Barramundi Nursery Areas in Central Queensland 2004/05

Transcription

1 Capricorn Sunfish Inc Barramundi Nursery Areas in Central Queensland 2004/05 Report No: CS200510

2 Barramundi Nursery Areas in Central Queensland 2004/05 Capricorn Sunfish Inc Bill Sawynok (1) John Platten (2) (1) Infofish Services PO Box 9793 Frenchville Qld 4701 (2) Capricorn Bunker Consulting 2/17 Bernard Street North Rockhampton 4701 Published November 2005 Cover photographs: Small pond below causeway at southern end of Sandfly Creek in Corio Bay created by high flows through a drain. Inset is four Barramundi taken from the pond in February 2005 showing the different sizes of recruits. This pond dries regularly and the fish die. Information in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. Capricorn Sunfish Inc has taken all steps to ensure the information contained in this publication is accurate at the time of publication. Readers should ensure that they make the appropriate enquiries to determine whether new information is available on a particular subject matter. Report No: CS Copyright Capricorn Sunfish Inc and Infofish Services All rights reserved. No part of this publication may be reprinted, reproduced, stored in a retrieval system or transmitted, in any form or by any means, without prior permission from Capricorn Sunfish Inc and Infofish Services. Barramundi Nursery Areas Central Queensland 2004/05 1

3 Table of Contents Acknowledgements... 4 Terminology in the Report Summary Background Objectives Study Area Barramundi in Study Area Introduction Methods Results Discussion Level of Recruitment Timing of Spawning Conclusions References Appendix 1 Calculating Age of Juvenile Barramundi Appendix 2 Reported juvenile Barramundi in 2004/ Barramundi Nursery Areas Central Queensland 2004/05 2

4 Tables and Figures Table 1: Size range of Barramundi recruits in month of earliest recording each year Table 2: Percentage frequency of Barramundi spawnings by month as predicted from juvenile recaptures Table 3: Correlations between the predicted percentage frequency of barramundi spawning in each month between August and February and rainfall events, SOI values, the number of days of thunder and the gauged flow in Raglan Creek Figure 1: Location of monitored sites from north of Yeppoon to Turkey Beach Figure 2: Sampling with castnet Figure 3: Derived length at age curve for Barramundi Figure 4: Numbers of juvenile Barramundi from each recruitment year Figure 5: Number of 0+ Barramundi reported each year by method Figure 6: Sizes of juvenile Barramundi in CQ over time from 1998/98 to 2004/ Figure 7: Estimated time of spawning of Barramundi recruits in 2004/ Figure 8: Summary of number of Barramundi estimated to have been spawned each month Figure 9: Days each month where thunder or thunderstorms were recorded at Rockhampton Figure 10: Rainfall recorded each month at Rockhampton Figure 11: MDS plot of patterns of similarity in the timing of spawning (as predicted from back-calculation from juvenile Barramundi size) for the years of sampling. Four groupings are indicated, 1998/99 and 2003/04; 2001/02 and 1999/00; 2002/03 and 2004/05; and an outlier 2000/ Figure 12: Barramundi length at age derived from GAWB data Figure 13: Daily growth of Barramundi in 2000/01 from 12 Mile Creek Figure 14: Comparison of daily growth using data from the GAWB and 12 Mile Creek Figure 15: Composite length at age curve for Barramundi Figure 16: Derived growth curve from 2003/04 compared with observed values in 2004/ Barramundi Nursery Areas Central Queensland 2004/05 3

5 Acknowledgements The assistance of the following are acknowledged in relation to this project. The Natural Heritage Trust Fisheries Action Program for their funding of the original projects and to the Department of Primary Industries and Fisheries for funding part of the project for the past three years. Thanks to Sunfish Queensland Inc for their continued support of this monitoring program. Thanks to all persons who assisted with sampling and provided details of juvenile Barramundi that they caught. It is impossible to acknowledge them all but the support and efforts of Kim Martin and Peter Stoneley are acknowledged. Thanks to all persons that have provided technical advice, information and support to the project including Peter Long, Jonathan Staunton-Smith, Michelle Sellin, Julie Robins and Marcus Sheaves. Thanks to Ken Cowden and Andrew Hamilton from the Gladstone Area Water Board Fish Hatchery for information on the age at length of Barramundi in their hatchery. Barramundi Nursery Areas Central Queensland 2004/05 4

6 Terminology in the Report Acronyms DPI&F: Department of Primary Industries and Fisheries Suntag: Queensland tagging program of the Australian National Sportfishing Association Coastal CRC: Cooperative Research Centre for Coastal Zone, Estuaries and Waterway Management NRM: Department of Natural Resources, Mines and Energy GAWB: Gladstone Area Water Board NHT: National Heritage Trust CQ: Central Queensland CQSS: Central Queensland Strategy for Sustainability FBA: Fitzroy Basin Association GBR: Great Barrier Reef Definitions Juvenile Barramundi: Barramundi that are 0-2 years old 0+ fish: Barramundi that are 0-1 year old and 0-300mm in length 1+ fish: Barramundi that are 1-2 years old and mm in length Nursery areas: saline, brackish and freshwater habitats used by juvenile Barramundi Recruits: Barramundi that survive in the first year Year class: a group of fish being born in the same year Barramundi Nursery Areas Central Queensland 2004/05 5

7 Barramundi Nursery Areas in Central Queensland 2004/05 1. Summary The aim of this monitoring program is to obtain a better understanding of the early life cycle of Barramundi, especially in relation to timing of spawning, recruitment to nursery areas and the associated environmental conditions. This information is important for fisheries and habitat management. The information is also important in guiding actions to meet the environmental targets set in the Central Queensland Strategy for Sustainability (CQSS) developed by the Fitzroy Basin Association (FBA) and identifying wetlands of significance under the Great Barrier Reef (GBR) Coastal Wetlands program. The identification, description and monitoring of Barramundi nursery areas in Central Queensland has been ongoing now for seven years since 1998/99 and this is the 4 th report resulting from that monitoring. Previous reports identified and described Barramundi nursery habitats and the species using those habitats (Sawynok 2002, 2003, 2004). This report has focused on Barramundi recruitment strength, timing of spawning and whether climatic factors such as storms or rainfall are cues for spawning. From 1998/99 to 2004/05 a total of 3,330 juvenile Barramundi were recorded in the Central Queensland (CQ) study area. Of these 1,524 were recorded at 0-300mm (0+ fish) and 1,897 were recorded at mm (1+ fish). In 2004/ juvenile Barramundi were recorded in the study area. Of these 323 were recorded at 0-300mm and 420 were recorded at mm. However of the fish from 0-300mm 91 were recorded prior to 8/2/2005 when the first recruits were recorded for 2004/05. These 91 fish were recruited in 2003/04 and provide the first evidence of significant survival of late recruits after winter. The level of recruitment in 2003/04 was moderate and this is confirmed by the numbers of 1+ fish from that year class recorded in 2004/05. In 2004/05 the level of recruitment is considered to have been moderate. The earliest recruits were recorded at 35-40mm in February In 2003/04 a length at age growth curve was developed from data supplied by the Gladstone Area Water Board (GAWB) hatchery and from tag and recapture data from 12 Mile Creek in 2000/01. This curve was considered to be a reasonable approximation of growth in the wild with rapid growth early and then a steady decline towards winter. In 2004/05 growth data for fish up to 200mm was obtained from the GAWB hatchery and this substantially supported the growth curve developed in 2003/04. This growth curve was used to back calculate an estimated date of spawning for 0+ fish reported in 2004/05. This indicated that spawning times for 2004/05 were from October 2004 to January 2005 with peak spawning in December. The spawning period has varied each year with the prime spawning period being October to December. Barramundi Nursery Areas Central Queensland 2004/05 6

8 Some spawning was likely to have occurred in September in some years, especially 2000/01 and possibly in 1998/99 and 2003/04. There was little evidence of spawning in January except perhaps for 2004/05. The closed season for Barramundi is November to January however this does not coincide with the prime spawning period in CQ. Preliminary investigation into the timing of Barramundi spawning and climatic factors points to a link between the timing of the first storms and the patterns of Barramundi spawning. However further investigation is required to determine if this is coincidental or it could be an indicator of another auto-correlated factor that is the real trigger. Barramundi Nursery Areas Central Queensland 2004/05 7

9 Barramundi Nursery Areas in Central Queensland 2004/05 2. Background The aim of this monitoring program is to obtain a better understanding of the early life cycle of Barramundi in Central Queensland, especially in relation to timing of spawning, recruitment to nursery areas and the associated environmental conditions that may influence these. This information is important in gaining a better understanding of the significance of these areas for fisheries and habitat management. The information is also important in guiding actions to meet the environmental targets set in the Central Queensland Strategy for Sustainability (CQSS) developed by the Fitzroy Basin Association (FBA) and identifying wetlands of significance under the Great Barrier Reef (GBR) Coastal Wetlands program. The identification, description and monitoring of Barramundi nursery areas in Central Queensland has been ongoing now for seven years since 1998/99 and this is the 4 th report resulting from that monitoring. From 1998/99 to 2001/02 this work was undertaken through grants provided by Natural Heritage Trust (NHT) projects and and a report produced by Capricorn Sunfish (Sawynok 2002). Capricorn Sunfish received a grant from the Department of Primary Industries and Fisheries (DPI&F) in 2002/03 to continue monitoring for that year and report CS covering that period was produced (Sawynok 2003). Capricorn Sunfish received a further grant from the DPI&F in 2003/04 to continue monitoring for that year and report CS was the third in this series. Capricorn Sunfish again received a further grant from the DPI&F in 2004/05 to continue monitoring for that year and this report CS is the fourth in that series. Previous project reports identified and described Barramundi nursery habitats and the species using those habitats (Sawynok 2002, 2003). The 2003/04 and the 2004/05 reports have focused on recruitment strength, timing of spawning and relating these to river flow and rainfall. This report should be read in conjunction with the earlier reports: Barramundi Nursery Areas in Central Queensland (Sawynok 2002) Barramundi Nursery Areas in Central Queensland 2002/03 (Sawynok 2003) Barramundi Nursery Areas in Central Queensland 2003/04 (Sawynok 2004) Barramundi Nursery Areas Central Queensland 2004/05 8

10 3. Objectives This monitoring program has evolved from a series of projects that commenced in 1998/99 and there have been a number of objectives set for the individual projects during that time. In 2004/05 the objectives were: Monitor the 2003/04 and 2004/05 year classes of Barramundi from July 2004 to June 2005 to determine recruitment strength. Determine if a correlation exists between early storm activity in the study area and the timing of spawning of Barramundi using data from 1998/99 to 2004/05. In 2003/04 the objective was: Monitor the 2003/04 year class of Barramundi from July 2003 to June 2004 (and then through to June 2005) to determine recruitment strength. In 2002/03 the objectives were: Monitor seven established key sites from Corio Bay to Turkey Beach in Central Queensland from December 2002-May Monitor one new site in Shoalwater Bay at least two times from January 2003-May Obtain data from fishers catching juvenile Barramundi to assess overall locations inhabited by juvenile Barramundi in their first year of life. From 1998/99 to 2001/02 the objectives of NHT projects and were: Identify freshwater/brackish/saltwater areas used by juvenile Barramundi as nursery habitats. Describe sites, their use by Barramundi and the water flow conditions required for access by Barramundi. Aging of juvenile Barramundi to determine if they had been spawned outside the closed season. Barramundi Nursery Areas Central Queensland 2004/05 9

11 4. Study Area 32 ROCKHAMPTON YEPPOON RAGLAN 20 Kilometers REGULAR MONITORING SITES INTERMITTENT MONITORING SITES TAGGING ONLY SITES NEW SITES IN 2002/03 6 GLADSTONE 24 7 TURKEY BEACH Figure 1: Location of monitored sites from north of Yeppoon to Turkey Beach The study area was from Corio Bay north of Yeppoon to Rodds Bay south of Gladstone as shown in figure 1. Site identification and descriptions are the same as for the previous studies for sites 1-41 (Sawynok 2002, 2003, 2004). 4. Barramundi in Study Area 5.1. Introduction Refer to the initial report (Sawynok 2002) for the introduction on Barramundi at study locations. It was known from Suntag data and earlier research (Russell and Garrett 1983, 1985, 1988) that juvenile Barramundi recruit to saline, brackish and freshwater nursery habitats. When this occurs in the Barramundi life cycle was known for north-east Queensland (Russell and Garrett 1983, 1988) but unknown for Central Queensland. Determining the numbers, size and timing when Barramundi enter Central Queensland habitats provides data on the use and importance of these habitats. Barramundi Nursery Areas Central Queensland 2004/05 10

12 Peak Barramundi spawning was considered to occur from November to Janaury, although it was acknowledged that it occurs outside that period. During this time there is a closed fishing season where the taking of Barramundi is not permitted to protect spawning fish. It is known that spawning occurs during full or new moon periods and that there may be multiple spawning events during the season. It was uncertain how many spawning events occur in a season and the extent to which they contribute to recruitment. Knowledge of the actual periods over which spawning occurred each year would assist in understanding the Barramundi life cycle. With spawning appearing to occur over a number of months each year and the variation in when that occurs each year provides an opportunity to investigate some possible triggers for Barramundi spawning. By using a growth equation to back calculate the probable month of spawning from the size of young fish, it is possible to estimate the proportion of fish spawned in each month of each year. This information can then be compared with a variety of climate and other factors that could be triggers for spawning Methods Refer also to the previous report (Sawynok 2002) for the initial methods of assessing juvenile Barramundi at study locations. Methods outlined in and were used initially and those in were used from 2002/03 onwards. This monitoring program is specifically interested in juvenile Barramundi in the first year of their lives, referred to as 0+ fish and from 0-300mm in length. Fish between mm were considered to be 1+ fish and were also included to track recruits into their second year. While fish of those ages can occur outside these size ranges no aging of specific fish was made so this general categorisation was used. The financial year was used to define the years for the monitoring as there is a lull in Barramundi activity and catchability over the colder winter months with little activity in offstream habitats. From 2002/03 there were three methods used to determine Barramundi at study sites while only the first two methods were used prior to that time. The methods used were: Sampling at study sites using a castnet; Fish caught using rod and line and tagged at study site; Reports of Barramundi caught by recreational fishers using castnets, baitnets or other fishing gear Sampling Using a Castnet Sampling by castnet was primarly aimed at determining the presence or absense of 0+ Barramundi at each site, however it was also used to collect data on other species. A permit was obtained from DPI&F to allow the use of sampling equipment in freshwater. The current permit is PRM03699D which is valid from 1 April 2003 to 31 March Barramundi Nursery Areas Central Queensland 2004/05 11

13 The use of a castnet was not as effective in freshwater due to the presence of extensive aquatic plant growth. In some cases this covered 95% of a waterhole and negated this as a sampling method. Figure 2: Sampling with castnet A standard nylon castnet with a 2.4m drop and 20mm stretched mesh size was used throughout the sampling period (figure 2) to ensure comparability of results from different samplings at each site. Each site was assessed to determine the most appropriate sampling regime. This was based on the size of the site and location of likely areas where 0+ Barramundi would be found. Each site was then sampled with a specific number of casts and this was repeated each time the site was sampled with casts being made in approximately the same location each time. Sampling was carried out at each site on an approximate monthly basis. Small sites were allocated 5 casts, medium sites were allocated 10 casts and large sites 20 casts. The maximum area that can be covered in a single cast of the selected castnet is 18m 2. A cast was considered to be acceptable if it covered 75% of the maximum area which is 13.5m 2. Casts where a lesser area was covered were discarded and repeated. The average area covered by each cast was estimated to be 15m 2. This method allowed a standardised comparison of sampling at a specific location and between locations based on the number of fish caught per cast. Barramundi Nursery Areas Central Queensland 2004/05 12

14 Based on this the area covered at different sites was: 75m 2 where 5 casts used 150m 2 where 10 casts used 300m 2 where 20 casts used At each site for each cast with the castnet the number of fish, species and fork length of each fish was recorded, except for round tail fish such as Barramundi where total length was recorded. Details of prawns and crabs caught were also recorded. Results of other species sampled were included in previous reports (Sawynok 2002, 2003) Fish Caught on Rod and Line and Tagged Barramundi in Central Queensland have been tagged under the Suntag program since the mid 1980 s. These fish were primarily caught using rod and line and this data has been included to assess the numbers of juvenile Barramundi recorded each year. This data was obtained from the Suntag database Fish Reported by Recreational Fishers It is common for recreational fishers to catch juvenile Barramundi while fishing for bait with castnets or baitnets and sometimes on rod and line. In 2002/03 it was considered that collecting data on the incidence of fish caught this way would increase the available data. This was done by requesting fishers to report incidences of juvenile Barramundi caught while catching bait or during fishing operations. Fishers were requested to record the date, location and length of juvenile Barramundi caught and provide details by ringing a toll free number Data on date and location were accurately obtained however some lengths were estimated as fishers did not have any means of measuring the fish prior to release Assessment of Barramundi Recruitment Barramundi caught by all methods were assessed at all monitoring sites and throughout the study area. Analysis was based on nominally 0+ fish (0-300mm) and nominally 1+ fish ( mm). The number of 0+ and 1+ fish each year was used to assess recruitment strength. An arbitrary allocation of numbers of recruits caught each year by all methods at all sites was adopted to describe recruitment strength. These figures are based on numbers of 0+ fish recorded between 1 January and 30 June each year and the number of 1+ fish recorded between 1 July and 30 June the following year: Low less than 100 Moderate High 500-1,000 Exceptional more than 1,000 Barramundi Nursery Areas Central Queensland 2004/05 13

15 While these figures are arbitrary there was historic tagging data to support such a classification. Recruitment data prior to 1998/99 is based only on tagging data, from 1998/99 to 2001/02 the data is based on tagging and sampling records and from 2002/03 to 2004/05 the data is based on tagging, sampling and reporting by recreational fishers. The timing of Barramundi recruits being reported each year was used to assess when Barramundi enter nursery areas and the water flow conditions that were associated with that movement. Data on the length at age (in days) for 0+ Barramundi was not available for fish in the study area. In 2003/04 length at age was derived from two data sources and a growth curve for Barramundi from 0-300mm generated. In 2004/05 data was collected on length at age by the GAWB hatchery for fish up to 200mm long. The derivation of the growth curve is described in appendix GROWTH CURVE FOR BARRAMUNDI 250 LENGTH AGE (DAYS) Figure 3: Derived length at age curve for Barramundi The derived age at length growth curve was applied to Barramundi recruits from 0-300mm reported each year from January to June. The growth curve was used to calculate an estimated spawning date for each fish in 2004/05. Spawning dates had previously been calculated for each season from 1998/99 to 2003/04 (Sawynok 2004). An assessment was then made of the number of recruits each month during the study period and the likely incidence of spawning each year from August to February Comparing Estimated Spawning Times with Climatic Factors To assess if there was a correlation between the estimated time of spawning and climatic factors three major parameters were investigated. These were the flow of Raglan Creek, rainfall patterns at Rockhampton and the number of storms in each month (as indicated by the number of days of thunder in each month). Barramundi Nursery Areas Central Queensland 2004/05 14

16 Daily rainfall and days on which thunder was heard or thunderstorms observed was obtained for Rockhampton Aero Site Number and located at latitude 23 o S and 150 o E for the period January 1985 to June The values of the 30 days average of the southern oscillation index at the end of each month were obtained from the Bureau of Meteorology. Monthly total gauged flow in Raglan Creek was obtained from the Department of Natural Resources and Mines gauging station on Raglan Creek. By using the growth equations to back calculate the probable month of spawning from the size of young fish, it was possible to estimate the proportion of fish spawned in each month of each year. This information was compared with a variety of climate and other factors that could be triggers for spawning. Two methods of investigation were attempted. Monthly rainfall at Rockhampton, monthly total gauged flow on Raglan Creek, the values of the 30 day average of the southern oscillation index at the end of each month and the number of days of thunder within each month were compared with the percentage of barramundi estimated to have been spawned in each month for each year. Correlations (Pearson product moment) between the parameter and the percentage of barramundi spawned were calculated using the routines of Microsoft excel. An alternative analysis was attempted to investigate if the initial onset of rainfall at the beginning of the wet season, the first storms of the year or the first post winter river flow were related to the pattern of spawning. Patterns in the percentage frequency of fish spawned in each month for each year were investigated using multi-variate analysis routines within the Primer5 computer software (Primer-E Ltd). A similarity matrix (Bray-Curtis similarities, square root transformed) was first calculated and the MDS (Multi Dimensional Scaling) plot showing the patterns of similarities established. This shows which years had similar spawning patterns. The patterns within the years were then compared with the month in which the first rainfall greater than 30mm occurred, the month when the first storm (as measured by thunder being observed) occurred and the month of the first major increase in flow of Raglan Creek. This was accomplished by assigning the months as factors within the Primer5 routines and then using the analysis of similarity (ANOSIM) routine to determine which factor explained the similarity matrix best. Barramundi Nursery Areas Central Queensland 2004/05 15

17 5.3. Results Juvenile Barramundi in Central Queensland Study Area From 1998/99 to 2004/05 a total of 3,330 juvenile Barramundi were recorded in the Central Queensland (CQ) study area. Of these 1,524 were recorded at 0-300mm (0+ fish) and 1,897 were recorded at mm (1+ fish) YEAR CLASSES OF JUVENILE BARRAMUNDI BARRA 0+ BARRA NUMBER OF FISH / / / / / / / /05 Figure 4: Numbers of juvenile Barramundi from each recruitment year In 2004/ juvenile Barramundi were recorded in the study area. Of these 323 were recorded at 0-300mm and 420 were recorded at mm. However of the fish from 0-300mm 91 were recorded prior to 8/2/2005 when the first recruits were recorded for 2004/05. These 91 fish were recruited in 2003/04 and have been included as 1+ fish for that year, even though some may have been 0+ fish. Figure 4 shows the numbers of fish recorded from each year class as either 0+ or 1+ fish. This indicates a high level of recruitment in 1999/00, 2000/01 and 2003/04 with moderate and low levels of recruitment in the other years. In 2000/01 the recruitment was primarily at one site, 12 Mile Creek, and was followed by a complete fish kill at that site. This is reflected in the lower numbers of 1+ fish from that year class recorded the following year. The level of recruitment in 2003/04 was moderate and this is confirmed by the numbers of 1+ fish from that year class recorded in 2004/05. In 2004/05 the level of recruitment is considered to be moderate. The figure for 2004/05 has been elevated by 80 small Barramundi reported from a tidal pool at Kinka Beach. Barramundi Nursery Areas Central Queensland 2004/05 16

18 NUMBER OF FISH JUVENILE BARRAMUNDI OTHER TAGGING SAMPLING/TAGGED SAMPLING / / / / / / /05 Figure 5: Number of 0+ Barramundi reported each year by method Figure 5 shows the numbers of 0+ fish reported each year by the method by which the data were obtained. From 1998/99 through to 2001/02 data were obtained from sampling and tagging only. Since 2002/03 data from the incidental capture of juvenile Barramundi while collecting bait or during other activities have also been recorded. This has provided useful additional data on the number of recruits each year LENGTH (MM) BARRAMUNDI SIZES IN CQ 0 05-Jan May Oct Feb Jun Nov Mar-06 Figure 6: Sizes of juvenile Barramundi in CQ over time from 1998/98 to 2004/05 Barramundi Nursery Areas Central Queensland 2004/05 17

19 Figure 6 shows the length of Barramundi recorded over time during the study period. Arrows show new 0+ recruits each year and the growth (indicative only) of that year class over the following period. The greater density of the dots indicates larger numbers of fish Timing of Juvenile Barramundi Recruitment in Study Area The timing of recording of the first evidence of the earliest recruits varied each year, as shown in table 1, with earliest recruits appearing in January in 2000/01 and 2003/04. These were years of moderate and high recruitment. The latest recording of the first evidence of the earliest recruits was in March in 1999/00 and 2002/03. In 2004/05 the earliest recruits were recorded in early February at 35-40mm. SIZE (mm) OF EARLIEST RECRUITS EACH YEAR JUL AUG SEPT OCT NOV DEC JAN FEB MAR APR MAY JUN 1998/ / / / / / / Table 1: Size range of Barramundi recruits in month of earliest recording each year 28-Jan-05 ESTIMATED SPAWNING DATES 2004/05 08-Jan Dec Nov Nov Oct Sep Sep Figure 7: Estimated time of spawning of Barramundi recruits in 2004/05 Barramundi Nursery Areas Central Queensland 2004/05 18

20 The derived growth curve for age at length was applied to Barramundi recruits from 0-300mm reported each year from January to June. This provided an estimate of spawning date and minimised the effects of variable growth rates. Figure 7 shows the estimated spawning dates of 221 Barramundi recorded in 2004/05. This indicates most spawning was likely to have occurred from October 2004 to January Barramundi are known to spawn around the period of the full moon or the new moon. In that year the full moon was on 28 October, 27 November, 27 December 2004 and 25 January Figure 8 provides a summary of the numbers of Barramundi calculated to have been spawned each month from 1998/99 to 2004/05. This indicates spawning in August however this is highly unlikely as no 0+ fish have been recorded earlier than January in any year. This is likely to be the result of uncertainty and insufficiency in the data rather than spawning actually occurring at the time. There was no evidence of late spawning the previous season that could account for the larger fish in January. However there was evidence of fish with daily growth rates of mm/day and this is supported by the growth data from the GAWB hatchery (GAWB 2004, 2005). This would suggest that fish indicated as being spawned in August were actually spawned later in September or October with higher than average growth rates. NUMBER OF BARRAMUNDI SPAWNING PER MONTH 1998/ / / / / / / AUG SEPT OCT NOV DEC JAN FEB Figure 8: Summary of number of Barramundi estimated to have been spawned each month Barramundi Nursery Areas Central Queensland 2004/05 19

21 In three of the seven years, 1998/99, 2000/01, and 2003/04, the earliest spawning most likely occurred in September and October. In four of the years, 1999/00, 2001/02, possibly 2002/03 and 2004/05 the earliest spawning was likely to have been October and November. Prior to 2004/05 there was little evidence of recruits from spawning in January or later. A small number of Barramundi of less than 100mm were recorded in May- June however these fish were generally not recorded after winter. It is possible that these smaller fish were cannibalised by larger fish including earlier recruits. However in 2004/05 there appears to have been significant spawning and December and some spawning in January. This is supported by 91 fish recorded from July to December 2004 that were from mm. This is the first year where any numbers of fish of those sizes have been recorded after winter. The data suggests that the most important months for spawning are likely to be October to December with some evidence to support spawning in September in a number of years, including substantial spawning in 2000/01. However in 2004/05 it would appear that January (or the full moon period in late December) could also have been important Time of Spawning compared with Climatic Factors Each year the timing of the initial spawning event appears to vary. This could be a natural variation or it may be influenced by climatic factors. It may also be that spawning commences at the same time each year however climatic factors may influence the numbers of survivors to become 0+ recruits. DAYS DAYS OF THUNDER 1998/ / / / / / / AUG SEPT OCT NOV DEC JAN Figure 9: Days each month where thunder or thunderstorms were recorded at Rockhampton Barramundi Nursery Areas Central Queensland 2004/05 20

22 . MILLIMENTRES ROCKHAMPTON RAINFALL 1998/ / / / / / / AUG SEPT OCT NOV DEC JAN Figure 10: Rainfall recorded each month at Rockhampton It was already known that rainfall and flooding, especially in December or January was associated with strong recruitment or a high level of recruitment survival (Sawynok 1998). However, as the timing of initial spawning appears to be variable and occurs from September to November, it was considered that early storm activity or rainfall could be a climatic trigger for spawning activity to commence. Crocodiles are known to commence breeding activity when storms are around (John Lever Korana Crocodile Farm pers comm). Figure 9 shows the number of days each month that storm activity was recorded at Rockhampton. There was little storm activity recorded in August or September during the study period. Storm activity generally commences in October and that generally coincides with the earliest spawning activity each year. Figure 10 shows the monthly rainfall for Rockhampton. This indicates rainfall in August and September was generally not associated with storm activity. 1998/ / / / / / /05 AUG SEPT OCT NOV DEC JAN FEB Table 2: Percentage frequency of Barramundi spawnings by month as predicted from juvenile recaptures Barramundi Nursery Areas Central Queensland 2004/05 21

23 The percentage frequency of barramundi spawned in each month for each year is shown in Table 2. No significant correlations were observed between the percentage frequency of fish spawned in each month and any of the parameters in Table 3. The MDS plot shows that the years 2002/03 and 2004/05, 1998/99 and 2003/04, 1999/2000 and 2001/02 cluster closely together (figure 11). The 2000/01 year seems significantly different to the other years. 2002/03 and 2004/05 had most spawning occurring late (in Dec/Jan), 1998/99 and 2003/04 had most spawning occurring in Oct/Nov, 1999/00 and 2001/02 had peaks in Nov with significant numbers in Oct and Dec (table 2). The outlier year (2000/01) showed very early spawning (Aug/ Sept). The month when first storms were observed (as indicated by observed thunder) best explains the patterns in the data. The ANOSIM routine showed significance at 2.9% (the factor explains 97.1% of the similarity between the years). The only year not explained was the outlier year 2000/01. The first post winter flow in Raglan Creek explained some of the clustering (significance 8.6%), (although this may be auto-correlated with the thunder measures), while the first post winter Rockhampton rainfall explained little of the similarities (significance 99%). Stress: / / / / / / /05 Figure 11: MDS plot of patterns of similarity in the timing of spawning (as predicted from backcalculation from juvenile Barramundi size) for the years of sampling. Four groupings are indicated, 1998/99 and 2003/04; 2001/02 and 1999/00; 2002/03 and 2004/05; and an outlier 2000/01. Barramundi Nursery Areas Central Queensland 2004/05 22

24 barra spawning rain SOI Thunder flow barra spawning 1 rain SOI Thunder flow Table 3: Correlations between the predicted percentage frequency of barramundi spawning in each month between August and February and rainfall events, SOI values, the number of days of thunder and the gauged flow in Raglan Creek. 6. Discussion 6.1. Level of Recruitment The number of 1+ fish recorded from the 2003/04 recruitment year has confirmed that this was a year of moderate to high recruitment and was the strongest recruitment since 1999/00. In 2003/04 the recruitment level was moderate with recruits recorded from a wide range of sites, however the number of 0+ fish at 12 Mile Creek was low. Monitoring of 1+ fish in 2004/05 indicated a higher level of recruitment there than was apparent in the previous year. This year produced the first evidence of recruits from later spawning events in December or January 2003/04, surviving in numbers over the winter period with 91 fish recorded from July 2005 to February 2005 between mm. All these fish were recruited in 2003/04 however no dates of spawning were estimated for these fish due to the effects of changing growth rates over winter. Data for 2004/05 suggests that this was a year of moderate recruitment with fish recorded from a wide range of sites. This was despite low levels of rainfall. However these falls occurred at important times from October to January in local creek catchments, especially 12 Mile Creek and 8 Mile Creek Timing of Spawning Russell reported that in the Rockhampton area Barramundi gonads underwent early development with evidence of some spawning occurring as early as September with spent fish indicating spawning continuing as late as the beginning of April (Russell 1990). This year the age to length curve developed in 2003/04 for fish up to around 300mm in size, based on a combination of hatchery and wild fish growth rates, was confirmed from hatchery data of the growth of fish to 200mm. This indicates that the dates of spawning calculated using this growth curve are likely to be valid in providing an approximate date of spawning, especially for fish up to 200mm. This date can only be considered as approximate due to the variability of growth Barramundi Nursery Areas Central Queensland 2004/05 23

25 rates of individual fish. In 2004/05 it is likely that spawning commenced in October and extended through to January with possibly a peak in December. The data of this study could contribute towards the prediction of the timing of barramundi spawning. The management implications of this could be considerable. The preliminary analysis points to a link between the timing of the first storms and the patterns of barramundi spawning. If this link was established as a cause or trigger for spawning, it could provide a powerful predictive tool for indicating when spawning was likely to have occurred. However the analysis and data available must be considered a very preliminary exploration of data trends at this stage. The storm link could be purely coincidental or it could be an indicator of another auto-correlated factor that is the real trigger. Establishing a link between the timing of storms and the patterns of spawning does not establish a trigger, particularly since the indicator for storms was indirect (the presence of thunder). It would be unlikely that thunder would be a direct trigger for spawning (how would barramundi sense thunder underwater?) and it may be that storms that are not accompanied by thunder could be just as important. There is a need for more detailed investigation of a range of other factors including other indicators of storm events, eg rapid changes in barometric pressure that might explain the patterns of spawning. It is also possible that water temperature is another variable that could influence the time of spawning. The GAWB hatchery spawn their fish at water temperatures of 28 o C to ensure maximum success (A Hamilton pers comm) however in the wild at least partial spawning success could be expected at lower temperatures. These conditions exist in October each year and the importance of this month is supported by spawning in most years. 7. Conclusions The early life cycle of Barramundi in the study area is gradually becoming better understood with improved information on timing of spawning, recruitment to nursery areas and the associated environmental conditions. In the study area the main spawning period is from October to December with spawning also possible in September but limited succesful spawning occurring after December. Preliminary analysis has indicated a link between the timing of the first storms and the pattern of Barramundi spawning. The finding of the main spawning period being from October to December needs to be considered in future management arrangements for Barramundi. Barramundi Nursery Areas Central Queensland 2004/05 24

26 8. References Bureau of Meteorology (2005): Daily Precipitation and Thunder heard or Thunderstorms observed from January 1985 to June 2005: data available from the Bureau of Meteorology Cheetham (2005): Monthly rainfall from Saltponds rain gauge on south side of Inkerman Creek: unpublished data GAWB (2004): Growth of Barramundi in the Gladstone Area Water Board hatchery in 2003: unpublished data GAWB (2005): Growth of Barramundi in the Gladstone Area Water Board hatchery in 2004: unpublished data NRM (2004): Monthly flow data for the Riverslea gauge B on the Fitzroy River: data available from the Department of Natural Resources and Mines Russell DJ and Garrett RN (1983): Use by Juvenile Barramundi, Lates calcarifer (Bloch), and other Fishes of Temporary Supralittoral Habitats in a Tropical Estuary in Northern Australia: Aust Journal of Marine and Freshwater Research 34: Russell DJ and Garrett RN (1985): Early Life History of Barramundi, Lates calcarifer (Bloch), in North-eastern Queensland: Aust Journal of Marine and Freshwater Research 36: Russell DJ and Garrett RN (1988): Movements of Juvenile Barramundi, Lates calcarifer (Bloch), in North-eastern Queensland: Aust Journal of Marine and Freshwater Research 39: Russell DJ (1990): Some aspects of the biology of the Barramundi, Lates calcarifer, (Bloch) in eastern Queensland, M App Sc Thesis, Department of Biology and Environmental Science, Queensland University of Technology, Brisbane: 194pp Sawynok W (1998): Fitzroy River Effects of Freshwater Flows on Fish Impact on Barramundi Recruitment, Movement and Growth: National Fishcare 97/ report: 59pp Sawynok W (2002): Barramundi Nursery Areas in Central Queensland: Natural Heritage Trust projects and report: 88pp Sawynok W (2003): Barramundi Nursery Areas in Central Queensland 2003/04: Capricorn Sunfish report CS200308: 30pp Sawynok W (2004): Barramundi Nursery Areas in Central Queensland = 2004/05: Capricorn Sunfish reort CS200409: 40 pp Barramundi Nursery Areas Central Queensland 2004/05 25

27 9. Appendix 1 Calculating Age of Juvenile Barramundi In 2003/04 data on the length at age (in days) for 0+ Barramundi was not available for fish in the study area. Length at age was derived from two data sources and a growth curve for Barramundi from 0-300mm generated. Data was obtained on the growth of Barramundi from 0-55mm in length from the Gladstone Area Water Board hatchery as shown in figure 11 (GAWB 2004). The hatchery is within the study area and used stock obtained from the study area. While this growth data related to fish reared in a hatchery it was considered that it was consistent with the expected growth rates of fish in the wild in the study area. A formula was derived from this data to calculate the age in days based on the length of the fish however this data only provided length at age data for fish up to 55mm long. The derived formula was: y = 0.007x x Length (mm) / Temp ('C) BARRAMUNDI LENGTH/AGE Length (mm) Temperature ('C) Poly. (Length (mm)) y = 0.007x x R 2 = Age (Days) Figure 12: Barramundi length at age derived from GAWB data Data for 50 Barramundi was available on growth from tag and recapture records of fish from between mm from 12 Mile Creek in 2000/01. A daily growth increment was calculated and a formula was derived for daily growth increment of these fish as shown in figure 12. The derived formula was: y = LN(x) Barramundi Nursery Areas Central Queensland 2003/04 26

28 2 1.8 BARRAMUNDI GROWTH RATE DAILY GROWTH (MM) y = Ln(x) LENGTH (MM) Figure 13: Daily growth of Barramundi in 2000/01 from 12 Mile Creek Comparisons were made of daily growth at different sizes using both formulas for fish between mm where no growth data was available as shown in figure 13. This indicated that growth at 150mm was approximately the same using both formulae. DAILY GROWTH (MM) DAILY GROWTH DG12M DGGAWB LENGTH (MM) Figure 14: Comparison of daily growth using data from the GAWB and 12 Mile Creek Barramundi Nursery Areas Central Queensland 2004/05 27

29 It was considered that the GAWB data provided the best estimate of daily growth up to 150mm while the 12 Mile data provided a better estimate of daily growth for fish greater than 150mm. This daily growth data was then used to generate a composite length at age curve for fish for 0-300m as shown in figure LENGTH (mm) GROWTH CURVE FOR BARRAMUNDI AGE (DAYS) Figure 15: Composite length at age curve for Barramundi LENGTH (mm) BARRAMUNDI GROWTH CURVE 2003/ / DAYS Figure 16: Derived growth curve from 2003/04 compared with observed values in 2004/05 Barramundi Nursery Areas Central Queensland 2004/05 28

30 This curve was considered to be a reasonable approximation of growth in the wild with rapid early growth and a then a steady decline towards winter. Tagging data indicates that growth over winter is minimal or significantly reduced for most fish. In 2003/04 the GAWB data was only available for fish from 0-65 days old. In 2004/05 the hatchery produced a large number of fish at around 200mm and growth data was available for those fish (GAWB 2005). Figure 15 shows the data used from 2003/04 to derive the growth curve compared with the observed data from 2004/05 for fish from 0-200mm. This shows a strong correlation between the two datasets and the derived growth curve was used in calculations in 2004/05 to maintain consistency with the previously presented data. Barramundi Nursery Areas Central Queensland 2004/05 29

31 10. Appendix 2 Reported juvenile Barramundi in 2004/05 Date Location Map Grid Barramundi Tagged Barramundi Not tagged Min Max Method 11-Jul-04 Fitzroy Riv FRR R Bait 12-Jul-04 Fitzroy Riv FRR G Bait 13-Jul-04 Fitzroy Riv FRR G Bait 14-Jul-04 Fitzroy Riv FRR C2/F Castnet 17-Jul-04 Fitzroy Riv FRR D Bait 27-Jul-04 Munduran Ck CIS Q Castnet 30-Jul Mile Ck RAG N Castnet 30-Jul-04 Fitzroy Riv FRR R16/C Bait 31-Jul-04 Fitzroy Riv FRR R Bait 31-Jul-04 Raglan Ck RAG W Castnet 31-Jul-04 Gonong Ck CIS G Lure 1-Aug Mile Ck RAG N Lure 14-Aug Mile Ck RAG N Castnet 5-Sep-04 Pumpkin Ck EMP G Castnet 5-Sep-04 Frenchman Ck FRR G Castnet 8-Sep-04 Calliope Riv CR02 S Lure 11-Sep-04 Moores Ck FRR D Castnet 12-Sep Mile Ck RAG N Castnet 12-Sep-04 Fitzroy Riv FRR C Bait 10-Oct-04 Moores Ck FRR D Castnet 14-Oct Mile Ck RAG N Castnet 20-Oct-04 Graham Ck GLD JZ Lure 22-Oct-04 Fitzroy Riv RBB 23-Oct-04 Fitzroy Riv RBB 28-Oct Mile Ck RAG N Castnet 31-Oct-04 Auckland Ck GLD E Castnet 31-Oct-04 Moores Ck FRR D Lure 31-Oct-04 Fitzroy Riv FRR G Bait 3-Nov-04 Graham Ck GLD NZ Lure 6-Nov-04 Fitzroy Riv FRR C Lure 7-Nov Mile Ck RAG N Castnet 7-Nov-04 Moores Ck FRR D Castnet 7-Nov-04 Fitzroy Riv FRR D Bait 7-Nov-04 Fitzroy Riv FRR G Castnet 7-Nov-04 Gonong Ck CIS F Lure 10-Nov-04 Fitzroy Riv FRR D Bait 10-Nov-04 Calliope Riv CR02 I Lure 11-Nov-04 Fitzroy Riv FRR D Bait 20-Nov-04 Fitzroy Riv FRR K Lure 21-Nov-04 Fitzroy Riv FRR D Bait 21-Nov Mile Ck RAG N Lure 22-Nov-04 Calliope Riv CR02 R Lure 28-Nov-04 Fitzroy Riv FRR D Castnet 6-Dec-04 Fitzroy Riv FRR L Bait Barramundi Nursery Areas Central Queensland 2004/05 30

32 Date Location Map Grid Barramundi Tagged Barramundi Not tagged Min Max Method 7-Dec-04 Fitzroy Riv FRR P Bait 8-Dec-04 Fitzroy Riv FRR C Lure 11-Dec-04 Moores Ck FRR D Castnet 12-Dec-04 Raglan Ck Culvert RAG X Lure 13-Dec Mile Ck RAG N Lure 14-Dec Mile Ck RAG N Castnet 16-Dec Mile Ck RAG N Lure 16-Dec Mile Ck RAG N Lure 16-Dec-04 Blacks Hole RAG x Lure 19-Dec-04 Raglan Ck RAG W Lure 19-Dec-04 Raglan Ck RAG W Lure 19-Dec Mile Ck RAG N Lure 21-Dec-04 Calliope Riv CR02 R Lure 26-Dec-04 Blacks Hole RAG X Lure 27-Dec Mile Ck RAG N Lure 27-Dec Mile Ck RAG N Lure 28-Dec-04 Blacks Hole RAG Y Lure 2-Jan-05 Monte Christo Ck CIS W Lure 2-Jan Mile Ck RAG N Lure 2-Jan-05 Raglan Ck RAG W Lure 3-Jan-05 Blacks Hole RAG Y Lure 5-Jan-05 Blacks Hole RAG Y Lure 7-Jan-05 Blacks Hole RAG Y Lure 8-Jan-05 Blacks Hole RAG X Lure 8-Jan-05 Calliope Riv CR02 R Lure 9-Jan-05 Blacks Hole RAG Y Lure 9-Jan-05 Blacks Hole RAG Y Lure 10-Jan-05 Causeway Lake KBY R Bait 10-Jan-05 Blacks Hole RAG X Lure 11-Jan-00 Blacks Hole RAG X Lure 12-Jan-05 Blacks Hole RAG X Lure 12-Jan-05 Raglan Ck RAG W Lure 13-Jan-05 Causeway Lake KBY R Bait 15-Jan-05 Blacks Hole RAG X Lure 17-Jan-05 Blacks Hole RAG X Lure 18-Jan-05 Raglan Ck RAG w Lure 20-Jan-05 Blacks Hole RAG X Lure 21-Jan Mile Ck RAG N Lure 21-Jan-05 Raglan Ck RAG W Lure 21-Jan-05 Blacks Hole RAG X Lure 22-Jan Mile Ck RAG N Lure 23-Jan-05 Blacks Hole RAG X Lure 23-Jan-05 Blacks Hole RAG X Lure 27-Jan-05 Auckland Ck GLD E Lure 28-Jan-05 Moores Ck FRR D Lure 30-Jan-05 Blacks Hole RAG X Lure 30-Jan Mile Ck RAG N Lure 31-Jan-05 Graham Ck GLD KZ Lure Barramundi Nursery Areas Central Queensland 2004/05 31