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Identifying inanga spawning sites in plans: options for addressing post-quake spawning in Ōtautahi Christchurch

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Abstract and Figures

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 protection. 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.
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Identifying inanga spawning sites
in plans: options for addressing post-quake
spawning in Ōtautahi Christchurch
PREPARED FOR:
Christchurch City Council and Environment Canterbury
Shane Orchard
Waterways Centre for Freshwater Management
University of Canterbury
10 February, 2016
Table of Contents
Page
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
1
1. Introduction
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
protection.
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.
2. Methods
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
2
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
1).
3. Results
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
1b).
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
3
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
others.
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
needed.
4
Figure 1. Comparison of inanga spawning records. (a) Heathcote/Ōpāwaho catchment.
5
(b) Avontākaro catchment
6
Figure 2. Inanga spawning reaches by year.
(a) Heathcote/Ōpāwaho catchment. Detail in the boxed area is shown in Figure 2c.
7
(b) Avon/Ōtākaro catchment. Detail in the boxed area is shown in Figure 2c.
8
(c) Detailed view of sites near Opawa Road (top) and Avondale Road (bottom).
9
4. Discussion
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 habitatthat 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
near future.
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.
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5. Conclusions
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.
6. Acknowledgements
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
research.
7. References
[CCC] Christchurch City Council. (2015). Proposed Christchurch Replacement District Plan.
Chapter 9 Natural and Cultural Heritage. Christchurch: Christchurch City Council. 145pp.
Eldon, G.A., Kelly, G.R., Bonnett, M.L. & Taylor, M.J. (1989). Fisheries survey of the Heathcote
River, January 1989. MAFFish, Christchurch. New Zealand Fisheries Report No. 111. 50pp.
[ECan] Environment Canterbury (2015a). Plan Change 4 to the Canterbury Land and Water
Regional Plan. Christchurch: Environment Canterbury. 127pp.
[ECan] Environment Canterbury (2015b). Section 32 Evaluation Report for Plan Change 4
(Omnibus) to the Canterbury Land and Water Regional Plan. Christchurch: Environment
Canterbury. 189pp.
Greer, M., Gray, D., Duff, K. & Sykes, J. (2015). Predicting inanga/whitebait spawning habitat in
Canterbury. Report No. R15/100. Christchurch: Environment Canterbury. 12pp.
Hickford, M.J.H., & Schiel, D.R. (2014). Experimental Rehabilitation of Degraded Spawning
Habitat of a Diadromous Fish, Galaxias maculatus (Jenyns, 1842) in Rural and Urban Streams.
Restoration Ecology 22(3): 319-326.
Margetts, B.I. (2016). Statement of evidence of Dr Belinda Isobel Margetts for the Christchurch
City Council. 28 January 2016. 21pp.
Meurk, C.D. (1989). Vegetation of the inanga spawning grounds on the banks of the lower Avon
River. Botany Division DSIR report. 4pp.
Orchard, S. & Hickford, M. (2016). Spatial effects of the Canterbury earthquakes on inanga
spawning habitat and implications for waterways management. Report prepared for IPENZ
11
Rivers Group. Waterways Centre for Freshwater Management and Marine Ecology Research
Group. Christchurch: University of Canterbury.
QGIS Development Team (2015). QGIS Geographic Information System. Open Source Geospatial
Foundation Project. http://qgis.osgeo.org
Taylor, M.J. (1994). Whitebait spawning on the Heathcote River. Letter to Christchurch City
Council, 10 May, 1994. 3pp.
Taylor, M.J. (1995). Inanga spawning on the Heathcote River. National Institute of Water and
Atmospheric Research, Christchurch. Consultancy Report No. CCC007. 10pp.
Taylor, M.J. (1996). Inanga spawning in the Avon and Heathcote Rivers. National Institute of
Water and Atmospheric Research, Christchurch. Consultancy Report No. CCC60517. 7pp.
Taylor, M.J. (1997). Inanga spawning activity on the Avon and Heathcote Rivers. National
Institute of Water and Atmospheric Research Limited, Christchurch. NIWA Client Report CHC
97/57. 10pp.
Taylor, M.J. (1998). Inanga spawning on the Avon and Heathcote Rivers, April 1998. National
Institute of Water and Atmospheric Research Limited, Christchurch. NIWA Client Report CHC
98/42. 12pp.
Taylor, M.J. (1999). Inanga spawning on the Avon and Heathcote Rivers, 1999. National Institute
of Water and Atmospheric Research, Christchurch. NIWA Client Report No. CHC99/27. 9pp.
Taylor, M.J. (2000). Inanga spawning in the city region during the year 2000. Letter to
Christchurch City Council, 17 July, 2000. 5pp.
Taylor, M.J. (2002). The National Inanga Spawning Database: trends and implications for
spawning site management. Department of Conservation, Science for Conservation No. 188.
37pp.
Taylor, M.J. & McMurtrie, S.E. (2004). Inanga spawning grounds on the Avon and Heathcote
Rivers. Aquatic Ecology Limited, Christchurch. AEL Report No. 22. 34pp.
Taylor, M.J. & Blair,W. (2011). Effects of Seismic Activity on Inaka spawning grounds on City
Rivers. Aquatic Ecology Limited, Christchurch. No. 91. 29pp.
Taylor, M.J., Buckland, A.R. & Kelly, G.R. (1992). South Island inanga spawning surveys, 1988-
1990. Ministry of Agriculture and Fisheries, Christchurch. New Zealand Freshwater Fisheries
Report No. 133. 69pp.
Taylor, M.J. & Chapman, E. (2007). Monitoring of fish values; inanga and trout spawning.
Aquatic Ecology Limited, Christchurch. AEL Report No. 58. 22pp.
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Appendix 1. Original information sources++
Year of survey
Information sources
1989
Eldon et al. (1989), Meurk (1989), Taylor et al. (1992)
1991
Taylor et al. (1992)
1993
Taylor (1996)
1994
Taylor (1994)
1995
Taylor (1995)
1996
Taylor (1996)
1997
Taylor (1997)
1998
Taylor (1998)
1999
Taylor (1999)
2000
Taylor (2000)
2002
University of Canterbury unpubl. data
2004
Taylor (2004)
2006
University of Canterbury unpubl. data
2007
Taylor & Chapman (2007)
2008
Hickford & Schiel (2014)
2010
Taylor & Main (2010) unpubl. data
2011
Taylor & Blair (2011)
2015
Orchard & Hickford (2016)
++ Additional information was sourced the National Inanga Spawning Database
(NISD) and communication with local researchers
13
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.
14
(b) Avon/Ōtākaro catchment.
... Postquake studies have shown further more subtle changes in a variety of drivers important to ecological structure and function. These include substrates (Cochrane et al., 2014;Zeldis et al., 2011), river bank and channel profiles (Allen et al., 2014, Orchard & Hickford, 2016 and alterations to the salinity regimes of the lower rivers (Orchard, 2016a;Orchard & Measures, 2016). The magnitude of these effects has been sufficient to drive long-term ecological changes in the distribution of species and habitats. ...
... The magnitude of these effects has been sufficient to drive long-term ecological changes in the distribution of species and habitats. Examples include rapid responses in the distribution of glasswort (Sarcocornia quinqueflora) and other saltmarsh species (Cochrane et al., 2014), and spawning sites for īnanga (Galaxias maculatus) (Orchard, 2016b;Orchard & Hickford, 2016). The full extent of these effects remains poorly understood yet is fundamentally important to the current ecology and ongoing successional processes in the AORZ. ...
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... This is a species of high cultural and recreational value with a current conservation status of 'At Risk -Declining' under the New Zealand Threat Classification System (Goodman et al., 2014). The protection of īnanga spawning habitat is an objective specifically identified in a range of policies and plans (Orchard, 2016). This recognises the widespread occurrence of degraded riparian margins in lowland waterways that is thought to be a major contributor to īnanga population decline (Jowett et al., 2009). ...
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... seeOrchard (2016). ...
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Technical Report
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The inanga whitebait fishery is hugely important in New Zealand, both commercially and culturally. The complex life cycle of inanga has put them under pressure from multiple sources (Hickford & Schiel, 2011; David et al., 2014), and the species is now classified as “declining” (Goodman et al., 2014). Overall, the biggest threat to the species is considered to be the destruction and restriction of spawning habitats (Hickford & Schiel, 2011). Through the proposed Land & Water Regional Plan, Environment Canterbury aims to provide protection for inanga spawning via a schedule of known inanga spawning areas. The effectiveness of the current schedule system is, however, extremely limited. Inanga spawning surveys have not been conducted in most waterways in the region and the majority of confirmed spawning areas are not listed in the current schedule. To improve the protection of inanga spawning habitat in the Canterbury Region, Environment Canterbury has conducted an investigation aimed at: • Developing a model that predicts the areas within which inanga spawning is likely to occur based on saltwater wedge intrusion; • Determining the effectiveness of replacing the current inanga spawning site list within Schedule 17 in the LWRP with the maps produced by the model; • Justifying the inclusion of the maps into the LWRP omnibus plan change. The model proved extremely successful at predicting where inanga spawning could occur, and 98% of currently known spawning sites were within the area identified by the model as potential spawning habitat. Therefore, the replacement of Schedule 17 with the maps developed from the model would markedly improve the protection provided to this commercially and culturally valuable species. This would help meet objectives in the National Policy Statement for Freshwater Management 2014 (NPS) and the Canterbury Regional Policy Statement 2013 (RPS) as well as a number of the targets set out in the Canterbury Water Management Strategy (CWMS) in 2009 and subsequent CWMS Zone Committee Zone Implementation Plans. In its current state Schedule 17 fails to protect the vast majority of inanga spawning habitat, and limits the ability of Environment Canterbury to fulfil its responsibility to protect this aspect of the life supporting capacity of the environment under the Resource Management Act. It is unlikely that the recorded distribution and abundance of inanga in Canterbury would significantly increase even if an intensive region-wide survey was completed and Schedule 17 expanded to include all current inanga spawning areas in Canterbury. A fundamental flaw in the schedule-based approach is that it fails to provide protection to sites where spawning could occur, but has ceased in response to human activities or does occur, but has not been observed. Given the declining status of inanga, it is vital that on a regional basis all potential habitats are given protection. Replacing Schedule 17 with the maps of predicted spawning habitats would achieve this.
Technical Report
Full-text available
The Canterbury earthquakes resulted in numerous changes to the waterways of Ōtautahi Christchurch. These included bank destabilisation, liquefaction effects, changes in bed levels, and associated effects on flow regimes and inundation levels. This study set out to determine if these effects had altered the location and pattern of sites utilised by inanga (Galaxias maculatus) for spawning, which are typically restricted to very specific locations in upper estuarine areas. Extensive surveys were carried out in the Heathcote/Ōpāwaho and Avon/Ōtākaro catchments over the four peak months of the 2015 spawning season. New spawning sites were found in both rivers and analysis against pre-earthquake records identified that other significant changes have occurred. Major changes include the finding of many new spawning sites in the Heathcote/Ōpāwaho catchment. Sites now occur up to 1.5km further downstream than the previously reported limit and include the first records of spawning below the Woolston Cut. Spawning sites in the Avon/Ōtākaro catchment also occur in new locations. In the mainstem, sites now occur both upstream and downstream of all previously reported locations. A concentrated area of spawning was identified in Lake Kate Sheppard at a distinctly different location versus pre-quake records, and no spawning was found on the western shores. Spawning was also recorded for the first time in Anzac Creek, a nearby waterway connected to Lake Kate Sheppard via a series of culverts. Overall the results indicate that spawning is taking place in different locations from the pre-quake pattern. Although egg survival was not measured in this study, sites in new locations may be vulnerable to current or future land-use activities that are incompatible with spawning success. Consequently, there are considerable management implications associated with this spatial shift, primarily relating to riparian management. In particular, there is a need to control threats to spawning sites and achieve protection for the areas involved. This is required under the New Zealand Coastal Policy Statement 2010 and is a prominent objective in a range of other polices and plans.
Article
New Zealand whitebait comprises the migratory juveniles of five species of native Galaxias. The most abundant of these is inanga, Galaxias maculatus. In 1987, the Department of Conservation (DOC) commissioned nationwide field surveys to identify (with the aim of protecting) inanga spawning sites, with data to be collated into a database administered by the National Institute of Water and Atmospheric Research Ltd (NIWA). The database currently holds 562 records from a total of 194 inanga spawning sites. Spawning sites have been located in every coastal DOC conservancy except Auckland. Further work to identify spawning sites is required, particularly in Northland, Auckland, Waikato, Wellington and Southland Conservancies. At least some protection work has been carried out in every conservancy where spawning has been located. Inanga spawning usually occurs on autumnal spring tides, with the nationwide peak spawning activity taking place 2 or 3 days after the new or full moon; however, some spawning may also occur in spring. Preferred spawning sites appear to be the banks of tidally-influenced flow-stable waterways, and tributaries and small creeks in very large catchments, often where there are embayments and confluences. Inanga spawn gregariously amongst inundated bankside vegetation. Consequently, spawning sites and eggs are prone to damage by cattle trampling or grazing. Exotic vegetation commonly associated with inanga spawning includes a number of grass and herb communities, often dominated by tall fescue (Festuca arundinacea). A wide variety of native plants are also associated with inanga spawning. These include New Zealand rush (wiwi, Juncus gregiflorus), bull rush (raupo, Typha orientalis), flax (harakeke, Phormium tenax) and toetoe (Cortaderia richardii). The spread of reed sweet grass (Glyceria maxima) and other exotic grass species unfavourable for fish spawning into spawning areas is of concern.
Article
Riparian vegetation has been compromised worldwide by anthropogenic stressors, including urbanization and livestock grazing. In New Zealand, one consequence has been a reduction in the obligate riparian spawning habitat of Galaxias maculatus. This diadromous species forms the basis of an important fishery where juveniles are caught as they migrate into freshwater. Spawning success of G. maculatus is closely associated with the nature of available riparian habitat. We used a field experiment in a rural stream to test whether livestock grazing limits egg production and whether there is a lag in increased egg production after protection from grazing because of the recovery time of riparian vegetation. In a separate experiment in an urban stream we tested whether improved riparian management can increase egg production. Livestock exclusion produced an immediate and long-lasting increase in the height and density of riparian vegetation with reduced fluctuations in the ground-level physical environment, and positive changes to the density and survival of eggs. After 4 years, egg densities in exclosures were 400 times greater than in grazed controls and egg survival had doubled. Mowing riparian vegetation 2 months prior to spawning reduced egg densities by 75% and survival by 25%. Our experiments showed that altering grazing and mowing in spawning sites produced dense riparian vegetation, that this improved the microsite environment and resulted in greatly increased egg deposition and survival over several years. This clearly indicates that the single most effective step in rehabilitating G. maculatus spawning habitat is a simple reduction in grazing/mowing pressure.
Article
In habitats such as estuaries, which are characterised by large and fluctuating gradients in abiotic variables, finding appropriate habitat for successful spawning and egg development can be critical to a species' survival. We explored how salinity requirements for successful fertilisation may govern the distribution of estuarine spawning habitat for the diadromous fish, Galaxias maculatus, which spawns in inundated vegetation on estuary banks during spring tides. Artificial fertilisation experiments confirmed that successful fertilisation only occurs at low salinities (<20). Thus, we predicted that egg distributions would depend upon the extent of low-salinity surface waters in an estuary. Using estuary geomorphology classification schemes, which classify estuaries by physical and chemical characteristics such as their salinity dynamics, we hypothesised that stratified estuaries would provide a greater extent of low salinity surface water than well-mixed estuaries. This prediction was supported by surveys of egg distributions in five estuaries in Victoria, Australia. Eggs were distributed over a greater proportion of 'stratified' v. 'mixed' estuary types. We suggest that combining knowledge of the spawning requirements of a species and physical properties of the habitat, such as those encapsulated in estuary geomorphic classification schemes, can greatly facilitate efforts to identify critical habitats and thus aid in species management and conservation.