WIOMSA-CORDIO spawning book Full Doc 10 oct 13.pdf

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Chapter 6: Shoemaker spinefoot rabbitfish (Siganussutor) spawning aggregations in Seychelles: temporaldynamics, residency times and site fidelityJude Bijoux, Jan Robinson, Laurent Dagorn and Gregory BerkeIntroductionThe Shoemaker spinefoot rabbitfish (Siganus sutor) is endemic to the southwest Indian Ocean(Woodland 1990) and is a commercially important target species in much of the region (Grandcourtand Cesar 2002; Kaunda-Arara et al. 2003). Siganus sutor leave their home range during thespawning season and migrate to form transient spawning aggregations (Robinson et al. 2011). InSeychelles, the locations of several S. sutor spawning aggregation sites are known to fishers and havebeen targeted since the early 1900s (Hornell 1927; Robinson et al. 2004).A small percentage (ca. 15%) of the annual catch of S. sutor in Seychelles is taken at spawningaggregations and current trends in yield indicate that siganid resources are being fished withinsustainable limits (Robinson et al. 2011). However, a precautionary approach has been recommendedas part of an ongoing co-management initiative for this fishery, including consideration of gearbasedcontrols and capacity/effort limitations (Robinson et al. 2011). Co-management plans alsoneed to incorporate the fact that fishers on Praslin Island exhibit informal resource partitioning intheir exploitation of S. sutor aggregations, with fishers generally exploiting aggregations that formclosest to their district of residence. In an emerging management context that may involve inputcontrols and technical measures applied spatially and temporally, a basic understanding of spawningaggregation dynamics is required. Spawning aggregation parameters, such as residency time andsite fidelity, are also important to the application of models that aim to examine the effects of notakereserves and other management measures for spawning aggregation-based fisheries (Chapter12). Spawning aggregation site fidelity is a critical parameter if resource partitioning is to serve as abasis for co-management arrangements.In this study we applied passive acoustic telemetry to provide information on key spawningaggregation parameters. The technology enabled detection of tagged fish at spawning sitesinstrumented with acoustic receivers over a 3-month period. These data were used to determinethe lunar and diel timing of arrivals and departures of individuals at spawning sites, spawning siteresidency times and site fidelity.Materials and MethodsStudy area and receiver arrayAn array of eighteen Vemco VR2 and VR2W acoustic receivers (Amirix Systems, Inc., HalifaxNova Scotia) was deployed at three known S. sutor spawning aggregation sites off the west coastof Praslin Island, Seychelles (Fig. 1). The acoustic receivers were installed between 15 and 19October 2010 and retrieved between 16 and 20 April 2011, giving a 6 month deployment acrossa large portion of the known spawning season of September to June (Robinson et al. 2011). Sixreceivers were deployed at each of the three spawning aggregation sites of Paté Polite, Paté Désiréand Paté Dividi, hereafter called Polite Désiré and Dividi. The spawning sites had similar physicalcharacteristics in that they were all fully submerged granite patch reefs surrounded by sandy areas ata base of about 20 m. The minimum depth was about 15 m. Receivers were secured to the bottomon concrete blocks (+40 kg), which had been strategically deployed on and around the patch reefsto provide maximum area coverage. Tag signal detection was 70% at 25 m but declined to nil at50 m and beyond.46
Fig. 1. The location of the study sites off the West coast of Praslin Island, Seychelles. The black dots on the 3 lowerfigures shows the location of the acoustic receivers and the circle around each dot is the 25 m reception range of thereceivers. The dotted lines shows the location of transects used in the underwater visual censusTaggingTagging took place in two periods at the spawning aggregation sites: 20-22 October 2010 and19-21 January 2011. Since battery life was approximately 3 months and given that tagging wasconducted in two periods at the start and middle of the spawning season, the study essentiallycomprised two acoustic monitoring periods (period 1: October 2010-January 2011; period 2:January-April 2011). During monitoring period 1, 10 fish were tagged and released at the Politefish spawning aggregation (FSA) site and 9 at the Désiré FSA site. During monitoring period 2,11 fish were tagged and released at the Polite FSA and 9 at the Dividi FSA. Tagged fish measuredbetween 22.6 and 29.7 cm fork length and were considered sexually mature, based on the reportedsize at first maturity for this population (Robinson et al. 2011).Fish were caught by local fishermen using traditional bamboo traps, following a 1-2 hour soaktime. To reduce barotrauma, traps were hauled slowly to the surface, where fish were immediatelytransferred to a holding tank. Fish were then transported to an aerated holding tank on a largership, where they were allowed to acclimatize for at least 30 minutes prior to tagging. Fish wereanaesthetized by placing them in a continuously aerated 30-l container filled with a 30 mg l -1seawater/benzocaine solution. Opercula and fin movements were monitored and recorded. After5 minutes fish were removed, measured and double tagged using uniquely numbered T-bar tags(Floy Tag and Mfg, Inc., Seattle, WA) inserted at the 4th dorsal pterygiophore. Fish were thentransferred to a small continuously aerated aquarium and placed dorso-ventrally to enable continualsubmergence of the gills. A V8-4H-S256 (69 kHz, 110-250 sec delay, 93 day battery life, 2 g inair, < 1% weight of smallest tagged fish) acoustic tag (Amirix Systems, Inc., Nova Scotia, Canada),sterilized in absolute ethanol, was then inserted in the body cavity through a small incision 2 cm47
Page 4: The designation of geographical ent
Page 9: Chapter 1: IntroductionJan Robinson
Page 12 and 13: limited, subsistence levels of expl
Page 14: NTRs for spawning aggregations usin
Page 17 and 18: al. 2003). Verification may include
Page 19 and 20: a fraction of spawning sites are pr
Page 21 and 22: Chapter 3: Targeted fishing of the
Page 23 and 24: verifying spawning aggregations, we
Page 25 and 26: ecorded from inshore close to the c
Page 27 and 28: (a)(b)Fig. 3. Spatial patterns ofca
Page 30 and 31: pooled sizes of the three spawning
Page 32 and 33: found S. sutor contributed up to 44
Page 34 and 35: 2011b). However, observations of fi
Page 36 and 37: MethodsTo identify seasonal and lun
Page 38 and 39: n=199Females GSI (mean ± SE)2.521.
Page 40 and 41: The estimate of size at maturity in
Page 42 and 43: This study was designed to verify S
Page 44 and 45: were selected. Fish selected for ta
Page 46 and 47: The number of traps increased on th
Page 48 and 49: Of the 9 tagged fish detected by re
Page 50 and 51: Fig. 7. Diel patterns ofdetection f
Page 52 and 53: Spawning aggregation site fidelity
Page 56 and 57: anterior of the anus and below the
Page 58 and 59: A high percentage (80.8%) of depart
Page 60 and 61: arrivals and departures at these tw
Page 62 and 63: are typically applied for reef fish
Page 64 and 65: (a)(b)(c)Chapter 3, Figure 3. Spati
Page 66 and 67: (1)(2)(3)(4)(5)(6)Chapter 7, Table
Page 68 and 69: Chapter 12, Fig. 1 Fraction of fema
Page 70 and 71: Plates 8. Selected photographs from
Page 72 and 73: MethodsStudy sitesThe study area wa
Page 74 and 75: which shelved gently ( ca. 25 o ) t
Page 76 and 77: Fig. 4. Lunar periodicity in number
Page 78 and 79: Behaviour and appearanceDescription
Page 80 and 81: eported aggregations forming betwee
Page 82 and 83: The sizes of E. fuscoguttatus aggre
Page 84 and 85: Materials and methodsStudy area and
Page 86 and 87: TL. All fish tagged were considered
Page 88 and 89: Lunar timing of arrivals and depart
Page 90 and 91: Fig. 8. The presence and absence of
Page 92 and 93: aggregation fishing. This critical
Page 94 and 95: Chapter 9: Persistence of grouper (
Page 96 and 97: ResultsBetween 2003 and 2006, the c
Page 98 and 99: Fig. 2. Mean (± standard error, SE
Page 100 and 101: A few species (e.g. Epinephelus gut
Page 102 and 103: (a)(b)Fig. 1. Map of (a) study site
Page 104 and 105:
Fig. 2. Number of E. lanceolatus ob
Page 106 and 107:
was having any impact on the popula
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A spawning aggregation is said to o
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Chapter 11: Evaluation of an indica
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Table 1 Aggregation fisheries asses
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the lists of Jennings et al. (1999)
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with the more vulnerable labrids an
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The remaining serranid populations
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Spawning aggregation behaviour is c
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tiger grouper, Mycteroperca tigris:
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of protecting the normal residence
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• Since grouper males are afforde
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Fig. 2 Yield-per-recruit normalized
Page 130 and 131:
The approaches identified above are
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during full moon periods. Siganus s
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model, many parameter estimates are
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ReferencesAbunge C (2011) Managing
Page 138 and 139:
Cox DR (1972) Regression models and
Page 140 and 141:
Grüss A, Kaplan DM, Hart DR (2011b
Page 142 and 143:
Kaunda-Arara B, Rose GA (2004a) Eff
Page 144:
Newcomer RT, Taylor DH, Guttman SI
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Sancho G, Petersen CW, Lobel PS (20
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Appendix 1. QuestionnaireMASMA SPAW
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8. Spawning aggregation knowledgeUs
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Example items KSh Furthest site Clo
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Appendix II. Experimental testing o
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Clove oil concentrationAt a concent
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Appendix III. Application of acoust
Page 161 and 162:
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