in the environment court of new zealand christchurch registry · 2021. 2. 5. · 24 ramezani, j.,...

In the Environment Court of New Zealand Christchurch Registry I Mua I Te Kōti Taiao o Aotearoa Ōtautahi Rohe

ENV-2020-CHC-127

Under the Resource Management Act 1991

In the matter of a notice of motion under section 149T(2) to decide proposed Plan Change 7 to the Regional Plan: Water for Otago

Between Otago Regional Council

Applicant

Statement of Evidence of Morgan John Trotter for the Otago Fish and Game Council and Central South Island Fish and Game Council

5 February 2021

Applicant's solicitors:

Maree Baker-Galloway | Roisin Giles

Anderson Lloyd

Level 2, 13 Camp Street, Queenstown 9300

PO Box 201, Queenstown 9348

p + 64 3 450 0700

[email protected] | [email protected]

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Table of contents

1 Qualifications and experience............................................................. 2

2 Code of conduct for expert witnesses ................................................ 2

3 Scope of evidence................................................................................ 3

4 Impacts of flow reduction on freshwater habitats and trout fishery values .................................................................................................... 4

5 The duration of low flow events is an important consideration ....... 6

6 The importance of maintaining a functioning river corridor ............. 7

7 Assessing the risk of adverse ecological impacts from abstraction 8

8 Some examples of Otago Rivers that have had reductions in abstraction levels ............................................................................... 10

9 Multiple Stressor impacts associated with flow reduction ............. 10

10 Consequences of high levels of abstraction in Otago .................... 11

11 Fishery values of some Otago irrigation storage waters ................ 12

Table 1. Estimates of angler visits (per season) from the National Angler Surveys ................................................................................................ 13

12 Fishery Values of the Manuherekia River ......................................... 13

Table 2. Estimates of angler visits (per season) in the Manuherekia River .................................................................................................... 14

13 Species interactions .......................................................................... 14

14 No more than minor ........................................................................... 16

15 Conclusions ....................................................................................... 16

16 References ......................................................................................... 18

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Qualifications and experience

1 My name is Morgan John Trotter.

2 I hold a Postgraduate Diploma (with distinction) in Environmental Science

gained at the University Otago in 2001 and a Master of Science (MSc) in

Zoology (with distinction) gained in 2016, also at the University of Otago.

My masters research was on the effects of flow reduction on trout

populations and stream habitat in the Lindis River, Central Otago.

3 I am employed as a Fish and Game Officer at the Otago Fish and Game

Council, which is located at 247 Hanover Street, Dunedin 9016. I have held

this position for approximately 17 years. Prior to this I was employed at the

Otago Regional Council as a Field Advisor for 2 years.

4 I have extensive knowledge of trout fishery values in Otago waters and

have given advice to the Otago Fish and Game Council on ecological flow

requirements on various rivers throughout the region over the last 17 years.

I have presented evidence on trout fishery and angling values at a number

of hearings including the Nevis (Kawarau Water Conservation Order

Amendment) and Lindis River (Plan Change 5A) Environmental Court

cases. I am a member of the Manuherekia River minimum flow technical

advisory group.

5 I am basing this advice on my general knowledge of the impacts of flow

reduction on stream ecosystems, information gained from reading

supporting material for this hearing, plus the Review of the Rational for

Assessing Fish Flow Requirements and Setting Ecological Flow and

Allocation Limits for them in New Zealand (2019) and the draft National

Environmental Standards on Ecological Flows and Water Levels

Discussion Document (2008).

Code of conduct for expert witnesses

6 I confirm that I have read the Code of Conduct for expert witnesses

contained in the Environment Court of New Zealand Practice Note 2014

and that I have complied with it when preparing my evidence. Other than

when I state I am relying on the advice of another person, this evidence is

within my area of expertise. I have not omitted to consider material facts

known to me that might alter or detract from the opinions that I express.

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Scope of evidence

7 I have been asked to prepare evidence on Plan Change 7 by the Otago

Fish and Game Council and Central South Island Fish and Game Council,

in relation to the impacts of flow reduction on trout fishery values in Otago.

8 In preparing this evidence I have reviewed: Dr Allibones’ and Dr Hayes'

evidence.

9 My evidence will address the following matters:

(a) The general impact of flow reduction on freshwater ecosystems and

trout fishery values;

(b) The duration of low flow events is an important consideration;

(c) The importance of maintaining a functioning river corridor;

(d) Assessing the risk of adverse ecological impacts of flow reduction;

(e) Multiple stressor impacts;

(f) Some examples of Central Otago Rivers that have had reductions in

abstraction levels;

(g) Consequences to fisheries if high allocation continues;

(h) Fishery values of some irrigation storage fisheries;

(i) Fishery values of the Manuherekia River;

(j) Species interaction management;

(k) What would be considered a ‘no more than minor’ impact.

Executive summary

10 Many streams in Central Otago experience high levels of abstraction and

do not have effective environmental flows (a minimum or residual flow and

associated allocation limit) to protect habitat and ecological values. This is

often due to historic allocation under deemed permits.

11 In general, the lower the minimum flow and/or higher the allocation limit the

greater the risk of adverse effects on ecosystem health and trout fishery

production.

12 Higher minimum flows (80-90% of Mean Annual Low Flow (MALF) and

lower allocation limits (less than 30% of MALF) are likely to have only minor

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effects on ecosystem values. Outside of these precautionary guideline’s

comprehensive assessment on a case-by-case basis would be required.

Impacts of flow reduction on freshwater habitats and trout fishery values

13 Most trout fisheries in Otago are wild and self-sustaining and reliant on the

health and productivity of the freshwater habitats in which they occur.

14 As river flows drop to low levels both the area and quality of freshwater

habitat declines progressively which may result in a range of negative

impacts on trout fishery values. This may result in a reduction in

invertebrate food supply and increased competition between fish for food

and space depending on the magnitude of the event1.

15 As flows decrease to very low levels trout (and other fish such as upland

bullies) may experience a loss of cover and increased fish mortality as a

result of predation by shags and herons. Predation impacts are more likely

to occur in small rivers and streams where cover (turbulence in riffles and

over hanging vegetation etc) is reduced and juvenile trout and other small

fish are vulnerable. The reduction in cover makes it easier for terrestrial

predators to target fish in the remaining surface water.2

16 When surface flow connection along the river corridor is lost (and flow

between remaining pools ceases) remaining stranded fish can experience

mortality due to water quality stress such as high temperature and low

oxygen levels 3.

17 Very low water levels, flow diversion or complete drying of reaches can

delay or interfere with the timing of migratory movements and prevent fish

from reaching potential refuge habitat4.

18 Riffles and shallow runs are important for providing habitat for juvenile trout

and other small fish and benthic invertebrate production. It is often the riffle

habitat that is most reduced by severe levels of flow reduction5.

1 Hayes, J., Hay, J., Gabrielsson, R., Goodwin, E., Jellyman, P., Booker, D., Thompson, M. 2018. Review of the rationale for assessing fish flow requirements and setting ecological flow and allocation limits for them in New Zealand - with particular reference to trout. Nelson: Cawthron Institute.

2 Trotter, M. 2016 Juvenile trout survival and movement during summer low flow abstraction period in the Lindis River, Central Otago. MSc thesis, Department of Zoology, University of Otago, Dunedin.

3 Caruso, B. S. 2001. Regional river flow, water quality, aquatic ecological impacts and recovery from drought. Hydrological Sciences Journal, 46, 677-699.

4 Magoulick, D. D. and Kobza, R. M. 2003. The role of refugia for fishes during drought: a review and synthesis. Freshwater biology, 48, 1186-1198


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19 As flows decline the cover for fish provided by turbulence in riffles and

shallow runs is diminished. When riffles become nearly dewatered small

fish are often forced into remaining slow run and pool habitat. In these

environments small fish may be vulnerable to predation by larger trout, eels,

shags, and herons.

20 During times of low flow stress adult brown trout are often restricted to

perennial reaches of smaller streams6 generally where there are deeper

pools and other cover such as undercut banks.

21 In many Central Otago Rivers, the effects of flow reduction are often most

severe in losing reaches where surface water losses to groundwater

compound the effects of abstraction.

22 The effects of extreme low flow events can result in long term impacts on

salmonid population structure7,8,9. Reaches of rivers and streams that are

annually dried to isolated pools and dewatered riverbed are likely to act as

populations sinks, where breeding effort and recruitment potential is lost10.

23 Diversion structures such as gravel bunds and channels used to capture

surface flow for abstraction can impede fish migration to refuge habitat and

entrain fish in irrigation raceways and result in high mortalities of out-

migrating juvenile trout.11

24 When river reaches are dewatered rapidly fish kills may occur. Scavengers

(such as wild cats, ferrets, hawks) remove dead fish leaving little evidence

of the extent of the fish kill. Because of this, observed mortalities are likely

to represent only a small proportion of the number of fish killed.12

6 ORC 2008. Management flows for aquatic ecosystems in the Lindis River. Otago Regional Council, Dunedin

7 Elliott, J. M., Hurley, M. A. and Elliott, J. A. 1997. Variable Effects of Droughts on the Density of a Sea-Trout Salmo trutta Population Over 30 Years. Journal of Applied Ecology, 34, 1229-1238.

8 Jonsson, B. and Jonsson, N. 2011. Ecology of Atlantic salmon and brown trout: habitat as a template for life histories, Springer.

9 Elliott, J. M. 1993. The pattern of natural mortality throughout the life cycle in contrasting populations of brown trout, Salmo trutta L. Fisheries Research, 17, 123-136

10 Magoulick, D. D. and Kobza, R. M. 2003. The role of refugia for fishes during drought: a review and synthesis. Freshwater biology, 48, 1186-1198

11 Jellyman, D. J. and Bonnett, M. L. 1992. Survey of juvenile trout in the Lindis and Cardrona Rivers, and Clutha River in the vicinity of Cromwell, March 1992, including a review of previous surveys, NZ Fisheries Miscellaneous Report # 120. Christchurch, New Zealand, Freshwater Fisheries Centre, MAF Fisheries.

12 Trotter, M. 2016 Juvenile trout survival and movement during summer low flow abstraction period in the Lindis River, Central Otago. MSc thesis, Department of Zoology, University of Otago, Dunedin.

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25 Prolonged low flow events in streams can increase water temperatures

resulting in reduced trout growth rates and condition13.

The duration of low flow events is an important consideration

26 The longer the duration of the low flow event the higher the risk of adverse

ecological impacts. As the duration of the low flow event increases

periphyton biomass also increases and, in some stream, reaches algae

blooms smother much of the stream bed.

27 When very high algae biomass accumulates, algae respiration at night, and

the decomposition of the lower layers may reduce oxygen levels.

Periphyton build up can also clog up the interstitial spaces in cobble

substrate commonly used as cover by juvenile trout and small fish. Thick

blooms can impact fish passage and habitat in shallow riffles.

28 Low flows and thick algae blooms can also degrade the angling experience

and many anglers will be deterred from fishing rivers reaches that are

experiencing very low flow conditions and algae blooms. As flows drop

previously wetted riverbed margins matted with algae can be exposed

leaving a band of decomposing algae along the river margin which has a

negative impact on recreational amenity values.

29 Minimum and residual flows act in concert with water allocation limits to

protect ecological values from over abstraction. Naturalised (unabstracted)

mean annual low flows (MALF) are an ecologically relevant statistic that

can be correlated to the abundance of brown trout14. Allocation limits of up

to 10-30% of MALF are likely to be conservative and precautionary in terms

of adverse impacts on freshwater ecosystems. Conservative allocation

limits retain a high degree of natural flow variability, reducing the risk of a

river being ‘flat lined’ for long periods (weeks to months).15 Small freshes

can improve fish passage opportunities and increase food delivery in the

form of invertebrate drift.

30 High allocation limits usually increase the amount of time the river will be

flat lined at or about the minimum flow and also reduce the invertebrate

production capacity of the river. This is due to a reduction of time the river

would be in the minimum flow to median flow range. This reduces

13 Hayes, J., and R. Young. 2001. Effects of low flow on trout and salmon in relation to the Regional

Water Plan: Otago. Cawthron Institute Report. 14 Jowett, I.G. 1992. Models of abundance of large brown trout in New Zealand rivers. North American Journal

of Fisheries Management 12 417-432.


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invertebrate habitat and general river ecosystem production and the

potential fish biomass that the stream can support16.

31 The draft National Environmental Standard discussion document17 on

Ecological Flows and Water Levels contains a supporting document Beca

(2008)18 which gives guidance regarding the duration of abstraction

induced low flow events and the likely state of hydrological alteration. It

assumes a high degree of hydrological alteration (when compared to

unabstracted flows) when abstraction increases the duration of low-flow

conditions to 30 days or more, with moderate and low levels of hydrological

alteration corresponding to increases of about 20 and 10 days respectively.

32 The above timeframes could also be used to give guidance on the likely

risk of an adverse ecological impact. This is of course dependant on the

magnitude of the low flow event.

The importance of maintaining a functioning river corridor

33 From an ecological point of view, it is important to set a minimum flow or a

residual flow at a level that provides the opportunity for fish movement along

the river corridor. This is to provide for outmigration of juvenile fish as they

grow and their habitats become restricted, and movement to larger refuge

waters under stressful low flow conditions when possible.

34 In Central Otago many smaller rivers and streams have reaches that lose

surface flow to groundwater where they cross deeper gravel deposits after

they flow from mountain ranges. This can result in reaches with very low

surface flows and in some cases, streams will disconnect (dry in places)

over summer without abstraction.

35 In these circumstances maintaining as much surface connection for as long

as practical following the higher flows and freshes of spring will often

provide an opportunity for fish movement along the river corridor to reach

refuge habitat. Providing significant pulse flows (when water is available)

during summer may allow surviving fish to reach refuge habitat.


17 MfE 2008, Proposed National Environmental Standard on Ecological Flows and Water Levels Discussion

Document, Ministry for the Environment New Zealand.

18 Becca 2008. Draft guidelines for the selection of methods to determine ecological flows and water levels. Report prepared by Beca Infrastructure Ltd for MfE. Ministry for the Environment. New Zealand.

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Assessing the risk of adverse ecological impacts from abstraction

36 Determining the actual impact of flow reduction on fish populations with any

precision requires a very large allocation of resources and in most cases is

simply not achievable. As an example, I undertook research into juvenile

trout mortality in the Lindis River. Over two summer low flow periods I

marked approximately 1000 juvenile trout with radio transponders and

studied the impacts of flow reduction. In this study flow reduction to

approximately 25% of naturalised MALF for several months was associated

with approximately 66-71 % mortality of the monitored fish. This appeared

to be related to a lack of cover for fish at very low flows and high levels of

terrestrial animal predation (shags and herons).

37 Monitoring the movements and mortality of fish under low flow conditions in

the Lindis River was a labour-intensive exercise. I spent approximately 85

days in the field and was assisted by at least one other person and often

five or six. Many gave their time voluntarily

38 In most cases there simply isn’t enough resource (or funding) available to

conduct a mark and recapture study of this extent. Historical flow (or

percentage of MALF) estimates and habitat modelling are more commonly

employed to estimate the risk of adverse ecological impact from flow

reduction.

39 MALF (that is a naturalised or unabstracted MALF) often acts as a

bottleneck on the productivity of trout fisheries (notwithstanding the effects

of floods etc)19 and can influence trout abundance20.

40 The draft National Environmental Standards (NES) discussion document

proposed interim limits for rivers that do not have existing ecological flows.

For larger rivers (mean flow > 5 m³/s) a minimum flow of 80 % of MALF or

higher was recommended, and 90 % of MALF for smaller streams with

(mean flow < 5 m³/s).

41 The NES recommended allocation limits were in the range 30-50% of

MALF, depending on the size of the river (< 5m³/s > mean flow). In general,

smaller streams have a higher risk of adverse ecological impacts from flow

reduction than larger rivers.


20 Jowett, I.G. 1992. Models of abundance of large brown trout in New Zealand rivers. North American Journal

of Fisheries Management 12 417-432.

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42 An international review of flow setting by Richter et al. (2012)21, advised

that minimum flows and allocation limits that ensure that natural flows are

altered by no more than 10% would be considered environmentally

conservative (precautionary).

43 Hayes et al 2018 review of Ecological Flow setting in New Zealand advised

that minimum flows within 80-90% of MALF (that is a naturalised or

unabstracted MALF) and allocation limits in the order of 10-20% of MALF

are considered precautionary. That is 80% MALF and 20% allocation for

rivers larger than 5 m³/s and 90% MALF and 10 % allocation for smaller

streams. Higher allocation of up to 30% for larger rivers may be justifiable

provided they retain flow variability and are not flat lined for long periods.

Dr Hayes has recently refined this allocation advice to recommending no

more than 20% allocation for small streams and 30% allocation for rivers

larger than 5 m³/s (please refer to his evidence). In my opinion Dr Hayes'

precautionary limits would likely have a low risk of negative impacts on trout

fishery values. As minimum flows and allocation rates are reduced below

these levels the risk of a negative ecological outcome increases. Habitat

area and ecosystem productivity progressively reduce as flows decline.

This progressive reduction and loss of productivity is a continuum. Dr Hayes

discusses this concept in more detail.

44 In the support document for the draft NES Beca (2008) advised abstraction

of more than 40% of MALF or any flow alteration using impoundments

would be considered a high degree of hydrological alteration. This would

be dependent on the size and nature of the stream.

45 Rivers subject to abstraction resulting in a high degree of hydrological

alteration can and often do support trout fishery values. But the fisheries

and ecosystems they support will not be as productive or as resilient as

fisheries where more conservative ecological flows and allocation limits

have been applied. Dr Hayes discusses this concept in more detail.

46 Where abstraction levels are likely to exceed the precautionary limits

mentioned above based on percentages of naturalised MALF, habitat

modelling is often applied to assess the risk of adverse impact of flow

reduction on aquatic habitat. Dr Hayes discusses this concept in more

detail.

21 Richter BD, Davis MM, Apse C, Konrad C 2012. A presumptive standard for environmental flow protection. River Research and Applications 28: 1312-1321.

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Some examples of Otago Rivers that have had reductions in abstraction

levels

47 The Kye Burn in Central Otago has historically experienced very high levels

of abstraction resulting in dewatering of lower river reaches. A residual flow

regime established through a reconsenting process will now see a

continuous connecting flow to the Taieri River and a residual flow of

approximately 40% of MALF. I would expect this to result in improved

ecosystem functioning and juvenile trout survival/outmigration and

improvement in adult trout fishery values in stream as well.

48 The Upper Taieri was historically reported to dry in reaches and now has a

minimum flow of 1 m³/s at Waipiata and continuous flow (I have been

unable to obtain a naturalised MALF estimate for comparison). It is heavily

abstracted but storage water from the Logan Burn Dam assists with

maintaining flow. Under this regime the Upper Taieri supports a productive

trout fishery. Much of the river is incised in nature and it has many deep

pools and long runs and oxbow backwaters. These features assist in

providing habitat at moderate environmental flow levels. The Upper Taieri

Wai (a catchment group composed of farmers and various stakeholders)

are working towards improving water quality and habitat values which will

be expected to increase fishery productivity.

Multiple Stressor impacts associated with flow reduction

49 There are both direct and indirect impacts of flow reduction on stream

health.22 Some direct impacts on habitat are discussed in paragraphs 13 –

25 of my evidence. Low stream flows can also increase fine sediment

deposition and algal proliferation, which can impact invertebrate production

and aquatic food resources23 24 25 26 27.

22 Lake, P. S. 2003. Ecological effects of perturbation by drought in flowing waters. Freshwater Biology, 48, 1161-1172.

23 Dewson, Z. S., James, A. B. & Death, R. G. 2007. A review of the consequences of decreased flow for instream habitat and macroinvertebrates. Journal of the North American Benthological Society, 26, 401-415.

24 Hayes, J., and R. Young. 2001. Effects of low flow on trout and salmon in relation to the Regional Water Plan: Otago. Cawthron Institute Report

25 Hakala, J., and K. Hartman. 2004. Drought effect on stream morphology and brook trout (Salvelinus fontinalis) populations in forested headwater streams. Hydrobiologia 515:203-213.

26 Matthaei, C. D., Piggott, J. J. & Townsend, C. R. 2010. Multiple stressors in agricultural streams: Interactions among sediment addition, nutrient enrichment and water abstraction. Journal of Applied Ecology, 47, 639-649.

27 Ramezani, J., Rennebeck, L., Closs, G. P. & MATTHAEI, C. D. 2014. Effects of fine sediment addition and removal on stream invertebrates and fish: a reach-scale experiment. Freshwater

Biology.

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50 Many Otago pastoral streams are experiencing sedimentation and nutrient

runoff which is impacting stream invertebrate and fish communities28 29 30 31 32 33 34. High levels of abstraction on streams experiencing poor water

quality will likely compound the impact on ecosystem functioning.

Consequences of high levels of abstraction in Otago

51 Many streams in Central Otago experience high levels of abstraction and

do not have effective environmental flows (a minimum or residual flow that

protects ecological values). This is often due to historical over-allocation

under mining privileges, also known as deemed permits.

52 The scale of the actual adverse ecological impacts from abstraction varies

from river to river (and along the length of each river corridor) and is in some

cases resulting in adverse ecological conditions as described in paragraphs

13 to 25 of my evidence.

53 Coastal and south Otago streams do not in general have the historical over

allocation issues that many Central streams have. They often have more

conservative minimum flows and allocation limits (refer to Fish and Game

planning evidence for examples). However South Otago streams can

experience water quality issues (particularly sedimentation) which, as

discussed above, can compound the effects of flow reduction on stream

health.

54 For streams such as the lower Lindis where abstraction has historically

resulted in drying of lower reaches and associated fish mortality there will

not be meaningful gains in fishery production (or angler enjoyment) until

minimum flows and allocation limits that provide aquatic habitat protection

are restored.

28 Ramezani, J., Akbaripasan, A., Closs, G. P. and Matthaei, C. D. 2016. Instream water quality, invertibrate and fish community health across a gardient of diary farming prevalence in a New Zealand river catchment. Limnologica 61 Pp14-28

29 Harding, J. S., Young, R. G., Hayes, J. W., SHearer, K. A. & Stark, J. D. 1999. Changes in agricultural intensity and river health along a river continuum. Freshwater Biology, 42, 345-357.

30 Lange, K., Townsend, C. R., Gabrielsson, R., Chanut, P. C. M. & Matthaei, C. D. 2014. Responses of stream fish populations to farming intensity and water abstraction in an agricultural catchment. Freshwater Biology, 59, 286-299.

31 YOUNG, R. G. 1999. Trout energetics and effects of agricultural land use on the Pomahaka trout fishery, Cawthron Institute.

32 Matthaei, C. D., Weller, F., Kelly, D. W. & Townsend, C. R. 2006. Impacts of fine sediment addition to tussock, pasture, dairy and deer farming streams in New Zealand. Freshwater Biology, 51, 2154- 2172.

33 Townsend, C. R., Uhlmann, S. S. & Matthaei, C. D. 2008. Individual and combined responses of stream ecosystems to multiple stressors. Journal of Applied Ecology, 45, 1810-1819.

34 Kitto, J. 2011. Water quality and ecosystem health in the Manuherikia catchment, Otago Regional Council,

Dunedin.

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55 Providing environmental flows in historically heavily allocated streams and

rivers will also contribute to building the productivity and resilience of larger

receiving trout fisheries such as Lake Dunstan, Lake Roxburgh and the

Upper Clutha and Manuherekia Rivers.

56 Trout fisheries with a diversity of spawning and rearing habitat across a

wide geographical area have a reduced vulnerability to environmental

events. Events such as flooding, and droughts can adversely impact cohort

(year class) recruitment success35.

Fishery values of some Otago irrigation storage waters

57 Irrigation storage waters can provide high value angling experiences

provided the management regime ensures the water level is kept relatively

stable and lake levels are not drawn down too frequently.

58 The Poolburn Reservoir and Upper Manorburn Reservoir provide highly

regarded trout angling and have been designated as regionally important

sports fisheries (SFMP). The opening weekend of the new angling season

traditionally attracts high numbers of anglers. All methods may be

employed, although trolling from boats is often the most popular in the early

season. The other high use period is the cicada season in the late summer,

attracting fly anglers, who in the right conditions can experience high catch

rates as trout targeting insects blown on to the water.

59 Angler usage of the larger Manuherekia catchment irrigation reservoirs has

generally been consistently high for all four of the national angler surveys

(Table 1)36. These are surveys where random anglers are surveyed and the

results are extrapolated to estimate annual angler visits.

35 Hayes, J. W. 1995. Spatial and temporal variation in the relative density and size of juvenile brown trout in

the Kakanui River, North Otago, New Zealand. New Zealand Journal of Marine and Freshwater

Research, 29, 393-407.

36 Unwin, M. (2016). Angler usage of New Zealand lake and river fisheries: results of the 2014/15 National Angling Survey. NIWA Client Report CHC2016-021 prepared for Fish & Game New Zealand.

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Table 1. Estimates of angler visits (per season) from the National Angler Surveys

Waterway/Year 1994/95 2001/02 2007/08 2014/15

Poolburn

Reservoir

5090 3650 2810 2270

Manorburn

Reservoir

1240 3220 2350 510

Falls Dam 50 170 130 30

60 In contrast to Poolburn and Manorburn Reservoirs estimated angler effort

is significantly lower at Falls Dam Reservoir with less than 200 angler days

for each of the surveys, and no apparent trend across the years.

61 When Falls Dam is high (often at the start of the irrigation season) it can

provide a scenic and productive fishery for small to medium sized brown

and rainbow trout. It generally fishes best when it has not been drawn down

to very low levels for some time. There are numerous other small irrigation

storage dams throughout the Maniototo and Manuherekia catchments that

can provide fishing opportunities for medium to large trout.

Fishery Values of the Manuherekia River

62 The Manuherekia River is the fifth most fished river in the Otago Fish and

Game Region and a regionally significant adult trout fishery37. Spawning

and juvenile rearing habitat is widespread across the catchment. This

catchment contains a large number of deemed permits used for irrigation.

63 The Upper Manuherekia mainstem is often braided in nature below the East

and West Branches and flows over a predominately gravel bed with some

boulders. Headwater tributaries, including several springs provide a large

area of juvenile trout rearing habitat. The Lower Manuherekia flows through

a series of gorges with deep pools and open reaches that follow a typical

riffle-run-pool morphology. The riverbed substrate is often dominated by

coarse gravel and large cobbles. Its gravel-bed tributaries follow a similar

riffle-run-pool structure.

64 This range of habitats support self-sustaining sports fish populations and

provide for a variety of angling experiences. The Upper Manuherekia above

37 OFGC 2015. Sports Fish and Game Bird Management Plan 2015-2025. Otago Fish and Game Council, Dunedin.

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Falls Dam, and Dunstan Creek have backcountry fishery characteristics

because of their largely unmodified settings, scenic qualities, and low

angler encounter rates. Such sites are often favoured by fly anglers

because of the opportunity to sight fish for trout which are often large and

typically challenging to catch. These characteristics also attract fishing

guides and resident and non-resident tourist anglers (pre-covid). The

middle and lower reaches of the Manuherekia River provide fishing

opportunities in a rural setting for bait, spin and fly anglers. These areas

provide for easily accessible local angling for a wide range of anglers

including junior anglers and families. The lower river is popular around the

summer holiday period with visitors camping alongside the river and

enjoying the ease of access.

65 Summer low flow periods are significantly exacerbated by abstraction for

irrigation. Habitat values can be degraded in lower river reaches and many

tributaries because of flow reduction and in places sedimentation and

nutrient run-off. Below Falls Dam the lack of flushing flows often results in

algae bloom issues. Urban discharges such as the Omakau wastewater

discharge also impact water quality in the river.

66 Although the fishing experience in the lower river is heavily impacted the

Manuherekia River still supports a regionally important trout fishery and

experiences an estimated 1880 to 5630 visits annually over the last four

national angler surveys (Table 2).

Table 2. Estimates of angler visits (per season) in the Manuherekia River

Waterway/Year 1994/95 2001/02 2007/08 2014/15

Manuherekia

River

3570 5630 1880 2100

Species interactions

67 The predatory impact of introduced sports fish present a significant risk to

rare non-migratory galaxiids (NMG) populations in Otago (refer to Mr

Allibone’s evidence).

68 In my opinion there is significant room for improvement regarding co-

ordination between various statutory organisations and resource allocation

towards improving the plight of NMGs in Otago.

69 The recently formed Otago non-migratory Galaxiid Group including

representatives of DOC, Fish and Game and ORC, aims to improve the

2101895 | 5755417v1 page 15

current understanding of galaxiid population distributions and secure

selected non-migratory galaxiid habitat areas. These would generally be

small tributary streams (or reaches of these) where natural barriers to trout

passage exist or barriers can be put in place. And then removing trout

upstream. Ongoing management will be required to maintain structures and

check for incursions of trout.

70 A range of sports fish including brown, rainbow trout and brook char are

found within Otago waters. Of these brown trout have the widest

distribution. They are a very adaptable species with a wide range of life

history types and readily populate new habitats38.

71 In Otago small sexually mature trout can often reside year-round in

headwater streams. While large adult brown trout often reside in rivers and

lakes for much of the year and enter small tributaries to spawn following

autumn and winter freshes. This means that although low summer flows

may exclude trout from tributaries unless there is a fish barrier in place (and

all trout are removed from upstream), they may well repopulate that habitat.

72 The highly adaptive nature of brown trout and wide distribution throughout

Otago waterways enables populations to survive (and repopulate) in

systems that experience flooding and droughts.

73 These life histories and their ability to migrate between river systems means

that that care should be taken when assuming the distribution of trout is

static at any one time within a catchment.

74 It also means that it is simply not practical to attempt to remove trout from

most larger rivers and tributary streams (because in time they will likely

recolonise). Even if it was possible to keep trout out, I am not aware of any

methodology that would effectively remove trout from large streams, rivers

and lakes without major consequences for other stream life.

75 A pragmatic approach to managing species interactions would be to

manage larger river and stream ecosystems for multi species (sports fish,

eels and bullies etc) and excluding trout from smaller NMG habitats (often

smaller tributary streams) where they can be kept out using fish barriers.

76 This would involve improving water quality and providing environmental

flows to increase invertebrate and fish production in both the NMG streams,

and larger receiving streams and rivers to support their instream values. In

38 Jonsson, B., and N. Jonsson. 2011. Ecology of Atlantic salmon and brown trout: habitat as a template for life histories. Springer Publishing, London.

2101895 | 5755417v1 page 16

selected NMG habitats this would require maintenance or enhancement of

fish barriers and physical removal of trout plus ongoing maintenance to

check barrier integrity and for trout incursions.

77 Sports fish such as brown trout co-exist in streams with native species such

as bullies and long finned eels provided the stream has reasonable water

quality (to provide quality invertebrate habitat) and enough flow and

channel diversity to provide a range of fish habitat requirements (shallows

and riffles for small fish - runs, pools and undercut banks for various fish

species and sizes). Improving the water quality and habitat of rivers in

Otago will be expected to also improve recreational fishing (for both eels

and trout) and amenity values.

No more than minor

78 I have been asked to give advice on what level of abstraction I consider

would have a no more than minor effect on ecosystem values.

79 In my opinion Dr Hayes' revised precautionary abstraction and allocation

rates discussed in paragraph of 43 of my evidence are likely to have only

minor effects on ecosystem values.

80 As environmental protection limits are reduced below these precautionary

guidelines the risk of environmental impact increases as abstraction levels

increase.

81 To determine what would be considered more than minor effects beyond

the precautionary guidelines, comprehensive assessment on a case-by-

case basis would be required. Dr Hayes discusses a framework for using

habitat modelling outputs to determine what would likely be more than

minor instream effects (when this information is available).

Conclusions

82 Environmental flows are required to better protect ecological values in

heavily abstracted Central Otago streams and rivers.

83 The lower the minimum flow and/or higher the allocation limit the greater

the risk of adverse effects on ecosystem health and trout fishery production.

84 Sportfish present a high risk to threatened non-migratory galaxiid

populations. Exclusion of trout from areas of non-migratory galaxiid habitat

(generally smaller streams where they can be kept out using fish barriers)

is recommended.

2101895 | 5755417v1 page 17

85 Elsewhere managing larger streams and rivers for multi-species (trout,

eels, bullies etc) by improving water quality and providing environmental

flows is recommended.

86 A continuation of status quo levels of abstraction in many Central Otago

rivers and streams will not allow for improvements in ecological health and

fishery productivity.

87 Brown trout are a highly adaptable species and have a wide distribution

throughout Central Otago. In my experience trout respond very quickly to

meaningful flow restoration (but of course there won’t be improvements in

fishery values until environmental flows are provided).

Dated 5 February 2021

_____________________________

Morgan John Trotter

2101895 | 5755417v1 page 18

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in the environment court of new zealand christchurch registry · 2021. 2. 5. · 24 ramezani, j.,...

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