Headwater trout fisheries ln New Zealand D.J. Jellyman E" Graynoth New Zealand Freshwater Research Report No. 12 rssN 1171-9E42 New Zealmtd, Freshwater Research Report No. 12 Headwater trout fïsheries in New Zealand by D.J. Jellyman E. Graynoth NI\ryA Freshwater Christchurch January 1994 NEW ZEALAND FRBSHWATER RESEARCH REPORTS This report is one of a series issued by NItilA Freshwater, a division of the National Institute of Water and Atmospheric Research Ltd. A current list of publications in the series with their prices is available from NIWA Freshwater. Organisations may apply to be put on the mailing list to receive all reports as they are published. An invoice will be sent for each new publication. For all enquiries and orders, contact: The Publications Officer NIWA Freshwater PO Box 8602 Riccarton, Christchurch New Zealand ISBN 0-47848326-2 Edited by: C.K. Holmes Preparation of this report was funded by the New Zealand Fish and Game Councils NIWA (the National Institute of Water and Atmospheric Research Ltd) specialises in meeting information needs for the sustainable development of water and atmospheric resources. It was established on I July 1992. NIWA Freshwater consists of the former Freshwater Fisheries Centre, MAF Fisheries, Christchurch, and parts of the former Marine and Freshwater Division, Department of Scientific and Industrial Research (Hydrology Centre, Christchurch and Taupo Research hboratory). Ttte New Zealand Freshwater Research Report series continues the New Zealand Freshwater Fßheries Report series (formerly the New Zealand. Ministry of Agriculture and Fisheries, Fisheries Environmental Repon series), and Publications of the Hydrology Centre, Chrßtchurch. CONTENTS Page SUMMARY 1. INTRODUCTION 2. METHODS 9 2.I Definition and identification of "headwater rivers" 9 2.2 Characterisation of the fish stocks 9 2.2.1 Estimation of age 10 2.2.2 Growth rates and the problem of eroded scales 11 2.2.3 Drift diving and density estimates 12 2.3 Benthic invertebrates T2 2.4 Trout movements and behaviour t2 3. RESULTS l3 3.1 Location of headwater rivers l3 3.1.1 Fishery managers' opinions 13 3.1.2 Comparison with the National Angling Survey 13 3.2 Characteristics of the fish stocks 2T 3.2.I Speciesdistribution 2l 3.2.2 Sex distribution 2l 3.2.3 Size 2T 3.2.4 Condition 26 3.2.5 Age composition 27 3.2.6 Growth rates and length at age 27 3.2.7 Densities 29 3.2.8 Benthicinvertebrates 29 3.3 Behaviour of the fish 31 3.3.t Seasonal movements 3l 3.3.2 Effect of angling on trout behaviour 34 3.4 Characteristics of the frshery 35 3.4.1 Bag limits 35 3.4.2 Angling methods 37 3.4.3 Length of season 37 3.4.4 Catch rates 37 4. DISCUSSION 38 NIWA tr'reshwater Page 4.t Characteristics of the fish stocks 38 4.1.1 Species distribution 38 4.1.2 Sex distribution 38 4.1.3 Size 38 4.1.4 Condition 38 4.1.5 Age composition 39 4-1.6 Growth rates 39 4.I.7 Problems associated with estimation of age from scales 39 4.1.8 Benthic invertebrates & 4.I.9 Feeding 4l 4.1 .10 Differentiation of stocks 43 4.2 Behaviour of the fish 43 4.2.1 Seasonal movements 43 4.2.2 Effects of angling on fish behaviour 46 4.3 Characteristics of the fishery 48 4.3.I Bag limits 48 4.3.2 Angling methods 49 4.3.3 Length of season 49 4.3.4 Catch rates 49 4.4 Management concerns 5l 4.4.1 Reduction in numbers and size of fish 5l 4.4.2 Riparian access 5l 4.4.3 Aerial access and use of concessions 52 4.4.4 Environmentalimpacts 52 4.4.5 l-ack of co-ordinated management 53 5. CONCLUSIONS 54 6. ACKNOWLEDGEMENTS 55 7. LITERATURE CITED 55 APPENDIX I. Headwater fisheries questionnaire and accompanying notes 63 APPENDIX II. Questionnaire to trout angling guides and experienced anglers 68 APPENDIX III. Information on access, usage, management, and attributes of "4" list rivers 72 APPENDIX IV. Information on access, usage, management, and attributes of "8" list rivers 80 APPENDIX V. A list of "trophy" rivers, identified from the National Angling Survey, that received more than five replies 84 APPENDIX VI. A list of "headwater" rivers, identified from the National Angling Survey, that received more than five replies 85 NIWA Í'reshwater Page APPENDIX VII. Number of benthic invertebrates (mean of three replicate Surber samples) per 0.1 m2, from the upper Wairau, Karamea, and Oreti Rivers 86 TABLES l. Comparison of repeat reading of scales by the same scale reader l0 2. Comparison of original estimates of age at capture with revised estimates for Wairau River brown trout 12 3. The "4" (all-season) headwater trout rivers, compiled from a survey of fishery managers in July 1989 14 4. The "8" (early-season) headwater trout rivers, compiled from a survey of fishery managers in July 1989 18 5. Trout species of headwater rivers ZO 6. Characteristics of the fish stocks of all-season ("4" list) headwater rivers 20 7 . Distribution of rainbow trout among angler catches, for those catchments where the number of rainbow was ten or greater 21 8. Proportions of male and female trout recorded by anglers per month 2l 9. Sizes of brown and rainbow trout from scale samples 22 10. Comparison of sizes of brown trout from upper, middle, and lower reaches of the Wairau and Oreti Rivers 22 I l. Variation in size of brown trout from the Buller catchment 25 12. Average length and condition of male brown trout, October-April, all sites and years combined 25 13. Average length and condition of brown trout from the Ohikanui River for years from 1957-1992 26 14. Length-weight relationships for brown and rainbow trout 26 15. Mean condition per size group for male and female brown trout 27 16. Age composition of brown trout from selected catchments 28 I7. Age composition of rainbow trout from selected catchments 29 18. Mean length at age of brown trout from selected catchments 30 19. Mean length at age of rainbow trout from selected catchments 3t 20. Results of drift dives of headwater rivers carried out during present study 32 2I. Percentages of size classes of fish recorded during drift dives of headwater brown trout rivers þresent study) and lower reaches of rivers 33 22. Summary of benthic invertebrate samples from the upper Wairau, Karamea, and Oreti Rivers 33 NIWA Freshwater Page 23. Movement of tagged brown trout in the Oreti River, 1989 to 1992 34 24. Variation in catch rate (and mean fish length and condition) for brown trout from the Motueka River below the Wangapeka River confluence 37 25. Densities of benthic invertebrates recorded in New Zealand rivers 4I 26. Sex composition of trout recorded during spawning migrations 45 27. Comparison of average length and catch rate of trout from headwater rivers, I947-L992 50 FIGURES 1. Influence of scale size on back-calculated lengths at ages 1-5 for brown trout from the upper Wairau River l1 1 I-ength frequencies of all brown and rainbow trout samples and selected catchments 23 3. Distribution of weight of angler caught brown and rainbow trout from selected catchments 24 4. Relationship between initial length at beginning of each year's growth and annual growth rate, and annual growth rate calculated from length increments for upper Oreti brown trout 3t 5. Comparison of daily bag timits for "4" list rivers, 1989 and l99l 36 6. Comparison of fishing methods permitted in "4" list rivers, 1989 and 1991 36 7. Comparison of season lengths for "4" list rivers, 1989 and 1991 36 8. A school of about 65 large brown trout (1.8-4.1 kg) in the upper Pomahaka River, 25Illay 1992 47 NIWA Freshwater STJMMARY modal ages being five and six. Nine percent were nine years or older. Rainbow trout averaged slightly younger (5.6 years), with the modal age being five New Zealand possesses a type offishery that appears to years, and the range generally from four to seven yeårs. be unique in the world: large, wild trout in the clear, Compared with growth rates from other rivers and lakes upper reaches ofscenic and often remote, back-country in New Zæland,, brown trout from headwater areas tend rivers. For convenience, such fisheries are collectively to grow slightly faster but rainbow trout slightly slower. termed "headwater fisheries", although it is recognised that there are a number of distinct categories. From a Results from drift dives of 10 South Island rivers gave survey of fishery managers, lists were drawn up of density estimates of 3-55 large trout/km. Compared headwater rivers that fished well all season and of with published biomass estimates e,stablished for a wide headwater rivers that fished well for early season only. range of New Zealand rivers, most of the 2l reaches A total of 89 all-season rivers (18 North Island, 71 dived had a "moderate" biomass of trout. Densities of South Island) were identified, of which 50% of North benthic invertebrates were determined from three rivers Island and 12% of South Island rivers were dominated only, but results suggested that invertebrates \t/ere not by brown trout. Of the 4l early-season rivers, two of especially abundant, certainly not to the extent that the three North Island rivers were dominated by would provide substantially enhanced conditions for rainbows, while three-quarters of the 38 South Island growth compared with other rivers.