Assessment of Groundfish Stocks in Northern Australian Waters Between 127-137°E
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Assessment of Groundfish Stocks in Northern Australian Waters between 127-137°E D. C. Ramm OF'� DEPARTMENT PRIMARY INDUSTRY AND FISHERIES �- FISHERIE S RESEARCH & DEVELOPMENT CORPORATION Project 90/15 Fishery Report No. 38 ISBN 0 7245 3017 7 Table of Contents Topic Page Non-technical Summary 2 Background 3 Need 4 Objectives 4 Methods 5 Detailed Results 8 Benefits 35 Intellectual Property and Valuable Information 35 Further Development 35 Staff 35 Final Cost 36 Acknowledgments 36 Attachments 1 Herding of groundfish and effective pathwidth 37 of trawls 2 Dynamics of the deepwater snapper 55 (Pristipomoides) resource in the Timor Sea 3 A simple generalized model of allometry, with 68 examples of length and weight relationships for 14 species of groundfish 4 Collaborative research and management - the 7 6 key to the sustainable management of groundfish resources in the Timor and Arafura Seas Ramm, D.C. (1997). Assessment of Groundfish Stocks in Northern Australian Waters between 127-1 37°E. Final report to the Fisheries Research and Development Corporation on project 90/15, and the Australian Fisheries Management Authority. Northern Territory Department of Primary Industry and Fisheries. FisheryReport 38, 85 pp. Assessment of Groundfish Stocks in Northern Australian Waters between 127-137"E 1 Assessment of Groundfish Stocks in Northern Australian Waters between 127-137°E Principal Investigator Dr David Ramm Address Fisheries Division Department of Primary Industry and Fisheries GPO Box 990 Darwin NT 0801 Telephone: 08 8924 4170 Fax: 08 8981 3420 Objective Assess the size of groundfish stocks in the Australian sectors of the Timor and Arafura Seas, including the northern trawl fishmanagement zones, between longitudes 127-137°E. Non-technical Summary The project provided data forasses sing the size of groundfish stocks in the Australian sectors of the Timor and Arafura Seas, between longitudes 127-137°E and latitudes 8-l5°S. This was the first integrated approach to the scientific management of the groundfish stocks in this region. Bottom trawl surveys were conducted in depths of 20-200 m in the Timor and Arafura Seas during October-December 1990 (57 days), and in the Arafura Sea during September-October 1992 (48 days) aboard the chartered 25 m stern trawler FV Clipper Bird. Two hundred and seventy six randomly allocated stations were sampled using a standard Frank and Bryce trawl. A further 211 tows were made during trawl gear calibration experiments in 1992 to evaluate the effect of herding and the level of escapement of target species such as saddle-tailed snapper (Lutjanus malabaricus). Snappers and other species were collected during both surveys to provide information on age, growth, mortality and reproduction. A novel and simple model for fishherding was developed relating trawl catches to trawl net width and door spread, allowing definition of the effective trawl pathwidth and substantially improving the swept area method. This method is commonly used around the world for estimating fishdensity and biomass from trawl survey data. The project provided new information on the relative abundance and biomass of major species of fish in the Timor and Arafura Seas between 127-137°E. Together with the new information on herding and escapement, the project allowed fishery scientists and managers to review estimates of yield and resource management strategies for saddle-tailed snapper and gold-band snapper (Pristipomoides multidens) in northern Australia. Prior estimates of yield, based on logbook and observer data, are now considered less reliable than those derived from survey data. The results of analyses based on project data are published in scientific papers, fishery status reports and workshop proceedings. Keywords Lutjanusmalabaricus, snapper, groundfish, herding, trawl survey, Timor Sea, ArafuraSea Assessment of Groundfish Stocks in N orthem Australian Waters between 127-1 37"E 2 Background The Northern Territory Fisheries Division has researched groundfish stocks in the Timor and Arafura Seas since the declaration of the Australian Fishing Zone in 1979. This research is conducted within the Division's Aquatic Resource Management Program and focuses on tropical snappers including saddle-tailed snapper (Lutjanus malabaricus) and gold-band snapper (Pristipomoides multidens). The principal objectives of that program are to: • estimate the size of tropical snapper stocks in the Timor and Arafura Seas; • examine spatial and temporal variations in the distribution and abundance, and biology of major fishstocks in northern waters; • identify stocks which are shared between Australia and Indonesia; and, • refine fishery models and review stock assessments. A new proposal, describing a fishery-independent assessment of groundfish stocks in northern Australian waters between longitudes 127-1 37°E, was submitted to the former Fishing Industry Research and Development Council (FIRDC) for funding during 1990-93. The FIRDC Board advised that it would not fund the charter vessel component for the proposal; however FlRDC would fund requested salaries and operational expenses if an alternative source of funding could be secured for the charter component. Alternative sources of funding for the charter vessel components were found for surveys in 1990 and 1992, and the revised project began in 1990 (Table 1). The project's salary and operational funds were provided by the Northern Territory Government (approx $413000 during 1990-94), FIRDC ($230000 during 1990-92) and the Fishing Research and Development Corporation (FRDC $162000 in 1992-94). The charter vessel component of the project was funded by the Fisheries Development Trust Account held by the former Australian Fisheries Service (AFS $150000 in 1990-91), and the Australian Fisheries Management Authority (AFMA $154000 in 1992-93). Table 1. Summary of grants received for the project. External funding was provided by the Australian Fisheries Management Authority (AFMA), former Australian Fisheries Service (AFS), Fisheries Research and Development Corporation (FRDC) and formerFishing Industry Research and Development Council (FIRDC). Year Agency Operational and Salaries ($) Charter Component ($) 1990-91 FIRDC 115000 AFS 150000 1991-92 FIRDC 115000 1992-93 FRDC 112000 AFMA 154000 1993-94 FRDC 50000 Total Grants 392000 304000 Assessment of Groundfish Stocks in Northern Australian Waters between 127-137"E 3 Need Under the Offshore Constitutional Settlement agreement between the Commonwealth and the Northern Territory, the groundfish trawl and longline fisheries off northern Australia remained "status quo" and were managed by the former AFS, and later AFMA, from 1979 until 1995; under this "status quo" agreement, the Northern Territory managed demersal trap, dropline and gillnet fisheries in waters adjacent to the Northern Territory. Staff from the CSIRO Division of Fisheries (notably Keith Sainsbury) and the NT Fisheries Division (notably Rex Edwards) were involved with the initial determination of Total Allowable Catches (TACs) forthe northern trawl fishery. These analyses were based on logbook data collected by Taiwanese and Australian authorities since 1974 and 1979, respectively, and exploratory surveys conducted on the Northwest Shelf, and in the Kimberley-Timar Region, Arafura Sea and Gulf of Carpentaria during 1978-80. After that time, research by CSIRO on the Northwest Shelf provided further input to regular revisions of TACs for this region. In contrast, there were no adequate data for management based on scientificassess ments of the multi-species, multi-fleet trawlfisheries in the Kimberley-Timar Region, and the Arafura Sea. This project addressed this lack of data within Australian sectors of the Timor and Arafura Seas, between longitudes 127-137°E. Objective Assess the size of groundfish stocks in the Australian sectors of the Timor and Arafura Seas, including the northern trawl fishery management zones, between longitudes 127-1 37°E (Fig. 1), and specifically: • acquire data on the status of groundfish stocks; • obtain fishery-independent indices of abundance for groundfishin the study area; • determine important population parameters for abundant taxa; and, • assess groundfish stocks between 127-137°E. 7 - 10 ..c........ :::J 0 ._.CJ) 13 AUSTRALIA 19 115 118 121 124 127 130 133 136 139 142 145 148 Longitude (East) Figure 1. Australian sectors of the Timor and Arafura Seas, between longitudes 127-137°E, surveyed during the project (shaded). Relevant fishery management zones are indicated: Arafura Sea Trawl Fishery Management Zone (AS); Northern Prawn Fishery Seasonal Closure Zone (NPF); Timor Sea Trawl Fishery Management Zone (TS); and, Timor Box (TSb). The seaward boundary of the Australian Fishing Zone is indicated (-). Assessment of Groundfish Stocks in N orthem Australian Waters between 127-1 37"E 4 Methods Bottom trawl surveys were conducted in depths of 20-200 m in the Timor and Arafura Seas during October-December 1990 (57 days), and in the Arafura Sea during September-October 1992 (48 days) aboard the chartered 25 m stem trawler FV Clipper Bird (owned by Raptis and Sons). A total of 276 randomly allocated stations were sampled using a standard Frank and Bryce trawl net with a headline length of 26 m and stretched mesh sizes of 38-230 mm (Fig. 2); the net was configured with 30 m bridles and 30 m sweeps. A further 211 tows were made during trawl gear calibration experiments in 1992 to evaluate the effect of herding and the level of escapement of target species, including