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Walking into the past to explore the future: Utulizing larval densities to measure the effects of two climate change factors, temperature and salinity on Poorohe (common smelt, Retropinna retropinna) abundance in Te Puuaha o Waikato

Abstract
Poorohe (common smelt, Retropinna retropinna) are a highly valued kai species in Te Puuaha o Waikato (the lower 66 km of the Waikato River). Fisher whaanau have observed changes in the amount Poorohe that are harvested during annual fish harvests. Since Poorohe are particularly vulnerable to environmental changes, whaanau are particularly concerned about the how climate change might impact Poorohe populations. Climate change vulnerability assessments (CCVA) currently exist for several native New Zealand fish freshwater species; however, one does not yet exist for Poorohe. Previous larval distribution studies in the lower Waikato River only sampled as far downstream as Tuakau bridge (approximately 45km from the river mouth). These studies indicated that important spawning habitats likely existed downstream of Tuakau bridge. Temperature increases and saltwater intrusion have been identified as two climate change factors that will likely impact Poorohe in Te Puuaha o Waikato, because ambient temperatures have increased since the industrial revolution and the proximity of the study area to the ocean. A literature review was used to explore the experiences of fisher whaanau through the past, present and how the experiences will continue to change in a changing climate. The effects of temperature and saltwater intrusion on Poorohe populations were explored through replicating the methods of past research carried out in the 1980s and 2010s. Current river temperatures are in the optimal temperature range (12°C - 18°C) for Poorohe spawning. The saltwater wedge was suppressed by the high river flow during the eight-week sampling period, and it is unclear whether saltwater intrusion has an impact on Poorohe spawning. Larval densities did not significantly increase down river, which suggests large spawning habitat is not found downstream of Tuakau bridge. Furthermore, there were no decreases in larval densities in the two saltwater sites. This study has contributed to the available literature necessary to develop a CCVA for Poorohe and explored the cultural heritage of traditionally significant practices in Te Puuaha o Waikato relating to Poorohe.
Type
Thesis
Type of thesis
Series
Citation
Date
2024-11-23
Publisher
The University of Waikato
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