The role of non-indigenous benthic macrofauna in the diet of snapper (Pagrus auratus) Suzannah Dodd A thesis submitted to Auckland University of Technology in partial fulfilment of the requirement for the degree of Master of Applied Science (MAppSc) 2009 School of Applied Science Primary Supervisor: Dr Kay Vopel Secondary Supervisor: Dr Barbara Breen Table of contents List of figures iii List of tables iv Attestation of authorship v Acknowledgements vi Abstract vii Introduction 1 The snapper fishing industry 1 Biology and ecology of snapper 2 The diet of snapper 4 Materials and methods 8 Sample collection 8 Spatial survey 8 Monitoring 12 Sample processing 14 Benthic macrofauna 14 Sediment properties 14 Seafloor video 15 Snapper 15 Snapper diet 15 Snapper feeding trials 16 Collection of snapper and prey 16 Trial procedure 17 Data analysis 20 Spatial survey 20 Bimonthly monitoring 22 Snapper feeding trials 24 Results 25 Spatial survey 25 Benthic macrofauna 25 Sediment properties 36 i Linking environmental factors and faunal associations 36 Bimonthly monitoring 43 Benthic macrofauna 43 Snapper 47 Snapper diet 48 Prey availability 55 Snapper feeding trials 58 Discussion 59 Non-indigenous species in the diet of snapper 59 Macrobenthic communities within Rangitoto Channel 62 The diet of snapper 65 Temporal variations in the diet of snapper 66 General observations regarding the diet of snapper 68 Limitations of the study 69 Recommendations for further study 70 Summary 71 References 72 Appendices 79 Appendix 1 79 Appendix 2 82 Appendix 3 84 Appendix 4 91 Appendix 5 95 Appendix 6 98 Appendix 7 100 Appendix 8 105 ii List of figures Figure 1. Study site, Rangitoto Channel, New Zealand 9 Figure 2. The locations of samples collected during the spatial survey 11 Figure 3. Bimonthly monitoring sites 12 Figure 4. Long line set at Site three 13 Figure 5. Tank used for the feeding trials 17 Figure 6. An example of the amount of prey offered to fish 18 Figure 7. Biomass of three non-indigenous species within Rangitoto Channel 33 Figure 8. Assemblages of benthic macrofauna in Ranitoto Channel 35 Figure 9. Sediment types present throughout the Channel 39 Figure 10. An MDS ordination showing the faunal assemblages within two sediment type 42 Figure 11. Four MDS ordinations showing the temporal trends in the faunal assemblages at the four monitoring sites 46 Figure 12. Size frequency distribution of snapper caught from June to December 47 Figure 13. The mean gonad somatic index of snapper from June to December 48 Figure 14. The mean abundance of three prey species within the sediment 56 Figure 15. The mean abundance of three prey species within the diet of snapper 57 Figure 16. Change in benthic macrofaunal assemblages in Rangitoto Channel since 1937 63 iii List of tables Table 1. Details of each of the feeding trials 19 Table 2. Conversion of particle size (µm) to phi scale equivalent (φ) and the corresponding size class 21 Table 3. Taxa recorded within Rangitoto Channel, 2008 25 Table 4. Combinations of environmental variables, yielding the best matches of biotic and abiotic similarity matrice 36 Table 5. Sediment grain size properties of 26 samples taken within Rangitoto Channel, 2008 38 Table 6. Presence and dominance of benthic macrofaunal species within shell-mud sediments 40 Table 7. Presence and dominance of benthic macrofaunal species within mud sediments 41 Table 8. Indices relating to the temporal variation in benthic macrofaunal species within Rangitoto Channel 43 Table 9. A table displaying the ANOVA results comparing the number of species and species diversity between sediments collected during the four monitoring periods 44 Table 10. The presence and dominance of prey species within the stomach and intestinal content of snapper over all of the monitoring periods 49 Table 11. One-way ANOSIM analysis comparing the stomach and intestinal content of snapper for each monitoring period 50 Table 12. Indices relating to the temporal consumption of prey species by snapper from June to December 50 Table 13. Dominance and presence (%), of prey species within the diet of snapper during the four monitoring periods 52 iv Attestation of authorship I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person (except where explicitly defined in the acknowledgements), nor material which to a substantial extent has been submitted for the award of any other degree or diploma of a university or other institution of higher learning. Signed Date v Acknowledgments Firstly I would like to thank my primary supervisor Dr Kay Vopel for the professionalism, guidance and support he has provided me with. Kay took me on as a student in the final stages of my thesis and for this I am very grateful. He has instilled in me such professionalism and scholar at a time this was needed. I would like to thank my secondary supervisor, Barbara Breen who has been supportive and enthusiastic throughout this research. I would like to acknowledge Steve O‟Shea as it was he who captured my interest in marine science, gave his input into the initial ideas of the thesis, provided support in the beginning part of the thesis as well as gave assistance with the identification of species particularly the identification of polychaetes. I would like to thank the Earth and Oceanic Sciences Research Institute for financial assistance. Financial assistance was also gratefully received through a postgraduate fees scholarship as well as a laptop scholarship provided by the Auckland University of Technology. I would like to acknowledge the Auckland University Animal Ethics Committee for the approving of our application (AEC Number R721, approval date 23/04/09). The collection of the data for this research required many days in the field and I am very grateful to the many wonderful people who endured a day or two fishing, grab sampling or participating in intertidal collection. Special thanks to Emma Beatson, who skippered the boat and Severine Dewas. Between the three of us we made a great crew and now have many memories of the wonderful times on the water. Thanks to all of my friends at AUT for their support and friendship. A special thanks to Kelly Tarlton‟s Aquarium for providing the location and tank for the feeding experiments, in particular Nik Hannam for his help and expertise in regards to the husbandry of fish. I would like to thank Kat Bolstad and Matthew Jones for their comments on the thesis. I can not thank enough my wonderful family who provided me with much support and love. My greatest thanks go to my amazing partner, Tonchi Rosandich as this thesis would not have been possible without the unwavering love, guidance and support from him. Tonchi has always been there for me even when times were rough, for this, I can not thank him enough. vi Abstract Snapper, Pagrus auratus is a valuable coastal fish species in New Zealand and forms an important commercial and recreational fishing industry in the north-east of New Zealand. Previous studies revealed evidence that this carnivorous, primarily benthic feeder consumes a non-indigenous macrobenthic species. Many non-indigenous macrobenthic species have now become established in New Zealand waters. For example, in Rangitoto Channel, Hauraki Gulf, non-indigenous macrobenthic species are prolific, with three bivalve species in particular having thriving populations: Limaria orientalis, Musculista senhousia, and Theora lubrica. The role of these species in the diet of snapper, however, is unknown. To assess the availability of indigenous and non-indigenous prey species to snapper, benthic macrofaunal assemblages throughout Rangitoto Channel were surveyed. To do so, sediment samples were collected at 84 sites. At 24 of these sites sediment was also collected for grain size analysis and at 40 of these sites the seafloor was surveyed with video. To investigate the diet of snapper, fish were collected from four monitoring sites within the channel. Bimonthly monitoring of the diet of snapper as well as the benthic macrofauna was completed at these monitoring sites and trends in the abundance of three prey species, two of which were non-indigenous species, within the sediment and the diet of snapper were compared from June to December 2008. A detailed description of the benthic macrofaunal assemblages throughout Rangitoto Channel confirmed that three non-indigenous species are established throughout this area. The analyses revealed that the diet of snapper has shifted compared to previous studies. Snapper now consume large quantities of two non-indigenous species, M. senhousia and L. orientalis. Consumption of the former species apparently results from its dominance and biomass within the sediment. It is therefore not surprising that snapper consumed large amounts of this species. In contrast, L. orientalis occurred disproportionately in the diet of snapper compared to its abundance within the sediment. I suggest that the establishment of some non-indigenous species benefits snapper. vii Introduction The snapper fishing industry Snapper, Pagrus auratus (Bloch & Schneider, 1801) is a fish that inhabits the coastal waters of New Zealand, Australia and Japan and has formed important commercial and recreational fishing industries within all three countries (Willis et al. 2003). Once described as two species it was only in 1990 that the Japanese species Pagrus major, and the Australian and New Zealand species Chrysophrys auratus were recognised as one (Paulin 1990). In New Zealand the snapper fishery is the largest and most valuable commercial and recreational coastal fishery (Ministry of Fisheries 2008). The earliest coastal fishing in New Zealand was undertaken by Maori in the pre 1800‟s (Gibbs 2008). The bones of snapper have been found during archaeological excavations of middens (Leach & Davidson 2000).