Management Zones from Small Pelagic Fish Species Stock Structure in Southern Australian Waters

Management zones from small pelagic fish species stock structure in southern Australian waters C. Bulman, S. Condie, J. Findlay, B. Ward & J. Young FRDC 2006/076 March 2008 Fisheries Research and Development Corporation and Australian Fisheries Management Authority Commercial–in–Confidence ii Bulman, Cathy. Management zones from small pelagic fish species stock structure in southern Australian waters. Bibliography. ISBN 9781921424007 (pdf). 1. Deep-sea fishes - Australia. 2. Marine fishes - Australia. 3. Fish stock assessment - Australia. 4. Fishery resources - Australia. 5. Fishery management - Australia. 6. Fisheries - Australia. I. CSIRO. II. Title. 333.9560994 Management zones from small pelagic fish species stock structure in southern Australian waters iii Enquiries should be addressed to: Dr Catherine Bulman CSIRO Marine and Atmospheric Research GPO Box 1538, Tasmania 7001 Australia W 03 6232 5357 F 03 6332 5053 [email protected] Distribution list On-line approval to publish (CSIRO) 1 (pdf) FRDC 6 (+ pdf) AFMA 5 (+ pdf) Authors 5 ComFRAB 1 SPFRAG scientific members (Drs Ward, Lyle & Neira) 3 State Fisheries Managers (NSW, Vic, Tas, SA, WA) 5 CMAR Library (not for circulation) 1 (pdf) Important Notice © Copyright Fisheries Research and Development Corporation and Commonwealth Scientific and Industrial Research Organisation (‘CSIRO’) Australia 2008 All rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of the copyright owners. 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Management zones from small pelagic fish species stock structure in southern Australian waters iv GLOSSARY AAIW Antarctic Intermediate Water AFMA Australian Fisheries Management Authority AFZ Australian Fishing Zone BRS Bureau of Rural Sciences CARS CSIRO Atlas of Regional Seas CSIRO Commonwealth Scientific and Industrial Research Organization DPIW Department of Primary Industries and Water (Tasmania) EAC East Australian Current EEZ Exclusive Economic Zone FL Fork length FRDC Fisheries Research and Development Corporation GAB Great Australian Bight ITW Indonesian Throughflow Water OCS Offshore Constitutional Settlement PIRVic Primary Industries Research Victoria SAMW Subantarctic Mode Water SARDI South Australian Research and Development Institute SDODE Spatial Dynamics Ocean Data Explorer SICW South Indian Central Water SLW Subtropical Lower Water SMP Statutory Management Plan SPF Small Pelagic Fishery SPFMAC Small Pelagic Fisheries Management Advisory Committee SPFRAG Small Pelagic Fisheries Research Advisory Group SPRAT Small Pelagic Research and Assessment Team SPRFMO South Pacific Regional Fisheries Management Organisation TAC Total Allowable Catch TACC Total Allowable Commercial Catch TAFI Tasmanian Aquaculture and Fisheries Institute TCL Trigger Catch Levels Management zones from small pelagic fish species stock structure in southern Australian waters v NON TECHNICAL SUMMARY 2006/076 Management zones from small pelagic fish species stock structure in southern Australian waters PRINCIPAL INVESTIGATOR: Dr C. Bulman ADDRESS: CSIRO Marine and Atmospheric Research GPO Box 1538 Hobart Tas 7001 ph: 03 6232 5357 Objectives: 1. Undertake a review of the global literature on the subject of small pelagic species stock structures and delineations. The review should focus on available scientific knowledge and current understanding from similar species or general knowledge of the spatial structure of physical and biological processes in this area to suggest an appropriate spatial structure for immediate management. 2. Consolidate and review existing information on small pelagic fish species. Derive from this information, one or a range of reasonable interpretations or hypotheses for the spatial stock structuring of small pelagic species in the Commonwealth Small Pelagics Fishery off southern Australia. 3. Develop from the above interpretations/hypotheses a suite of potential and appropriate interim spatial management zones and measures, recognising the alternative hypotheses and the likely need for precaution. 4. From these hypotheses, generate recommendations regarding sampling design and appropriate analytical techniques to use in a future study to resolve the key uncertainties for future management Non Technical Summary: The available literature and data on the biology, habitat and catches of target species in the Commonwealth Small Pelagic Fishery was reviewed. This information suggests that, for at least 4 of the 5 species, there are likely to be two major subpopulations, one on the eastern seaboard of Australia including East Tasmania and another to the west of Tasmania across the Management zones from small pelagic fish species stock structure in southern Australian waters vi Great Australian Bight and the Western Australia region. In the Eastern region, there is no evidence to suggest that jack mackerel Trachurus declivis is not one stock. The most recent information arising from ichthyoplankton surveys combined with the surveys of jack mackerel off eastern Tasmanian in the late 1980s are indicative of a specific association of the spawning stocks with the cool water masses of the Tasman Front. While it has been suggested that spawning is triggered by the warmer East Australian Current impinging on the shelf, there is evidence to suggest that the fish spawn in the cooler water under the surface currents. However, the eggs rise into the surface waters of the East Australian Current where development would be expected to be faster due to the warmer temperatures. While jack mackerel is caught widely throughout its distribution, catches were highest off East Tasmania in the mid 1980s for a couple of seasons, and have continued to fluctuate until redbait became the primary target in the early 2000s. While this suggests that jack mackerel are more abundant in southern regions, market forces strongly influence fishing practices and consequently the resulting catch history. Similarly, redbait Emmelichthys nitidus appears to be more strongly associated with the cooler water masses in the Tasmanian region. There is some suggestion that redbait accumulate on the cooler side of the East Australian Current front. There is evidence for faunal contrast between the East Australian Current eddies and cooler Tasman Sea waters and it has been suggested that species such as tuna prefer either the cooler or warmer sides of the fronts. Simultaneous spawning of redbait throughout its range in eastern Australia also suggests one stock in the Eastern region. Historically, the largest catches of redbait have been from eastern Tasmania but again this could possibly reflect fishing practices more than abundances. Blue mackerel Scomber australasicus and yellowtail scad Trachurus novaezelandiae are more commonly caught off New South Wales and southern Queensland. The major oceanographic influence in this region is the East Australian Current which carries warm, higher salinity water from the Coral Sea along the east coast surfacing along the Tasman Front and flowing eastwards. The position of the Tasman Front moves south in summer and north in winter and ichthyoplankton surveys off NSW and Victoria have found a mixed species composition of eggs and larvae. Blue mackerel eggs and larvae were caught exclusively in the “mixed” and East Australian Current waters. Yellowtail scad appear to prefer the warmer more northern waters although identification to species level of the Trachurus eggs has not yet been possible. Ongoing analyses of these data are expected to help to clarify species’ associations. There is insufficient local data on Peruvian jack mackerel Trachurus murphyi to make any conclusions about stock structure in Australia. This species is widely distributed throughout the Pacific with populations in the northern and southern hemisphere considered to be two subspecies. The Southern Pacific Ocean subspecies is distributed

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