Planning for whitebait conservation


Introduction

Juvenile īnanga (Galaxias maculatuscomprise the bulk of the ‘whitebait’ catch (McDowall & Eldon 1980), an immensely popular recreational fishery (DOC, 2010; Kelly 1988; McDowall 1965). The whitebait are approximately 6 months old having been swept out to sea as larvae after hatching from the eggs. The whitebait run is a migration of these juveniles back into lowland river systems around the country where they will mature into adult īnanga. The adults stay in the same river system for the rest of their life and rely on suitable areas near the rivermouth for their turn to spawn in the following season. Both juvenile and adult īnanga were traditionally harvested by for Māori, and the protection and enhancement of īnanga populations is a cultural priority (Lang et al. 2012; Jolly et al. 2013, NZ Government, 1998).

Īnanga are known to use very specific locations for spawning. These occur on riparian margins in upper estuarine areas near the spring high tide waterline. The availability of suitable spawning habitat in these locations is essential to spawning success (Hickford et al. 2010; Hickford & Schiel 2011). Eggs are laid in riparian vegetation just below the spring tide high-water level and are effectively in a terrestrial environment for most of their development period. The eggs hatch in response to inundation (e.g., on subsequent spring tides) after a 2-4 week development period. Over this time the eggs are vulnerable to a variety of threats primarily involving terrestrial influences.

Human activities that occur in the same area may present threats to the availability and condition of spawning habitat. Many of these relate to land use activities and are amenable to management.This habitat may also be susceptible to future land use changes and will undoubtedly be affected by sea level rise.


Inanga in Steamwharf stream, a tributary  of the  Heathcote River/Ōpāwaho,
December 2015 


Conservation needs

The need for īnanga conservation is identified in a range of statutory documents at national, regional and local levels. Under the New Zealand Threat Classification System the species is currently listed in the ‘at risk - declining’ category (Goodman et al. 2014). In many instances, īnanga spawning habitat is specifically identified as the focus for policy and planning objectives. This recognises the widespread occurrence of degraded riparian margins in lowland waterways that is thought to be a major contributor to īnanga decline. The restoration and protection of spawning habitat is thus an urgent requirement as well as being a practical focus for management.

Īnanga are of particular significance for Ngāi Tahu and are an important species for mahinga kai. The protection and enhancement of īnanga populations is a cultural priority for manawhenua in the Avon-Heathcote Estuary/Ihutai and other waterways in the takiwā.


Inanga eggs in the  Heathcote River/Ōpāwaho.
March, 2015
 

Focus on riparian management

Riparian management is a key activity for whitebait conservation in New Zealand's lowland coastal waterways. To protect īnanga spawning habitat and ensure resilience to longer term changes it is essential to identify the locations involved. However, this is not a straightforward task given that strong predictors such as salinity patterns and water levels are highly dynamic. In reality, the biogeography of spawning habitat varies spatially and temporally. Unraveling these spatial patterns is a key requirement for quantifying the impacts of current and future activities and for assessing the effectiveness of protection measures.


Whitebaiters on the South Island's West Coast

Conservation planning studies

The focus of our work on īnanga is to develop methods and gather evidence for assessing the spatial extent and condition of spawning habitat on upper estuarine margins. Several important topics for management are being addressed including: 
  • providing evidence to determine the relationship between salinity conditions and the spatial ecology of īnanga spawning sites;
  • investigating relationships between indigenous vegetation and īnanga spawning habitat, especially at sites for which restoration with native species is desired;
    RTK-GPS measurements help to establish 
    the exact position of spawning sites
  • investigating whether site fidelity factors may be important to the location of īnanga spawning sites;
  • evaluating the implications of these relationships for integrated waterway management; and
  • developing methods to predict the occurrence of īnanga spawning habitat and application to assess the vulnerability of spawning sites to sea level rise.

Follow these links to read more:

Support is gratefully acknowledged from Brian Mason Scientific & Technical Trust, NIWA, IPENZ Rivers Group, Ngāi Tahu Research Centre and the Marine Ecology Research Group at UC.


REFERENCES

[DOC] Department of Conservation (2010). The Whitebaiter’s Guide to Whitebaiting on the West Coast. Wellington: Department of Conservation.
Goodman, J.M., Dunn, N.R., Ravenscroft, P.J., Allibone, R.M., Boubee, J.A.T., David, B.O., Griffiths, M., Ling, N., Hitchmough, R.A. & Rolfe, J.R. (2014). Conservation status of New Zealand freshwater fish, 2013. New Zealand Threat Classification Series 7. Wellington: Department of Conservation. 12pp.
Hickford, M., Cagnon, M. and Schiel, D. (2010). Predation, vegetation and habitat-specific survival of terrestrial eggs of a diadromous fish, Galaxias maculatus (Jenyns, 1842). Journal of Experimental Marine Biology and Ecology 385(1): 66-72.
Hickford, M.J.H. & Schiel, D.R. (2011). Population sinks resulting from degraded habitats of an obligate life-history pathway. Oecologia 166: 131–140.
Jolly, D. & Ngā Papatipu Rūnanga Working Group (2013). Mahaanui Iwi Management Plan 2013. Ōtautahi Christchurch: Mahaanui Kurataiao Ltd. 391pp.
Kelly, G.R. (1988). An Inventory of Whitebaiting Rivers in the South Island. New Zealand Freshwater Fisheries Report No. 101. Freshwater Fisheries Centre, MAFFish, Christchurch, New Zealand.
McDowall, R.M. (1965). The composition of the New Zealand whitebait catch, 1964. New Zealand Journal of Science 8(3): 285–300.
McDowall, R.M. & Eldon, G.A. (1980). The ecology of whitebait migrations (Galaxiidae: Galaxias spp.). New Zealand Ministry of Agriculture and Fisheries, Fisheries Research Bulletin 20: 1-172.
New Zealand Government (1998). Ngāi Tahu Claims Settlement Act 1998. Wellington: New Zealand Government.
Lang, M., Orchard, S., Falwasser, T., Rupene, M., Williams, C., Tirikatene-Nash, N., & Couch, R. (2012). State of the Takiwā 2012 -Te Ähuatanga o Te Ihutai. Cultural Health Assessment of the Avon-Heathcote Estuary and its Catchment. Christchurch, N.Z., Mahaanui Kurataiao Ltd.

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Read more about other work on upper estuarine ecosystems here

Marking out sites for straw bale installations in the
Whaka Inaka project, December 2015. Photo: EOS Ecology
Straw bales used as a tool 
for locating spawning areas in the
Heathcote River/Ōpāwaho,
April 2015
 



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