Assessment of barotrauma and its mitigation measures on the behaviour and survival of snapper and mulloway. Julian M. Hughes and John Stewart NSW Department of Primary Industries Sydney Institute of Marine Science Building 19, Chowder Bay Road Mosman NSW 2088 RFT Project No. DPI60 July 2013 NSW Department of Primary Industries – Fisheries Final Report Series No. 138 ISSN 1837-2112 Assessment of barotrauma and its mitigation measures on the behaviour and survival of snapper and mulloway. July 2013 Authors: Julian M. Hughes and John Stewart Published By: NSW Department of Primary Industries Postal Address: Port Stephens Fisheries Institute, Locked Bag 1, Nelson Bay NSW 2315 Internet: www.dpi.nsw.gov.au © Department of Primary Industries and NSW Recreational Fishing Trusts This work is copyright. Except as permitted under the Copyright Act, no part of this reproduction may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owners. Neither may information be stored electronically in any form whatsoever without such permission. DISCLAIMER The publishers do not warrant that the information in this report is free from errors or omissions. The publishers do not accept any form of liability, be it contractual, tortuous or otherwise, for the contents of this report for any consequences arising from its use or any reliance placed on it. The information, opinions and advice contained in this report may not relate to, or be relevant to, a reader’s particular circumstance. ISSN 1837-2112 Note: Prior to July 2004, this report series was published by NSW Fisheries as the ‘NSW Fisheries Final Report Series’ with ISSN number 1440-3544. Then, following the formation of the NSW Department of Primary Industries the report series was published as the ‘NSW Department of Primary Industries – Fisheries Final Report Series’ with ISSN number 1449-9967. The report series is now published by Industry and Investment NSW as the ‘Industry and Investment NSW – Fisheries Final Report Series’ with ISSN number 1837-2112 Contents i TABLE OF CONTENTS TABLE OF CONTENTS.................................................................................................................................I LIST OF TABLES.........................................................................................................................................IV LIST OF FIGURES ......................................................................................................................................VI ACKNOWLEDGEMENTS........................................................................................................................... X NON-TECHNICAL SUMMARY ................................................................................................................XI 1. INTRODUCTION ................................................................................................................................ 15 1.1. BACKGROUND ................................................................................................................................ 15 1.2. NEED .............................................................................................................................................. 16 1.3. OBJECTIVES .................................................................................................................................... 18 2. ESTIMATING SWIMBLADDER GAS EXCHANGE RATES AND BUOYANCY CONTROL 19 2.1. INTRODUCTION ............................................................................................................................... 19 2.2. MATERIALS & METHODS................................................................................................................. 21 2.2.1. Experimental fish collection.................................................................................................. 21 2.2.2. Swimbladder size & fish buoyancy........................................................................................ 21 2.2.3. Gas secretion rates................................................................................................................ 22 2.2.4. Gas resorption rates.............................................................................................................. 24 2.3. RESULTS ......................................................................................................................................... 26 2.3.1. Swimbladder size & fish buoyancy........................................................................................ 26 2.3.1.1. Snapper ............................................................................................................................................ 26 2.3.1.2. Mulloway ......................................................................................................................................... 27 2.3.2. Change in pressure before swimbladder rupture.................................................................. 28 2.3.3. Gas secretion rates................................................................................................................ 30 2.3.3.1. Snapper ............................................................................................................................................ 30 2.3.3.2. Mulloway ......................................................................................................................................... 31 2.3.4. Gas resorption rates.............................................................................................................. 32 2.3.4.1. Snapper ............................................................................................................................................ 32 2.3.4.2. Mulloway ......................................................................................................................................... 33 2.4. DISCUSSION .................................................................................................................................... 34 2.4.1. Swimbladder size & fish buoyancy....................................................................................... 34 2.4.2. Swimbladder gas secretion ................................................................................................... 35 2.4.3. Swimbladder gas resorption ................................................................................................. 38 2.4.4. Implications for vertical range.............................................................................................. 38 2.4.5. Implications for hyperbaric chamber experiments ............................................................... 39 3. MULLOWAY CHAMBER EXPERIMENTS ................................................................................... 40 3.1. INTRODUCTION ............................................................................................................................... 40 3.2. MATERIALS & METHODS................................................................................................................. 41 3.2.1. Experiment 1 ......................................................................................................................... 41 3.2.1.1. Sampling Design .............................................................................................................................. 44 3.2.1.2. Statistical Analyses .......................................................................................................................... 44 3.2.2. Experiment 2 ......................................................................................................................... 45 3.2.2.1. Sampling Design .............................................................................................................................. 46 3.2.2.2. Statistical Analyses .......................................................................................................................... 47 3.3. RESULTS ......................................................................................................................................... 48 Assessment of barotrauma and its mitigation. Julian M. Hughes and John Stewart 2 Contents 3.3.1. Experiment 1..........................................................................................................................48 3.3.1.1. In situ observations........................................................................................................................... 48 3.3.1.2. Barotrauma symptoms...................................................................................................................... 51 3.3.1.3. Mortality........................................................................................................................................... 54 3.3.1.4. Post-mortems.................................................................................................................................... 56 3.3.1.5. Delayed mortality............................................................................................................................. 61 3.3.2. Experiment 2..........................................................................................................................62 3.3.2.1. In situ observations..........................................................................................................................