Kakahi, our Freshwater Taonga

The ecology division have been battling the elements... Recent weather events are illustrating how vunerable our water systems are to modifed human activities on the land.

The Kaipara District and its associated catchments is home to the little known freshwater mussel -kakahi/kaeo (Echyridella spp.). Kakahi are widespread in New Zealand currently consisting of three species, found from fast-flowing streams to lakes. Kakahi populations have been decreasing, impacted by destruction of their habitat. Koaro (Galaxias brevipinnis), which are fish hosts for parasitic larval stage of the freshwater mussel are also impacted by the destruction of  suitable stream habitat (NIWA, Kakahi, 2018). The two freshwater mussel species recorded in the district are (Echyridella aucklandica) listed as 'Threatened, Nationally Vulnerable’ and (Echyridella menziesii) ‘At risk’  (Williams, et al., 2017).

This shell found within the Hakaru Stream belongs to (Echyridella aucklandica), which would have been transported downstream by the recent flood events. It is anticipated that there is also (Echyridella menziesii) upstream as the two species generally co-exist. Kahai are important indicators of freshwater quality as they filter feed food particles. Being filter feeders the kahai are susceptible to a range of pollutants including agricultural activities. Kakahi are naturally predated by fish, birds and koura but also by rats (Williams, et al., 2017).

Whole catchment management approaches are a key way to improve the habitat and potential habitat of these species via pest animal and plant eradication coupled with eco sourced riparian planting.   

Further reading please see:-

Williams, E., Crow, S., Murchie, A., Tipa, G., Egan, E., Kitson, J., . . . Fenwick, M. (2017). Understanding Taonga Freshwater Fish Populations in Aotearoa-New Zealand. National Institute of Water & Atmospheric Research Limited, Wellington. Retrieved June 29, 2018

NIWA. (2018). Kakahi. Retrieved June 26, 2018, from NIWA: https://www.niwa.co.nz/our-science/freshwater/tools/kaitiaki_tools/species/kakahi

Echyridella aucklandica: Found in our local Hakaru River Catchment.

Echyridella aucklandica: Found in our local Hakaru River Catchment.

The Banded Kokopu, A Kaipara Local

The Banded kokopu is listed as a ‘regionally significant species’ and is an amphidromous fish, spawning in estuaries and sea from autumn/early winter. To be able to return to freshwater in spring larvae are skilled climbers and well known as whitebait (West, Crow, David, Ling, & Allibone, 2014). However, the population has declined, mainly due to loss and degradation of habitat. The New Zealand large galaxiid recovery plan, 2003–13, conducted by the DOC, allowed time-bound management actions and research needs to counteract threats (Department of Conservation, 2005). This specimen of banded kokopu found on an assessment site was an adult approx. (14 cm), most likely going to the estuary to spawn.

This observation has important implications for the whole catchment affected by the urban sprawl as historically man-made drains associated with the draining of swamps and land reclamation do provide habitat for native fish. The discovery of this species near future development sites such as ‘Mangawhai Central’ highlight the need to consider ecological implications and methodologies to the construction of infrastructure. Fish need to be able to swim upstream to natural living areas. Without fish ladders (both natural and man made) the fish will not be able to complete their natural life cycle and numbers will decline.

This Banded Kokopu was found in a modified stream channel that exits into Mangawhai estuary.

This Banded Kokopu was found in a modified stream channel that exits into Mangawhai estuary.