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

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tiger grouper, Mycteroperca tigris: Matos-Caraballo et al. 2006). Coupled with the slow life historiesof these species (Coleman et al. 1999), conservation objectives are paramount in these extremecases and may be met by NTRs alone. However, since many aggregative spawners are also heavilyfished as juveniles and as adults outside of the spawning season, and when migrating to and fromspawning sites (e.g. Fulton et al. 1999; Claro et al. 2009; Robinson et al. 2011), conservation benefitsare unlikelyto be attained by NTRs alone. In those instances, additional fisheries managementinterventions are requisite. Benefits for fisheries are even less tangible, since any benefits of NTRswill take time to emerge for slow life histories, and large and immediate losses in yield usuallyresult from closing areas of high fish density (Gaines et al. 2010). As with conventional applicationof NTRs for fisheries management, critical knowledge gaps remain regarding the effectiveness ofNTRs for spawning aggregations in supporting socio-economic objectives, (Sale et al.2005; Grüsset al. 2011a).The impetus for this component of the project resulted from experiences of the lead author duringan earlier MASMA-funded study on spawning aggregations in Seychelles (Robinson et al. 2007).That project identified and studied two important aggregation fisheries: a commercial trap fisherytargeting aggregations of the Shoemaker spinefoot rabbitfish (Siganus sutor) and a subsistenceand semi-commercial fishery targeting aggregations of camouflage (Epinephelus polyphekadion)and brown marbled (E. fuscoguttatus) groupers (Robinson et al. 2008b; Robinson et al. 2011).In discussing the findings of this research with key stakeholder groups, a divergence in opinionemerged in terms of the required management response. The environmental and conservationagencies and environmental non-governmental organisations argued that complete protectionof spawning aggregations through the establishment of NTRs was required, whereas fishers andfishing companies argued that aggregations could be fished sustainably and that a conventionalfisheries management approach was required. Attempts to inform the ensuing debate highlighteda critical science question, namely: would closing the spawning aggregations to fishing throughthe use of NTRs be beneficial for conservation (i.e. protection of high levels of spawning stockbiomass, and normalization of the sex ratio of protogynous populations) and fisheries (i.e. byenhancing yield from the non-spawning areas and periods)?The aim of this study was to develop and use a simple model to address concerns regarding thebenefits of spawning aggregation-based NTRs. The specific objectives were to: (1) design a generalmodel that can be applied to a variety of gonochoristic and protogynous fish populations formingtransient spawning aggregations; (2) apply the model to two transient aggregation-forming reef fishpopulations from Seychelles and analyse NTR scenarios for these two populations; and (3) derivegeneral observations on the conservation (spawning stock biomass-per recruit) and fisheries (yieldper-recruit)effects of spawning aggregation-based NTRs.This chapter presents a simplified description of the model attributes and highlights the mainfindings from the study. The full model specifications and detailed results are reported in Grüsset al. (in press). That submission focuses exclusively on scenarios for NTRs sited on spawningaggregations, while in this chapter we also present the detailed results of an additional scenario thatexamined the effects of NTRs protecting the normal residence areas of both juveniles and nonspawningadults.MethodsWe developed a non-spatial, per-recruit model for evaluating the conservation and fisheries effectsof spawning aggregation-based NTRs for gonochoristic populations and protogynous populationswith age-mediated sex change. The model can be run with information that is relatively easy toobtain, namely:• the level of annual fishing effort exerted on fish populations and the fraction of thisannual fishing effort that is directed towards spawning aggregations;114
• estimates (by proxy) of catchability at spawning and non-spawning sites, and• estimates of a limited set of life history parameters.The model is therefore highly flexible and can be widely applied for examining the effects of NTRson spawning aggregations and their fisheries. In this study, we apply the model to populationsof two species that form transient spawning aggregations in Seychelles: the protogynous brownmarbledgrouper (Epinephelus fuscoguttatus) population of a remote atoll (Robinson et al. 2008b)and the gonochoristic shoemaker spinefoot rabbitfish (Siganus sutor) population of the maingranitic islands (Robinson et al. 2011).To evaluate the effectiveness of spawning aggregation-based NTRs, we use two metrics forgonochoristic populations: female spawning stock biomass-per-recruit (female SSBR) and yieldper-recruit(YPR). For protogynous populations, we use an additional metric: sex ratio (SR),defined here as the number of adult females over the number of adult males. Female SSBR isan indicator of reproductive capacity, SR is an indicator of the chances of egg fertilization forprotogynous populations, and YPR is an indicator of fisheries benefits.The age-structured model includes two life history stages for the gonochoristic population: juvenilesand adults, and three life history stages for the protogynous population: juveniles, adult femalesand males. Adults can either be in a spawning or a non-spawning state, and catchability differsbetween spawning sites and normal residence areas. The model incorporates the fact that maleE. fuscoguttatus remain longer than females at spawning sites (Robinson et al. 2008b; Rhodes etal. 2012). Juveniles of both species are considered not to be harvestable at spawning aggregationsites, whereas adults are exposed to fishing mortality at both spawning and non-spawning sites. Weassume that fish recruit to the fishery before or at sexual maturation. Natural mortality is assumedto be the same for adults and juveniles. While sex change in E. fuscoguttatus can occur over a widerange of sizes and ages (Pears et al. 2006), for mathematical simplicity a single mean age at sexchange is used. The model was parameterised for the two study populations according to publishedparameter estimates or observations of the fisheries.The model was run to examine the effects of setting aside either a fraction of or all spawning sitesas NTRs. Fishing mortality with NTRs depends on spawning-site fidelity (faithful or not faithful)and on the fate of the fishing effort that was in reserves before they were closed. Several scenarios forthe fate and redistribution of fishing effort after reserve creation were considered: effort previouslyin reserves disappears; pre-reserve effort is fully redistributed to spawning sites remaining open tofishing after some are protected, and pre-reserve effort is fully redistributed to non-spawning sitesat the time of reserve creation for cases where all spawning sites are closed to fishing.Underlying these scenarios for fishing effort evolution is the assumption that fishers willpreferentially move to other known spawning sites if not all spawning areas are closed to fishing.In this latter case, fishers will only resort to intensifying fishing in non-spawning areas if they haveno other alternative. In total, six scenarios of spawning aggregation-based NTRs were assessedfor both species (NTR Scenarios 1-6; Table 1). In parallel, two scenarios were evaluated where afraction of normal residence areas is set aside as reserves (NTR Scenarios 7-8). Effort previously inreserves disappears for the first of these two scenarios, while pre-reserve effort is fully redistributedto normal residence areas remaining open to fishing at the time of reserve creation for the second(Table 1).ResultsIn this section, the main findings from the model are highlighted. Firstly, we present the fisherieseffects (i.e. effects on YPR) of protecting a fraction or all spawning aggregations. Secondly, theconservation effects (i.e. effects on SSBR and sex ratio) of protecting a fraction of spawningaggregations are provided, and thirdly the conservation effects of protecting all spawningaggregations. Finally, we compare the results of NTRs protecting spawning aggregations with those115
Page 4:
The designation of geographical ent
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Chapter 1: IntroductionJan Robinson
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limited, subsistence levels of expl
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NTRs for spawning aggregations usin
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al. 2003). Verification may include
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a fraction of spawning sites are pr
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Chapter 3: Targeted fishing of the
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verifying spawning aggregations, we
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ecorded from inshore close to the c
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(a)(b)Fig. 3. Spatial patterns ofca
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pooled sizes of the three spawning
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found S. sutor contributed up to 44
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2011b). However, observations of fi
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MethodsTo identify seasonal and lun
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n=199Females GSI (mean ± SE)2.521.
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The estimate of size at maturity in
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This study was designed to verify S
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were selected. Fish selected for ta
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The number of traps increased on th
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Of the 9 tagged fish detected by re
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Fig. 7. Diel patterns ofdetection f
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Spawning aggregation site fidelity
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Chapter 6: Shoemaker spinefoot rabb
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anterior of the anus and below the
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A high percentage (80.8%) of depart
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arrivals and departures at these tw
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are typically applied for reef fish
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(a)(b)(c)Chapter 3, Figure 3. Spati
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(1)(2)(3)(4)(5)(6)Chapter 7, Table
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Chapter 12, Fig. 1 Fraction of fema
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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
Page 108 and 109: A spawning aggregation is said to o
Page 110 and 111: Chapter 11: Evaluation of an indica
Page 112 and 113: Table 1 Aggregation fisheries asses
Page 114 and 115: the lists of Jennings et al. (1999)
Page 116 and 117: with the more vulnerable labrids an
Page 118 and 119: The remaining serranid populations
Page 120 and 121: Spawning aggregation behaviour is c
Page 124 and 125: of protecting the normal residence
Page 126 and 127: • Since grouper males are afforde
Page 128 and 129: Fig. 2 Yield-per-recruit normalized
Page 130 and 131: The approaches identified above are
Page 132 and 133: during full moon periods. Siganus s
Page 134 and 135: model, many parameter estimates are
Page 136 and 137: 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
Page 147 and 148: Sancho G, Petersen CW, Lobel PS (20
Page 149 and 150: Appendix 1. QuestionnaireMASMA SPAW
Page 151 and 152: 8. Spawning aggregation knowledgeUs
Page 153 and 154: Example items KSh Furthest site Clo
Page 155 and 156: Appendix II. Experimental testing o
Page 157 and 158: Clove oil concentrationAt a concent
Page 159 and 160: Appendix III. Application of acoust
Page 161 and 162: 153
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