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Evaluating the Effects of Invasive Brown Bullhead Catfish (Ameiurus Nebulosus) on Kōura (Freshwater Crayfish, Paranephrops Planifrons) in Lake Rotoiti

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Evaluating the Effects of Invasive Brown Bullhead Catfish (Ameiurus Nebulosus) on Kōura (Freshwater Crayfish, Paranephrops Planifrons) in Lake Rotoiti Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science (Research) in Biological Sciences at The University of Waikato by Laura Beverley Francis 2019 This thesis is dedicated to Margaret Francis, Tracey Wemyss and Margaret McQuarrie whom passed away peacefully during my studies. Gone but never forgotten. i Abstract Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura i were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources. ii Acknowledgements Firstly, I would like to thank Brendan Hicks my supervisor for taking me on as a student and helping me on my masters’ journey. I would also like to thank Kevin Collier for his help with developing my methods and his endless advice and feedback, it’s been much appreciated. Warmest thank you to the Ewart family, Geoff, Van and Mandy for letting me stay at their home in Rotorua during my fieldwork on Lake Rotoiti. I had a wonderful time and Geoff is an excellent cook. Ian Kusabs, I wouldn‘t be doing this project without you. Thank you for sharing your mātauranga Māori on whakaweku construction and tau kōura with me, kia ora. Also, thanks to David Bach on your help with sampling the whakaweku and catching me a trout, you’re a legend. Many thanks to Shane Grayling from the Bay of Plenty Regional Council for initiating the netting programme in Lake Rotoiti and allowing me to use the data. The Te Arawa Lakes Trust and the Komiti Whakahaere for granting me access to fish Lake Rotoiti. Cheers to Fish and Game, especially Matt Osborne for putting out the word that I required trout flesh. Sue Clearwater provided excellent advice on many subjects. Grant Tempero was also very helpful for reading the manuscript (chapter 3) and giving constructive feedback. I would like to thank past and current students and staff for their help, who without which, my thesis wouldn’t have been possible, Manawa Huirama, Kelly Le Quesne, Cheryl Ward, Anjana Rajendram, Judith Hoult, Ian Duggan, David Culliford, Lee Laboyrie, Anita Pearson, Bruce Patty, Dylan Smith, Simon Stewart, Nigel Binks, Matt Allan, Amy Waters, Tofeeq Khan, Chris McBride and Michéle Melchior, you guys are awesome. Massive shout out to the R block crew Anita Pearson, Mike Davy, Dylan Smith, Kelly Le Quesne, Melissa Collins, Heather Taitibe, Februanty Purnomo, Michéle Melchior and Nicole Hanrahan, you all made the last two years amazing. Also, to my non-varsity mates’ thanks for the quality banter and good times, I love you all. I would also like to extend my gratitude to Mike Lake, thank you for giving me a chance to work as a student intern at the Waikato Regional Council and introducing me to the freshwater world. Your passion has rubbed off. iii Thank you to my funders the Ministry of Business, Innovation and Employment (New Zealand’s Biological Heritage National Science Challenge, C09X1501) and the Waikato University for the masters’ scholarships I received. Last and foremost, I want to acknowledge my whānau for the support and encouragement I’ve received over the last six years of study; and Lou, thank you for putting up with me and helping me through my journey. I know it hasn’t always been easy. Aroha nui. iv Table of Contents Abstract .................................................................................................................... i Acknowledgements ................................................................................................ iii Table of Contents .................................................................................................... v List of Figures ...................................................................................................... viii List of Tables.......................................................................................................... xi List of Appendices ............................................................................................... xiii Chapter 1 ..................................................................................................... 1 General introduction................................................................................................ 1 Brown bullhead catfish ........................................................................... 1 1.1.1 Effects of catfish ................................................................................. 3 1.1.2 Biology of the brown bullhead catfish ................................................ 4 Freshwater crayfish in New Zealand....................................................... 7 1.2.1 Loss of kōura ....................................................................................... 8 1.2.2 The effects of catfish on kōura ............................................................ 9 1.2.3 Biology of kōura ............................................................................... 10 Study objectives .................................................................................... 13 Thesis overview .................................................................................... 14 References ............................................................................................. 15 Chapter 2 ................................................................................................... 22 Study area .............................................................................................................. 22 Lake Rotoiti ........................................................................................... 22 2.1.1 Lake water quality ............................................................................. 23 2.1.2 Fish .................................................................................................... 25 2.1.3 Macrophytes ...................................................................................... 25 Study sites ............................................................................................. 26 2.2.1 Te Weta Bay ...................................................................................... 27 2.2.2 Southern Shoreline ............................................................................ 28 2.2.3 Okere Inlet ........................................................................................
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