draft - university of toronto t-space · 104 < 20 km from the embayments (fig. 2a; wakefield et...
TRANSCRIPT
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Does a spatio-temporal closure to fishing Chrysophrysauratus (Sparidae) spawning aggregations also protect
individuals during migration?
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Manuscript ID cjfas-2017-0449.R2
Manuscript Type: Article
Date Submitted by theAuthor: 15-Jun-2018
Complete List of Authors: Crisafulli, Brett; Government of Western Australia Departmentof Primary Industries and Regional Development, FisheriesDivisionFairclough, David; Government of Western AustraliaDepartment of Primary Industries and Regional Development,Fisheries DivisionKeay, Ian; Government of Western Australia Department ofPrimary Industries and Regional Development, FisheriesDivisionLewis, Paul; Government of Western Australia Department ofPrimary Industries and Regional Development, FisheriesDivisionHow, Jason; Government of Western Australia Department ofPrimary Industries and Regional Development, FisheriesDivisionRyan, Karina; Government of Western Australia Department ofPrimary Industries and Regional Development, FisheriesDivisionTaylor, Steve; Government of Western Australia Department ofPrimary Industries and Regional Development, FisheriesDivisionWakefield, Corey; Government of Western Australia Departmentof Primary Industries and Regional Development, FisheriesDivision
Keyword:FISHERY MANAGEMENT < General, MARINE PROTECTED AREAS< Environment/Habitat, REPRODUCTION < General,RECREATIONAL FISHERIES < General, MIGRATION < General
Is the invited manuscriptfor consideration in a
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Does a spatio-temporal closure to fishing Chrysophrys auratus (Sparidae) 1
spawning aggregations also protect individuals during migration? 2
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1Crisafulli, B.M., 1Fairclough, D.V., 1Keay, I.S., 1Lewis, P., 1How, J.R., 7
1Ryan, K.L., 1Taylor, S.M. and 1Wakefield, C.B. 8
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Corresponding author: 15
Brett M. Crisafulli 16
E: [email protected] 17
Ph: +61 8 9203 0111 18
1Department of Primary Industries and Regional Development, Fisheries Division 19
Government of Western Australia 20
39 Northside Drive, Hillarys 21
Western Australia 6025 22
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Abstract 23
Understanding migration dynamics of fishes that aggregate-spawn is critical if spatio-24
temporal closures to fishing are expected to protect them. Concern over fishing of 25
Chrysophrys auratus spawning aggregations in embayments near a west Australian city led to 26
an annual four-month spatial fishing closure. However, the extent to which it protects fish 27
migrating to and from aggregations is unclear. Acoustic telemetry demonstrated a bimodal 28
pattern of entry to and departure from the main embayment via only one of several pathways. 29
Among years, 33-56% of fish occurred in the pathway prior to the closure, but most left 30
before it ceased. Fish were detected within the closure in multiple but not always consecutive 31
years. Variation in migration timing and aggregation philopatry may alter capture risk, but 32
pre- and post-spawning migratory fish are fished in the main pathway and adjacent reefs, 33
which would presumably impact spawning aggregation biomass. Assessment of this would 34
assist in understanding whether expansion of the closure’s spatial and temporal limits is 35
necessary to ensure spawning biomass or if current management is sufficient. 36
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Keywords: recreational fisheries, migration, marine protected areas, reproduction, fishery 41
management 42
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Introduction 44
A diverse array of fishes aggregate to spawn, including epinephelids, carangids, 45
labrids and sparids (Sadovy de Mitcheson and Colin 2012). Fish spawning aggregations 46
(FSA) are usually predictable, occurring repeatedly at specific sites at the same time of year, 47
during particular environmental cycles (e.g. lunar phases, water temperatures, diel cycles, 48
tidal regimes etc.) and with fish using the same migratory pathways to join them (Zeller 49
1998; Wakefield 2010; Domeier 2012; Nanami et al. 2014). This predictability and associated 50
increase in catchability has led, in many cases, to overexploitation of spawning aggregations 51
via commercial, subsistence and/or recreational fishing (Sadovy de Mitcheson and Erisman 52
2012; Grüss et al. 2014; Sadovy de Mitcheson 2016). 53
Spatial and temporal closures to fishing are often implemented to protect FSAs. 54
However, of 17 reviewed closures, less than half (43%) led to purported species benefits, 55
such as increases in abundance or body size, and only 17% indicated specific fisheries 56
benefits, e.g. increased yield or catch per unit effort (Grüss et al. 2014). Expected benefits of 57
fishing closures to FSAs or the broader stocks are influenced by the (1) often transient nature 58
of aggregating fish vs the fixed spatio-temporal constraints of closures to fishing, potentially 59
leaving adults exposed to exploitation when not aggregating, (2) variation in whether all or 60
only part of the adult population aggregates to spawn and (3) limited understanding of the 61
complex patterns of behaviour and movement of species that aggregate-spawn, such as 62
predictability of migration pathways, spawning site philopatry and habitat use (Zeller 1998; 63
Erisman et al. 2017). This information is critical if implemented closed areas are expected to 64
contribute to resource management (Heupel et al. 2006). 65
The sparid Chrysophrys auratus (Forster 1801) supports large commercial and 66
recreational fisheries in Australia and New Zealand, including the targeting of its spawning 67
aggregations (e.g. Parsons et al. 2009; Hamer et al. 2011; Sadovy de Mitcheson and Colin 68
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2012). On the west coast of Australia, this functional gonochorist only aggregates to spawn in 69
two regions almost 1 000 km apart at ~26 and 32°S (Wakefield 2010; Jackson and Moran 70
2012; Fig. 1). Peak spawning occurs when water temperatures are within a narrow range 71
(~19-21°C) and thus at different times of the year in the latitudinally separate regions. At 72
32°S on the lower west coast, this usually occurs during austral spring (around November), 73
although spawning can extend from August to January (Wakefield 2010; Wakefield et al. 74
2015). The restricted environmental parameters for peak spawning by C. auratus would 75
contribute to its high interannual recruitment variation, which may include spawning 76
omission in some years and latitudinal variation in recruit abundance (Francis 1993; Fowler 77
and Jennings 2003; Sim-Smith et al. 2012; Wakefield et al. 2015; 2017). 78
On the lower west coast of Australia, C. auratus can reach over 1 300 mm total length 79
and 40 y, and matures at ~6 y and ~600 mm, making it inherently vulnerable to fishing 80
(Randall et al. 1997; Norriss and Crisafulli 2010; Wakefield et al. 2015). These large fish 81
aggregate to spawn in three adjacent marine embayments at ~32°S, that are close to the major 82
population centre of this region. Here, they are exposed to substantial anthropogenic 83
activities, including industry and ports, naval and trade vessels, recreational boating and 84
fishing (Wakefield 2010; Wakefield et al. 2013a). The aggregations are easily accessible and 85
historically they were fished both commercially and recreationally until an annual six-week 86
closure (15 Sept-31 Oct) to fishing for C. auratus in two of the embayments (Cockburn 87
Sound and Warnbro Sound) was introduced in 2000 (Fig. 1). This was extended to four 88
months (1 Oct-31 Jan) by 2005 to better protect fish during their spawning period 89
(Wakefield, 2010). As demersal species such as C. auratus are a major target of commercial 90
and recreational fisheries along the broader west coast and they had experienced overfishing, 91
significant changes to management were made between late 2007 and early 2010 to recover 92
stocks (Wise et al. 2007). Commercial fishing for these species became limited to permitted 93
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vessels in late 2007, which were prohibited from fishing in the Metropolitan Area of this 94
coast (31-33°S, Fig. 1). Recreational fishing from private- and charter-boats is allowed in the 95
Metropolitan Area under input and output controls introduced at the end of 2009. These 96
included a two-month (15 Oct - 15 Dec) fishing closure for demersal species in the West 97
Coast Bioregion (WCB; Fig. 1), boat-fishing licences and small daily bag limits (two 98
demersal fish per person). The minimum length for retention of C. auratus was also increased 99
to 500 mm total length for both sectors in the Metropolitan and South-west Areas of the 100
WCB (see Fig. 1). 101
Adult C. auratus tagged in the embayments in the spawning periods from 2003 to 102
2016 during this and previous studies disperse after spawning, with ~79% of fish recaptured 103
< 20 km from the embayments (Fig. 2a; Wakefield et al. 2011). About 91% of recaptures 104
have occurred within 4 y of tagging and 72% during the same or subsequent spawning 105
seasons, i.e. Aug-Jan (Fig. 2b; Wakefield et al. 2011; 2015). A small number of C. auratus 106
have been recaptured ~100-700 km from the embayments (Fig. 2a). However, otolith 107
microchemistry of C. auratus in this region indicated that adults typically do not move 108
distances greater than the scale of the large management areas along this coast, e.g. the 109
Metropolitan Area, which encompasses the embayments (Fairclough et al. 2013). Such 110
patterns are broadly consistent with movement variation described for this species in small- 111
to large-scale studies across Australia and New Zealand (e.g. Moran et al. 2003; Parsons et al. 112
2014; Harasti et al. 2015; Fowler et al. 2017). The recapture of fish in the lower west coast 113
embayments indicates that, if they did leave following the spawning period in which they 114
were tagged, they also returned. However, this does not demonstrate whether they return to 115
spawn in multiple or consecutive years, given the nature of mark-recapture methods. While 116
spawning also occurs in surrounding marine waters and along the extensive coast beyond the 117
Metropolitan Area (Lenanton 1974; Lenanton et al. 2009; Wakefield et al. 2011), there may 118
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be selective advantages in returning, as oceanography in the embayment facilitates the 119
retention of eggs and larvae, ensuring recruits remain in relatively more productive waters 120
during early life (Lenanton 1974; Wakefield 2010; Wakefield et al. 2011). 121
Biological studies have contributed critical information to the spatial management of 122
C. auratus across this extensive coastline. Knowledge of the reproductive behaviour and peak 123
spawning times in the embayments specifically, informed the introduction of the spatio-124
temporal fishing closure to protect aggregations (Wakefield 2010; Wakefield et al. 2015). 125
However, despite this knowledge and the comprehensive management of this species, 126
locations and timing of migrations in relation to the closure on the lower west coast have not 127
been assessed and thus neither has the exposure of migrating C. auratus to fishing. 128
Acoustic telemetry is frequently used to identify fine-scale movement patterns, that 129
mark-recapture data does not. It has been used to investigate the potential effectiveness of 130
spatial closures for protecting species or stocks (e.g. Meyer et al. 2010; Parsons et al. 2010; 131
Abecasis et al. 2009; 2015), but rarely in fisheries management (Sadovy de Mitcheson et al. 132
2008; Donaldson et al. 2014; Crossin et al. 2017). Over three years, we examined the spatial 133
and temporal patterns of occurrence of adult C. auratus in relation to the three embayments 134
on the lower west coast of Australia where it aggregates to spawn. Data were used to infer 135
migration patterns to and from the main embayment of Cockburn Sound. Detection data from 136
an acoustic receiver array, which included receivers provided by the Canada Foundation for 137
Innovation-funded international Ocean Tracking Network, were used to (1) determine the 138
entrance/exit pathways used by individuals to migrate, (2) identify the timing of immigration 139
and emigration and (3) evaluate the hypothesis that individuals exhibit spawning site 140
philopatry by returning to Cockburn Sound in consecutive years. These lines of evidence 141
were then used to investigate the potential for exploitation of migrating C. auratus given 142
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current spatial management arrangements, broader stock management measures and available 143
data on fishing in the vicinity of the embayments. 144
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Materials and methods 146
Sampling regime 147
Chrysophrys auratus were caught by line fishing during the spawning periods in 2009 148
(n = 30) and 2010 (n = 10) on the lower west coast of Australia, either between Garden and 149
Carnac Island (Site A), or at locations within Cockburn Sound (Sites B and C; Supplementary 150
Table 1; Fig. 1). Each fish was placed in a circular 250 L plastic tank with aerated seawater 151
and anaesthetised using clove oil (0.27 ml L-1 seawater) until stage II anaesthesia, i.e. ~60 s 152
(Munday and Wilson 1997). Fork length was then measured to the nearest 1 mm and sex 153
determined by cannulation or during surgery if possible. Each fish was laid inverted in a v-154
shaped foam support covered in wet plastic and its gills irrigated with fresh seawater. A 155
Vemco© acoustic transmitter (V16-4H, V13-1L, V13-1H) was inserted into the body cavity 156
via a ~3 cm incision in the abdominal wall, ~2 cm anterior of the cloaca and 1 cm lateral of 157
the ventral mid-line. The incision was closed using absorbable sutures (Ethicon Vicryl CP-1 158
with 36 mm, ½ circle reverse cutting needle) and the fish injected with Bivatop antibiotic 159
(200mg mL-1 tetracycline) at 0.1 ml kg-1 of body weight, estimated using the fork length-total 160
weight relationship of Wakefield et al. (2015) (Supplementary Table 1). Two 13 cm dart tags 161
(PDS: Hallprint ©) were inserted into the dorsal musculature of each fish for potential 162
recapture identification. Fish recovered from anaesthesia in a 500 L tank of aerated sea water 163
until they oriented and swam independently, which took 2-11.5 min (mode = 3 min). Fish 164
were then immediately released. The time between capture and release ranged from ~7.5-165
17 min (mode = 9 min; based on data recorded for 21 fish). In Western Australia, the Animal 166
Welfare Act 2002 does not require the Department of Primary Industries and Regional 167
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Development to obtain a permit to use animals (fish) for scientific purposes unless the species 168
are outside the provisions of the governing legislation (i.e. Fish Resources Management Act 169
1994 and Fish Resources Management Regulations 1995). However, all sampling was 170
undertaken in strict adherence to the Department’s Policy for the handling, use and care of 171
marine fauna
for research purposes. In addition, surgery was conducted following methods of 172
previous ethically approved work (Fairclough et al. 2011) and with input from the 173
Department’s Animal Health staff and is consistent with the guidelines of the Committee for 174
the Update of the Guide for the Care and Use of Laboratory Animals (National Research 175
Council 2011). 176
No significant difference (Kolmogorov-Smirnov two-sample test, Da = 0.035; df = 1; 177
p > 0.05) was identified between the length frequency distributions of the C. auratus tagged 178
for telemetry and a larger sample of C. auratus (n = 549) captured from the same spawning 179
aggregations during 2009 and 2010 (Fig. 3). Thus, the sample of C. auratus used for 180
telemetry was considered representative of the broader population that aggregated to spawn 181
in Cockburn Sound during the study period. 182
183
Receiver array 184
Vemco© receivers were deployed across five potential pathways to Cockburn Sound 185
to produce double-gates that could detect immigration and emigration of C. auratus (Fig. 1). 186
Cockburn Sound is bounded at its northern end by a shallow bank, while at the southern end, 187
a narrow, shallow passage between Garden Island and the mainland delineates the 188
embayment from the open ocean. The five pathways each comprised two lines of receivers: 189
(1) Rottnest Island to Fremantle and Garden Island to Woodman Point, 190
(2) Rottnest Island to Straggler Rocks and Garden Island to Woodman Point 191
(3) Straggler Rocks to Carnac Island and Garden Island to Woodman Point 192
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(4) Carnac Island to Garden Island and Garden Island to Woodman Point, and 193
(5) the southern end of Garden Island and the mainland. 194
The array comprised 47 VR2W receivers (the ‘aggregation array’), 53 VR2Ws in the 195
Canada Foundation for Innovation-funded international Ocean Tracking Network’s Perth line 196
(OTN; http://oceantrackingnetwork.org; Cooke et al., 2011) and 19 VR2Ws and 20 VR4Gs 197
that form the Metropolitan component of the Department's Shark Monitoring Network (SMN; 198
McAuley et al. 2016). For analyses, the gate represented by Site A comprised the western line 199
of seven receivers between Garden and Carnac islands and the nine most western receivers 200
between Garden Island and Woodman Point (Fig. 1). As part of the ‘aggregation array’, a 201
VR2W was deployed at site B and C in Cockburn Sound and at three locations in Warnbro 202
Sound, where C. auratus also aggregate to spawn. A temporary array of 19 receivers was 203
deployed in Cockburn Sound from Dec 2009–Feb 2010 and Aug 2011–Mar 2012 to increase 204
the potential for detection of C. auratus. The SMN also comprised cross-shelf lines of 205
VR2Ws deployed in Apr/May 2012 off the south-west (48 VR2Ws) and western south coasts 206
of Australia (two lines, 44 and 33 VR2Ws; Fig. 1). Receivers in the SMN and OTN arrays 207
were deployed at 800 m intervals (McAuley et al. 2016). 208
Each VR2W in the aggregation array was attached to a stainless-steel pole mounted 209
vertically in a concrete-filled car tyre. VR2Ws were deployed ~500 m apart in water depths 210
of 4–17 m, at locations not obstructed by reef structure. Distances between receivers were 211
determined from (1) knowledge of an expected range of 525 m for V16-4Hs (158 dB re 1 µPa 212
@ 1 m) in wind conditions of 28–34 knots (https://vemco.com/range-calculator/) and (2) 213
range testing of a V16–4H (fixed 120 s delay) in the study area, where detections decreased 214
by 50 and 95% of the theoretical maximum number per day by 531 and 717 m, respectively 215
(How and deLestang 2012). Receivers were retrieved from the water annually to remove 216
fouling, download data via Vemco VUE (version 1.6.5) and install new batteries. 217
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Analysis of detection data 219
Detection data from all receivers in all the arrays were kept within a central data 220
management system. This contained transmitter ID, date and time, spatial coordinates of 221
receiver (decimal degrees), Receiver Station ID and depth of Receiver Station associated with 222
transmitters detected from this study and tagged sharks from other studies (McAuley et al. 223
2016; Braccini et al. 2017). The False Detection Analyser in Vemco VUE v2.30 was used to 224
identify false transmitter detections; i.e. Type A (invalid transmitter codes, which can be 225
produced as a result of environmental sounds or transmitter code collisions) and Type B 226
(false detections of valid transmitters due to detections occurring on a single receiver at 227
shorter time intervals than the programmed ping rate) (Heupel et al. 2006; Simpfendorfer et 228
al. 2015). Approximately 0.01% of a total 3.5 million detections were Type A false 229
detections, with the vast majority occurring at site B. These would have been influenced by 230
the six V16 transmitters which which produced almost continuous detections at that site and 231
may have been deceased fish. These were removed from analyses (see later in Methods). 232
While the cause of false detections could not be ascribed to transmitters used in this study, 233
due to transmitters also having been deployed for other studies simultaneously, they 234
represented a very low percentage of total detections and would have had little effect on the 235
outcomes of the analyses. No Type B false transmitter detections were identified. A further 236
195 detections from one fish were removed due to a receiver station code transcription error. 237
Data were analysed using R (R Core Team, 2017). Six C. auratus with V16 238
transmitters contributed ~2 million detections to the total 3.5 million during the study and 239
were all recorded at site B (Fig. 1). As these detections were essentially continuous, it was 240
not possible to distinguish whether these fish had become resident or were deceased and still 241
within proximity of the receiver. Daily variations in detection rates may have been caused by 242
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environmental or anthropogenic noise interference, rather than movement towards and away 243
from the Site B receiver or a combination of all these factors. These data were omitted from 244
analyses. One fish (#60358) was predated on by a shark at the time of release (pers. obs.) and 245
thus its detections were removed from analyses. 246
Detections from the remaining 33 C. auratus, with 23 V16 and 10 V13 transmitters 247
were used to determine the locations of entry to or exit from Cockburn Sound, while only the 248
V16 transmitters were used to investigate migration timing and philopatry after 2009/10. 249
These transmitters were programmed to last for ~ 1000 d, with short and long delay periods 250
to coincide with spawning months and non-spawning months, respectively. The V13 251
transmitters were surplus from other studies and were beyond their recommended shelf life. 252
Thus, they were potentially less reliable for analyses of timing of migrations. The daily 253
presence/absence of each C. auratus within the entire array (aggregation array, OTN and 254
SMN) was determined from the day it was released until either its last detection within the 255
array (if this occurred before the end of the transmitter’s expected life) or the estimated end 256
of the transmitter’s life (see Supplementary Table 1). The sequence of detections of each fish 257
in double gate arrays at each entrance/exit and/or at receivers inside Cockburn Sound were 258
used to evaluate directionality of movement. 259
As detections of C. auratus among the five potential gates occurred almost 260
exclusively at the gate between Garden and Carnac islands, i.e. Site A (see Results), these 261
data were used to evaluate whether there was evidence of immigration and emigration via a 262
bimodal pattern of occurrence at Site A and whether it was consistent among years. This was 263
predicted to occur based on the expectation that C. auratus move into and out of Cockburn 264
Sound prior to and after the spawning period, respectively. These analyses were also used to 265
relate this movement to the timing of the spatio-temporal closure, commencing on 1 Oct each 266
year. The number of unique C. auratus detected from 1 Aug to 28 Feb in 2010/11 and 267
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2011/12 in each discrete week (7 days) prior to and after 1 Oct in each year was expressed as 268
a proportion of the total possible number of transmitters that could be detected in each year 269
(i.e. 20 fish, which did not include the three fish which became resident at Site A or inside 270
Cockburn Sound). The data were assumed to be normally distributed around a mean week of 271
immigration and emigration. Single, bimodal and tri-modal finite mixture distribution models 272
were fitted to the data for each year according to the function 𝐹𝐹(𝑥𝑥) = ∑ 𝑤𝑤𝑖𝑖𝑛𝑛𝑖𝑖=1 𝑃𝑃𝑖𝑖(𝑥𝑥), where 273
𝑃𝑃𝑖𝑖(𝑥𝑥) is the probability density function for each distribution (with mean �̅�𝑥 and standard 274
deviation 𝑠𝑠) and 𝑤𝑤𝑖𝑖 is the weight of each distribution, such that ∑𝑤𝑤𝑖𝑖 = 1. Model parameter 275
estimates were derived using a maximum likelihood approach. Akaike Information Criterion 276
(AIC) values were calculated to determine which of the models provided the best fit (lowest 277
AIC), where AIC = -2LL + 2K and K is the number of parameters in the regression equation 278
(including the estimate of the residual variance). Models were compared after adjusting for 279
sample size, as the ratio of n/K was less than 40 (n is the sum of the number of transmitters 280
observed per week from 1 Aug to 28 Feb), as follows: AICc = AIC + 2𝐾𝐾(𝐾𝐾+1)𝑛𝑛−𝐾𝐾−1
(Burnham and 281
Anderson 2002). Note that the assumption of the presence/absence data being gamma 282
distributed was also evaluated using single, bi- and tri-modal mixture models. However, the 283
shapes of the fitted distributions and their log likelihoods were similar to those of the normal 284
distributions in each case in each year. The bimodal model again produced the lowest AICc 285
values. Thus, the normal distribution fits were considered appropriate. Daily sea surface 286
water temperature (SST) data (multi-scale ultra-high resolution SST analysis fv04.1, 1 km 287
resolution) were obtained for an area bounded by 32.1-32.2 ºS and 115.6-115.7 ºE from 1 288
Aug to 28 Feb in 2010/11 and 2011/12 from https://coastwatch.pfeg.noaa.gov/erddap/griddap 289
(downloaded 6 April 2018). Moon fraction (percentage full) data were obtained for the same 290
period from http://aa.usno.navy.mil/data/docs/MoonFraction.php (downloaded 6 April 2018). 291
Mean weekly SST and moon fraction were then calculated, as per detection data. 292
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293
Fishery and biological data 294
Fishery and biological data were obtained from time periods as close as possible to 295
that of the telemetry study. These data were used to provide general patterns of fishing for 296
C. auratus and of its reproductive biology. Available retained catch data for C. auratus from 297
the commercial and recreational sectors were used to provide an indication of the typical 298
spatial distribution of catches per year by the two sectors across the four management areas 299
of the west coast. These include the Kalbarri (from 26°30′–28°S), Mid-west (28–31°S), 300
Metropolitan (from 31–33°S) and South-west areas (from 33°S on the west coast to 115°30′E 301
on the south coast; Fig. 1). Commercial fishing for C. auratus in the Metropolitan Area has 302
been prohibited since 2008, other than by a small line fishery which occasionally catches 303
C. auratus (Fairclough et al. 2014a). Catch data from compulsory logbooks of commercial 304
line fishers between 2008 and 2016 were used to calculate the average annual commercial 305
catch from each area. The recreational sector comprises both charter- and private-boat fishers. 306
Catch data from charter-boat fishing between 2008 and 2016 were obtained from compulsory 307
Tour Operator Returns and used to calculate their average annual catch for each area. As 308
catches from private-boat based recreational fishing are not surveyed annually, estimated 309
annual catches from each area were derived from a recent one year survey of recreational 310
fishers during 2013/14, which integrated phone-diary surveys and boat-ramp validation 311
surveys (Ryan et al. 2015). These estimates were combined with the average charter catches 312
by area to provide an estimate of the typical average annual catch of the recreational sector in 313
each area. The average annual catches of C. auratus in each area by the commercial and 314
recreational sectors were then used to calculate the percentage of the total catch taken by each 315
sector in each area. 316
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Charter- and private-boat data were further examined to infer any changes in fishing 317
activity (targeting) associated with the presence of migrating or aggregating C. auratus, prior 318
to, during and after the spawning period. Reported catches by charter-boats in each 10×10 nm 319
block in the Metropolitan Area (encompassing the area of the study) in each month in 320
2015/16 were plotted to identify the spatio-temporal distribution of their catch. These data are 321
not available for private vessels. Thus, to provide information on private vessel activity in the 322
area of the study, the estimated number of powered-vessel launches was determined for each 323
hour of the day in each month from March 2011 to February 2012, calculated from footage 324
obtained from a remote camera installed at Woodman Point, typically the Metropolitan 325
Area’s most-used boat ramp (Fig. 1; Ryan et al. 2013; 2015). Although not all vessels 326
launched are used in fishing activities, the number of launches is positively correlated with 327
recreational fishing effort and thus provides an index of fishing effort (Steffe et al. 2017). 328
Data on the frequency of occurrence of C. auratus in the Metropolitan Area, including 329
Cockburn Sound, that contained either stage III (i.e. developed or pre-spawning) or stage IV 330
(i.e. ripe or spawning) ovaries between 2002 and 2006 were obtained with permission from 331
Wakefield et al. (2015). The percentage frequency of these two stages in each month of the 332
year was used to compare the timing of the spawning period to the timing of detections 333
within the array and the annual closure to fishing in the embayments. Although this work was 334
conducted prior to the telemetry study, other studies of C. auratus in Cockburn Sound that 335
have focused on aspects of its reproductive biology (e.g. egg production) provide evidence of 336
consistent interannual timing of the spawning period (cf. Wakefield 2010; Dias et al. 2016; 337
Partridge et al. 2017). 338
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Results 339
Over one million valid detections of C. auratus with transmitters were recorded 340
throughout the study by the aggregation, OTN and SMN arrays combined. The total number 341
of detections of individual transmitters ranged from 113 to 265,742, while V16 transmitters 342
were detected on up to 675 d (�̅�𝑥 = 148.5 d; Supplementary Table 1) over the three year study. 343
The majority of C. auratus detections (~83%) occurred between September and January, with 344
> 99% of those recorded from 29 of the 33 valid transmitters at Site A (the line of seven 345
receivers between Garden and Carnac islands and the nine most western receivers between 346
Garden Island and Woodman Point) and sites B and C inside Cockburn Sound (Figs 1, 4, 5). 347
Relatively few C. auratus were detected in the other pathways to Cockburn Sound, i.e. 348
eastern receivers between Garden Island and Woodman Point (< 1% of detections, 10 fish), 349
Rottnest Island to Fremantle (< 1%, 13 fish), Rottnest Island to Straggler Rocks and Carnac 350
Island (< 1%, 8 fish) and the southern end of Cockburn Sound (< 1%, 4 fish) (Fig. 4). 351
352
Timing of detections in relation to the fishing closure and environmental parameters 353
Detections of V13 and V16 transmitters provided strong circumstantial evidence of 354
sequential movement to and/or from Cockburn Sound. After fish were tagged in 2009, 25 of 355
the 29 V16 and V13 transmitters detected at sites A (Garden Island to Carnac Island), B or C 356
(inside Cockburn Sound) between October and December 2009 were subsequently detected 357
at Site A before the end of the closure to fishing on 31 Jan 2010 (Fig. 5). Twenty three of 358
those 25 ceased to be detected at Site A by 31 Jan. One remained at Site A for a further 1.5 y 359
and then was no longer detected (#60352), while another (#1367) was detected again at Site 360
A in early February 2010. Fourteen fish were subsequently detected outside the embayment 361
on SMN or OTN receivers between Garden and Rottnest islands, or briefly east of Site A, 362
towards Woodman Point. Four of the 29 fish continued to be detected at Site B in the 363
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embayment where they were tagged. However, three of those (#60361, 60639, 60371) ceased 364
to be detected by 31 January, while one (#51857) was detected until early February 2010 at 365
Site B and then once in April 2010 outside the embayment, immediately north of Carnac 366
Island (Fig. 5). 367
Of a possible 23 fish with valid V16s, six of the 17 fish detected during the 2010/11 368
closure and 9 of the 15 fish detected during the 2011/12 closure were first detected prior to 369
the closure commencing on Oct 1 (Fig. 5). This occurred 32-36 d before the closure in those 370
years, respectively, either beyond the Site A gate on SMN or OTN receivers, at Site A or at 371
Site B. In contrast, the last detections of almost all fish at either Site A or B in the 2010/11 372
and 2011/12 spawning seasons were recorded before the end of the closure to fishing on 31 373
Jan. During the 2010/11 spawning period, six of 19 fish with V16s were recorded 374
consecutively at Site A, followed by Site B or C within Cockburn Sound and then five were 375
later recorded at Site A (Fig. 5). Seven fish were only detected at Site A, two of which 376
demonstrated evidence of residency and one was only detected late in November, thus later in 377
the spawning period. A hiatus in detections occurred at Site A with four of the seven fish, 378
during which time they were not detected elsewhere. However, three were last detected on 379
the eastern (or inside) line of receivers leading in to Cockburn Sound. While three fish were 380
not detected that year, the remaining three were detected at only Site A early in the spawning 381
season or only at Site B intermittently during the spawning season. Of the four fish tagged at 382
Site B in the 2010/11 spawning season with valid V16s, each was detected for a period at Site 383
B and three were subsequently detected at Site A before the end of the closure. 384
Of 23 valid V16s, detections at Site A, followed by Site B and then Site A were 385
recorded for two fish in 2011/12. Another 10 fish were detected at Site A, but not inside 386
Cockburn Sound. Four of those exhibited a hiatus in detections, preceded by detections on the 387
eastern (or inside) line of receivers at Site A. Three fish were detected intermittently only 388
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inside Cockburn Sound, while one was only recorded outside Cockburn Sound, detections of 389
another two indicated residency at Site A or B and five fish were not detected. 390
Across all years of the study, the relatively small number of detections (n = 5576) of 391
22 transmitters on receivers other than at Site A, B or C between September and January 392
occurred over short periods and for the majority of these fish (n = 17) indicated sequential 393
movement to and from Site A. For example, two individuals (#60366 and 60370) were 394
detected on OTN and SMN receivers near Fremantle in Oct 2010 over one and five 395
consecutive days, respectively (808 detections not visible on Fig. 4). They were preceded by 396
detections at Site A 2.2 and 1.25 d before, respectively, and followed by detections at site A 397
0.4 d later and Site B 0.9 d after that. Fish #60370 was then detected at Site B for 44 d and at 398
Site A 0.25 d later. Two C. auratus (#60364, 60368) were detected briefly (12 detections 399
over 33 min; 6 detections over 17 min) on the two western-most receivers of the southern 400
entrance of Cockburn Sound in Aug and Oct 2010 and subsequently on the western receivers 401
at Site A 15 h and 3.8 h later, respectively. Another two individuals were detected in 402
Warnbro Sound for short periods (#60360 for 2 d in Nov 2010 and 5 d in Oct 2011; #60368 403
for 13 d in Oct 2010) and subsequently at Site A within ~1 d. 404
The number of fish with V16 transmitters detected at Site A in each week between 1 405
Aug and 28 Feb in both 2010/11 and 2011/12 had a bimodal frequency pattern. AICc values 406
indicated that bimodal mixture distributions produced the best fit to these data in each year, in 407
comparison to both single mode and tri-modal models (Table 1). In both the 2010/11 and 408
2011/12 spawning seasons, the number of fish detected at Site A began to increase prior to 409
the commencement of the closure on 1 October, while mean water temperatures were < 19 ºC 410
(Fig. 6). The first of the means of the bimodal distributions occurred at ~ 1.0 and 0.6 weeks 411
after the commencement of the closure in 2010/11 and 2011/12, respectively, when water 412
temperatures were ~19 ºC (Table 2, Fig. 6). Fewer fish were detected during subsequent 413
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weeks, with the lowest frequencies recorded while water temperatures were < 21 ºC and at 414
the time of the new moon in November in 2010 and between the approximate times of the 415
new moons in October and November in 2011 (Fig. 6). This occurred when the percentage of 416
female C. auratus in Cockburn Sound with ovaries in pre-spawning/spawning condition is 417
typically increasing to or is at its maximum (Fig. 6; cf. Figs 4,8,9). The second mode 418
occurred at 9.6 and 8.0 weeks after the closure commenced, when water temperatures had 419
reached 21 ºC in both years (Table 2; Fig. 6). Frequencies of occurrence then declined as 420
water temperatures increased above 21 ºC, which occurred before the end of the fishing 421
closure on 31 Jan in both years and as the percentage of females with ovaries in pre-422
spawning/spawning condition declined (Fig. 6, cf. Figs 4,7,9). The standard deviation of the 423
mean number of fish detected per week indicated relatively consistent variation around the 424
two means in 2010/11, but the second mean in 2011/12 exhibited less variation than the first 425
and less than both means in 2010/11 (Table 2; Fig. 6). 426
427
Spawning aggregation philopatry 428
The majority (n = 21) of the 23 C. auratus with V16 transmitters were detected either 429
at Site A, B or C in at least one spawning season subsequent to being tagged. Seven fish were 430
detected in only one spawning season following tagging with two of those only detected 431
again two years after being tagged. Ten and four fish were respectively detected in two and 432
three consecutive seasons after being tagged. However, two of the latter four fish appeared to 433
remain at site A or site B for extended periods including the non-spawning period. Although 434
unexpected, two of the ten fish with V13 transmitters were also detected in one or two 435
subsequent spawning seasons (Fig. 5). After detection at sites A and B in two consecutive 436
spawning seasons after being tagged, one fish (#60360) was detected once in March 2012 on 437
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the SMN array #1, ~240 km south of the embayments, while another (#60362) was captured 438
and retained by a recreational angler ~135 km north of the embayments. 439
440
Fishing Effort 441
The majority of the average annual retained catch of C. auratus in the WCB is taken 442
by the commercial fishery in the Kalbarri (26°30′-28°S) and Mid-west areas (28-31°S), i.e. 443
~74% (Fig. 7). The recreational sector lands ~25% of the average annual catch in the WCB, 444
of which, ~14% is taken in the Metropolitan Area (31-33°S; Fig. 7). Average annual retained 445
charter fishing catches comprise 32% of the recreational sector catch in the WCB and the 446
largest component of that (16%) is from the Metropolitan Area (not shown in Fig. 7). 447
In the Metropolitan Area, the largest monthly catches (102-200 fish per 10×10 nm 448
block) from charter boat recreational fishing typically occurred west, north or north-west of 449
Rottnest and/or Garden islands (Fig. 8). In July to October, leading up to the peak of the 450
spawning season, the closure to fishing for C. auratus in the embayments (1 Oct-31 Jan) and 451
the closure to fishing for all demersal species, including C. auratus, across the WCB (15 Oct-452
15 Dec), catches were reported only in blocks north of Garden Island (~36.15°S; Fig. 8). The 453
largest of these catches per block were concentrated mostly between Rottnest and Garden 454
Islands and particularly the block encompassing Site A. Between December and March, i.e. 455
towards the end of, and following the spawning season, the largest total catches per block 456
were reported from the same area between Rottnest and Garden islands, but catches were also 457
widely dispersed across the Metropolitan Area, including southwards from Garden Island. 458
From April to June, charter catches were typically low and dispersed northwards from 459
Garden Island. 460
At Woodman Point, the majority of vessel launches in each month occurred in the 461
morning from ~06:00-12:00, followed by relatively fewer launches for the rest of the day and 462
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night (Fig. 9). However, in August and September, just prior to the October commencement 463
of the fishing closure, a prominent second mode of launches was detected in the late 464
afternoon/dusk. During these two months, ~30 and 44% of adult female C. auratus in the 465
Metropolitan Area contained ovaries which were in pre-spawning or spawning condition 466
(Fig. 9). This is in contrast to the 68% of adult females with ovaries in pre-spawning or 467
spawning condition in October and > 92% in November and December, when spawning is 468
typically at its maximum in that area. These months also exhibited a unimodal frequency of 469
boat launches in the morning, when fishing for C. auratus is prohibited. By January, adult 470
female C. auratus with ovaries in pre-spawning or spawning condition have declined below 471
50%, and after January when fishing is allowed, little spawning activity occurs (Fig. 9). 472
473
Discussion 474
This study used acoustic telemetry to determine the migration patterns of C. auratus 475
to and from an embayment on the lower west coast of Australia where it aggregates to spawn 476
and is protected by a spatio-temporal fishing closure. Detections of C. auratus indicated 477
predictable and repeated movement behaviours consistent with the relationship between 478
reproduction and environmental parameters in this species. Individuals (1) migrated via only 479
one of several pathways into the main embayment of Cockburn Sound where spawning 480
occurs, (2) often occurred in that pathway before the fishing closure began and spent varying 481
periods of time there, but most left before the closure ceased, (3) were detected in the 482
pathway and/or aggregation locations in the embayment in more than one year, confirming 483
spawning site philopatry, but (4) may not always return in consecutive years. The spatio-484
temporal closure offers limited protection to migrating and pre-spawning fish, as individuals 485
begin arriving at the main pathway before the closure commences and are fished there and 486
over adjacent reef systems at that time. This is likely to impact spawning aggregation 487
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biomass. Assessment and monitoring of mortality or spawning biomass would help to 488
identify whether current management is sufficient to ensure the sustainability of the 489
aggregations and their contribution to the broader stock. 490
491
Biological relevance of Chrysophrys auratus movements 492
Recurrent detections of C. auratus in only one of the several pathways to the main 493
embayment in which they aggregate-spawn implies that this pathway provides navigational 494
cues for migration. The pathway lies just to the east of two north-south oriented reef systems 495
(the Garden Island ridge on the western side of the island and Five Fathom Bank further to 496
the west), which both extend southwards from the south-eastern end of Rottnest Island, past 497
Garden Island and, in the case of Five Fathom Bank, beyond 33°S (Fig. 1). Migrating fish 498
may use these to navigate to and from the pathway to Cockburn Sound, which is supported 499
by the recapture of tagged C. auratus along Five Fathom Bank and is consistent with the 500
locations of charter catches of C. auratus. These and other reef lines in deeper water (~80 and 501
110 m) along the west coast may provide important pathways that some C. auratus use to 502
disperse substantial distances from Cockburn Sound as recorded during this and previous 503
studies (Wakefield et al. 2011). Reef lines and shelf margins or ridges comprise obvious 504
bathymetric characteristics which are commonly-used by demersal fishes, such as 505
epinephelids, to migrate to aggregation sites. This usage may be a learned behaviour, 506
particularly in the case of young maturing fish (Domeier and Colin 1997; Starr et al. 2007; 507
Colin 2012; Nemeth 2012; Sadovy de Mitcheson 2016). In southern Australia, C. auratus 508
also demonstrates systematic habitat/location use patterns, dispersing across areas of > 100 509
km2 from a location, but revisiting that location at the same time in different years (Fowler et 510
al. 2017). The pathway in to Cockburn Sound used by C. auratus may also provide resources 511
that others do not, such as habitat that offers protection from predation or food. As some 512
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C. auratus may migrate substantial distances, continued feeding may be necessary to provide 513
energy for gonadal development and spawning, as in the carnivorous Epinephelus guttatus 514
and herbivorous Chlorurus sordidus (Sancho et al. 2000; Nemeth 2012; Kawabata et al. 515
2015). 516
Acoustic telemetry has demonstrated that the timing of entry to and departure from 517
Cockburn Sound is consistent with the strong link between the reproductive periodicity of 518
spawning aggregations of C. auratus in the embayment and annual, lunar, diel and 519
oceanographic cycles (cf. Scott et al. 1993; Wakefield 2010; Saunders et al. 2012; Wakefield 520
et al. 2015). A bimodal frequency of occurrence of C. auratus was identified in the main 521
pathway to Cockburn Sound in both 2010/11 and 2011/12, with the first and second modes in 522
each year corresponding with the time when water temperatures were ~19 and 21ºC, 523
respectively. Spawning peaks in these waters within that narrow temperature range, which 524
typically occurs in November (late austral spring), while gonadal atresia occurs when water 525
temperatures exceed 21°C, usually in December/January (summer) (Wakefield 2010; 526
Wakefield et al. 2015). Thus, the two modes presumably reflect periods of accumulation in 527
the pathway, as individuals migrate to and from the aggregations and this migration is linked 528
with water temperature. The trough between the two modes would represent the time during 529
which most individuals are within Cockburn Sound, consistent with the detections of tagged 530
fish at sites in the embayment. This period coincided with one or more new and full moons in 531
2010/11 and 2011/12, during which greater spawning activity typically occurs, particularly 532
on the new moon that coincides with water temperatures of 19-21ºC (Wakefield 2010). The 533
difference in the number of new moons experienced in the time during which water 534
temperatures rise from 19 to 21ºC may thus influence the extent of spawning activity in any 535
one year. 536
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As there is a strong relationship between water temperatures and gonadal maturation, 537
migration and/or formation of spawning aggregations of C. auratus, predicted ocean 538
temperature increases (Pearce et al. 2016) may influence the timing or location of those 539
behaviours. This would alter the efficacy of the associated spatio-temporal fishing closure 540
(Sheaves 2006; Jackson et al. 2015; Wakefield et al. 2015). Furthermore, marine ‘heatwaves’ 541
have increased in duration and frequency in the last century (Lenanton et al. 2017; Oliver et 542
al. 2018), which may have rapid and unpredictable effects on C. auratus spawning success in 543
the embayments. Individuals may no longer enter the embayment if water temperatures 544
exceed the preferred range for successful spawning. Such phenological variations in relation 545
to water temperature are common in marine organisms in shallow and deep waters across 546
tropical and temperate regions, including among cephalopods (e.g. Loligo forbesi) and 547
teleosts (Dascyllus albisella, Platichthys flesus, Clupea pallasi, Gadus morhua, Hyporthodus 548
octofasciatus) (Lawson and Rose 2000; Sims et al. 2001; Asoh and Yoshikawa 2002; Sims et 549
al. 2004; Wakefield et al. 2013b). 550
551
Exploitation of migratory and aggregatory fish 552
The predictability of spawning aggregations is the key reason they are susceptible to 553
over-exploitation and consequent negative impacts on abundance and/or biology (e.g. 554
Coleman et al. 1996; Sadovy and Cheung 2003; Erisman et al. 2012; Sadovy de Mitcheson 555
and Erisman 2012). Fishing has the potential to extirpate aggregations and negate any 556
selective advantage conferred by such behaviour and has often led to the need for significant 557
management intervention. For example, while relatively few of the ~150 sparids aggregate-558
spawn (Nemeth 2012), some that do in southern Africa (Petris rupestris, Polysteganus 559
undulosus and Chrysoblephus gibbiceps) are now endangered or critically endangered due to 560
exploitation. This has led to complete closures to fishing for those species (Mann et al. 2014a, 561
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2014b; Sadovy de Mitcheson 2016). Commercial and recreational fishing of aggregations of 562
demographically separate but genetically-related C. auratus stocks on the upper west coast of 563
Australia also resulted in stock depletions (Jackson and Moran 2012; Gardner et al. 2017). 564
However, restrictive management to limit catches via a range of measures, including 565
temporal closures and harvest tags, has allowed recovery of some of those stocks over 15+ 566
years (Jackson and Moran 2012; Jackson et al. 2016). Recent overfishing of the coastal 567
Arripis georgianus in the same region would be influenced by the exploitation of spawning 568
biomass both during its pre-spawning migration along 100s to 1 000s of km of the southern 569
Australian coastline and during the spawning period (Fairclough et al. 2000; Smith et al. 570
2013). Similarly, impacts of recreational fishing of migrating Albula vulpes in Kiribati 571
resulted in the need for a fishing closure during its spawning period (Sadovy de Mitcheson 572
and Erisman 2012). 573
Exploitation of C. auratus on the lower west coast of Australia by the recreational 574
sector occurs along the reef systems between Rottnest and Garden islands, adjacent to the 575
fishing closure, and in the main migratory pathway between Garden and Carnac islands. An 576
increase in evening launches of private vessels at Woodman Point, the most proximal boat 577
ramp to the main pathway, in August and September just prior to the fishing closure, is 578
consistent with anecdotal information that recreational fishers target C. auratus at that time. 579
The combination of telemetry and reproductive data (Wakefield 2010; Wakefield et al. 2015) 580
confirms that fishers would be catching both pre-spawning migratory fish and fish that have 581
become periodically resident in the area. However, not all fish may be exposed to fishing 582
each year. Telemetry data also demonstrated that while the majority of fish were detected in 583
subsequent years after tagging, exhibiting philopatry, other fish may have returned but were 584
not detected, or may return but not in consecutive years. As some fish can travel substantial 585
distances (100s of km) from the embayments, they may never return, instead living and 586
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reproducing elsewhere. Such long distance movements have been documented in several 587
studies of C. auratus (e.g. Parsons et al. 2014; Harasti et al. 2015), but the reasons for them 588
are not known. Whether such individuals would return and what proportion of fish undertake 589
this type of movement remains unclear. Thus, philopatry rates may be underestimated. This is 590
similarly not well understood for aggregations of C. auratus in Port Phillip Bay in southern 591
Australia (Hamer et al. 2011). Fish that travel substantial distances along the west coast of 592
Australia are exposed to different levels of fishing mortality, associated with the varying 593
management regimes, including different size limits and commercial fishing. Despite 594
restrictive management of the spawning aggregations and broader stocks of C. auratus along 595
the west coast, migratory fish are not protected until they have crossed the boundary of the 596
spatio-temporal closure, after it has commenced. Thus, if exploitation of migratory pre-597
spawning C. auratus in the pathway and over adjacent reef systems is high enough, it may 598
influence migratory patterns and/or reduce spawning biomass. 599
600
Social importance and monitoring of Chrysophrys auratus spawning aggregations 601
While recreational fishers enjoy targeting the seasonally amassing C. auratus in 602
waters adjacent to or within the embayments, many presumably understand that targeting 603
aggregations would have negative consequences. This recognition can increase their 604
willingness to contribute to ensuring suitable management is in place (e.g. Hamilton et al. 605
2012; Heyman and Granados-Dieseldorff 2012). For example, public outcry occurred when 606
over 250 C. auratus died during an environmentally driven fish-kill in Cockburn Sound 607
around the time of peak spawning in 2015 (Department of Fisheries 2016). With recreational 608
sector support and crowd-sourced funding, hatchery-reared juvenile C. auratus, originally 609
bred for scientific purposes (Partridge et al. 2017), were released into the embayments on the 610
premise that stocks would benefit. Government subsequently committed additional funding 611
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for further releases of hatchery-reared juveniles in 2017 and 2018. The otoliths of released 612
fish are marked with alizarin red via immersion, allowing them to be identified at a later stage 613
if collected via C. auratus stock assessment sampling regimes (see Fairclough et al. 2014b). 614
However, the probability of this is low and there were no plans to evaluate the release 615
program with respect to its purported benefits to stocks or recreational fishing. The releases 616
are promoted as a mechanism to ensure ongoing occurrence of C. auratus in Cockburn 617
Sound, but given juveniles leave this embayment by ~18 months of age, disperse widely 618
along the coast and may not return, as occurs elsewhere in Australia, such benefits may never 619
be realised (Lenanton 1974; Fowler et al. 2005; Hamer et al. 2011; Wakefield et al. 2011). 620
Furthermore, such enhancement was not required to recover stocks of C. auratus on the upper 621
west coast of Australia, where traditional management methods, such as closures to fishing, 622
were adopted, accepted and successful (Jackson and Moran 2012, Molony et al. 2003). Thus, 623
education on the biology of C. auratus and the realistic benefits of stock enhancement vs 624
traditional input/output management controls is needed. 625
There are currently no data to demonstrate any decline in abundance of aggregating 626
C. auratus on the lower west coast since the fishing closure was introduced, which was 627
supported strongly by the recreational sector. Furthermore, the extent and effect of 628
recreational fishing of migratory C. auratus have not been measured. Surveys of private boat-629
based recreational fishers’ catch and effort are conducted at larger spatial scales and are more 630
relevant to the broader stock on the west coast (Ryan et al. 2017). These surveys have not 631
detected a significant change in the total retained catches of C. auratus by private recreational 632
fishers between 2010/11 and 2015/16, but estimated catches have been at levels around the 633
predicted maximum that would allow stocks of C. auratus on the west coast to recover (Ryan 634
et al. 2017). However, the stocks are yet to recover and continued management is needed 635
(Fairclough and Holtz 2017). In addition, the number of private boat-based recreational 636
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fishing licences in the metropolitan region, which is adjacent to the embayments, has 637
increased by ~20% from 2010/11 to 2015/16, i.e. from ~57 000 to 69 000. Also, the numbers 638
of C. auratus released by recreational fishers is very high, i.e. ~78% of fish landed in the 639
Metropolitan Area in 2015/16, where a majority of the retained recreational catch is taken 640
(Ryan et al. 2017). If post-release mortality is high in C. auratus, caused by factors such as 641
barotrauma, gut-hooking and on-board handling (e.g. Stewart 2008; Grixti et al. 2010), or 642
there are sub-lethal effects, such as skipped spawning, recovery of stocks or increases in 643
biomass of aggregations may be restricted or prevented. 644
The social importance of the C. auratus spawning aggregations and their likely 645
importance to its broader stocks along the west coast of Australia warrants further 646
investigation and potential direct monitoring. This could benefit both management and the 647
social desire for the aggregations to be sustained. A variety of methods may be applicable, 648
but may vary in their cost-effectiveness. Assessment of age-based fishing mortality rates 649
requires the collection of large numbers of fish from the aggregations, which would have 650
undesirable impacts on biomass and reproductive behaviour. Mark-recapture models could be 651
used to estimate fishing mortality, whereby aggregating fish are tagged and released. 652
Estimation of aggregation biomass may be a more direct approach. This possibly could be 653
achieved via daily egg production methods (DEPM), which have been used for C. auratus 654
elsewhere (e.g. Jackson et al. 2012). However, DEPMs require significant laboratory time, as 655
C. auratus eggs must be identified and counted from plankton surveys (Wakefield, 2010). 656
This is challenging due to their visual similarities to eggs of other species, but the use of 657
recently tested molecular identification techniques (real-time PCR and in-situ hybridisation) 658
may help (Dias et al. 2016; Oxley et al. 2016). Acoustic surveys of aggregations using multi- 659
or single-beam technology have been tested on other demersal species in this region and are 660
commonly used elsewhere to estimate biomass (Rose 2003; Gastauer et al. 2017). However, 661
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the relatively shallow waters of Cockburn Sound (< ~20 m) would require modifications to 662
the technique, given they are normally used in deeper water. In addition, a dynamic survey 663
design would be required that allows for the potential interannual variation in the timing of 664
peak spawning due to environmental change and thus the potential to bias annual relative 665
spawning biomass estimates. Determining the cost-effectiveness of the various methods and 666
comparing the information they could provide to management in terms of responsiveness to 667
changes in status (e.g. biomass) of the C. auratus aggregations would inform a discussion on 668
which method may be preferable for long-term monitoring. 669
670
This study has explored the relevance of a spatio-temporal closure to fishing for 671
C. auratus migrating to and from spawning aggregation sites in embayments on the lower 672
west coast of Australia. This species exhibits predictable migratory patterns to and from the 673
main embayment and, as a result, such fish are exploited by the recreational sector outside the 674
embayment. Individual variation in the timing of migration and interannual philopatry to the 675
aggregations may reduce the risk of capture. In addition, the current temporal and spatial 676
extent of the closure protects the aggregations specifically, which is widely accepted by 677
fishers. In conjunction with the restrictive management of stocks at the broader west coast 678
scale, overexploitation of the spawning aggregations of C. auratus in lower west coast 679
embayments is likely to have been avoided, but ongoing monitoring is required to ensure this 680
does not occur in the future as the recreational sector grows. In addition, the effect that 681
targeting of migratory fish may have on reproductive success of spawning aggregations may 682
limit the benefits offered by current management, by interruption of migrations and removal 683
of spawning biomass. Thus expansion of the spatial limits of the closure, to include the reef 684
systems adjacent to the embayments where C. auratus are fished, or extension of the closure 685
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to include August and September, when fish are beginning to arrive at the main pathway to 686
the embayment, may be required. 687
The importance of C. auratus spawning aggregations to the broader population along 688
the west coast of Australia is assumed, with progeny expected to disperse widely prior to 689
maturing. However, it is unclear to what extent this is the case. Indeed, aggregations in 690
southern Australia have been demonstrated to produce >70% of the recruits to ~800 km of 691
coastline (Hamer et al. 2011). Thus, identifying such source-sink relationships is important 692
and could be explored using contemporary genetic or possibly otolith microchemistry 693
techniques (Hamer et al. 2011; Ovenden et al. 2015; diBattista et al. 2017). Furthermore, such 694
an understanding would help to identify whether it is critical to monitor the status (e.g. 695
spawning biomass) of the spawning aggregations directly from a sustainability perspective, or 696
whether monitoring and appropriate management of fishing mortality of the broader stocks of 697
the west coast is sufficient to ensure the ongoing reproductive function of the aggregations 698
and also satisfy social expectations. 699
700
Acknowledgements 701
This project was supported by the Canada Foundation for Innovation’s international 702
Ocean Tracking Network 703
(http://oceantrackingnetwork.org; https://members.oceantrack.org/project?ccode=CCK) and 704
Western Australia’s Shark Monitoring Network, which each provided acoustic receivers and 705
access to detection data. Gratitude is expressed to staff of the Department of Primary 706
Industries and Regional Development, for assistance in the field, particularly S. Mountford 707
and other SMN staff, to R. McAuley and T. Pinnel for database support; S. Blight for boat-708
ramp camera support; A. Hesp and A. Denham for statistical advice and internal reviewers R. 709
McAuley, G. Jackson and B. Molony. We are extremely grateful to D. Wimpress and 710
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R. Thipthorp for assistance in tagging, to other recreational fishers who have reported 711
recaptured snapper and to the Department of Transport and Fremantle Ports for assistance in 712
deployment of acoustic arrays. We also thank two anonymous reviewers for their 713
constructive feedback on the manuscript. 714
715
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implications for management. Fish. Res. 90(1-3): 289–295. 1028
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west coast of Australia. J. Fish Biol. 77(6): 1359–1378. doi:10.1111/j.1095-1032
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lower west coast of Australia. Fish. Res. 109(2–3): 243–251. 1036
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Wakefield, C.B., Lewis, P.D., Coutts, T.B., Fairclough, D.V., and Langlois, T.J. 2013a. Fish 1038
assesmblages associated with natural and anthropogenically-modified habitats in a marine 1039
embayment: comparison of baited videos and opera-house traps. PLOS One 8(3): e59959. 1040
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2013b. Contrasting life history characteristics of the eightbar grouper Hyporthodus 1043
octofasciatus (Pisces: Epinephelidae) over a large latitudinal range reveals spawning 1044
omission at higher latitudes. ICES J. Mar. Sci. 70(3): 485–1045
497. doi.org/10.1093/icesjms/fst020 1046
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variations in reproductive characteristics of snapper (Chrysophrys auratus, Sparidae) and 1048
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Timing of growth zone formations in otoliths of the snapper, Chrysophrys auratus, in 1052
subtropical and temperate waters differ and growth follows a parabolic relationship with 1053
latitude. ICES J. Mar. Sci. 74(1): 180-192. doi.org/10.1093/icesjms/fsw137 1054
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populations of demersal scalefish: implications for management. Part 1: stock status of the 1056
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key indicator species for the demersal scalefish fishery in the West Coast Bioregion. Final 1057
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Prog. Ser. 162: 253–263. doi:10.3354/meps162253. 1064
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Figure captions 1065
Fig. 1. Study location in the inshore Metropolitan Area (cross-hatched on inset) of the West 1066
Coast Bioregion (WCB) of Western Australia. Inset shows main fishery areas of Kalbarri 1067
(K), Mid-West (MW) and South-West (SW) and Shark Monitoring Network arrays outside 1068
the Metropolitan Area (1,2,3). Main map shows (i) acoustic receiver arrays comprising the 1069
aggregation array (○) around Cockburn (CS) and Warnbro (WS) sounds and Owen 1070
Anchorage (OA), the Ocean Tracking Network (▲) and the Shark Monitoring Network 1071
(VR2W ■ and VR4W □) in the Metropolitan Area, (ii) the area closed to fishing for 1072
Chrysophrys auratus from 1 Oct-31 Jan (diagonal hatching), (iii) the five pathways to/from 1073
Cockburn Sound (arrows). OTN Receivers (▲) west of Rottnest Island extend to ~115°13´E 1074
(not all shown). A, tagging location and double gate array between Garden Island (GI) and 1075
Carnac Island (CI); B and C are tagging locations within Cockburn Sound; F, Fremantle; RI, 1076
Rottnest Island; S, Straggler Rocks; WP, Woodman Point. Map produced in ArcGIS v10.3 1077
(ESRI 2014). 1078
1079
Fig. 2. (a) Recapture frequency of Chrysophrys auratus at different distances from tagging 1080
locations within the embayments and (b) frequency of recaptures in each month inside 1081
(black) and outside (grey) the area annually closed to fishing. Mark-recapture data derived 1082
with permission from Wakefield et al. (2011) for 2003-2009 is combined with ongoing data 1083
from the Department of Primary Industries and Regional Development for 2009-2016. 1084
1085
Fig. 3. Length-frequency distributions of Chrysophrys auratus tagged with dart tags (grey) 1086
and acoustic tags (white) in Cockburn Sound during the spawning seasons in 2009 and 2010. 1087
1088
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Fig. 4. Proportion of total detections per month (combined across years) of Chrysophrys 1089
auratus at each receiver in the aggregation array, Ocean Tracking Network and Shark 1090
Monitoring Network calculated as 𝑛𝑛 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑𝑛𝑛𝑑𝑑 𝑝𝑝𝑑𝑑𝑝𝑝 𝑚𝑚𝑑𝑑𝑛𝑛𝑑𝑑ℎ 𝑝𝑝𝑑𝑑𝑝𝑝 𝑝𝑝𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑𝑟𝑟𝑑𝑑𝑝𝑝𝑁𝑁 𝑑𝑑𝑑𝑑𝑑𝑑𝑡𝑡𝑡𝑡 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑𝑛𝑛𝑑𝑑
; nfish = number of fish 1091
detected per month; %III/IV = percentage of female C. auratus in each month with ovaries in 1092
pre-spawning (III) and spawning (IV) condition (from Wakefield et al. 2015). Red shading 1093
indicates the spatial area closed to fishing for Chrysophrys auratus from 1 Oct-31 Jan. CI = 1094
Carnac Island, CS = Cockburn Sound, F = Fremantle, GI = Garden Island, OA = Owen 1095
Anchorage, RI = Rottnest Island, S = Straggler Rocks, WP = Woodman Point. Maps 1096
produced in ArcGIS v10.3 (ESRI 2014). 1097
1098
Fig. 5. Daily detections of 34 Chrysophrys auratus at site A (black), outside the embayments 1099
(blue) and sites B and C inside Cockburn Sound (red), between the day they were tagged (Oct 1100
2009-Dec 2009 or Sept 2010) and the day they were last detected. Expected end of each 1101
transmitter's life shown as vertical dashes. Grey shading indicates timing of closure to fishing 1102
for C. auratus from 1 Oct-31 Jan. †fish last detected on Shark Monitoring Network array 1 in 1103
Fig. 1; *fish recaptured at latitude 31° S. 1104
1105
Fig. 6. Frequency of occurrence of acoustic transmitters in tagged Chrysophrys auratus 1106
recorded at Site A between Garden and Carnac Islands (see Fig. 1) in each week of the 1107
spawning season in (a) 2010/11 and (b) 2011/12 relative to 1 Oct (Week 0 begins on 1 Oct 1108
when the fishing closure commences), with bimodal mixture models fitted to the frequency 1109
distributions. Mean weekly sea surface temperatures adjacent to Site A and mean weekly 1110
moon fraction (% full) shown above for the same period. Solid arrows identify where SSTs 1111
reached ~19 and 21ºC and dashed arrow identifies the time of the November new moon 1112
(lowest moon fraction) in each year. 1113
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1114
Fig. 7. Average percentage of the annual commercial and recreational sector catch of 1115
Chrysophrys auratus in each management area of the West Coast Bioregion; based on the 1116
average annual catch of the main commercial fishery (WCDSIMF) from 2008 to 2016 and 1117
the recreational sector catch, which combines catches of private vessels from the 2013/14 1118
survey of Ryan et al. (2015) and the average annual charter vessel catch from 2008 to 2016. 1119
1120
Fig. 8. Monthly numbers of Chrysophrys auratus retained by charter fishers in 2015/16 in 1121
each 5nm × 5nm block of the Metropolitan Area of the West Coast Bioregion (31 - 33°S). 1122
%III/IV = percentage of female C. auratus in each month with ovaries in pre-spawning (III) 1123
and spawning (IV) condition (created using reproductive data from Wakefield et al. 2015 1124
with permission). Red shading indicates the spatial area closed to fishing for Chrysophrys 1125
auratus from 1 Oct-31 Jan. Nil catch in November is due to an annual closure to recreational 1126
fishing for demersal fishes in the West Coast Bioregion from 15 Oct–15 Dec (inclusive). 1127
Depth contours are 20, 50, 100, 200 m. 1128
1129
Fig. 9. Estimated number of private recreational vessels launched from Woodman Point boat 1130
ramp during each hour of the day (24 h clock) in each month in 2011/12 (from Ryan et al. 1131
2013 with permission). Grey shading indicates closure to fishing for Chrysophrys auratus 1132
from 1 Oct-31 Jan. Bars on right show relative reproductive activity represented as 1133
percentage of female C. auratus in each month that contained ovaries in pre-spawning (III) 1134
and spawning (IV) condition (created using reproductive data from Wakefield et al. 2015 1135
with permission). 1136
1137
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Table 1. Results of adjusted Akaike Information Criterion (AICc) comparisons between
single, bi- and tri-modal mixture distributions fitted to frequencies of occurrence of
Chrysophrys auratus at Site A (Garden Island to Carnac Island pathway) during the 2010/11
and 2011/12 spawning seasons. n = sum of occurrence of C. auratus with transmitters per
week between 1 Aug and 28 Feb. K = number of parameters estimated by the models.
Spawning Season n Model K AICc
2010/11 68 Single mode 2 415
Bimodal 5 407
Tri-modal 8 412
2011/12 87 Single mode 2 516
Bimodal 5 503
Tri-modal 8 507
Table 2. Means (𝑥𝑥𝑖𝑖) and standard deviations (𝑠𝑠𝑖𝑖) of bimodal mixture distributions fitted to
frequencies of occurrence of n Chrysophrys auratus at Site A (Garden Island to Carnac Island
pathway) during the 2010/11 and 2011/12 spawning seasons.
Spawning Season n 𝒙𝒙𝟏𝟏, 𝒔𝒔𝟏𝟏 𝒙𝒙𝟐𝟐, 𝒔𝒔𝟐𝟐
2010/11 15 0.96, 2.34 9.57, 2.56
2011/12 12 0.57, 1.56 8.05, 3.22
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