New directions for research in prawn (shrimp) stock enhancement and the use of models in providing...

Fisheries Research 80 (2006) 91–100

New directions for research in prawn (shrimp) stock enhancementand the use of models in providing directions for research

Neil R. Loneragan ∗, Yimin Ye, Rob A. Kenyon, Mick D.E. HaywoodCSIRO Marine Research, Cleveland Marine Laboratories, P.O. Box 120 Cleveland, Qld. 4163, Australia

Abstract

Despite attempts in many countries, large-scale prawn (shrimp) stock enhancement programmes have only been implemented and continueto operate in Japan (Penaeus japonicus) and China (Penaeus chinensis). In these countries, prawn stock enhancement has been possiblebecause of the capacity to produce large numbers of small individuals for release as a result of aquaculture. While exploring the feasibility andbio-economics of tiger prawn (Penaeus esculentus) stock enhancement in Exmouth Gulf, Australia, a broad framework for stock enhancementresearch was developed. This framework included developing a bio-economic model and risk assessment for all components of a stockenhancement operation, i.e., hatchery, grow-out, harvest–transport–release, population dynamics of released and wild prawns, and monitoringthe fishery. However, predictions from the bio-economic model were made with great uncertainty about the values for post-release mortalityolewwroraC

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f prawns because there were no data from experiments on optimal release strategies. Consequently, data from field studies of growth, andaboratory studies of predation, were used to set values for growth and mortality in Monte-Carlo simulations of the potential success of P.sculentus releases in different habitats. The survival of 2 mm carapace length (CL) prawns to the size at emigration from the nursery habitatas ∼1.9 times higher for individuals associated with seagrass of high (∼100 g m−2) than for those in low (∼10 g m−2) plant biomass. Survivalas 19 times higher for prawns in high biomass seagrass than for those on bare substratum. The differences in survival between habitats were

educed greatly when the releases of much larger prawns (10 mm CL) were simulated. These findings highlight the importance of researchn developing optimal release strategies for prawns in stock enhancement programmes. In particular, the size, habitat, time and density atelease needs to be identified to provide more reliable information for the bio-economic assessments of releasing hatchery-reared juveniles tougment production in stock enhancement programmes.rown Copyright © 2006 Published by Elsevier B.V. All rights reserved.

eywords: Penaeus chinensis; Penaeus esculentus; Penaeus japonicus; Bio-economics; Release strategies; Release habitat

. Introduction

Prawns (=shrimp) in the family Penaeidae are heav-ly fished in tropical to temperate regions throughout theorld. Despite the resilience of their life history strategies,

.g., fast growth, high fecundity, and early maturity (Dallt al., 1990), major declines have been reported in prawnsheries in several countries, e.g., kuruma prawns Penaeus

aponicus in Japan (Fushimi, 1999; Hamasaki and Kitada,006), Penaeus chinensis in China (Liu, 1990; Wang et al.,006), Penaeus duorarum on the Campeche Banks, Mex-

∗ Corresponding author. Present address: Centre for Fish and Fisheriesesearch, Division of Science and Engineering, Murdoch University, WA150, Australia. Tel.: +1 618 9360 6453; fax: +1 618 9360 6303.

E-mail address: [email protected] (N.R. Loneragan).

ico (Ramirez-Rodriguez et al., 2000), Penaeus setiferus inMexico (Gracia, 1991, 1996) and Penaeus esculentus in Aus-tralia (Penn and Caputi, 1986; Wang and Die, 1996; Penn etal., 1997). The decline in P. setiferus and P. esculentus hasbeen attributed to recruitment over-fishing and in ExmouthGulf, Australia, the decline in the P. esculentus fishery wasonly reversed after the fishery was closed for 1 year (Pennand Caputi, 1986). This evidence of recruitment over-fishingin prawn fisheries led to a re-evaluation of the paradigmthat the dynamics of prawn stocks were largely influencedby environmental variation, and that stock–recruitment rela-tionships would not be found for these species. Recently, ameta-analysis of a range of prawn populations concluded thatprawn recruitment was related to the abundance of spawners,and that prawn populations should be managed to maintainsufficient mature adults to yield high recruitment (Ye, 2000).

165-7836/$ – see front matter. Crown Copyright © 2006 Published by Elsevier B.V. All rights reserved.oi:10.1016/j.fishres.2006.03.014

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92 N.R. Loneragan et al. / Fisheries Research 80 (2006) 91–100

Table 1Summary of shrimp stock enhancement initiatives (modified from Bell et al., 2005)

Species (country/countries) Years Location and scaleof release

Scale of releases(M = million, B = billion)

Reference

P. japonicus (Japan) 1964 onwards All Japan 200–300 M Kurata (1981), Kitada (1999),Fushimi (1999)

Seto Inland Sea 100–150 M Tanida et al. (2002), Miyajimaand Toyota (2002)

Hamana Lake 2–11 M

P. chinensis (China) 1980s onwards Bohai Sea 1 B (max = 2.2 B) Liu (1990), Xu et al. (1997),Wang et al. (2006)

Northern Yellow Sea 800 M juveniles (max = 2.2 B)300 M postlarvae (max = 520 M)

Southern Shandong 800 M juveniles (now 300 M)

P. aztecus 1971–1974 Florida 16–52 M Kittaka (1981)P. setiferus, P. duorarum (United

States)3–137 M

P. semisulcatus, P. japonicus,Metapenaeus affinis (Kuwait)

1972–1978 Kuwait 4–25 M Farmer (1981)

P. monodona (Taiwan, Sri Lanka) 1983–1984 Taiwan 6340 Su and Liao (1999)1995–1997 Rekawa Lagoon, Sri Lanka 55,000–70,000 Davenport et al. (1999)

P. esculentus (Australia) 2001–2002 Exmouth Gulf, Australia 250,000 Loneragan et al. (2003, 2004)a Annual releases of P. monodon, P. japonicus and “bear prawn” totaling ∼3 million juveniles carried out between 1985 and 1992 (Liao, 1999).

The high commercial value of prawns, the declines insome fisheries, and the ease of producing prawns in aqua-culture facilities, has prompted much interest in the stockenhancement of prawn fisheries (for a detailed summary ofprawn stock enhancement, see Bell et al., 2005). Varyingscales of prawn stock enhancement, from thousands to bil-lions of released individuals each year, have been documentedin seven countries since the 1960s (Table 1). However, despitethe many attempts at prawn stock enhancement, releasescurrently occur only on a large scale in Japan (Hamasakiand Kitada, 2006) and China (Wang et al., 2006). Someof the details of the prawn stock enhancement programmesin Japan and China are briefly summarised below. Both ofthese countries have large aquaculture industries with thecapacity to produce very large numbers of small prawns forrelease into marine waters (Xu et al., 1997; Fushimi, 1999;Hamasaki and Kitada, 2006; Wang et al., 2006). Until rel-atively recently, research and development for prawn stockenhancement in Japan and China appears to have focussedmainly on increasing the efficiency of producing prawnsfor aquaculture/stock enhancement and hence the number ofprawns available for release (i.e., ‘seed’ prawns, left handside of Fig. 1), rather than stock enhancement as one ofthe options available to fishery managers (see Leber, 2002;Fig. 1).

The approach to prawn stock enhancement in Japan andCetficpt

one component of the necessary research and development(Loneragan et al., 2003, 2004). The other componentsinvolved developing a bio-economic model, determiningthe best areas for release, developing genetic markers andmonitoring and evaluating trends in the fishery. The researchtherefore also took into account management options for thefishery and potential release strategies (i.e., on increasing theefficiency of the stock enhancement operation, right handside of Fig. 1), as well as increasing the efficiency of hatcheryproduction.

This aims of this paper are to: (1) briefly summarisesome of the history of prawn stock enhancement and theassessments of its bio-economic feasibility; (2) describean approach to evaluate the potential influence of releasehabitat on the success of stock enhancement, and (3) identifysome of the important future directions for prawn stockenhancement.

FadiL

hina contrasts with that taken for brown tiger prawn P.sculentus populations in Exmouth Gulf, Australia, wherehere was no existing prawn aquaculture and the prawnshery has been closely managed for >40 years. In thisase, stock enhancement was considered as one of theotential management options for the fishery and increasinghe efficiency of producing juveniles in culture was only

ig. 1. Stock enhancement programmes as a component of a fishery man-gement plan, highlighting the production/stock enhancement efficiencyichotomy, and the components of research and development required toncrease the efficiency of stock enhancement operations (modified fromeber, 2002).

N.R. Loneragan et al. / Fisheries Research 80 (2006) 91–100 93

2. History of prawn stock enhancement

2.1. Large-scale prawn stock enhancement

2.1.1. JapanTrials with the stock enhancement of kuruma prawns P.

japonicus began in the Seto Inland Sea in the mid-1960sfollowing a decline in catches from >3000 t in the 1950s to∼1300 t in 1965. This decline was attributed to environmentaldegradation during the time of rapid economic expansion(Imamura, 1999). The stock enhancement of P. japonicusin Japan started with production and release of 1.6 millionmysis stage larvae in 1963, increasing to 10 million juvenilesin 1965. Since the early 1980s, the total number of juvenileP. japonicus released to enhance stocks throughout Japan hasranged from ∼300 to 500 million juvenile prawns each year,with ∼50% of the numbers being released into the Seto InlandSea (Imamura, 1999, Kitada, 1999) but has declined in recentyears (Hamasaki and Kitada, 2006).

Following the initiation of large-scale releases of P. japon-icus in Japan, catches for the whole of Japan increased to>3000 t by the mid-1980s. However, catches for the whole ofJapan declined again and, in 2002, were at levels similar tothose in the mid-1960s (i.e., ∼1500 t p.a.), before prawn stockenhancement was initiated (Hamasaki and Kitada, 2006).Catches in the Seto Inland Sea, which accounts for abouthajc(Phas2

2

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market economy (Xu et al., 1997; Wang et al., 2006). In oneregion of China, a strategy of releasing prawns at 3–4 mm CLinto earthen ponds before releasing them into the wild wasadopted to reduce production time and minimize the risk ofdisease.

2.2. Assessing the success of large-scale prawn stockenhancement

2.2.1. JapanIn Japan, the early efforts at P. japonicus stock enhance-

ment were evaluated by monitoring changes in catches andlength distributions following releases of juveniles. However,since the application of coded microwire tags and uropodclipping as marking techniques in the mid-1990s (Miyajimaet al., 1999), estimates of recovery rates have been madethrough stratified surveys of the markets for prawns markedmainly by these methods (Table 2; Hamasaki and Kitada,2006). From 40 attempts at stock enhancement of P. japon-icus, involving releases of 17,000–860,000 juvenile prawns,recovery rates equalled or exceeded ∼4% in only 7 cases andwere 2% or lower in 25 of the cases (Hamasaki and Kitada,2006). A simple estimate of the break-even point of stockenhancement, calculated by comparing the costs of produc-tion with the market price of landed prawns, ignoring othercosts, e.g., costs of harvest, transport and release, indicatedto

2

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alf of the P. japonicus catches in Japan, have not declineds markedly as those in other regions. The decline in P.aponicus catches has been paralleled by a decline in theatch of all other species of prawns for the whole of JapanHamasaki and Kitada, 2006). These declines in catches of. japonicus and other commercially important invertebratesave been attributed to loss of the tidal nursery habitatsnd poor water quality, rather than a reduction in spawningtocks leading to poor recruitment (Hamasaki and Kitada,006).

.1.2. ChinaAlthough prawn stock enhancement in China appears to

ave started later than in Japan, the numbers of P. chinensiseing released have been much greater, reaching ∼5 bil-ion prawns in some years (Table 1; Wang et al., 2006).he stock enhancement of P. chinensis in China has reliedn the very large aquaculture industry with double stock-ng of ponds and the release of excess juveniles at a size of

30 mm total length [∼8 mm carapace length (CL)] (Wangt al., 2006). Since the early 1990s, the release strategiesnd number of P. chinensis released in Chinese waters havehanged; fewer smaller prawns (4 mm CL prawns) are noweing released, possibly as a consequence of the outbreaksf disease in the farming operations and the introduction of aree-market economic policy in China. The outbreak of dis-ase seems to have led to a reduction in stocking densitiesn ponds earlier in the production cycle to minimize the riskf its occurrence. In addition, smaller release sizes appear toave been used to reduce production costs in the more open

hat stock enhancement was likely to have been profitable innly five cases.

.2.2. ChinaThe bio-economics of stock enhancement in China has

een evaluated by calculating the ratio of costs to benefits.cost:benefit ratio of 1:5.2 has been estimated for the trans-

lantation of P. chinensis in Hangzhou Bay (Xu et al., 1997)nd a return ratio of 1:7 to 1:10 has been estimated for theaiyangdao and Qinghai fishing grounds (Wang et al., 2006).owever, it is not clear what costs were included in these

alculations and whether the cost:benefit ratio provides anccurate estimate of the real economic returns from stocknhancement.

In general, the recapture rates for P. chinensis in Chinappear to be lower than those of P. japonicus. Xu et al. (1997)stimated that it would require 500,000 juvenile P. chinensiso produce 1 t of catch, compared with about 200,000 juvenile. japonicus, corresponding to recapture rates of 10 and 25%,espectively, assuming that the average size at capture is 20 g.

The recapture rates of released P. chinensis declined fromn average of about 10% in the 1980s to 3% between 1993nd 1996, the period immediately following the outbreakf disease in 1993 (Wang et al., 2006). Release site haseen reported to have an important influence of the recov-ry rates of P. chinensis (Table 2). Releases in estuarine andoastal waters around Bohai Bay were much more success-ul than those in upstream river areas. Releasing prawns inurbid waters with few predators can increase the survivalf released prawns—no prawns were recovered after being


released into clear waters near the mouth of an embayment(Wang et al., 2006). The recovery rates of P. chinensis havebeen estimated from physical tags, catches and catch per uniteffort in areas of transplantation (i.e., where prawns have beenreleased in areas where they are not normally found) and theanalysis of size frequency distributions.

2.3. Other investigations of prawn stock enhancement

Prawn stock enhancement has been attempted at muchsmaller scales and for much shorter durations in a number ofother countries such as the United States, Kuwait, Taiwan,and Australia (Table 1; Bell et al., 2005). In all cases, exceptAustralia, prawn stock enhancement was explored because ofthe ability to produce postlarvae from aquaculture. Accord-ingly, we focus here on the Australian experience.

The approach taken to prawn stock enhancement in Aus-tralia concentrated initially on a feasibility study, and then ondeveloping techniques for the stock enhancement of browntiger prawns P. esculentus in Exmouth Gulf, Western Aus-tralia (Loneragan et al., 2004). This research included devel-oping a framework for the bio-economic evaluation and riskassessment for all components of a stock enhancement oper-ation, i.e., hatchery, grow-out, identifying release sites, pop-ulation dynamics, fishery and monitoring (Fig. 2; Ye et al.,2wp

apP2alrcmi

Fig. 2. Summary of the components in the bio-economic model for evalu-ating the potential for Penaeus esculentus stock enhancement in ExmouthGulf, Western Australia (modified from Ye et al., 2005). PL15 = 15-day oldpostlarvae, W0 = weight at release, Wm = weight at migration.

for the production of these juveniles. The sensitivity analysisshowed that the largest contributor to the overall uncertaintyof the enhanced prawn catch, was the post-release mortality(53.6%), followed by density-dependent mortality (17.0%)(Ye et al., 2005). Male and female growth parameters (L∞ andk) contributed between 4 and 13% to the overall uncertaintyin the forecasts for prawn stock enhancement, while all otherparameters contributed <1% to the variation. These resultssuggested that post-release mortality and density-dependentmortality are the factors most likely to affect the success ofP. esculentus stock enhancement in Exmouth Gulf.

Diver and video observations of the behaviour of prawnsreleased into Exmouth Gulf highlight the importance ofprawn acclimation and appropriate release protocols to max-imise the survival of released animals (Crocos et al., 2003;Bell et al., 2005). For example, prawns grown at high densitiesin raceways had damaged antennae and missing legs but wereable to recover in about seven days after being transferredto low density conditions (Crocos et al., 2003). In addition,when prawns were accidentally released in mid-water, insteadof on the substratum, they took some time to determine thelocation of the substratum and swim towards it, increasing

TS als in China, Japan and Australia (modified from Bell et al., 2005)

S Season Recovery rates (% Reference

P June–JrecruitAugus

P July–A

P Decem

to CL i

005). In this case, increasing the efficiency of productionas only one component of the overall framework for tigerrawn stock enhancement (Figs. 1 and 2).

Prawn stock enhancement has not been carried out oncommercial scale in Australia. However, its commercial

otential has been evaluated using a bio-economic model for. esculentus in Exmouth Gulf. The model estimated that4 million juvenile prawns would be needed to produce andditional catch of 100 t (Ye et al., 2005). This is equiva-ent to a recapture rate of about 17%, assuming a size atecapture of 25 g. The results from this model, based on theurrent available knowledge, found that the probability ofaking a profit was only about 36% and that significant cap-

tal investment of about Aus$ 4 million would be needed

able 2trategies used to release prawns in stock enhancement programmes and tri

pecies Habitat Size/stage at release

enaeus japonicus Saltmarsh Postlarvae

Shallow coastal water 10–30 mm TL(2–8 mm CL)b

enaeus chinensis Direct fromaquaculture ponds

Postlarvae

30 mm TL (7–10 mmCL)

enaeus esculentus Seagrass, one releaseregion

7–12 mm CL(0.5–1.0 g)

a Recovery rates estimated from cohort analysis.b TL: total length; CL: carapace length; approximate conversion from TLc Recovery rates estimated from uropod (tail–fin) clipping.

of release prawns)

uly (no naturalment)

8.4%a Kurata (1981)

t–September 27.6%a Tanida et al. (2002)

18%c Miyajima and Toyota (2002)

ugust 35.6% (13.7–62.9%) Liu (1990)

4.5–10% Wang et al. (2006)

ber Not monitored Loneragan et al. (2003, 2004)

s TL = 4 CL.


their vulnerability to predators. The releases took place dur-ing daylight; the time when P. esculentus would normally beburied. However, once on the seabed, very few of the releasedprawns buried into the substratum, also increasing their vul-nerability to predation. Released prawns did, however, exhibitsome of the appropriate behaviours, i.e., a natural escaperesponse (a sudden ‘flick’ backwards’) when approached byfish predators (Kenyon et al., 1995; Crocos et al., 2003).

3. Evaluating the potential influence of differentrelease habitats on prawn stock enhancement

Experimental releases and simulation studies have beenused to evaluate the influence of site, size, density and timeat release on the survival of animals following their releasefor stock enhancement. Dramatic increases in the successof stock enhancement have followed experimental studies ofrelease strategies for striped mullet Mugil cephalus, with thecontribution of released fish to the subsistence and commer-cial fisheries reaching between 15 and 20% after pilot releasesof 30,000–90,000 fish each year (Leber, 2002).

Despite the long history of prawn stock enhancement, sys-tematic studies to develop optimal release strategies do notappear to have been carried out. In the absence of data fromexperimental releases, simulation studies can provide an indi-cdto

3

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Table 3Mean value (± 1 S.D.) used for growth and mortality in the simulationsof numbers of prawns surviving to emigrate from different shallow waterhabitats (CL = carapace length)

Habitat type Mean (± 1 S.D.) for

Growth (mm CL/week) Mortality (per week)

Bare substratum 0.75 ± 0.15 0.200 ± 0.060Low biomass seagrass 1.00 ± 0.20 0.100 ± 0.030High biomass seagrass 1.50 ± 0.30 0.075 ± 0.023

et al., 1995). Survival in the seagrass with greatest leaf widthand height (Cymodocea, 67%) was over twice the survival inthin, short seagrass (Halodule, 27%) and three times higherthan over bare substratum (11%) (Kenyon et al., 1995). Themortality of juvenile prawns has also been estimated fromfield data and was found to vary as a function of length, withan average weekly total mortality M for individuals associ-ated with seagrass of 0.075 per week (Wang and Haywood,1999). This value was chosen as the mean weekly total mor-tality in high biomass seagrass, with values of 0.10 for lowbiomass seagrass and 0.20 for bare substratum (Table 3). Themean weekly mortality was also assumed to have a normaldistribution, with a standard deviation that was 30% of themean (Table 3).

The mean and standard deviations for growth and mor-tality were used as parameters to simulate the numbers andweight of prawns growing to the size at emigration in highbiomass seagrass, low biomass seagrass and bare substra-tum. One thousand individuals were seeded in each habitatand 10,000 runs were completed in Excel using the CrystalBall add-in (Werckmand et al., 1998), assuming that juve-nile prawns migrate from the shallows at a size of 15 mm CL(∼60 mm total length) at a latitude similar to Exmouth Gulf(O’Brien, 1994). This size is likely to vary with latitude asfew P. esculentus and P. semisulcatus exceed 10 mm CL inmore tropical seagrass beds (Loneragan et al., 1994; Vance etaoos

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f

ation of how survival is influenced by factors such as site,ensity, size and time at release. Here, we use ecological datao investigate the potential influence of site and size at releasen the survival of released prawns.

.1. Growth and survival of P. esculentus

Experimental studies of the growth of P. semisulcatus,closely related species to P. esculentus, in small (0.9 m2)

nclosures in two estuarine seagrass beds found that growthas about twice as fast in beds with a high (70 g m−2) rather

han a low (7 g m−2) plant biomass (Loneragan et al., 2001).he mean growth rate at the lowest initial stocking densityf four prawns per enclosure was ∼1.3 mm CL per weekompared with a value of ∼0.6 mm CL per week in the lowiomass bed. Detailed studies of the recruitment of P. esculen-us and P. semisulcatus to seagrass beds in northern Australiaave shown that natural densities of juvenile prawns rarelyxceed 2 prawns m−2 (Loneragan et al., 1994, 1998; Vance etl., 1996). From these studies, the following values of averagerowth were chosen for Monte-Carlo simulations of prawnurvival in three different habitats: 1.5 mm CL per weekor high biomass seagrass (∼100 g m−2 of above-ground-iomass), 1.0 mm CL per week for low biomass seagrass∼10 g m−2) and 0.75 mm per week for bare substratumTable 3). We assumed that the growth parameter is normallyistributed and that the standard deviation is ∼20% of meanrowth (Table 3).

Laboratory studies of fish predation on juvenile P. esculen-us found that survival varied greatly with the habitat (Kenyon

l., 1996). Two scenarios were simulated: a release of prawnsf 2 mm CL (about the size at first settlement), and at a sizef 10 mm CL (∼1 g wet weight), i.e., the modelled optimalize at release for P. esculentus (Ye et al., 2005).

The number surviving in the population at time t (Nt) inach habitat was modelled by:

t = N0e−Mt (1)

here M is the total weekly mortality rate, t the time in weeksnd N0 is the initial number of prawns. We did not includeterm for size-dependent mortality in these simulations but

he effects of size on mortality are discussed below.In this approach, we have assumed that growth and

ortality are independent parameters and have not includedny density-dependent effects in the simulations. We havelso assumed that the size of emigration is the same for allabitats.

The mean carapace length in the population was estimatedor each week and the mean wet weight (WWt in grams) in


the population was calculated from the carapace length (CLin mm), using the relationship:

log10 (WWt) = −3.46 + 3.43 log10(CL)

The total biomass of prawns surviving was then calculatedfor each week until the time at emigration.

3.2. Results of simulation studies

From the initial population of 1000 prawns, in highbiomass seagrass, the 2 mm CL prawns took 9 weeks toreach the size at emigration, when 510 prawns remainedalive, weighing about 2.2 kg wet weight (Fig. 3a and b). Inlow biomass seagrass, the time to emigration was about 4weeks longer than in high biomass seagrass, resulting in fewerprawns (272) and a lower total biomass (1.0 kg) survivinguntil this size (Fig. 3a and b). Over the bare substratum, thetime to emigration was much longer (18 weeks) than in eitherof the seagrass habitats and only 27 prawns were estimated toreach the size at emigration. From the Monte-Carlo simula-tions, many of the values for the percent survival to the size atemigration in high biomass seagrass were found in the rangeof 40–60%, which reduced to 18–33% in low biomass sea-grass (Fig. 4a and b). The distribution of percentage survivalto the size at emigration over bare substratum was highlyskewed, with most values less than 5%, but a few high values(

ts

surviving to the size at emigration was 74 and 24% in thesehabitats, respectively (Fig. 3c and d). The differences in timeto emigration and percent survival between high and lowbiomass seagrass were much lower than in the simulationsfor 2 mm CL prawns (cf. Fig. 3c and d, and a and b). Thedistribution of the percentage survival over bare substratumfor the 10 mm CL prawns (Fig. 4f) was less skewed than thatfor the 2 mm CL release size, and many of the simulationsgave estimates of between 10 and 30% survival.

It should be noted that a constant natural mortality wasused in all of our simulations. Natural mortality usuallyvaries with size and density. Ye et al. (2005) used differentapproaches to incorporate estimates of the influence of sizeand density on mortality: natural mortality rate was mod-elled as a function of size and the influence of density onmortality was estimated from the stock–recruitment relation-ship of the natural prawn population. The latter applies onlyto situations where the natural and released stocks live inthe same habitat. In this study, we focussed on the impactof different habitats on survival. It is not likely that a sin-gle stock–recruitment relationship would apply to the threedifferent types of habitats examined in this paper. A furthercomplication comes from the fact that the size–mortality rela-tionship depends very much on the density-dependent effect.To single out the effect of habitat on survival in a simple way,we used a constant natural morality. What is the impact oftn

M

F igrationM

Fig. 4c).When a release at a size of 10 mm CL was simulated,

he time to emigration ranged from 4 weeks in high biomasseagrass to 7 weeks over bare substratum. The proportion

ig. 3. The mean numbers of Penaeus esculentus surviving to the size at em
onte-Carlo simulations of release sizes of 2 mm carapace length (CL) (a–c) and 1
his constant assumption on our results? The size dependentatural mortality can be described as:

t = aL−bt (2)

in high biomass seagrass, low biomass seagrass and bare substratum from
0 mm CL (d–f).


Fig. 4. The probability and frequency of Penaeus esculentus survival (%) to the size at emigration from 10,000 runs of Monte-Carlo simulations for releasesizes of 2 mm carapace length (CL) (a–c) and 10 mm CL (d–f). Note that axes are not on the same scale for each figure.

(following Lorenzen, 2000; Ye et al., 2005), where Lt is thesize at time t; a and b are parameters defining how mortalitychanges with size. Substituting Eq. (2) into (1) gives

Nt = N0e−at/Lbt (3)

It is clear that the smaller the Lt, the faster the decline inNt. Prawns grow faster in high seagrass biomass than lowbiomass seagrass or over bare substratum (Table 3) and con-sequently have a larger size than their counterparts in otherhabitats at a specific time. Prawns of a larger size have alower natural mortality (Eq. (2)) and hence a larger popu-lation size (Eq. (3)). Therefore, the assumption of constantnatural mortality underestimates the difference in impact ofhabitat on survival (Fig. 3). Similarly, the differences in sur-vival between the 2 and 10 mm release sizes would also beunderestimated in our simulations.

The results from these simulations highlight the impor-tance of release habitat for the survival of P. esculentus tothe size at emigration. This effect is due to a combination oflower mortality and faster growth resulting in a reduction inthe time needed to reach the size at emigration in the highbiomass seagrass than in the low biomass seagrass and thebare substratum. The highly variable recovery rates for P.japonicus and P. chinensis from stock enhancement suggestthat release site and habitat are likely to be important fac-tsm

1997), Pacific threadfin Polydactylus sexfilis (Leber et al.,1998), abalone (Schiel, 1993) and sandfish Holothuria scabra(S. Purcell, personnel communications) have also high-lighted the significance of release sites for successful stockenhancement—mortality is greater and growth is slower atsome sites than at others. For example, striped mullet releasedin an embayment did not contribute to the subsistence orcommercial fisheries around Hawaii, whereas those releasedin streams feeding into coastal bays made significant con-tributions (Leber et al., 1997). Similarly, no released Pacificthreadfin released at one site were recovered and experimen-tal releases were halted at this site (Leber et al., 1998).

The simulations of P. esculentus releases in the currentstudy also show the influence of release size on the successof stock enhancement—differences in survival between thehabitats were much less marked for a release size of 10 mmCL than 2 mm CL due to the much shorter time needed for thelarger prawns to grow to the size at emigration. The impor-tance of size at release was also identified by comparingsimulations of the number of released prawns of 1 and 0.5 grequired to produce a 100 t increase in catch of P. esculentusin Exmouth Gulf (Ye et al., 2005). The 0.5 g size at releaserequired the production of an additional 5 million juvenileprawns, and had about half the chance of being profitablecompared with releases of 1 g prawns. This was attributed tothe longer exposure to natural mortality in the release envi-rnp

ors influencing the success of stock enhancement for thesepecies. Experimental releases of other species such as stripedullet Mugil cephalus (Leber and Arce, 1996; Leber et al.,

onment and the larger number of prawns needed, which wereot offset by the shorter production time and lower costs ofroduction.


Density-dependent effects were not considered in the cur-rent study because the results from enclosure experimentsfound growth rates were less influenced by density in highthan low biomass seagrass (Loneragan et al., 2001). How-ever, density-dependent effects are likely to accentuate anydifferences in survival due to release habitats. In a simulationstudy of the optimal release strategies for summer flounderParalichthys dentatus the influence of size, time and densityat release were investigated (Kellison and Eggleston, 2004).The inclusion of terms for density dependence (incorporatingType II and III predator response curves) affected the numberof survivors but not the recommended optimal release strate-gies, compared with simulations that did not include densitydependence (Kellison and Eggleston, 2004).

4. Conclusions

This brief overview of the current knowledge of prawnstock enhancement from continuing programmes in Japanand China, and the results of simulations for P. esculentus inAustralia, show the importance of systematic studies to iden-tify optimal release strategies for hatchery-reared juveniles.It has also highlighted the significance of the effects of siteand size at release on the survival of released prawns. Realis-tic estimates of density-dependent effects are likely to comeod

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release using a randomised block design with three densitiesat release (0.5, 3 and 6 prawns m−2), three replicates and twotimes.

The information from the experimental releases suggestedabove should greatly reduce the uncertainty in estimates ofmortality and density-dependent effects in the nursery habi-tats, and potentially in the fishery. It would also allow a muchmore accurate evaluation of the bio-economic viability ofstock enhancement operations. In addition to research onrelease strategies, research on maximising the health and fit-ness of released prawns prior to release would also increasethe probability of success.

Acknowledgements

We thank the Steering Committee of the Exmouth GulfStock Enhancement Project—George Kailis, James Penn,Ian Poiner and Peter Rothlisberg, and the stock enhancementproject team members for constructive discussions during theproject. Part of the research in Australia reported here wasfunded by the Fisheries Research and Development Corpo-ration of Australia (FRDC 1998/222, 1999/222). The con-tributions of Ken Leber as an independent reviewer of thisproject were invaluable in developing ideas for further direc-tciA

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nly through experimental investigations of the influence ofensity at release on survival.

Research on optimising release strategies requires the usef a marker to follow the fate of released prawns. Uropodlipping and coded microwire tags have been successfullysed as markers for P. japonicus in Japan (Hamasaki anditada, 2006) and might be applied to other species. It is

ikely that with some further development, microsatelliteoci could also be used as a marker to evaluate the suc-ess of stock enhancement for P. esculentus (Bravington andard, 2004). However, greater numbers of microsatellite

oci have been identified for P. japonicus than P. esculen-us (see Moore et al., 1999; Rothlisberg et al., 1999) andhey could therefore provide the basis for a genetic markero be used in evaluating P. japonicus stock enhancement inapan.

Experimental releases have improved recapture rates forome fish species and similar research is now needed to opti-ise the survival of released prawns. Such releases could

e carried out in a randomised block design as has beenone for striped mullet and Pacific threadfin (Leber et al.,997, 1998). For P. esculentus in Exmouth Gulf, an initialeries of release experiments has been designed to focus onize at release, holding the total biomass at release constantLoneragan et al., 2003). Three replicates (in different loca-ions) of three sizes (e.g., 0.3, 1.0 and 2.0 g, or ≈ 7, 10 and2.5 mm CL, ≈ 28, 40 and 50 mm body length) were envis-ged for release at two times of year, a design that requires aark capable of identifying 18 codes (9 in each season). Sim-

lar experiments have also been designed to test the density at

ions for stock enhancement. Greg Skilleter provided helpfulomments on the manuscript. We thank Johann Bell for thenvitation to present this paper, and the participants at the 7thsian Fisheries Forum for lively discussions.

eferences

ell, J.D., Rothlisberg, P.C., Munro, J.L., Loneragan, N.R., Nash, W.J.,Ward, R.D., Andrew, N.L., 2005. Restocking and stock enhance-ment of marine invertebrate fisheries. Adv. Mar. Biol. 49, 1–370.

ravington, M.V., Ward, R.D., 2004. Microsatellite DNA markers: eval-uating their potential for estimating proportions of wild-born andhatchery-reared offspring in an stock enhancement programme. Mol.Ecol. 13, 1287–1297.

rocos, P., Arnold, S., Sellars, M., Burford, M., Barnard, R., McCulloch,R., 2003. Technology development for the high density productionof juvenile Penaeus esculentus. In: Loneragan, N.R., Kenyon, R.A.,Crocos, P.J., et al. (Eds.), Developing techniques for enhancing prawnfisheries, with a focus on brown tiger prawns (Penaeus esculentus) inExmouth Gulf. CSIRO Marine Research, Australia, ISBN 1 87699637 4, p. 281.

all, W., Hill, B.J., Rothlisberg, P.C., Staples, D.J., 1990. The biology ofthe penaeidae. Adv. Mar. Biol. 27, 1–489.

avenport, J., Ekaratne, S.U.K., Walgama, S.A., Lee, D., Hills, J.M.,1999. Successful stock enhancement of a lagoon prawn fishery atRekawa, Sri Lanka using cultured post-larvae of penaeid shrimp.Aquaculture 180, 65–78.

armer, A.D., 1981. Historical review of the Kuwait shrimp cultureproject. Kuwait Bull. Mar. Sci. 2, 3–9.

ushimi, H., 1999. How to Detect the Effect in Releasing Operation ofHatchery Raised Kuruma Prawn Postlarvae?—Case Study of the Oper-ation in the Hamana Lake, vol. 62. Bulletin of the Tohoku NationalFisheries Research Institute, pp. 1–12.


Gracia, A., 1991. Spawning stock–recruitment relationships of whiteshrimp in the southwestern Gulf of Mexico. Trans. Am. Fish. Soc.120, 519–527.

Gracia, A., 1996. White shrimp (Penaeus setiferus) recruitment overfish-ing. Mar. Freshwater Res. 47, 59–65.

Hamasaki, K., Kitada, S., 2006. A review of kuruma prawn Penaeusjaponicus stock enhancement programme in Japan. Fish. Res. 80,80–90.

Imamura, K., 1999. The organization and development of sea farmingin Japan. In: Howell, B.R., Moskness, E., Svasand, T. (Eds.), StockEnhancement and Sea Ranching. Blackwell Science, Fishing NewsBooks, Oxford, UK, pp. 91–102.

Kellison, G.T., Eggleston, D.B., 2004. Coupling ecology and economy:modeling optimal release scenarios for summer flounder (Paralichthysdentatus) stock enhancement. Fish. Bull. 102, 78–93.

Kenyon, R.A., Loneragan, N.R., Hughes, J., 1995. Habitat type and lightaffect sheltering behaviour of juvenile tiger prawns (Penaeus esculen-tus Haswell) and success rates of their fish predators. J. Exp. Mar.Biol. Ecol. 192, 87–105.

Kitada, S., 1999. Effectiveness of Japan’s stock enhancement pro-grammes: current perspectives. In: Howell, B.R., Moskness, E.,Svasand, T. (Eds.), Stock Enhancement and Sea Ranching. BlackwellScience, Fishing News Books, Oxford, UK, pp. 103–131.

Kittaka, J., 1981. Large scale production of shrimp for releasing in Japanand in the United States and the results of the releasing programmeat Panama City, Florida. Kuwait Bull. Mar. Sci. 2, 149–163 (Interna-tional Shrimp Releasing, Marking and Recruitment Workshop, Kuwait1978).

Kurata, H., 1981. Shrimp fry releasing techniques in Japan, with specialreference to the artificial tideland. Kuwait Bull. Mar. Sci. 2, 117–147(International Shrimp Releasing, Marking and Recruitment Workshop,

L

L

L

L

L

L

L

L

L

L

ating the potential for stock enhancement of brown tiger prawns(Penaeus esculentus Haswell) in Exmouth Gulf, Western Australia.In: Leber, K.M., Kitada, S., Blankenship, H.L., Svasand, T. (Eds.),Stock enhancement and Sea Ranching: Developments, Pitfalls andOpportunities, second ed. Blackwell Publishing, Oxford, pp. 444–464(Chapter 32).

Loneragan, N.R., Kenyon, R., Crocos, P., Ward, B., Lehnert, S., Hay-wood, M., Arnold, S., Barnard, R., Bravington, M., Burford, M.,Caputi, N., Kangas, M., McCulloch, R., Penn, J., Sellars, M., Man-son, F., Harch, B., Ye, Y., Toscas, P., Grewe, P., 2003. DevelopingTechniques for Enhancing Prawn Fisheries, with a Focus on BrownTiger Prawn (Penaeus esculentus) in Exmouth Gulf. CSIRO MarineResearch, Australia, ISBN 1 876996 374, 281 pp.

Lorenzen, K., 2000. Allometry of natural mortality as a basis for assessingoptimal release size in fish-stocking programmes. Can. J. Fish. Aquat.Sci. 57, 2374–2381.

Miyajima, T., Toyota, K., 2002. Development of marking technique bytail-cutting in Kuruma prawn Penaeus japonicus and the application toestimate recapture rate. In: Abstract for Paper in Second InternationalSymposium on Stock enhancement and Sea Ranching, Kobe, Japan,28th January to 1st February 2002.

Miyajima, T., Hamanaka, Y., Toyota, K., 1999. A marking method forKuruma prawn Penaeus japonicus. Fish. Res. 65, 31–35.

Moore, S.S., Whan, V., Davis, G.P., Byrne, K., Hetzel, D.J.S., Preston,N., 1999. The development and application of genetic markers for theKuruma prawn Penaeus japonicus. Aquaculture 17, 19–32.

O’Brien, C.J., 1994. Population dynamics of juvenile tiger prawnsPenaeus esculentus in south Queensland, Australia. Mar. Biol. 104,247–256.

Penn, J.W., Caputi, N., 1986. Spawning stock–recruitment relationshipsand environmental influences on the tiger prawn (Penaeus esculentus)

P

R

R

S

S

T

V

W

W

Kuwait 1978).eber, K.M., 2002. Advances in marine stock enhancement: shifting

emphasis to theory and accountability. In: Responsible Marine Aqua-culture. CAB International, pp. 79–90.

eber, K.M., Arce, S.M., 1996. Stock enhancement in a commercial mul-let, Mugil cephalus L., fishery in Hawaii. Fish. Man. Ecol. 3, 261–278.

eber, K.M., Brennan, N.P., Arce, S.M., 1998. Recruitment patterns ofcultured juvenile pacific threadfin, Polydactylus sexfilis (Polynemidae),released along sandy marine shores in Hawaii. Bull. Mar. Sci. 62,389–408.

eber, K.M., Blankenship, H.L., Arce, S.M., Brennan, N.P., 1997. Influ-ence of release season on size-dependent survival of cultured stripedmullet, Mugil cephalus, in a Hawaiian estuary. Fish. Bull. 95,267–279.

iao, I.-C., 1999. How can stock enhancement and sea ranching helpsustain and increase coastal fisheries. In: Howell, B.R., Moskness,E., Svasand, T. (Eds.), Stock Enhancement and Sea Ranching. FirstInternational Symposium on Stock enhancement and Sea Ranching.Bergen, Norway/Blackwell Science, Oxford, pp. 132–149 (Chapter 9).

iu, J.Y., 1990. Resource stock enhancement of Chinese shrimp, Penaeusorientalis. Bull. Mar. Sci. 47, 124–133.

oneragan, N.R., Kenyon, R.A., Haywood, M.D.E., Staples, D.J., 1994.Population dynamics of juvenile tiger prawns in seagrass habitatsof the north-western Gulf of Carpentaria, Australia. Mar. Biol. 119,133–143.

oneragan, N.R., Kenyon, R.A., Staples, D.J., Poiner, I.R., Conacher,C.A., 1998. The influence of seagrass type on the distribution andabundance of postlarval and juvenile tiger prawns in the western Gulfof Carpentaria, Australia. J. Exp. Mar. Biol. Ecol. 228, 175–196.

oneragan, N.R., Heales, D.S., Haywood, M.D.E., Kenyon, R.A., Pen-drey, R.C., Vance, D.J., 2001. Estimating the carrying capacity ofseagrass for juvenile tiger prawns (Penaeus semisulcatus): enclosureexperiments in high and low biomass seagrass beds. Mar. Biol. 139,343–354.

oneragan, N.R., Crocos, P.J., Barnard, R.M., McCulloch, R.R., Penn,J.W., Ward, R.D., Rothlisberg, P.C., 2004. An approach to evalu-

fishery in Exmouth Gulf, Western Australia. Aust. J. Mar. FreshwaterRes. 37, 491–505.

enn, J.W., Watson, R., Caputi, N., Hall, N., 1997. Protecting vulnera-ble stocks in multi-species prawn fisheries. In: Hancock, D., Smith,D., Grant, A., Beumer, J. (Eds.), Developing and Sustaining WorldFisheries Resources: the State of Science and Management, SecondWorld Fisheries Congress. CSIRO, pp. 122–129.

amirez-Rodriguez, M., Chavez, E.A., Arreguin-Sanchez, F., 2000. Per-spective of the pink shrimp (Farfantepenaeus duorarum Burkenroad)fishery of Campeche Bank, Mexico. Ciencias Marinas 26, 97–112.

othlisberg, P.C., Preston, N.P., Loneragan, N.R., Die, D.J., Poiner, I.R.,1999. Approaches to reseeding penaeid prawns. In: Howell, B.R.,Moskness, E., Svasand, T. (Eds.), Stock Enhancement and Sea Ranch-ing. Blackwell Science, Oxford, pp. 365–378.

chiel, D.R., 1993. Experimental evaluation of commercial-scale stockenhancement of abalone Haliotis iris populations in New Zealand.Mar. Ecol. Prog. Ser. 97, 167–181.

u, M.S., Liao, I.-C., 1999. Research and development of prawn stockenhancement in Taiwan. In: Howell, B.R., Moskness, E., Svasand,T. (Eds.), Stock Enhancement and Sea Ranching. Blackwell Science,Oxford, pp. 379–392.

anida, K., Ikewaki, Y., Aoyama, E., Okuyama, Y., Nozaka, M., Fuji-warra, M., 2002. Investigation of stocking effectiveness for kurumaprawn (Penaeus japonicus) in the eastern Seto Inland Sea. In: Bookof Abstracts, Second International Symposium on Stock enhancementand Sea Ranching, Kobe, Japan 28th January to 1st February 2002.

ance, D.J., Haywood, M.D.E., Heales, D.S., Staples, D.J., 1996. Sea-sonal and annual variation in abundance of postlarval and juvenilegrooved tiger prawns Penaeus semisulcatus and environmental varia-tion in the Embley River, Australia: a six year study. Mar. Ecol. Prog.Ser. 135, 43–55.

ang, Q., Zhuang, Z., Deng, J., Ye, Y., 2006. Stock enhancement andtransplantation of marine shrimp Penaeus chinensis in China. Fish.Res. 80, 67–79.

ang, Y.-G., Die, D., 1996. Stock–recruitment relationships of thetiger prawns (Penaeus esculentus and Penaeus semisulcatus) in the


Australian Northern Prawn Fishery. Mar. Freshwater Res. 47, 87–95.

Wang, Y.-G., Haywood, M.D.E., 1999. Size-dependent natural mortal-ity of juvenile banana prawns Penaeus merguiensis in the Gulf ofCarpentaria, Australia. Mar. Freshwater Res. 50, 313–317.

Werckmand, C., Hardy, T., Wainwright, E., 1998. Crystal Ball User Man-ual. Decisioneering, Colorado.

Xu, J., Xia, M., Ning, X., Mathews, C.P., 1997. Stocking, stockenhancement, and mariculture of Penaeus orientalis and other species

in Shanghai and Zhejiang Provinces, China. Mar. Fish. Rev. 59,8–14.

Ye, Y., 2000. Is recruitment related to spawning stock in penaeid shrimpfisheries? ICES J. Mar. Sci. 57, 1103–1109.

Ye, Y., Loneragan, N.R., Die, D.J., Watson, R.A., Harch, B., 2005.Bioeconomic modelling and risk assessment of tiger prawn (Penaeusesculentus) stock enhancement in Exmouth Gulf, Australia. Fish. Res.73, 231–249.

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