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Correction factors derived from acoustic tag data for a juvenile southern bluefin tuna abundance index in southern Western Australia
Alistair J. Hobday Ryo Kawabe Yoshimi Takao Kazushi Miyashita Tomoyuki Itoh Prepared for the CCSBT 5 th Management Procedure Workshop 2-7 September and the 13 th Meeting of the Extended Scientific Committee 8-12 September 2008 Rotorua, New Zealand CCSBT-ESC/0809/Info 02
Electronic Tagging and Tracking in Marine Fisheries II. Reviews: Methods and Technologies in Fish Biology and Fisheries (REME ). Correction factors derived from acoustic tag data for a juvenile southern bluefin tuna abundance index in southern Western Australia Alistair J. Hobday 1,2 Ryo Kawabe 3 Yoshimi Takao 4 Kazushi Miyashita 5 Tomoyuki Itoh 6 1. CSIRO Marine and Atmospheric Research, Hobart, Tasmania, 7001, Australia 2. School of Zoology, University of Tasmania, Private Bag 5, Hobart, Tasmania 7001, Australia 3. Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan 4. NRIFE, Ibaraki, Japan 5. Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Japan 6. National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Shizuoka, Japan Corresponding author: [email protected] June 26, 2008 Running head : Use of acoustic tagging data for abundance indices Keywords : recruitment index, abundance estimates, southern bluefin tuna, residence time
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1 Abstract 2 3 Juvenile southern bluefin tuna (SBT, Thunnus maccoyii ), migrate down the coast of 4 Western Australia reaching the southern coast at age 1. In these waters an acoustic 5 survey for SBT schools was initiated to generate a fisheries independent abundance 6 index. A decline in this abundance index led to an acoustic tagging and monitoring 7 project to determine if a change in migration route or timing could explain the decline. 8 Five years of acoustic monitoring revealed interannual differences in key factors that 9 could impact the abundance index. Acoustic tag data were used to demonstrate that (i) 10 a high proportion of fish (~70%) may be too shallow for detection in the acoustic 11 survey, and that interannual variation in (ii) inshore offshore fraction (~30 70% each 12 year) and (iii) residence time (12 – 37 days) will impact calculation of an index. These 13 factors should be included in estimating an abundance index for SBT, together with a 14 correction for (iv) the fraction of juvenile SBT that migrate to southern Western 15 Australia. Collectively, these results illustrate how electronic tagging data can be used 16 to improve understanding of abundance patterns necessary for sustainable 17 management of this exploited species. 18
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19 Introduction
20 Southern bluefin tuna (SBT, Thunnus maccoyii ) are an economically important 21 species internationally and in Australia, however, they are currently at historically low 22 population levels (Caton 1991; CCSBT 2007; Hobday et al. in review). SBT spawn in 23 the northeast Indian Ocean between October and February (Farley and Davis 1998). 24 Juvenile SBT move down the west coast of Australia and occur as age 1 and 2 year 25 old fish in southern Western Australia and until about age 5 occur further east in the 26 shelf waters of the Great Australia Bight during the austral summer (Caton 1991; 27 Cowling et al. 2003; Willis and Hobday 2007). SBT are a highly exploited species 28 with international management by the Commission for the Conservation of Southern 29 Bluefin Tuna (CCSBT) (Polacheck 2002; Hobday and Hartmann 2006; Hobday et al. 30 in review). One of the continuing CCSBT research priorities has been to develop a 31 fishery independent recruitment index for SBT (e.g. CCSBT 2007), particularly for 32 age 1 fish in southern Western Australia. Such an index is seen as crucial to detect 33 potential recruitment failure years before similar signals might be detected in CPUE 34 analyses based on high seas fisheries data. 35 36 In southern Western Australia, a ship based acoustic survey was initiated in 1995 to 37 estimate the relative abundance of 1 year old SBT (Itoh and Tsuji 2004, Figure 1a ), 38 with the goal of generating a fishery independent recruitment index. The survey, 39 conducted in January February of each year, consisted of repeat transects within the 40 survey area. Schools of SBT were identified on the vessel sonar and echo sounder 41 images by experts, and school biomass estimated (Itoh and Tsuji 2004). Beginning in 42 about 2000, however, the abundance of juvenile SBT within the acoustic survey area 43 declined dramatically, leading to very low abundance indices ( Figure 1b) . It was 44 suggested that either (i) changes in the migration behavior of juvenile SBT or (ii) a 45 real decline in the number of juvenile fish was responsible for the apparent change in 46 SBT abundance. Acoustic monitoring of SBT using tags and moored receivers was 47 initiated in 2001/02 to examine the first possibility; a change in migration behavior in 48 southern Western Australia had occurred. 49 50 Two alternative migration hypotheses were that juvenile SBT (i) were now moving 51 inshore of the acoustic survey area, or (ii) were moving through the area before the
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52 survey had commenced. Examining the SBT migration timing and pathway was thus 53 considered crucial to correctly interpret the abundance indices and assess population 54 trends of this exploited species. Key needs were to determine how quickly juvenile 55 SBT move east along the southern Western Australia coast during the austral summer, 56 and how close to shore the movements occur, in particular, would they avoid 57 detection in the acoustic survey (Hobday 2003). 58 59 Information on behavior and movement of 3, 4 and 5 year old SBT in southern 60 Australia has been successfully obtained using internal archival tags (Gunn et al. 61 1995), however, these tags do not provide location information on a fine horizontal 62 scale (< 60 nautical miles) (Welch and Eveson 1999; Musyl et al. 2001; Teo et al. 63 2004), and so were not suited to this problem. An alternative approach with finer 64 resolution was required and funded through the Japan Australia Recruitment 65 Monitoring Program (RMP). This approach, using acoustic tags and moored acoustic 66 receivers that detect tagged fish, had been developed and tested in both Western 67 Australia (Hobday et al. 2001) and South Australia (Hobday 2002) and was 68 appropriate for SBT movement studies at scales of 1 100 km (Heupel et al. 2006). 69 70 In this paper, we summarize the results from five years of acoustic monitoring 71 experiments (2002 03 to 2006 07), and demonstrate how results obtained using this 72 technology can be used to correct an abundance index for SBT. Before describing the 73 experimental design of the acoustic experiment, we first describe how the results from 74 acoustic tagging and monitoring can assist the refinement of an abundance index. 75 76 An abundance index for southern bluefin tuna 77 In the early years of the acoustic survey, while SBT abundance was high, it was 78 implicitly assumed that all fish passed through the survey area, such that,
79 Nfish ≈ E fish (1)
80 where N fish , the final abundance index, is proportional to E fish , the estimated 81 abundance based on the fish that were encountered during the survey ( Figure 1b) . 82 While it was recognized that other factors could also impact on the encounter rate of 83 schools, these factors were assumed to be constant over years. Multiple replicates of 84 the survey each year (8 12 per year) also allowed confidence intervals to be calculated. 85
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86 Early results from the acoustic monitoring experiment showed that the fraction of fish 87 encountered within the survey area varied according to several factors with 88 interannual variation, such that the estimate of the abundance index could be 89 expressed as,
90 Nfish ≈ E fish • D detection • F offshore • T survey /T residence (2)
91 where, D detection is the proportion of fish swimming at a depth such that they can be
92 detected by the acoustic survey instruments, F offshore is the fraction of fish swimming
93 through the survey area (compared with the fraction swimming inshore), and T residence 94 is the time in days for the fish to pass through the survey region. The time to complete
95 an acoustic transect is T survey . If fish move through the survey area more slowly than 96 the survey vessel (long residence time), then fish may be double counted on 97 subsequent transects, or an assumption of relative stationarity may be valid, while if 98 fish pass through the survey area more rapidly than the survey vessel completes 99 transects (short residence time), then the abundance of SBT may be underestimated. 100 This paper will illustrate how each of these factors was obtained from the acoustic 101 monitoring of SBT, and thus demonstrate how tag data can be used to advance 102 sustainable management. Movement pathways of individual fish are not presented 103 here, it is the population level descriptions of movement that are the focus and 104 required to correctly estimate an abundance index. 105 106 Methods
107 Information on the distribution and movement of juvenile SBT was gathered using 108 acoustic receivers and acoustic tags. We first describe the data collection, and then the 109 data analyses conducted to allow corrections to the abundance index.
110 Data collection
111 Listening stations consisted of a mooring anchor (125 kg section of railway track), 112 wire cable, VEMCO VR2 receiver, timed electronic release, 50 meters of release rope 113 in a PVC canister, and floats. VEMCO temperature depth recorders (TDR) were 114 attached to a subset of receivers at regularly spaced intervals to provide environmental 115 data. When deployed, the receivers were at a depth of 20 25 meters, just below the 116 sub surface floats ( Figure 2) . Receivers were deployed in cross shelf lines (numbered 117 1 3 from west to east), and in clusters at inshore lumps. Inshore lumps are known to
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118 attract SBT for variable periods of time (Willis and Hobday 2007, Hobday and 119 Campbell, in review). 120 121 The number of lines and receivers increased from 1 line of 20 receivers (Line 2, 2002 122 03) to 2 lines of 40 receivers (Line 1 and 2, 2003 04) and since 2004 05 has consisted 123 of 70 listening stations in deployed in three lines and three lumps ( Figure 3) . In 124 addition, 3 stations were deployed at each of three lumps between the western and 125 central lines (2004 05 to 2006 07). Water depth ranged from 55 m at the coast to 115 126 m at the furthest offshore station (water depth was ~170 m at the edge of this stations’ 127 detection range). Water depth at the inshore lumps averaged 52 59 m ( Table 1 ). 128 Stations were separated by approximately 1500 m, which was too large for complete 129 acoustic coverage by the receivers. This spacing decision was based on a desire to 130 cover the width of the shelf; a tag detection range of up to 450 m (for all models of 131 tag) was expected based on detection experiments conducted while receivers were 132 deployed (Hobday and Pincock in review). Stations were deployed to the edge of the 133 continental shelf: validated trolling captures during the acoustic survey showed that 134 age 1 SBT were restricted to the shelf in this region and time ( Figure 4) . 135 136 The electronic releases on each listening station were programmed to activate after a 137 specified interval. At this time the floats and acoustic receiver would float to the 138 surface, still attached to the mooring anchors via polypropylene rope ( Figure 2) . All 139 parts of the listening stations were recovered using an attending vessel. Receivers 140 were tested immediately after recovery to ensure that a test tag could be detected and 141 that the internal clock had not drifted. Data were downloaded using VEMCO software 142 and results analyzed with custom software written in Matlab. 143 144 Acoustic tags (V8, V9 and V16, VEMCO) were activated and tested prior to 145 deployment. These tags transmitted a coded pulse at a frequency of 69 kHz at random 146 intervals every 20 60 seconds with a predicted lifetime of 365 days (V8) and 700 days 147 (V16). The same protocol used for the capture and selection of SBT for conventional 148 tagging (Williams 1983) was followed for the acoustic tagging (Hobday et al. 2001). 149 In brief, fish were caught by poling or trolling at the stern of the vessel and then 150 carried to a tagging cradle and length to caudal fork (LCF) measured. An acoustic tag 151 was surgically implanted in the belly of each fish (see West and Stevens 2001) for an
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152 explanation of this procedure), which was also double tagged with conventional 153 orange tags on each side just posterior to the second dorsal fin. The time from capture 154 to release for each fish was under two minutes and all fish were tagged by a single 155 experienced operator (AH). 156 157 The location of fish tagging varied each year due to the availability of fish ( Figure 5 ). 158 The general goal was to catch and release fish both inshore and offshore (shelf break), 159 at lumps and away from lumps, and between the lines and to the west of the lines. 160 Groups of 10 15 fish were preferred, although individual and smaller groups were 161 released when more fish could not be captured – it is not easy to determine the 162 number of fish that can be captured in a school ahead of time. The releases were 163 predominately between Line 1 and Line 2, with the exception of 2006 07, where SBT 164 were also released much further west (these western fish were excluded from some 165 analyses presented here) ( Figure 5 ). These western releases were to test specific 166 hypotheses about movements from the west coast to the southern coast; however, 50 167 tags were still released between Lines 1 and 2 which allows comparisons with the 168 previous years. When acoustically tagged fish passed close to a receiver, the identity, 169 date and time, and if the tag contains a pressure sensor, the depth at the time was 170 recorded on the receiver. 171 172 Data analyses 173 The acoustic data were used to estimate the following three factors from equation 2. 174 Each factor can be estimated for each year the experiment was conducted, as outlined 175 below. 176
177 Estimation of D detection 178 The acoustic survey instruments (sonar and echosounder) have difficulty detecting 179 SBT that were closer than 10 meters to the surface (Watanabe et al. 2004). Thus, the 180 observed number of SBT should be corrected for the fraction too shallow to be
181 encountered ( Ddetection ). This detection estimate can range from 0% (all SBT were 182 shallower than the detection depth) to 100% (all were deeper than the detection 183 depth). The depth distribution of SBT in the survey area was derived from a limited 184 set of tags that also had pressure sensors (VEMCO V16P, accuracy > 1 m). Each 185 acoustic detection of such tags at a receiver was thus accompanied by a depth
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186 measurement. Aggregation of all the depth measurements provides an estimate of the 187 total time spent at each depth. At this time, limited use of V16P tags in southern
188 Western Australia has occurred, so to illustrate the estimation of D detection we also 189 provide information collected with the same technology in the Great Australia Bight 190 (Willis and Hobday 2007). 191
192 Estimation of F offshore 193 To estimate the fraction of SBT passing within the acoustic survey box ( Figure 1a ), 194 and hence could be encountered by the acoustic survey vessel, we used the pattern of 195 detections at the cross shelf lines. Fish could transit the cross shelf lines on more than 196 one occasion if they swam east and west; we used the total detections at each receiver 197 as an indication of the amount of time all fish were spending at that distance from the
198 coast. Because the number of lines changed between years, the estimates of F offshore 199 may be biased between years. In this example, we show data for all lines to estimate a
200 value of F offshore each year. The lines are divided into the inshore half and offshore 201 half. 202
203 Estimation of T residence 204 Residence time is important as an indicator of how long fish remained in the array 205 area. The residence time calculations can be biased by the number of lines and 206 receivers that were deployed in any year, and by the location of fish releases. For 207 example, residence time can be calculated using Line 2 alone (used in 5 years), Line 1 208 and Line 2 (used for 4 years) or Line 1, Line 2, and Line 3 (used in 5 years), including 209 or removing the inshore lumps. In this paper, we used detections at Line 2 only, to 210 allow a 5 year time series of residence time to be constructed. We used half life 211 (sensu survival analysis) as an estimate of residence time. Here we define half life as 212 the length of time at which half the tags detected in the study remain in the study area.
213 The second element (T survey ) is not derived here, but can be obtained from the time the 214 survey vessel takes to complete a transect replicate. Only fish released east of 118.2°E 215 were included in the residence time analysis to ensure consistency between years. 216 217 Results
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218 The deployment configuration for each year is shown in Table 1 , with experiments 219 lasting from 101 to 177 days. In general, the length of the experiment increased each 220 year, as the mooring design improved and in order to ensure that all tagged fish had 221 left the area when the experiment concluded. Between 59 and 130 SBT were tagged 222 each year. The number of tags detected each year was in part due to locations in 223 which fish were tagged. In 2005 06, over 80% of tagged fish were detected; however, 224 they were all tagged between Line 1 and Line 2 ( Figure 2, Figure 5) . In contrast, a 225 lower overall percentage was detected in 2006 07; however, over 50% of the fish 226 were tagged to the west of the array of receivers (Figure 5E ). 227 228 Juvenile tuna implanted with the acoustic tags ranged from 43 90 cm in length, with 229 the mean size each year between 50.5 and 60.8 cm ( Table 2). In four of the five years 230 there was no difference between the size of tagged and detected fish (t tests, p<0.05, 231 Table 2 ). The final year (2006 07) showed a difference because small fish were 232 tagged on the west coast, and only one of these fish was subsequently detected. These 233 west coast fish were the same size as had been detected in previous years, and so this 234 difference is likely due to migration, and not mortality. 235 236 Fish were detected throughout the experimental season, although the detections 237 sharply declined or ceased by the end of each season. The total number of detections 238 from all tags each year ranged between 261 and 28,023 ( Table 1) , and forms a robust 239 data for estimate of the key factors. The number of detections increased with the 240 number of stations that were deployed, particularly the three years when receivers 241 were deployed on inshore lumps. 242
243 Depth distribution - estimating D detection 244 The depth distribution inferred from the acoustic tags with pressure sensors shows 245 that juvenile SBT (age 1 and age 2) spend the majority (> ~70%) of time shallower 246 than 10 m ( Figure 6) . Thus, approximately 30% of fish would be detected in the 247 sonar based acoustic survey. 248
249 Inshore-offshore pathways – estimating F offshore 250 The percentage of fish moving inshore or offshore through the survey area varied 251 between years ( Table 3) . In some years, the majority of tuna were detected at the
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252 inshore half of the receiver line (2002 03, Line 2, 68%), while the opposite was true 253 in other years (2005 06, Line 2, 30%) ( Figure 7) . There was also variation in the 254 inshore/offshore fraction between lines in the same year (2005 06), indicating spatial 255 variability in movement pathways. These differences were not consistent between 256 years, suggesting that some other time variable factors, such as ocean conditions, may 257 be important. This variation in the inshore offshore detection of fish illustrates 258 interannual variation in how fish use the southern Western Australia region. 259
260 Residence times – estimating T residence 261 Residence time in the monitoring area varied by year ( Figure 8 , Table 3 ). Using 262 detection of tagged SBT only at Line 2 to estimate half life, the half life in the array 263 area was only 11 and 19 days in 2002 03 and 2004 05, respectively. For the other 264 three years, the half life was between 30 and 34 days. The movements of the fish from 265 release locations to Line 2 are also shown in Figure 8 , to illustrate the detection 266 patterns. 267 268 Discussion
269 The calculation of an abundance index for juvenile southern bluefin tuna requires that 270 either a constant fraction of fish occur within the survey area each year, or that the 271 variation between years can be measured and accounted for. Evidence gathered using 272 acoustic monitoring of tagged fish showed that the fraction of fish within the survey 273 area varied between years, and should be accounted for when calculating an 274 abundance index. Equation 2 showed how the index might need to be adjusted for 275 three factors, the proportion of fish that can be detected based on the depth 276 distribution by the survey methodology, the proportion of fish that move through the 277 survey area, and the speed at which the fish move through the survey area. 278 279 A caveat with the use of depth data is that most of the detections of fish with V16P 280 tags occurred around lumps (both Western Australia and GAB) (Willis and Hobday 281 2007). The acoustic survey took place away from lumps (which are a navigational 282 hazard), and so future efforts to collect information on SBT depth distribution should 283 concentrate on data collected as fish transit the open water cross shelf lines, as the 284 depth distribution may differ in open water compared to around lumps.
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285 286 Correcting the abundance estimate 287 Unfortunately the acoustic survey in southern Western Australia was halted in 2003, 288 in part due to the costs of the survey, and the realization that there was potential 289 variability in the estimated abundance index based on the correction factors (Itoh et al. 290 2005). Thus, calculation of an improved abundance index for the years of these 291 acoustic monitoring experiments cannot be demonstrated. If interannual variation in 292 the correction factors can be related to some additional variables, such as sea surface 293 temperature, then post hoc correction of the abundance index for the period 1995 294 2003 may be attempted. This analysis is underway, however, explaining interannual 295 variation is likely to be difficult with only five years of data. The dramatic decline in 296 the abundance index could be explained by inshore movement of fish, as observed in 297 the first year of the acoustic experiment (68% of fish passed at the inshore half of the 298 lines), if that pattern had occurred in some of the previous years. However, in 299 subsequent years, with more fish being detected in the offshore half of the lines, the 300 abundance index would have been expected to increase again. Unfortunately, by this 301 time, the acoustic survey had been suspended. 302 303 Each of the correction factors will also have uncertainty associated with the estimates, 304 which would also need to be included in estimating an overall abundance index. 305 Accepted methods for calculating uncertainty for these tag data do not currently exist, 306 and represent a challenge in utilizing data for management. Known issues include 307 non independence of detections, detection probabilities, and error propagation. 308 309 One additional complicating factor 310 In the austral summer of 2006/07, SBT were also tagged on the west coast of Western 311 Australia. This was to examine the proportion of fish that move into southern Western 312 Australia. Preliminary analysis shows that fish that were tagged on the west coast did 313 not all move to the south coast. This suggests that not all the juvenile SBT population 314 is in southern Australia during the austral summer. The southward movement of fish 315 is likely to be assisted by the Leeuwin current (e.g. Lenanton et al. 1991), which has 316 considerable interannual variation (Domingues et al. 2007; Waite et al. 2007). Thus, it 317 is reasonable to presume that the proportion of SBT moving in southern Western
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318 Australia may also vary between years and the equation for estimating the N fish , is 319 suggested to be better represented as;
320 Nfish ≈ E fish • D detection • F offshore • T survey /T residence • M pathway (3)
321 where M pathway is the fraction of fish that migrate through southern Western Australia. 322 This of course, further complicates the generation of an abundance index for age 1 323 SBT. Thus, the next step is to understand the fraction of fish that move through 324 southern Australia, from the west coast of Australia. This is a major uncertainty, 325 which will impact other population assessments for this species. While the acoustic 326 survey to generate an abundance index has been suspended indefinitely, these results 327 may also be applicable to other more cost effective survey methods being attempted
328 in southern Western Australia (Itoh et al. 2005; Itoh 2007), and in the case of M pathway , 329 to the estimation of SBT abundance in the Great Australia Bight (Cowling et al. 2003; 330 Eveson et al. 2007). 331 332 The purpose of this paper has been to illustrate how information gathered using 333 electronic tags, as part of an acoustic monitoring experiment, can improve abundance 334 estimates needed for sustainable fisheries management. The results presented here 335 indicate that estimates of residence time, migration pathways, and habitat use can be 336 derived from acoustic tag data. These factors are in turn important in correcting an 337 abundance index for juvenile SBT. The value of five years of data is apparent given 338 the interannual variation in these factors, and effort must be made to continue these 339 time series into the future. 340 341 Acknowledgements
342 The assistance and cooperation of Geoff Campbell and the crew of F/V Quadrant over 343 the years of this study are greatly appreciated. A number of field assistants also 344 assisted with deployment, tagging and recovery, and their contribution is gratefully 345 acknowledged. This research was supported by FAJ, JAMARC, CSIRO Marine 346 Research, School of Zoology, University of Tasmania, Australian Acoustic Tagging 347 and Monitoring System (AATAMS) a facility within the Integrated Marine Observing 348 System, and the Australian Fisheries Management Agency as part of the Japan 349 Australia SBT Recruitment Monitoring Program, and by a Grant in Aid from the 350 Japan Society for the Promotion of Science (16255010).
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351 References
352 Caton, A.E. (1991) Review of aspects of southern bluefin tuna biology, population 353 and fisheries. In: Shomura RS, Majkowski J, Langi S (eds) Proceedings of the 354 first FAO Expert Consultation on interactions of Pacific tuna fisheries. 355 Noumea, New Caledonia, p 296 343. 356 CCSBT (2007) Report of the Twelfth Meeting of the Scientific Committee. Available 357 from http://www.ccsbt.org/docs/meeting_r.html 358 Cowling, A., Hobday, A. J. and Gunn, J. (2003) Development of a fishery 359 independent index of abundance for juvenile southern bluefin tuna and 360 improvement of the index through integration of environmental, archival tag 361 and aerial survey data. CSIRO Marine Research. FRDC Final Report 96/118 362 & 99/105. 363 Domingues, C.M., Maltrud, M.E., Wjiffels, S.E., Church, J.A., and Tomczak, M. 364 (2007) Simulated Lagrangian pathways between the Leeuwin Current System 365 and the upper ocean circulation of the southeast Indian Ocean. Deep-Sea Res 366 II 54 , 797 817. 367 Farley, J.H., and Davis, T.L.O. (1998) Reproductive dynamics of southern bluefin 368 tuna, Thunnus maccoyii . Fish. Bull. 96 , 223 236. 369 Gunn, J.S., Davis, T.L.O., Polacheck, T., Betlehem, A., Sherlock, M. (1995) The 370 application of archival tags to study SBT migration, behavior and physiology 371 1995 Southern Bluefin Tuna Recruitment Monitoring Workshop Report No. 372 RMWS/95/8. CSIRO Marine Laboratories Hobart 373 Eveson, P., Bravington, M. and Farley, J. (2007) Aerial Survey: updated index of 374 abundance and preliminary results from calibration experiment. CCSBT 375 ESC/0709/12. Available from http://www.ccsbt.org/docs/meeting_r.html 376 Heupel, M.R., Semmens, J.M., and Hobday, A.J. (2006) Automated acoustic tracking 377 of aquatic animals: scales, design and deployment of listening station arrays. 378 Mar. Freshw. Res. 57 , 1 13. 379 Hobday, A.J. (2002) Acoustic monitoring of SBT within the GAB; exchange rates 380 and residence times at topographic features. Southern Bluefin Tuna 381 Recruitment Monitoring Workshop Report No. RMWS/02/03. CSIRO Marine 382 Research, Hobart, Australia.
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383 Hobday, A.J. (2003) Nearshore migration of juvenile southern bluefin tuna in 384 southern Western Australia, Southern Bluefin Tuna Recruitment Monitoring 385 Workshop Report. RMWS/03/15. CSIRO Marine Research, Hobart, Australia. 386 Hobday, A.J., Davis, T.L.O., Gunn, J.S. (2001) Determination of SBT residence time 387 via acoustic monitoring along the southern WA coast. Southern Bluefin Tuna 388 Recruitment Monitoring Workshop Report No. RMWS/01/05. CSIRO Marine 389 Research, Hobart, Australia. 390 Hobday, A.J., and Hartmann, K. (2006) Near real time spatial management based on 391 habitat predictions for a longline bycatch species. Fish. Manage. Ecol. 13 , 392 365 380. 393 Hobday, A. J. and D. Pincock (in review) Estimating detection probabilities for linear 394 acoustic monitoring arrays. Can. J. Fish. Aqu. Sci. 395 Hobday, A.J. and Campbell, G. (in review) Topographic preferences and habitat 396 partitioning by pelagic fishes in southern Western Australia. Mar. Freshw. Res . 397 Hobday, A.J., Flint, N., Stone, T., and Gunn, J. S. (in review) Electronic tagging data 398 supporting flexible spatial management in an Australian longline fishery. In J. 399 Nielsen (ed). Electronic Tagging and Tracking in Marine Fisheries II. 400 Reviews: Methods and Technologies in Fish Biology and Fisheries. 401 Itoh, T., and Tsuji, S. (2004) Review of Acoustic Monitoring Survey Analyses of 402 data for eight years. Southern Bluefin Tuna Recruitment Monitoring 403 Workshop Report No. RMWS/04/03. CSIRO Marine Research, Hobart, 404 Australia. 405 Itoh, T., Takao, T., and Tsuju, S. (2005) Proposal of RMP surveys in WA for age one 406 southern bluefin tuna in 2004/2005. Southern Bluefin Tuna Recruitment 407 Monitoring Workshop Report No. RMWS/05/16. CSIRO Marine Research, 408 Hobart, Australia. 409 Itoh, T. (2007) Some examination on the recruitment index of age 1 southern bluefin 410 tuna derived from the trolling survey.CCSBT ESC/0709/35. Available from 411 http://www.ccsbt.org/docs/pdf/meeting_reports/ccsbt_14/report_of_SC12_pub 412 lic_version.pdf 413 Lenanton, R.C., Joll, L., Penn, J., and Jones, K. (1991) The influence of the Leeuwin 414 Current on coastal fisheries of Western Australia. J. Royal Soc. West. Aust. 74 , 415 101 114.
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416 Musyl, M.K., Brill, R.W., Curran, D.S., Gunn, J.S., Hartog, J.R., Hill, R.D., Welch, 417 D.W., Eveson, J.P., Boggs, C.H., and Brainard, R.E. (2001) Ability of archival 418 tags to provide estimates of geographical position based on light intensity. In 419 Sibert J.R., Nielsen J.L. (eds) Electronic Tagging and Tracking in Marine 420 Fisheries. Kluwer Academic Publishers, London, p 343 367 421 Polacheck, T. (2002) Experimental catches and the precautionary approach: the 422 Southern Bluefin Tuna dispute. Mar. Pol. 26 , 283 294. 423 Watanabe, K., Takao, Y., Sawada, K., Abe, K. (2004) Acoustic survey of pelagic 424 fishes using a side scan sonar, preliminarily operated for the coming SBT 425 survey. Southern Bluefin Tuna Recruitment Monitoring Workshop Report No. 426 RMWS/04/04. CSIRO Marine Research, Hobart, Australia. 427 Teo, S.L.H., Boustany, A., Blackwell, S., Walli, A., Weng K.C., and Block, B.A. 428 (2004) Validation of geolocation estimates based on light level and sea surface 429 temperature from electronic tags. Mar. Ecol. Prog. Ser. 283 , 81 98. 430 Waite, A.M., Thompson, P.A., Pesant, S., Feng, M., Beckley, L.E., Domingues, C.M., 431 Gaughan, D., Hanson, C.E., Holl, C.M., Koslow, T., Meuleners, M., Montoya, 432 J.P., Moore, T., Muhling, B.A., Paterson, H., Rennie, S., Strzelecki, J,. and 433 Twomeya, L. (2007) The Leeuwin Current and its eddies: An introductory 434 overview. Deep-Sea Res. II 54 , 789 796. 435 Welch, D.W., and Eveson, J.P. (1999) An assessment of light based geoposition 436 estimates from archival tags. Can J Fish Aquat Sci 56 , 1317 1327. 437 West, G.J., and Stevens, J.D. (2001) Archival Tagging Of School Shark, Galeorhinus 438 Galeus, in Australia: Initial Results. Env. Biol. Fish. 60 , 283 298. 439 Williams, K. (1983) Big numbers of SBF tuna tagged off Esperance. Australian 440 Fisheries July: 26 27. 441 Willis, J., and Hobday, A.J. (2007) Influence of upwelling on movement of southern 442 bluefin tuna ( Thunnus maccoyii ) in the Great Australian Bight. Mar. Freshw. 443 Res. 58 , 699–708. 444
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445 Table 1 . Summary of the experiments for the acoustic experiment in southern 446 Western Australia. IL = inshore lumps. See Figure 3 for locations of the lines. 447 Year Number of lines Tags Experiment Length of Tags Total (receivers) deployed start date experiment detected detections (days) (%) 2002 03 1 (20) 73 Dec 3, 2002 101 32.9 261 2003 04 2 (40) 59 Dec 3, 2003 117 49.2 443 2004 05 3 (61) + 3 IL (9) 79 Dec 4, 2004 102 69.6 28,023 2005 06 3 (61) + 3 IL (9) 81 Dec 2, 2005 160 84.0 5,214 2006 07 3 (61) + 3 IL (9) 130 Dec 1, 2006 177 48.5 18,514 448
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449 Table 2 . Summary of the size of the tagged and detected southern bluefin tuna in 450 southern Western Australia over five years of acoustic experiments (N = no, Y = yes). 451 Year Acoustic tags Mean size of Mean size Difference between deployed all fish of all fish tagged and detected (n) tagged detected sizes (t test, p < 0.05) (cm) (cm) 2002 03 73 60.8 59.8 N 2003 04 59 57.8 55.6 N 2004 05 79 51.4 53.5 N 2005 06 81 49.3 49.6 N 2006 07 130 50.5 57.9 Y 452
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453 Table 3 . The percentage of tagged southern bluefin tuna detected in the offshore half 454 of each line of receivers. Percentages less (greater) than 50%, indicate that fish were 455 passing using a predominately inshore (offshore) pathway. Residence time, based on 456 detections at Line 2 and releases east of 118.2°E, is shown in the final column, 457 together with the number of detected tags and individual detections on which the 458 residence time was based. 459 Year Line Line Line Average of Movement Residence time 1 2 3 all lines pathway (days) (%) (%) (%) (%) (n tags, n pings) 2002 03 32 32.0 Inshore 11 (n = 19 & 226) 2003 04 42 45 43.5 Inshore 34 (n = 24 & 221) 2004 05 39 27 6 24.0 Inshore 19 (n = 27 & 575) 2005 06 21 70 73 54.6 Offshore 30 (n = 27 & 2118) 2006 07 44 38 61 48.0 ~Equal 34 (n = 23 & 438) Average 36.5 42.4 46.7 40.4 25.6 days 460
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461 Figure Legends 462 463 Figure legends are repeated on each figure to aid the review process 464 465 Figure 1 . A. Ship based acoustic survey area for southern bluefin tuna (blue polygon) 466 in southern Western Australia and sea surface temperature for an example summer, 467 showing the influence of the Leeuwin Current (warm water from the west). B. 468 Abundance index for juvenile southern bluefin tuna in the survey area, derived from 469 the ship based acoustic survey. The year (e.g. 1996) refers to the austral summer (e.g. 470 1995/96). 471 472 Figure 2 . Configuration of listening station moorings during the sub surface 473 deployment period (left) and ready for recovery (right). 474 475 Figure 3 . Locations of listening stations in the southern bluefin tuna acoustic 476 monitoring experiment in southern Western Australia. The acoustic survey area is 477 inside the blue polygon, the dashed line represents the outer boundary of the survey in 478 the years 2002 03. The years in which listening stations were deployed at these lines 479 and inshore lumps is described in the text. 480 481 Figure 4 . Locations of southern bluefin tuna detected by trolling in the acoustic 482 survey (1995 2003). The size of the marker refers to the number of individual fish 483 captured by trolling at a location. The location of the 200 m contour is shown. 484 485 Figure 5 . Release locations for acoustically tagged southern bluefin tuna (red stars), 486 together with the location of receivers for that year A. 2002 03 (n = 73 tags). B. 2003 487 04 (n = 59 tags). C. 2004 05 (n = 79 tags). D. 2005 06 (n = 81 tags). E. 2006 07 (n = 488 130 tags, but 50 tags east of 118.2°E). 489 490 Figure 6. Estimation of the depth distribution of southern bluefin tuna derived from 491 acoustic tags with a pressure sensor. A. A single fish in southern Western Australia. B. 492 Depth distribution for SBT based on acoustic tags in the Great Australian Bight (from 493 Willis and Hobday 2007). 494
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495 Figure 7. Cumulative frequency plots of detection of acoustically tagged southern 496 bluefin tuna across each line of receivers. A. Line 1, deployed for four years. B. Line 497 2, deployed for five years. C. Line 3, deployed for three years. The 1:1 line at 45 498 degrees shows the cross shelf distribution that would be observed if fish passed the 499 cross shelf line at random distances across the continental shelf. For example, 500 consider 2005 for Line 3: only 10% of detections were made offshore of station 50, 501 thus 90% are inshore. See text for full interpretation. 502 503 Figure 8 . Residence time and movements of SBT detected in the acoustic monitoring 504 study. Left hand column shows the number of fish remaining to be detected as a 505 function of time since each fish was released. A. 2002 03, B. 2003 04, C. 2004 05, D. 506 2005 06 and E. 2006 07. The half life is indicated by the vertical black line (numbers 507 provided in Table 3) . The right hand column indicates the tracks of fish from their 508 release point (circles), when only Line 2 detections (cross shelf line) and releases east 509 of 118.2°E are used. F. 2002 03, G. 2003 04, H. 2004 05, I. 2005 06 and J. 2006 07. 510 The acoustic survey box is indicated by the blue polygon. 1 degree of longitude 511 represents approximately 100 km at this latitude. 512
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513 A.
514 515 516 B.
9000
8000
7000
6000
5000
4000 Biomass Biomass (t) 3000
2000
1000
0 1996 1997 1998 1999 2000 2001 2002 2003 517 Year 518 519 Figure 1 . A. Ship based acoustic survey area for southern bluefin tuna (blue polygon) 520 in southern Western Australia and sea surface temperature for an example summer, 521 showing the influence of the Leeuwin Current (warm water from the west). B. 522 Abundance index for juvenile southern bluefin tuna in the survey area, derived from 523 the ship based acoustic survey. The year (e.g. 1996) refers to the austral summer (e.g. 524 1995/96).
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525 526
527 528 529 Figure 2 . Configuration of listening station moorings during the sub surface 530 deployment period (left) and ready for recovery (right). 531
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532 533
534 535 Figure 3 . Locations of listening stations in the southern bluefin tuna acoustic 536 monitoring experiment in southern Western Australia. The acoustic survey area is 537 inside the blue polygon, the dashed line represents the outer boundary of the survey in 538 the years 2002 03. The years in which listening stations were deployed at these lines 539 and inshore lumps is described in the text. 540
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541
-34.3
-34.4
-34.5
-34.6
-34.7
-34.8
Latitude -34.9
-35 < 5 5-10 -35.1 10-15 > 15 -35.2
-35.3
118.5 119 119.5 120 120.5 121 121.5 542 Longitude 543 Figure 4 . Locations of southern bluefin tuna detected by trolling in the acoustic 544 survey (1995 2003). The size of the marker refers to the number of individual fish 545 captured by trolling at a location. The location of the 200 m contour is shown.
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546
-33.5 -33.5 A. B.
-34 -34
-34.5 -34.5 Latitude Latitude
-35 -35
-35.5 -35.5 117 118 119 120 121 122 117 118 119 120 121 122 547 Longitude Longitude
-33.5 -33.5 C. D.
-34 -34
-34.5 -34.5 Latitude Latitude
-35 -35
-35.5 -35.5 117 118 119 120 121 122 117 118 119 120 121 122 548 Longitude Longitude
-32 E. -32.5
-33
-33.5
Latitude -34 Bremer Bay -34.5
Albany -35
-35.5 115 116 117 118 119 120 121 122 549 Longitude 550 551 Figure 5 . Release locations for acoustically tagged southern bluefin tuna (red stars), 552 together with the location of receivers for that year A. 2002 03 (n = 73 tags). B. 2003 553 04 (n = 59 tags). C. 2004 05 (n = 79 tags). D. 2005 06 (n = 81 tags). E. 2006 07 (n = 554 130 tags, but 50 tags east of 118.2°E). 555
25 CCSBT-ESC/0809/Info 02
556 557 A. B.
558 559 560 Figure 6. Estimation of the depth distribution of southern bluefin tuna derived from 561 acoustic tags with a pressure sensor. A. A single fish in southern Western Australia. B. 562 Depth distribution for SBT based on acoustic tags in the Great Australian Bight (from 563 Willis and Hobday 2007). 564
26 CCSBT-ESC/0809/Info 02
565 A. B. C.
566 567 568 Figure 7. Cumulative frequency plots of detection of acoustically tagged southern 569 bluefin tuna across each line of receivers. A. Line 1, deployed for four years. B. Line 570 2, deployed for five years. C. Line 3, deployed for three years. The 1:1 line at 45 571 degrees shows the cross shelf distribution that would be observed if fish passed the 572 cross shelf line at random distances across the continental shelf. For example, 573 consider 2005 for Line 3: only 10% of detections were made offshore of station 50, 574 thus 90% are inshore. See text for full interpretation. 575
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A. F.
60 -33.8
-34 50 -34.2 40 -34.4
30 -34.6 Latitude 20 -34.8 Tags remaining Tags
10 -35 -35.2 0 0 5 10 15 20 25 30 35 40 117.5 118 118.5 119 119.5 120 120.5 121 Days since fish tagged Longitude B. G.
60 -33.8
-34 50 -34.2 40 -34.4 30 -34.6 Latitude 20 -34.8 Tags remaining Tags -35 10 -35.2 0 0 10 20 30 40 50 60 70 80 117.5 118 118.5 119 119.5 120 120.5 121 Days since fish tagged Longitude C. H. 80 -33.8 -34
60 -34.2
-34.4
40 -34.6 Latitude -34.8 Tags remaining Tags 20 -35
-35.2 0 0 10 20 30 40 50 60 117.5 118 118.5 119 119.5 120 120.5 121 Days since fish tagged Longitude D. I. 80 -33.8
-34
60 -34.2
-34.4 40 -34.6 Latitude -34.8 Tags remaining Tags 20 -35
-35.2 0 0 10 20 30 40 50 60 70 80 90 100 117.5 118 118.5 119 119.5 120 120.5 121 Days since fish tagged Longitude E. J. 50 -33.8
-34 40 -34.2
30 -34.4
-34.6
20 Latitude -34.8 Tags remaining Tags 10 -35
-35.2 0 0 20 40 60 80 100 120 140 160 117.5 118 118.5 119 119.5 120 120.5 121 Days since fish tagged Longitude
576 577 Figure 8 . Residence time and movements of SBT detected in the acoustic monitoring 578 study. Left hand column shows the number of fish remaining to be detected as a 579 function of time since each fish was released. A. 2002 03, B. 2003 04, C. 2004 05, D. 580 2005 06 and E. 2006 07. The half life is indicated by the vertical black line (numbers 581 provided in Table 3) . The right hand column indicates the tracks of fish from their 582 release point (circles), when only Line 2 detections (cross shelf line) and releases east 583 of 118.2°E are used. F. 2002 03, G. 2003 04, H. 2004 05, I. 2005 06 and J. 2006 07. 584 The acoustic survey box is indicated by the blue polygon. 1 degree of longitude 585 represents approximately 100 km at this latitude.
28