Habitat utilisation and movement of black bream (Acanthopagrus butcheri, Munro 1949) in an Australian estuary Jeremy S. Hindell*, Gregory P. Jenkins and Brent Womersley * Arthur Rylah Institute, Department of Sustainability and Environment June 2009 Fisheries Victoria Research Report Series No. 41 Black bream tagging © The State of Victoria, Department of Primary Authorised by the Victorian Government, Industries, 2009. 1 Spring Street, Melbourne This publication is copyright. No part may be Printed by Fisheries Victoria, Queenscliff, reproduced by any process except in accordance Victoria with the provisions of the Copyright Act 1968. Published by the Department of Primary Preferred way to cite this publication: Industries. Hindell, Jenkins and Womersley (2009). Habitat Copies are available from the website: utilisation and movement of black bream www.dpi.vic.gov.au/fishing (Acanthopagrus butcheri, Munro 1949) in an General disclaimer Australian estuary. Fisheries Victoria Research This publication may be of assistance to you but Report Series No. 41. the State of Victoria and its employees do not ISSN 1448‐7373 guarantee that the publication is without flaw of any kind or is wholly appropriate for your ISBN 978‐1‐74217‐691‐8 particular purposes and therefore disclaims all Author Contact Details: liability for any error, loss or other consequence Jeremy Hindell which may arise from you relying on any ARI, DSE information in this publication. PO Box 137, Heidelberg Vic 3084 Black bream tagging ii Executive Summary Acoustic telemetry was used to document patterns of movement by black bream (Acanthopagrus butcheri) throughout Australia’s largest estuary, the Gippsland Lakes. Forty‐four fish were surgically implanted with acoustic transmitters and monitored over 12 months (November 2005 to October 2006). Fish moved throughout the Gippsland Lakes, with some fish moving distances of up to 2600 km, at average speeds of 8.7 km.d‐1 over 12 months. Fish frequently moved among the major estuarine rivers (Tambo, Mitchell and Nicholson Rivers), sometimes moving up to 30 km in a day. Fish use of the rivers, river entrances and lakes varied strongly with the time of year. Fish spent more time in the lakes than rivers in late summer and early autumn, but began to use the rivers more than the lakes at the end of autumn. River use was greatest in early to mid winter then gradually decreased through spring. Fish also spent more time in some rivers than others, with use of their respective entrances peaking during transition phases when fish were moving from the rivers to the lakes and vice versa. Time of the day was a weak predictor of regional patterns of fish use, but during the transitional phases (March through May) fish use of the lakes was greater at night, while use of the rivers was greater during the day. Monthly variation in times spent by fish in particular rivers varied positively with the discharge of freshwater (with a concomitant negative relationship between lakes use and overall river discharge). Black bream tagging iii Black bream tagging iv Table of Contents Executive Summary............................................................................................. iii Introduction............................................................................................................ 1 Project Design and Methods ............................................................................... 3 Study system...............................................................................................................................................................3 Selection of study sites and application of acoustic telemetry .........................................................................3 Tagging fish................................................................................................................................................................3 Flow Data ....................................................................................................................................................................4 Data Analyses.............................................................................................................................................................4 Results.................................................................................................................... 10 Discussion............................................................................................................. 22 Conclusions .......................................................................................................... 24 Acknowledgements............................................................................................. 25 References ............................................................................................................. 26 Black bream tagging v List of Tables Table 1. Summary of the release date (Date) and location (Location) of tagged fish (Tag ID); fork length (FL, mm) and weight (W, g) of tagged fish; time at liberty (D, days), estimated distance travelled (S, km) and mean rate of movement (km per day) of fish; and, the time (Year and Month) over which spatial information on the movements of individual fish (Tag ID) was collected. See Figure 1 for Release Locations. ** fewer than 20 data points on fish movement so distance parameters not calculated............................................................................................................................................................. 6 Table 2. Summary of probability values of 3‐factor randomised blocks analyses of variance comparing the time (sec.d‐1) spent by fish (F) in different regions (rivers ‐ R, lakes ‐ L, river entrances ‐ E) at different times of the day (T, dawn – 4 am to 8 am, day – 8 am to 4 pm, dusk – 4 pm to 8 pm, night – 8 pm to 4 am). Degrees of freedom shown in subscript. Bold represent significant at P < 0.05. ............................ 12 Table 3. Summary of probability values of 2‐factor randomised blocks analyses of variance and associated planned comparisons of the time (sec.d‐1) spent by fish among rivers, and between the entrance and inside each river (Mitchell entrance – ME, Tambo entrance – TE, Nicholson entrance – NE, Mitchell river – MR, Tambo river – TR, Nicholson river – NR) of the Gippsland Lakes. Degrees of freedom shown in subscript. Bold represent significant at P < 0.05.......................................................................... 13 Black bream tagging vi List of Figures Figure 1. Map of the Gippsland Lakes showing locations of acoustic receivers, and release locations of fish (NR – Nicholson River, TR, Tambo River, CA – Cunningham Arm, JB – Jones Bay, HL – Hollands Landing)............................................................................................................................................. 9 Figure 2. Relationship between average speed (km.d‐1) of movement and the length (fork length, mm) of tagged fish......................................................................................................................................................... 14 Figure 3. Examples of typical patterns of use of different regions of the Gippsland Lakes, based on the numbers of times fish were detected (hits), by four individual fish (Fish 1208, 1248, 1217, 1241) over 12 months.......................................................................................................................................................... 15 Figure 4. Examples of seasonal patterns of use of different regions of the Gippsland Lakes, based on the numbers of times fish were detected (hits), by fish 1219 over 12 months................................................ 16 Figure 5. Mean (+ se) time (sec.d ‐1) spent by all fish in each region (entrance , lake , river ) for each month of the study between November 2005 and October 2006. ............................................................. 17 Figure 6. Mean (+ se) time (sec.d ‐1) spent by all fish in each region (entrance , lake , river ) during each diel period (dawn, day, dusk, night) for each month of the study between November 2005 and October 2006. .................................................................................................................................................... 18 Figure 7. Mean (+ se) time (sec.d ‐1) spent by all fish in each region (Mitchell entrance – ME , Tambo entrance – TE , Nicholson entrance – NE , Mitchell river – MR , Tambo river – TR , Nicholson river – NR ) for each month of the study between November 2005 and October 2006... 19 Figure 8. Mean (+ se) time (sec.d ‐1) spent by fish in each region (entrance , lake , river ) through 24 hours during each month between November 2005 and October 2006. .................................................. 20 Figure 9. Monthly variability in flow ( ,average Ml.month‐1) and total time (seconds.day‐1) spent by fish ( ) in each of the rivers A) Tambo, B) Nicholson, C) Mitchell, and D) the lakes, and relationship between flows (average ML.month‐1) and total time (sec.d‐1) spent by fish in each of the rivers E) Tambo, F) Nicholson, G) Mitchell, and H) the lakes. Note different Y‐axis scales................................. 21 Black bream tagging vii Introduction Understanding patterns of habitat use and (Potter and Hyndes 1999), this potentially movement by fish is critical to the sustainable involves movement among different estuarine management of aquatic resources (Fromentin