoming winter season.

 

At the February meeting of the North Canterbury Fish and Game Council, a life-long fisherman of the Rakaia Catchment “Bill Southward” explained that he had taken a keen interest in the health of the Rakaia River System, including the lagoon and associated lowland streams.

 

Bill provided the Council with his observations of the Rakaia fishery, with particular reference to the number of sea-run trout which return to the Rakaia tributaries and headwaters to spawn.

 

Bill expressed his significant concerns with the decline in this local fishery over the last five years. He also indicated that other local anglers felt the same.

 

Bill’s evidence is based on scientific investigations and his anecdotal assessments of habitat degradation, particularly in the headwater spawning areas and lower reaches of the Rakaia Catchment. For example, he noted that many natural springs had gone dry or been significantly reduced in flow. He also believes the effects of stock intensification have caused damage through increased sedimentation, drainage, vegetation clearance and agricultural run-off.

 

Bill explained how in the past smelt were very abundant in the lagoon and spring-fed streams, providing a significant food source for trout. His recent observations indicate major reductions as well as what he describes as a “collapse” in this local trout fishery.

 

In response, the Fish and Game Council acted swiftly in agreeing to close the Rakaia fishery below SH1 for the winter. This was not in response to over-fishing, but in response to the current external pressures on the fishery, particularly in relation to reduced habitat quality. The effects of climate change were discussed as a contributing factor, but it was felt that increased levels of water take in the catchment, combined with conspicuous increases in irrigation and land use intensification were the major cause.

 

A special meeting was called by Fish and Game in March, with a very large turnout of approximately 110 anglers. A unanimous decision was made to close all rivers below SH1 to the river mouths for the winter. It was felt that by doing so increased pressure would not be substituted onto the other rivers.

 

Fish and Game has stated publically that the decision reflects years of over-allocation of water resources and deteriorating water quality from agricultural runoff and other forms of pollution; that has seen many formerly strong fisheries like the Selwyn, Hororata, Ashley and Waipara Rivers significantly degraded. It appears the effects are also flowing into the larger alpine fed rivers, which contain essential headwater spawning areas and whose flows affect groundwater recharge and connected streams.

 

The lower reaches of major alpine rivers play an important role in the development of juvenile fish and as habitat for mature fish. However, the ability to catch mature fish may not on its own be a reliable indicator of river health, particularly if cumulative effects may be reducing the quality of habitat over time. For example, it is still possible to catch trophy fish in the rivers flowing into Lake Ellesmere. The Selwyn once recorded 60,000 spawning fish in a fish trap in 1966, whereas now the tally is only counted in the hundreds and also gone is the world renowned status of the Selwyn fishery.

 

 

Other natural and human induced effects may also influence habitat quality, such as climate change, major floods and Didymo in rivers like the Hurunui. Variations in the ocean lifecycle stage for trout and salmon could also affect their health and abundance, but scientific evidence such as that provided in Table 1 and Figure 1, suggests land use intensification is still the biggest threat.

 

The following table produced for the Hurunui Waiau Regional River Plan hearing by Cawthron Institute freshwater ecologist Roger Young, demonstrates that across a range of environmental factors water quality has been deteriorating in most of the 10 National River Water Quality sites in Canterbury.

 

Table 1. Statistically significant and ecologically meaningful (RKSE>1%) declines (marked in red) and improvements (marked in green) in water quality parameters at the 10 National River Water Quality Network sites in Canterbury over the period from 1989 to 2011. Data for E. coli only cover the period from 2005 to 2011.

 

 

In the case of the Hurunui and Waiau Rivers, recent stabilising of nutrient concentrations in the Hurunui over the last couple of years is good news but not necessarily reflective of a long term trend. For example, nitrate levels in the Hurunui River at SH1 between 1989 and 2011 steadily increased, bringing the river into more of a “moderately polluted” state.

 

Increase in nitrate nitrogen concentration in the Hurunui River at the SH1 sampling site (Slope of trend 7.3 µg/L/yr, Relative slope 2.6%, P < 0.001). Data from NIWA.

 

There have been increasing outbreaks of potentially toxic Cyanobacteria (Phormidium) in the Hurunui (a neuro-toxin) with blooms and health warnings reported in 4 of the past 5 years, in the lower half of the Hurunui River.   On February 15 of this year a bloom was reported as high as the SH7 Bridge, next to the often packed public camp ground and swimming area. 

 

The presence of Phormidium is a strong indicator of elevated nitrates in the river, which makes swimming or drinking any algae infected water hazardous; for example there are several reported cases of dogs dying after ingestion of Phormidium in Canterbury. The proliferation of other algae is also common in the lower reaches and associated with reduced water quality and fishing quality.

 

 

Winter fishing in Canterbury was only introduced in the mid-nineties following public requests, despite the declining state of many rivers. The winter fishery closure is not seen alone as a way to turn around the current problems, but rather as a step in the right direction for achieving improvement. Anglers at the March meeting felt it was important to show they were playing their part in order to take pressure off this sports fishery.

 

As stated above, over 100 anglers voted unanimously to reduce the Rakaia River fishing season, extending to other North Canterbury rivers below SH1; a move prompted specifically by the deterioration in habitat and fish abundance in the lower Rakaia River system.  It was felt prudent to avoid increasing pressure on the lowland reaches of other rivers in the North Canterbury Region, as a result of the Rakaia closure.