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Improving the success of a translocation of black mudfish (Neochanna diversus)

All of New Zealand's five endemic species of mudfish (Neochanna) are threatened, and translocation has been recommended as an option for conservation. This research undertakes a translocation of black mudfish (Neochanna diversus) into wetland margins of Lake Kaituna, in the Waikato region, and addresses research questions applicable to improving translocation success. Results from this research are intended to aid possible future translocations of the more threatened Northland mudfish (Neochanna heleios) and other genetically distinct populations of black mudfish. Captive rearing of juveniles collected from the wild is currently the most feasible option for sourcing translocation stock. Mudfish juveniles (greater than 25 mm T.L.) had greater survival rates, compared to mudfish fry less than 25 mm T.L. Mudfish growth was far greater when fed on a combined diet of brine shrimp (Artemia salina) and white worms (Enchytraeus albidus) than when fed exclusively on brine shrimp. Temperature was found to have a small effect on mudfish growth, with a slightly greater growth in fish at 15 C than those at 10 C. The introduced species Gambusia affinis has been the subject of concern for mudfish conservation and commonly found at wetland sites suitable for mudfish translocation. Found to prey on mudfish fry and eggs in aquaria, it was important to determine the effects of Gambusia density prior to undertaking a translocation to a location where Gambusia were present. Investigations were made into the effect of Gambusia density on black mudfish juveniles in 9 outdoor mesocosms. Increasing Gambusia density was found to have an inhibitory effect on black mudfish growth. This may be due to increased competition for food, a theory supported by analysis of zooplankton communities, where, in the presence of Gambusia, large zooplankton had been removed and smaller rotifers flourished. Monitoring programmes are required to assess any impacts or improvements of mudfish populations, including those created by translocation. A Gee minnow trapping programme in outdoor mesocosms was conducted to test the reliability of traps, finding that water depth, mudfish density, mudfish memory and trap shyness had no effect on the trapability of mudfish. Trap position was found to have the most significant effect, with a greater number of mudfish caught when traps were set overnight at the surface than when set on the bottom of mesocosms. Black mudfish adults and juveniles were translocated into 18 pools (~1 m diameter) on the wetland margins of Lake Kaituna in September 2006, followed by monthly monitoring. Water quality monitoring and an assessment of hydrology and vegetation was undertaken. Habitat characterisation was found to be a key factor, with correlations between water quality data and trapping results finding fewer fish remaining in pools with less suitable characteristics for mudfish (e.g. high turbidity and conductivity). Other species were found to have a large impact, with predation by shortfinned eels (Anguilla australis) thought to have eliminated mudfish from some pools. In addition fewer mudfish were caught in pools with Gambusia, possibly due to increased competition.
Type of thesis
McDonald, A. E. (2007). Improving the success of a translocation of black mudfish (Neochanna diversus) (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2345
The University of Waikato
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