HAWKE’S BAY REGIONAL COUNCIL
Maori
Committee
Tuesday 22 February 2011
SUBJECT: Review of Fish Habitat Requirements
for the Tukituki and Ngaruroro Rivers
REASON FOR REPORT
1. Minimum flows set
within the Resource Management Plan are an important component of surface water
management.
2. This report covers the
re-assessments of all habitat models in the Tukituki River catchment and a new
assessment of the lower Ngaruroro River. Data and conclusions are provided to
support future water management in the Ngaruroro and Tukituki catchments.
3. The aim of recent
habitat modelling work was to provide accurate, robust, and peer reviewed
information on the habitat requirements for fish species in the Tukituki and
Ngaruroro Rivers.
4. The flows in this
report are based on instream habitat for a range of fish species. There are
many other values within each catchment that need to be considered in addition
to fish habitat when setting minimum flows.
Model Reviews:
Tukituki Catchment
5. A series of instream
habitat models were completed for the Waipawa, upper Tukituki, Tukipo, and
lower Tukituki Rivers between 1997 and 2007.
6. Full reports on each
model were not completed, rather a summary section was written on habitat
modelling data from 1997 as part of the report “Sustainable Low Flow Project:
Ruataniwha Rivers” (Wood 1998). Subsequent models were completed, but full
documentation of data collection and modelling methods was not provided in
formal reports.
7. No formal peer reviews
were completed for instream habitat models in the Tukituki catchment prior to 2008.
8. The Cawthron Institute
was contracted in September 2008 to review the instream habitat model for the
lower Tukituki River (Hay 2008). The primary purpose of the review was to
determine if the model was sufficiently robust to use for successive modelling
and would withstand scrutiny in Environment Court and other RMA processes.
9. The Cawthron review
concluded that the model was sufficiently robust if a number of issues were
addressed and proper model interpretation methods were employed.
10. The recommendations in
the Cawthron review were used to reconstruct the lower Tukituki model.
Additional reconstructions were completed for the Waipawa, upper Tukituki, and
Tukipo models, using the same considerations highlighted in the Cawthron
review.
11. The new versions of
models for 2011 in the Tukituki catchment were satisfactorily reviewed by the
Cawthron Institute.
Model Reviews: Ngaruroro River
12. The previous instream
habitat model for the lower Ngaruroro River suffered from a number of problems.
The decision was made to complete a new river survey to construct a new habitat
model for the lower Ngaruroro.
13. The Ngaruroro model was
completed in January 2011 and has been satisfactorily reviewed by the Cawthron
Institute.
Model Results
14. The modelling software
RHYHABSIM (River Hydraulics and Habitat Simulation) was used for instream
habitat modelling on all five rivers.
15. RHYHABSIM predicts
habitat in the form of weighted usable area (WUA). WUA is a metric that
incorporates habitat quantity and quality. The data are given per unit of flow
and are easily visualised in a graph (Figure 1).
16. The optimum flow and
slope of the WUA curve are the most important features when considering minimum
flows as this describes ideal flow for a given fish species and the sensitivity
of that species to changes in flow. The steeper the curve, the more sensitive
the species is to flow changes.
17. Where the optimum flow
exceeds the mean annual low flow (MALF), the slope of the curve is used to aid
the minimum flow setting process by choosing the flow which provides a
particular level of habitat protection. This is described in further sections.
Figure 1: WUA plot for several native species with
optimum flows indicated by blue arrows (from Ngaruroro River RHYHABSIM model).
Minimum Flow Considerations
Management Objectives
18. There are many
considerations to be made in the minimum flow setting process, not the least of
which is defining the values that the community wishes to maintain or enhance.
It is not the intention of this report to define those values as that process
involves all stakeholders in the Tukituki and Ngaruroro catchments as part of a
full assessment of RMA Section II (economic, cultural, social, and
environmental matters). However, there are many National and Regional examples
to guide minimum flow selection for instream habitat, which have been included
in this report.
19. One of the longstanding
management objectives in the major Hawke’s Bay catchments is maintaining high
quality rainbow trout fisheries. Rainbow trout have been a prominent
management species for the Tukituki and Ngaruroro Rivers and have been the
primary instream management objective for past minimum flow setting processes.
20. Native fish habitat is
becoming an increasingly important topic in minimum flow setting processes.
The latest report on the threat status of New Zealand native fish has assigned
a heightened threat status of “At Risk – Declining” to several species that
occur in Hawke’s Bay rivers (Allibone 2011). This indicates a heightened
importance of habitat protection for these species.
Habitat Retention Levels
21. Minimum flow
considerations for instream habitat requirements across New Zealand are almost
exclusively based on retaining a percentage of the optimum habitat available
for the key management species. Where the optimum habitat of a key species
occurs at flows greater than the mean annual low flow (MALF), the habitat
retention level is based on a percentage of the habitat level available at the
MALF.
22. This method incorporates
two significant concepts; that the instream environment is built around the
natural hydrology of the river (where MALF represents a significant control on
fish populations), and that reductions in the annual low flow by use of a minimum
flow represent an exercise in risk management, whereby increased reductions in
the annual low flow (as a result of water abstraction) represent increased risk
to fish populations.
23. The habitat retention
levels chosen for the existing lower Tukituki and lower Ngaruroro minimum flows
targeted an 80% habitat retention level. The rationale for this level was that
given the natural “variability around the MALF, then a reduction of 20% is
seen as reasonable to meet both instream and out of stream requirements”
(Wood 2004).
24. The report for the
Waipawa and upper Tukituki recommended minimum flows that provided for a range
of species including trout, native fish, and macroinvertebrates (Wood 1998). A
direct comparison cannot be made against new model results as no habitat
retention level was specified.
25. The 2011 Cawthron review
highlighted that the final minimum flow recommendation from the lower Tukituki
model neither met the objective of providing for 80% habitat retention, nor did
it align with habitat retention levels currently used across New Zealand for
highly valued rainbow trout fisheries.
26. National precedent in
minimum flow setting is to assign high habitat retention levels for high valued
fisheries. Jowett and Hayes (2004) provide suggested habitat retention levels
for trout and native fish. For rivers and streams with brown and rainbow trout
fisheries, the suggested habitat retention level provides for 90% of habitat
available at the MALF, as per Jowett and Hayes (2004). This level has been adopted
by several regional councils.
27. Habitat retention values
for native fish have yet to be thoroughly established through precedent as many
native fish often have flow requirements less than trout species and native
fish do not often comprise significant fisheries (with the exception of eels
and whitebait species).
28. The most up-to-date
native fish habitat data indicate that in many Hawke’s Bay rivers, the flow
requirements of some native species are equal or greater than rainbow trout.
29. Also, the recent
increase in threat status of a number of native fish species found in Hawke’s
Bay indicates that protection of their habitat would be of regional and
national importance.
Summary of Results
30. Data for all the
included catchments have been compiled to show the previous minimum flows, the
flows required to retain 80% of habitat available at the MALF, and the % of
MALF that each minimum flow represents (Table 1). This table has been compiled
to present a direct comparison of the current minimum flows and the minimum
flows required to meet the original management objective of 80% habitat
retention for rainbow trout, based on the updated model results. Please note
the minimum flows for the Waipawa and upper Tukituki incorporated a number of
species’ habitat requirements, so a direct comparison cannot be made. See Wood
(1998) for a full description of the minimum flow recommendations.
Table 1: Compiled
minimum flow data for all modelled rivers with comparisons to the mean annual
low flow (MALF).
|
River
|
Current Minimum Flow
|
Current Minimum Flow as %MALF
|
Flow Demanding Species
|
Flow necessary for 80% habitat retention
level*
|
Flow necessary for 80% habitat retention
level as %MALF
|
|
Lower Tukituki
|
3500 l/s
|
57%
|
Rainbow trout
Torrentfish
|
4300 l/s
5100 l/s
|
67%
80%
|
|
Waipawa
|
2300 l/s
|
77%
|
Rainbow trout and longfin eel
|
2000 l/s
|
67%
|
|
Upper Tukituki
|
1900 l/s
|
68%
|
Rainbow trout and longfin eel
|
1800 l/s
|
64%
|
|
Tukipo
|
150 l/s
|
81%
|
Rainbow trout and bluegill bully
|
150 l/s
|
81%
|
|
Ngaruroro
|
2400 l/s
|
53%
|
Rainbow trout
torrentfish
|
3400 l/s
3900 l/s
|
76%
87%
|
*all habitat
retention levels refer to the % of habitat available at MALF
31. Flow requirements for
key management species (defined here as the most flow demanding or having high
fishery value) have been compiled (Table 2). This table shows the flows
necessary to align with current precedent from other New Zealand river systems
regarding habitat retention levels.
Table 2: Flows
required to maintain 90% of habitat available at the MALF for key management
species and the %MALF each flow represents.
|
River
|
Key Management Species
|
Flow necessary for 90% habitat retention
level
|
Flow necessary for 90% habitat retention
level as %MALF
|
|
Lower Tukituki
|
Rainbow trout
Torrentfish
|
5300 l/s
5800 l/s
|
87%
95%
|
|
Waipawa
|
Rainbow trout
Longfin eel
|
2400 l/s
2500 l/s
|
80%
83%
|
|
Upper Tukituki
|
Rainbow trout and longfin eel
|
2200 l/s
|
79%
|
|
Tukipo
|
Rainbow trout
Bluegill bully
|
175 l/s
163 l/s
|
94%
88%
|
|
Ngaruroro
|
Rainbow trout
torrentfish
|
3900 l/s
4200 l/s
|
87%
93%
|
*all habitat
retention levels refer to the % of habitat available at MALF
References
Allibone,
R., David, B., Hitchmough, R., Jellyman, D., Ling, N., Ravenscroft, P., Waters,
J. 2010. Conservation status of New Zealand freshwater fish, 2009. New Zealand
Journal of Marine and Freshwater Research. v44:3, 129-148.
Hay,
J. 2008. Review of Hawke’s Bay Regional Council’s Instream Habitat Modelling on
the Lower Tukituki River. Prepared for Hawke’s Bay Regional Council. Cawthron
Report No. 1542.
Jowett
I.G., Hayes, J.W. 2004. Review of methods for setting water quantity conditions
in the Environment Southland draft Regional Water Plan. Prepared for Southland
Regional Council. NIWA Client Report HAM2004-018.
Wood,
G. 1998. Sustainable Low Flow Project: Ruataniwha Rivers Waipawa – Tukipo –
Tukituki. Hawke’s Bay Regional Council Environmental Management Group Technical
Report EMT 98/2. ISSN 1174-3077.
Wood, G. 2004. Lower
Tukituki IFIM. Hawke’s Bay Regional Council Environmental Management Group
Technical Report, Unpublished.
DECISION MAKING
PROCESS
32. Council is required to
make a decision in accordance with Part 6 Sub-Part 1, of the Local Government
Act 2002 (the Act). Staff have assessed the requirements contained within this
section of the Act in relation to this item and have concluded that, as this
report is for information only and no decision is to be made, the decision
making provisions of the Local Government Act 2002 do not apply.
|
RECOMMENDATION
1. That the Maori Committee receives
the report.
|
|
Kolt Johnson
Scientist
|
Rob Christie
Team Leader - Hydrology
|
|
Graham Sevicke-Jones
Manager
Enviromental Science
|
Darryl Lew
Group
Manager
Resource
Management
|
Attachment/s
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