Fish and invertebrate bycatch and discards in New Zealand hoki, hake, or ling trawl fisheries from 1990–91 until 2012–13 New Zealand Aquatic Environment and Biodiversity Report No. 163 S.L. Ballara R.L. O’Driscoll ISSN 1179-6480 (online) ISBN 978-1-77665-111-5 (online) November 2015 Requests for further copies should be directed to: Publications Logistics Officer Ministry for Primary Industries PO Box 2526 WELLINGTON 6140 Email: [email protected] Telephone: 0800 00 83 33 Facsimile: 04-894 0300 This publication is also available on the Ministry for Primary Industries websites at: http://www.mpi.govt.nz/news-resources/publications.aspx http://fs.fish.govt.nz go to Document library/Research reports © Crown Copyright - Ministry for Primary Industries Table of Contents EXECUTIVE SUMMARY 1 1. INTRODUCTION 3 2. METHODS 5 2.1 Definition of terms 5 2.2 Observer data 5 2.2.1 Data preparation and grooming 6 2.3 Commercial fishing return data 8 2.4 Analysis of factors influencing bycatch and discards 9 2.5 Calculation of bycatch and discard rates 9 2.6 Analysis of temporal trends in bycatch and discards 10 2.7 Comparison of trends in bycatch with data from trawl surveys 11 2.8 Discard information from Catch Landing Returns 11 2.9 Observer-authorised discarding 12 3. RESULTS 12 3.1 Distribution and representativeness of observer data 12 3.2 Comparison of estimators 13 3.3 Bycatch data (excluding discards) 14 3.3.1 Overview of raw bycatch data 14 3.3.2 Regression modelling and stratification of bycatch data 15 3.4 Discard data 15 3.4.1 Overview of raw discard data 15 3.4.2 Regression modelling and stratification of discard data 16 3.5 Estimation of retained bycatch 17 3.5.1 Bycatch rates 17 3.5.2 Annual bycatch levels 18 3.6 Estimation of discards 19 3.6.1 Discard rates 19 3.6.2 Annual discard levels 19 3.6.3 Discard information from Catch Landing Returns 20 3.6.4 Observer-authorised discarding 21 3.7 Efficiency of the hoki, hake, or ling trawl fishery 21 3.8 Annual retained bycatch by individual species 21 3.8.1 Comparison of trends in individual species bycatch in the hoki, hake, and ling trawl fishery with relevant trawl surveys 22 4. SUMMARY AND DISCUSSION 25 5. ACKNOWLEDGMENTS 28 6. REFERENCES 28 TABLES 31 FIGURES 40 APPENDIX A 76 APPENDIX B 107 EXECUTIVE SUMMARY Ballara, S.L.; O’Driscoll, R.L. (2015). Fish and invertebrate bycatch and discards in New Zealand hoki, hake, and ling fisheries from 1990–91 until 2012–13. New Zealand Aquatic Environment and Biodiversity Report No. 163. 120 p. Commercial catch-effort data and fisheries observer records of catch and discards by species were used to estimate the rate and level of fish bycatch and discards in the target hoki, hake, and ling trawl fishery for each fishing year from 1990–91 to 2012–13. Separate estimates, along with estimates of precision, were made for the following categories of catch and discards: all QMS species combined, all non-QMS species combined, all invertebrate species combined. In addition, estimates were made of the annual bycatch of a wide range of individual species. Linear mixed-effect models (LMEs) were used to identify key factors influencing variability in the observed rates of bycatch and discarding. These models consistently identified the hoki fishery areas as having the greatest influence on bycatch rates, therefore area was used to stratify the calculation of annual bycatch and discard totals in each catch category, although the WCSI was further split by fishing method. Ratio estimators were calculated for scaling up observed discard and bycatch rates to the total fishery. Bootstrapping techniques were used to select the most appropriate ratio estimator and to provide confidence limits for annual bycatch and discard estimates. For hoki, hake, and ling target fisheries two ratio estimators were applied, based on number of tows and duration respectively. Annual estimates of bycatch and discards calculated with the two forms of the estimator tended to be similar. Estimated ratios were then multiplied by the total number of trawls in each area stratum, derived from commercial catch-effort data, to make annual estimates for the target hoki, hake, or ling fishery as a whole. Multi-step bootstrap methods, taking into account the effect of auto- correlation between trawls in the same observed trip and area stratum, were used to estimate the variance in the rates and provide confidence intervals for the annual bycatch and discard estimates. Since 1990–91 the annual combined total landed catch of hoki, hake, and ling was between 109 600 and 301 600 t. Hoki, hake and ling have accounted for an average of 91% of the total estimated catch weight recorded by observers in these target fisheries. The remainder of the observed catch comprised mainly two QMS species, silver warehou (1.4% of the total catch), and spiny dogfish (0.9%), and the non-QMS javelinfish (1.4% of the total catch), and rattails (1.1%). Invertebrate species made up only a very small fraction of the overall catch, with arrow squid (0.1% of the total catch) the main species caught. All but a few edible invertebrates (crustaceans and molluscs) were discarded. Total bycatch in the hoki, hake, and ling fishery ranged from about 12 020 t to 37 730 t per year. The main bycatch species were silver warehou, javelinfish, rattails, and spiny dogfish. Bycatch ratios of QMS species were highest in Puysegur and lowest in Cook Strait. Bycatch ratios of non-QMS species were highest on the Chatham Rise and lowest for Cook Strait. Bycatch of invertebrates was low in all areas. Total annual discard estimates ranged from about 3699 to 16 633 t per year. Discards increased in the 1990s, peaked in 2000, and have since decreased. The main species being discarded were spiny dogfish, rattails, javelinfish, hoki, and shovelnose dogfish. Discard ratios of QMS species were highest in Cook Strait and the Sub-Antarctic and discard ratios of non-QMS and invertebrate species were lowest in Cook Strait. Discarding of hoki, hake, and ling accounted for 0.7% of total observed discards. There was an average of 0.05 kg of observed species discarded per kilogram of observed hoki, hake, and ling caught. Ministry for Primary Industries Bycatch and discards in hoki, hake, ling fisheries from 1990–91 to 2012–13 •1 The annual catch of 225 individual bycatch species was estimated using the same methods as for the combined species categories, and trends examined. A total of 40 species showed a decreasing trend and 19 species an increasing trend over time, although in some cases detection of trends was confounded by apparent changes over time in the species codes used by observers. Significant trends in bycatch ratios were not strongly supported by trends in relative biomass estimated from Sub-Antarctic and Chatham trawl survey time-series, although overall QMS and invertebrate groups showed some correlation with Chatham Rise trawl survey biomass trends for these species. The hoki, hake, and ling fishery is very complex, with many confounding factors. Changes in fishing practice in particular are likely to have contributed to variability in annual levels of bycatch and discards. There is a wide scope to take this analysis further. For example, there is potential for further analysis on each area separately focussing on trends within subareas, species groups, individual species, or trophic levels. Changes in bycatch ratios could be compared in more detail to survey biomass estimates for some species on the Chatham Rise and in the Sub-Antarctic, but further validation is required to determine whether estimates of commercial bycatch could provide long-term monitoring approaches for low-value species. 2 • Bycatch and discards in hoki, hake, ling fisheries from 1990–91 to 2012–13 Ministry for Primary Industries 1. INTRODUCTION The Ministry for Primary Industries (MPI) National Deepwater Plan includes the following Environment Outcome related management objective MO2.4: “Identify and avoid or minimise adverse effects of deepwater and middle-depth fisheries on incidental bycatch species”. This project addresses this objective by quantifying the level of bycatch of species or groups of species not managed separately in the QMS system. Significant changes in the relative catch of a species may be used to infer changes in abundance - although these may be due to other causes, such as changes in fishing practices. Bycatch species identified in this way as being in decline can be monitored and remedial action planned. The scampi (Metanephrops challengeri) trawl fishery was assessed in the first year of the programme (Anderson 2012), followed by the arrow squid (Nototodarus spp.) trawl fishery (Anderson 2013), and the ling (Genypterus blacodes) bottom longline fishery (Anderson 2014a) in the second and third years respectively. The hoki (Macruronus novaezelandiae)/hake (Merluccius australis)/ling (Genypterus blacodes) trawl fishery is the main subject of this report. Similar analyses will be carried out in subsequent years for each of the other Ministry for Primary Industries Tier-1 fisheries: jack mackerel (Trachurus spp.) trawl; southern blue whiting (Micromesistius australis) trawl; and orange roughy (Hoplostethus atlanticus)/oreo (Oreosomatidae) trawl. The intention for this analysis was to treat target hoki, hake, or ling tows as a single fishery with three target species, rather than treating each fishery (based on the declared target species) separately. The hoki fishery has historically been New Zealand’s largest, with total reported catches of between 90 000 t and 213 000 t per year for the fishing years 1990–91 to 2012–13 (Ballara & O’Driscoll 2014).