Identifying inanga spawning sites
in plans: options for addressing post-quake
spawning in Ōtautahi Christchurch
Christchurch City Council and Environment Canterbury
Waterways Centre for Freshwater Management
University of Canterbury
10 February, 2016
Table of Contents
1. Introduction 1
2. Methods 1
3. Results 2
4. Discussion 9
5. Conclusions 10
6. Acknowledgements 10
7. References 10
Appendix 1. Original information sources 12
Appendix 2. CCC spawning reaches compared to pre- and post-quake spawning records 13
The purpose of this assessment is to compare records of known inanga spawning sites in the
waterways of Ōtautahi Christchurch from before and after the Canterbury earthquakes, with
particular emphasis on information used in the design of planning methods for spawning site
Environment Canterbury (ECan) has recently notified a list of known inanga spawning sites in
Schedule 17 of the Plan Change 4 (ECan, 2015a) to the Canterbury Land and Water Regional Plan
(ECan, 2015b). Ecan has also prepared maps of ‘potential’ inanga spawning sites for planning
purposes (ECan, 2015b). Christchurch City Council (CCC) has developed maps of inanga spawning
sites for consenting purposes, as extra mitigation is required by the Council when working in
spawning areas (Margetts, 2016). ). These maps consist of reaches of waterways that include
locations at which eggs have been observed, as well as areas of suitable habitat immediately
upstream and downstream of these eggs. The mapping process consisted of a desktop
assessment of egg survey records, with the last update encompassing surveys from 2004-2011.
Suitable habitat was assessed on a site-specific manner, based on a number of factors, including
access for adult fish, aspect, soil conditions, bank slope and vegetation (B. Margetts, pers.
comm.). The suitable habitat areas were included in the inanga spawning sites defined by CCC to
address the difficulties in finding eggs in the field and the high potential for similar areas of
suitable habitat immediately adjacent to observed eggs to also have had eggs in the past, or in
the future. These sites informed, inter alia, the identification of Sites of Ecological Significance in
the Proposed Christchurch Replacement District Plan (CCC, 2015).
Inanga spawning in the waterways of Ōtautahi Christchurch has been well documented since the
late 1980s (Taylor et al., 1992). Following the Canterbury earthquakes, a change in the
distribution of spawning sites has been identified based on extensive surveys conducted in 2015.
The methodology used in these surveys is described in Orchard & Hickford (2016) together with
detailed results. This information is particularly relevant to planning methods which seek to
protect inanga spawning sites. It is therefore timely to consider the means by which spawning
sites are defined in plans, and whether any changes are needed to include the new information.
To assess potential need to update spawning site information in plans, results from both pre-
and post-quake surveys were comparing to current planning provisions. Differences between the
2015 results and pre-quake records were first characterised by reviewing all known information
on pre-quake spawning sites. The locations of these sites were mapped from the original data
sources and compared to the post-quake data. Similarly, inanga spawning site information in
plans was mapped and compared to the known sites.
A review of local literature and other data sources was completed with the assistance of Mark
Taylor (Aquatic Ecology Ltd) to identify records of inanga spawning (Appendix 1). This included
information held by local councils, the National Inanga Spawning Database (NISD), in published
and grey literature, and in the local knowledge of inanga researchers.
Council records of inanga spawning sites were obtained from CCC and ECan. Data for the
Ōtautahi Christchurch waterways was extracted from the National Inanga Spawning Database
(NISD), mapped, and reviewed for consistency. Some discrepancies such as unlikely coordinate
locations were evident. To address these, an amended shapefile was prepared containing the
estimated spawning locations for each record based on information in the ‘Comments’ field. As
with the data provided by ECan, the NISD point data are general locations or ‘centre-points’ of
spawning areas. They were mapped as point data and no attempt was made to estimate
upstream and downstream limits from these records. CCC spawning site records consisted of
upstream and downstream coordinates for reaches where eggs have been observed, and
shapefiles used to create the CCC spawning area maps. The latter are lines extending the above
reaches to include areas of suitable habitat upstream and downstream. For the other
information sources, upstream and downstream limits for the areas of spawning were identified
from the original records and all locations digitised in QGIS v2.8.2 (QGIS Development Team,
2015). Basemap imagery was sourced from LINZ.
Information held in reports was processed by identifying coordinates for upstream and
downstream extents from maps or photographs provided in the original reports, or using
original coordinates where possible. Where this information was not available, locations were
estimated using the text descriptions provided. Reach lengths were then digitising based on the
approximate shoreline position on the river bank to which each record related. Semi-continuous
stretches of spawning were lumped into a single reach in some cases, generally following the
description of discrete spawning areas and reaches given in the original records. Other details,
such as the methodologies used for field surveys, can be found in the original reports (Appendix
A comparison of ECan, CCC, and NISD spawning site records reveals considerable differences
(Figure 1). The most recent NISD records are dated 2004 and therefore more recent data are
lacking. The original NISD records also contain some discrepancies likely related to data capture
or transfer issues and the database as a whole generally retains these original entries (M.
Hickford, pers. comm.). A rudimentary QA exercise was conducted, as above, to produce an
amended set of spawning site locations more likely to be representative of the actual
observations (orange stars in Figure 1).
Current records held by ECan are a mixture of extracts from original NISD records and more
recent data from local researchers (M. Greer, pers. comm.). Discrepancies in the NISD records
have been addressed within the ECan records and new coordinates assigned. Other ECan data
points, such as at Lake Kate Sheppard and on Aynsley Terrace, relate to spawning locations
found in a variety of other pre-earthquake studies for which data is not present in the NISD
(blue triangles, Figure 1). In the Heathcote/Ōpāwaho these data points coincide well with the
known pre-earthquake locations. However in the Avon/Ōtākaro there are many known
spawning reaches that do not feature in the ECan spawning site records (orange lines in Figure
Current records held by CCC are spawning reaches that generally coincide well with the data
available on pre-quake spawning areas. Details of these reaches include start and end point
coordinates and text descriptions (Margetts, 2016). The descriptions indicate that both banks
are generally included in the spawning reach identified. These CCC records do not include the
site near Wilsons Road but this is much further upstream than other known sites and is thought
to relate to a markedly different tidal regime associated with the opening of the Woolston Cut
and before installation of the tidal barrage (M. Hickford, pers. comm.). A small discrepancy was
identified regarding the Woolston Park site as recorded by Taylor & Main (2010) which appears
to be located a little further upstream than the CCC records indicate (Figure 1a).
Results from the post-quake surveys add considerably to this picture. In the
Heathcote/Ōpāwaho, spawning was recorded further downstream on Clarendon Terrace and on
both banks throughout this reach. However, no spawning was recorded above the Opawa Road
site. New sites were found in the Radley Park area below the Woolston Cut. In the
Avon/Ōtākaro, spawning was found in the mainstem upstream of all previous records, on both
banks, and further downstream on the TLB. In Lake Kate Sheppard spawning was found within
the previously recorded reach and concentrated within a particular area on the TLB.
Overall, this comparison of records highlights that there are several options for conceptualising
and thus identifying spawning ‘sites’, or areas, for planning purposes. Decisions are needed on
whether to identify locations on each bank separately, how to lump or split records into
appropriate ‘sites’ or reach lengths, and how to recognise temporal aspects.
An overlay of all records by year illustrates some of the patterns to be addressed (Figure 2). In
some places, notably the Opawa Road and Avondale Bridge sites, spawning has been
consistently recorded in a similar area and the known spawning reach could be identified as the
maximum bank length involved. In other situations decisions are needed on whether to
‘connect’ discrete spawning sites both spatially and temporally eg. to regard all of the interstitial
areas as part of the ‘site’ or spawning reach. Examples include the records for the lower TRB of
the Avon/Ōtākaro where sites near Orrick Crescent are well downstream of others, or on the
TLB either side of Avondale Bridge where spawning has been recorded in some years but not
Whether to recognise each bank separately is another aspect for planning. The CCC approach is
inclusive of both banks of the waterway within identified reaches. The ECan approach, based on
points, clearly restricts attention to a relatively small area on a particular bank. Temporal
aspects have generally been dealt with by including all previous records within the concept of
‘known spawning sites’. The Wilson Road situation (described above) introduces an anomaly
that has been treated differently by the councils though is unlikely to be a current spawning site.
The post-quake records may help resolve these considerations towards a common approach to
recognising known spawning reaches. They show that spawning now occurs at a large number
of locations in both catchments. Although there are a few extensive reaches where spawning
was not recorded in 2015, many of these reaches supported spawning in the past with an
example being the TLB of the Avon/Ōtākaro either side of Avondale Bridge. In combination
these results suggest that it is appropriate to regard both banks as known spawning reaches
over a considerable length of the mainsteam in both rivers.
The new spawning sites in the lower Heathcote/Ōpāwaho present a remaining challenge in that
there is currently no evidence for spawning in the 800m reach between Radley Street Bridge
and Radley Park. More information on whether spawning does or could occur in this area is
Figure 1. Comparison of inanga spawning records. (a) Heathcote/Ōpāwaho catchment.
(b) Avon/Ōtākaro catchment
Figure 2. Inanga spawning reaches by year.
(a) Heathcote/Ōpāwaho catchment. Detail in the boxed area is shown in Figure 2c.
(b) Avon/Ōtākaro catchment. Detail in the boxed area is shown in Figure 2c.
(c) Detailed view of sites near Opawa Road (top) and Avondale Road (bottom).
This assessment highlights differences between the use of point data versus identifying
spawning reaches as the means to include spawning site locations in plans. In a planning
context, the effectiveness of either method can be related to the likelihood that spawning sites
actually occur within the area of protection specified in plans. In the case of Plan Change 4 to
the LWRP, point data for known locations are used and the area of protection is a 20m diameter
circle centred on the point coordinates (ECan, 2015a). Unless there were many such points to
include all known locations of spawning at this scale, a high proportion of known spawning
areas would not be included.
For these reasons the spawning reach approach is considered to be more appropriate and
practical for planning purposes. The concept of spawning reaches better addresses concerns
raised by tangata whenua in consultation on Plan Change 4 (ECan, 2015b) which included the
perspective that protecting known sites may not provide sufficient protection if limited to only a
few known sites based on limited records. In this regard both approaches are prone to data
deficiency and also currency issues, such as where survey and monitoring effort is not
sufficiently high to detect significant shifts in the location of sites.
A potential shortcoming for identifying spawning reaches is reliance on having defendable
information to indicate where the limits of known spawning are. This can be addressed by
ensuring sufficient survey effort is targeted at this aspect. In the case of the Ōtautahi
Christchurch waterways, there has been considerable survey effort made over many years from
Mark Taylor, Mike Hickford and others, and this has generated a rich dataset on the actual
locations used for spawning. It is practical and appropriate to capture this information as
spawning reach data to assist waterways management.
The comparison between CCC’s inanga spawning sites and the 2015 spawning survey results is
also of interest (Appendix 2). Many of the new locations where eggs were recorded in 2015
occur in areas of ‘suitable habitat’ that are included in the CCC maps of inanga spawning areas
(Margetts, 2016). In the case of the Avon/Ōtākaro mainstem the distribution of 2015
observations was a very close match to the reach mapped by CCC. However, in the
Heathcote/Ōpāwaho mainstem the actual spawning sites distribution extends further
downstream. No spawning was found in 2015 in the upstream portion of the reach mapped by
CCC (ie. above Opawa Road), although spawning has occurred there before. In Lake Kate
Sheppard the reach mapped by CCC extends much further upstream than the extent of
spawning found in 2015. However a large proportion of the riparian habitat in this area is
currently recovering from earthquake effects and vegetation communities have not yet
stabilised. It is possible that spawning may occur further upstream in these waterways in the
A different concept, that of ‘potential’ spawning areas, has been developed by ECan within its
planning approach (ECan 2015b, Greer et al., 2015). It differs from the CCC ‘suitable habitat’
work in that it is largely based on a predictive desktop model rather than field surveys. It is
potentially complementary though separate approach to the detection of known spawning sites.
Such approaches are not the focus of this assessment, and the ECan ‘potential spawning’ areas
are not further evaluated here.
This assessment provides updated information on inanga spawning reaches in Ōtautahi
Christchurch and a comparison with existing records. Recent changes in the location of
spawning reaches are considerable when compared to all previous records. These differences
are highlighted and are important for planning and waterway management purposes. In the
context of the Canterbury LWRP they are particularly relevant to planning methods specific to
the locations of known inanga spawning sites. To support the implementation of these methods,
it is recommended that council records are updated to reflect the findings presented here.
Assistance from Mark Taylor (Aquatic Ecology Ltd), Mike Hickford (University of Canterbury) and
Shelley McMurtrie (EOS Ecology Ltd) is gratefully acknowledged and was invaluable for
compiling inanga spawning reports and data. Assistance from council staff was also appreciated
with particular thanks to Belinda Margetts (CCC), Duncan Gray (ECan) and Michael Greer (ECan).
Support for the 2015 surveys and associated work was provided by the Ngāi Tahu Research
Centre and IPENZ Rivers Group. Thanks also to the staff of the Waterways Centre for Freshwater
Research, Marine Ecology Research Group and to the many volunteers who assisted with field
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Appendix 1. Original information sources++
Year of survey
Eldon et al. (1989), Meurk (1989), Taylor et al. (1992)
Taylor et al. (1992)
University of Canterbury unpubl. data
University of Canterbury unpubl. data
Taylor & Chapman (2007)
Hickford & Schiel (2014)
Taylor & Main (2010) unpubl. data
Taylor & Blair (2011)
Orchard & Hickford (2016)
++ Additional information was sourced the National Inanga Spawning Database
(NISD) and communication with local researchers
Appendix 2. CCC inanga spawning reaches identified by field survey of suitable habitat upstream and downstream of locations where eggs were
recorded (Margetts, 2016). The location of pre-and post-quake spawning sites is also shown. (a) Heathcote/Ōpāwaho catchment.
(b) Avon/Ōtākaro catchment.