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Investigating the translocation and seeding of wild Haliotis mariae wood, 1828, in the Sultanate of Oman.


The annual wild abalone fishery along the Dhofar coast has formed part of Omani fishing culture for decades. Fishermen from communities between Ras Mirbat in the west, through Sadah, Hadbin, Hassik, and Ras Sharbithat in the east, use the resource as part of a multispecies fishery, harvesting other species outside the abalone season (Sanders 1982, Al Hafidh 2006). The Omani abalone species has, as has most of the commercial abalone species internationally, shown signs of serious decline in abundance (Raemaekers et al. 2011), which is largely a result in the increase in value and demand from the East for this export species. To counter the decline in stocks and the potential negative economic impact on the fishery, the Ministry of Agriculture and Fisheries in Oman has, for some time, been considering strategies aimed at protecting the abalone fishery, including extreme measures such the temporary closure of the fishery from 2008 until 2011 and the development of stock enhancement technology.

During this process, hatchery-produced and farm-reared juvenile abalone are released into the ocean, with the aim of either harvesting them at a later date or leaving them to become part of the existing natural broodstock and enhance the process of natural recruitment. This approach has been used in a number of countries with varying degrees of success (de Waal 2002, Gallardo et al. 2003, Guzman del Proo et al. 2004, Huchette et al. 2005, Dixon et al. 2006, Heasman et al. 2007, James et al. 2007, Roodt-Wilding 2007, Prince & Peeters 2010). The development of abalone hatchery technology was initiated in Oman during the late 1990s for Haliotis mariae, Wood 1828 (Al-Rashdi & Iwao 2008). In the first steps of investigating the future of restocking H. mariae, this article describes a series of experiments that test the viability of relocating and reseeding wild juveniles kept in a hatchery facility for a period of 7 wk before reseeding. This research will form the basis of future seeding experiments with hatchery-bred and -reared juveniles.

Rationale Behind Seeding Abalone During the Juvenile Life Cycle Phase

The life cycle of abalone in general can be considered complex. It is important to determine which stage of the life cycle is the most viable for introduction or seeding (Huchette et al. 2005, James et al. 2007). In this study, we investigated the effects of seeding juvenile abalone ranging in shell length (SL) from 30-36 mm (i.e., the cryptic juvenile phase). These animals differ in diet and behavior from adult animals. The abalone Haliotis mariae in general is considered to become emergent at an SL of approximately 60 mm, moving to exposed sites on reefs or boulders. Adult H. mariae are grazers as well as trappers of a range of drift seaweed species, with the choice of species depending on the area and the abundance and diversity of seaweed present (Al-Hafidh 2006). Juveniles, on the other hand, have been shown to be grazers, and the epithelial layer of the encrusting corallines on which the recruits are found, together with benthic diatoms, is a source of nutrition for recruits and small juveniles (Al-Rashdi & Iwao 2008). In general, adult abalone occupy habitat less cryptic than that of juveniles. It is crucial, however, that the habitat requirements of juvenile abalone be met if seeding is to be successful, and a detailed understanding of the ecology of wild juvenile H. mariae is essential.

Seeding aims to mimic the specific stage of the natural life cycle after natural recruitment has taken place and recruits have grown to the juvenile stage. Internationally seeding research has been undertaken in a number of countries, including Japan, South Africa, Australia, and China (de Waal 2002, Gallardo et al. 2003, Guzman del Proo et al. 2004, Huchette et al. 2005, Dixon et al. 2006, Heasman et al. 2007, James et al. 2007, Roodt-Wilding 2007, Prince & Peeters 2010). This research has shown that seeding site selection, comprising juvenile habitat specifically, that is under-boulder habitat, cracks and crevices, is vital to the survival of seeded juveniles (de Waal 2005, Huchette et al. 2005, Dixon et al. 2006, Heasman et al. 2007, Roberts et al. 2007). There are species-specific and site-specific indications that relatively lower seeding densities result in relatively higher survival rates (Goodsell et al. 2006, Heasman et al. 2007, Roberts et al. 2007, Prince & Peeters 2010). The selection of a seeding density must be made based on an understanding of the ecology of juvenile abalone of the species in question. Although extensive mass seeding experiments have been undertaken in a number of countries (Heasman et al. 2007, Prince & Peeters 2010), research results from small-scale experiments lead to similar conclusions (de Waal 2005), which are that correct site selection targeting juvenile habitat (under boulders, and in cracks and crevices) and relatively low seeding densities optimize survival. Therefore, it is possible to collect the required data to develop seeding methodology without doing large-scale, extensive mass seeding experiments. Large-scale seeding and stock enhancement strategies can then be developed after seeding methodologies have been developed without having to go through an expensive learning curve, which is the basis on which our series of experiments was been developed.

The association between urchins and abalone is well documented for various abalone species worldwide. Recruits from some species that grow to the juvenile stage have been found predominantly under sea urchins (Day & Branch 2000, Day & Branch 2002, de Waal 2005, Goodsell et al. 2006). Although urchins are considered a source of shelter for juvenile abalone, the relationship between Haliotis mariae recruits and urchins has not yet been investigated (Al-Hafidh 2006). Introducing hatchery-reared animals into the wild involves processes of behavior, genetic selection, and natural selection in terms of individuals selected for release, and the effects of the mechanical process of release (Heasman et al. 2007, Roodt-Wilding 2007). Stocking densities, natural movement, and exposure to predation are all affected by the mode of release. Over the short term, seeding may induce mortalities associated with site selection and seeding methodology, natural mortality effects that impact wild abalone will impact those seeded juveniles that have survived the short-term effects of seeding. Recovery rates are an indication of the potential survival of the seeded juveniles: obviously, the longer the experimental period the more accurate long-term survival projections will be (Prince & Peeters 2010). However, short-term survival data combined with dispersal and growth data provide valuable insight into the potential survival of seeding juvenile abalone (de Waal & Cook 2001, de Waal 2005).


The study was done in 2 phases. The first phase comprised searching for and collecting juveniles from the wild. This phase also yielded qualitative information to be used during the second phase. In October 2011, wild juveniles were sourced from 8 sites over a 20-km stretch of coast stretching west from Mirbat (Fig. 1). Scuba divers picked up all small boulders, searched cracks and crevices, and picked up urchins to locate juvenile abalone up to a depth of approximately 7 m. Total time from removal from the sea to the Mirbat facility was never more than 1 h. During collecting, 5 10 x 1-m transect searches were conducted to calculate average juvenile abalone densities in the area. These searches were invasive, using the same process as that followed for collecting juveniles. During the process of collecting and surveying, observations were made regarding the ecology of wild juveniles.

It is important to remember that this study targeted habitats that sheltered wild juveniles, and that extensive exposed or sandy areas were avoided completely. The habitat investigated is, therefore, biased toward what is characterized as ideal juvenile habitat and excludes any habitat that is not considered suitable juvenile Haliotis mariae habitat. The specific habitats in which the juveniles were found, to a large extent, reflect the diver's ability to search certain habitats. Only small boulders can be rolled by divers, and deep cracks and crevices cannot be searched. It is therefore assumed that the habitat that has been searched and has yielded juveniles can be considered the minimum suitable seeding habitat for juvenile Haliotis mariae, but is not considered to include total habitat available.

On a small scale, physical topography and specific ecological habitat characteristics at the 8 collecting sites varied considerably. Habitat supporting wild juvenile abalone can be divided into 2 basic extreme area types (on a small scale, sites comprised a combination of characteristics ranging between the 2 extremes): (1) areas with an abundance of boulders that vary in size (diameter, <30 cm, 30-50 cm, >50 cm), with a substratum comprised largely sand; and (2) areas comprising large reef outcrops with deep cracks and crevices and few small boulders, with the substratum comprised predominantly of reef or bedrock.

The animal species occurring most predominantly under boulders, and in cracks and crevices included sea cucumbers (Holothuria sp. Linnaeus, 1767, and Actinopyga sp. Bron 1860) (Claereboudt & Al-Rashdi 2011), sea stars (Ferdina sadhaensis Marsh & Campbell, 1991; Holothuria sp., Lhwkia sp. Nardo, 1834; Culcita sp. (Agassiz, 1836), cowries (Cypraea Linnaeus, 1758), brittle stars (Ophiocoma L. Agassiz, 1835), and various urchin species (Diadema setosum (Leske, 1778), Echinostrephus molaris (Blainville, 1825), Echinometra mathaei (Blainville, 1825), Toxopneustes pileolus (Lamarck, 1816), Stomolmeustres variolaris (Lamarck, 1816), and Mesocentrotus franciscanus (A. Agassiz, 1863)). The most abundant algal species found at the time of collection the juveniles were Nizamuddinia zanardinii (Schiffner) P. C. Silva, 1996; Uh, a fasciata Delile, 1813; Uh, a grandis Saifullah & Nizamuddin, 1977; Sargassum ilicifolium (Turner) C. Agardh, 1820; Sarcodia sp. J. Agardh, 1852; Ptilophora sp. Kutzing, 1847: Euptilota fergusonii. A. D. Cotton, 1907; Stoechospermum polypodioides (Lamouroux) J. Agardh, 1848; and Gelidium spinosum (S. G. Gmelin) P. C. Silva, 1996.

Less than 5% of the juveniles found were in cracks and crevices; of these most were under urchins. Ninety-five percent of juveniles were found under boulders that were small enough to roll. The majority of juveniles were found alone, and the rest in groups of 2 or 3 under 1 boulder. The maximum number found under 1 boulder was 8, and in 2 cases, 5 juveniles were found together under 1 boulder. Adult wild abalone were found at all the sites. The information gathered led to the strategies followed during the next phase.

During the second phase, the juveniles that were collected and kept in tanks at Mirbat were reseeded in preselected seeding sites. Seeding for the small-scale experiments began December 3, 2011, and lasted until December 20, 2011, a minimum period of 7 wk after collecting. At the time of seeding, the average SL of the juveniles used for the small scale experiments was 34.51 [+ or -] 1.96 (SD) mm. Sampling took place after 30, 60, and approximately 90 days. Quantitative data regarding recovery rates and survival, growth, habitat selection, dispersal, and the percentage utilization of urchins for shelter by juvenile abalone were collected during this phase.

Criteria for Seeding Site Selection and Seeding Density

Criteria for seeding site selection were developed based on the observations made from the visual survey done while collecting wild juveniles. These were generally found under boulders and in cracks and crevices. Often in the presence of urchins and sea cucumbers, both juvenile and adult wild abalone, in areas abundant with pink crustose coralline algae, and generally in depths <8 m.

The 5 transect searches yielded an average density of 0.66 [+ or -] 0.21 juveniles/[m.sup.2] (range, 0.5-1 juveniles/[m.sup.2]). The juveniles counted during the survey and those collected were distributed patchily. Many juveniles were found in close vicinity to each other, and at times a number were found together under one boulder, surrounded by areas with similar habitat where no juveniles were found. Considering trends in recovery and survival increasing in relation to decreasing seeding densities (de Waal & Cook 2001, Prince & Peeters 2010), and assuming some mortality would take place as a result of the seeding action (de Waal & Cook 2001), we decided to seed approximately 10 juveniles/ [m.sup.2]. I n this context, it must be remembered that complexity of habitat determines surface area, and that a unit of area comprising many small boulders has more surface area than the same unit area with fewer larger boulders.

Selecting Suitable Seeding Sites

Specific seeding site selection was made based on the criteria listed earlier. Visually, they were selected to resemble those sites that supported wild juveniles. Experimental seeding requires some short-term sampling. Sampling (destructive) to determine, for example, recovery, growth, and dispersal, only allows access to a limited number of discrete or hidden juveniles. Although this is useful and necessary if data are required over the shorter term, large-scale seeding habitat for stock enhancement purposes should be selected that will include all potential habitat, including habitat that is not accessible to sampling but could shelter juveniles. Six experimental seeding sites were selected in each of three areas stretching over a distance of approximately 80 km of coast (Fig. 1): Raha, the most westerly; Haat, approximately 40 km northeast of Raha; and, the most easterly, Hassila, just outside Hadbin. In each of these 3 areas, each seeding site was separated from the next by a distance of 10-20 m.

Seeding Methodology

In all the experiments, two basic seeding methods were used concurrently in each of the sites. Using the first method, juvenile abalone were placed directly into cracks and crevices, and under boulders by hand. Normally, the juveniles clump together in the net bags in which they are transported, and so a number (2 or more) are usually seeded together. The abalone are held against the surface of the rock or crack until they attach themselves securely. Observations are made until the abalone are obviously stable.

The second method, to determine to what extent human handling of the juveniles impacts recovery rates (Huchette et al. 2005), required seeding using a small PVC tube measuring 10 x 3.8 cm. The diameter of the tube was determined by the size of the juveniles to be seeded. Small holes (diameter, 1 cm) were drilled through the tube to allow water circulation (Fig. 2). The juvenile abalone were placed into the tube by hand, and then the tubes were placed directly into the selected seeding habitat. This seeding mechanism allows the juvenile abalone time to move out and into natural shelter while offering protection against predators (Huchette et al. 2005, Goodsell et al. 2006, Heasman et al. 2007).

Two to 4 days prior to seeding, the juvenile abalone were tagged individually using Superglue and numbered plastic tape. Shell length was measured for each individual used in this series of experiments. One day prior to seeding, the loose juveniles were placed in small net bags, 10 at a time, and kept in the bags in tanks at the Mirbat facility. Approximately I h prior to seeding, the 5 juvenile abalone tagged to be released using the seeding mechanism described (Fig. 2) were placed in the PVC tubes by hand. The tubes were then sealed with duct tape and returned to the tanks. On the day of seeding, the net bags containing the juvenile abalone were placed in plastic cooler boxes and transported to the seeding sites by vehicle. Onsite, the bags with the abalone were placed immediately in the water. After the divers had transported bags to the preselected sites, the abalone were seeded by the divers.

Small-Scale Experiments

For all the small-scale experiments, a standard seeding method was used. Ten abalone, all the same average size (SL, 35 mm), were seeded in each site, 5 by hand and 5 using the PVC tube. All 10 abalone were released within a couple of centimeters from each other so that survival could be compared on the smallest microhabitat scale possible within the context of these experiments. The small-scale trials comprised 6 sites in each of the 3 areas. In each area, 2 sites were sampled after a period of 30 days, 2 after 60 days, and the last 2 after 90 days. In all, there were 18 sites in this series of experiments.

Each site comprised a circle 6 m in diameter. Sites were described in the following basic substratum categories (estimates were made by the same person throughout the series of experiments): (1) percent area exposed, sand, reef or big boulders, surface that cannot provide shelter for juvenile abalone: (2) percent area comprised of boulders with a diameter greater than 50 cm; (3) percent area comprised boulders with a diameter between 30 cm and 50 cm; and (4) percent area comprised of boulders with a diameter less than 30 cm.

Seeding at Greater Depth (10 m)

Although the bulk of abalone are found in depths shallower than 8 in (Al-Hafidh 2006), they do occur in deeper water. An experiment was conducted in which 10 tagged juveniles were seeded in each of 5 sites: 3 sites at Hassila and 2 at Raha. Exactly the same methodology used in the shallow experiments was followed, including site selection.

Larger Scale Tests

In late January, in each of 2 sites--Haat near Sadah (average depth, 5.5 m) and Ras Atian near Mirbat (average depth, 2.5 m)--80 juveniles were seeded over an area of 16 [m.sup.2]. Seeding was conducted at the same densities as in the other experiments. However at 1 site, Haat, all 80 juveniles were seeded using the PVC tubes described earlier, with 10 juveniles in each tube. At the other site, Ras Atian, all the juveniles were released by hand, approximately 10/[m.sup.2]. Both stations were selected using the same seeding site criteria used in the small-scale experiments. The Haat site was sampled after 72 days; the Ras Atian site was sampled after 99 days.

Statistical analyses were conducted using StatistiXL software. When data sets were limited in size, nonparametric analyses were used, with linear regression analyses conducted when data allowed. The following data were analyzed: (1) physical substratum similarities among the experimental areas according to the categories listed earlier, (2) relationships among juvenile abalone recovery rates and habitat characteristics described in the categories listed earlier, (3) relationships among recovery rates and use by recovered juveniles of specific habitat categories listed earlier, (4) seed size and its effect on juvenile abalone recovery and growth, (5) dispersal and its relationship to juvenile abalone recovery rates, (6) depth and its relationship to growth and juvenile abalone recovery, (7) urchin densities and their relationship to juvenile abalone recovery rates, and (8) wild juvenile densities and their effect on juvenile abalone recovery rates.


Small-Scale Experiments

Habitat Description, Habitat Selection, and Urchin Use by Seeding Site and Geographical Areas

Regardless of the use of a standardized site selection and seeding method, recovery rates were clearly site specific (Fig. 3). Calculation and interpretation of average recovery rates over a larger geographical scale must be done with caution. Even within areas where sites were seeded on the same day, within a time frame of no more than 30-45 min, recovery rates reflect site-specific characteristics and conditions. In some of data presented (Fig. 3), we have averaged recovery from the 2 sites from each area sampled on the same day. How these recovery rates reflect sea and environmental conditions at the time of seeding, site characteristics, human error, and seed condition, which is assumed constant for all the seed used, is discussed in later sections.

When site descriptions in the categories given earlier for the 6 sites in each geographical area are compared, there are significant differences in 3 of the 4 categories (Table 1). When these descriptions are averaged for each area (Fig. 4) and then compared using a nonparametric Mood median test, these small-scale differences are lost, and no significant difference in habitat description among the 3 areas is found (bottom row, Table 1). Spearman's rank correlation analyses were conducted to test for relationships between recovery rates and proportional habitat category availability, and they yielded no significant results (Table 2, Fig. 4). The same analyses were conducted to test for relationships between recovery rates and proportional use of habitat categories by recovered juveniles from all sites pooled. Results tested significant for boulder habitats 30-50 cm in diameter and less than 30 cm in diameter (Table 2, Fig. 5).

The graph in Figure 4 shows that even though we now know that Hassila and Haat yielded the highest recovery rates, respectively, they do not comprise a greater percentage of suitable habitat (boulder diameter, 30-50 cm and <30 cm) than Raha. In fact, both of these sites comprise extensive areas that are exposed and have boulders larger than 50 cm in diameter when compared with Raha. Approximately 30% of the habitat in which seeding was conducted was comprised of boulders less than 50 cm in diameter, whereas 55% of juveniles selected boulders in that size class, with the rest selecting larger boulders at a small fraction, 2.1% selecting crevices and cracks, and 3.2% selecting exposed habitat (Table 3). None of the seeded juveniles used urchins for shelter. The graph in Figure 5 shows that, in Hassila and Haat, the two most successful sites, a greater percentage of the abalone recovered selected boulders less than 50 cm in diameter for shelter, when compared with Raha, the least successful site.

Recovery rates varied over time and area between and within sites (Fig. 3). On average, sites at Hassila yielded greater recovery rates over all 3 periods--30, 60, and 90 days--when compared with the two other areas. There, recovery rates ranged between 55% and 70%. In Haat, there was a decline in recovery rate over time, from 60% to 30% over the 3 too. In Raha, the first 2 periods yielded 40% and then at the end of the last period recovery was low, at 5%. When data from the 18 sites sampled over 3 mo were pooled, no significant downward trend was found for average recovery over time. However, when average recovery of the 2 sites sampled every 30 days in each area are grouped, the difference between areas is significant (Mood median test, P = 0.043), with Hassila having the greatest recovery and Raha the least (Fig. 3).

Wild juveniles were found in all but 1 of the shallow seeding sites, which is indicative of suitable ecological factors for both juvenile survival and growth. None were found in the deeper (10-m) sites. The number of wild juveniles and the number of urchins in a 6-m diameter was recorded at each site. The greatest concentrations of wild juveniles were found in the seeding sites at Raha, the area with the lowest recovery rates and the lowest growth rates. Both linear regression and Spearman's rank correlation analyses showed that no significant relationships existed between seeded juvenile abalone recovery and either urchin or wild juvenile densities.

Dispersal and Recovery

Dispersal from the actual point of release was measured for all abalone recovered in a 6-m diameter. Spearman's rank correlations were conducted to test for relationships between recovery per site and average distance moved, time and distance moved, and average site depth and average distance moved. All relationships analyzed were not significant. A Kruskal-Wallis test was conducted to examine differences in the frequencies of dispersal within 1-m distance classes from the point of release, and a significant variance was found (P = 0.008, Table 4). In total, an average of 68% of seeded juveniles recovered were found within 1 m from where they were seeded (Table 4). Recovery rates here are calculated as an average of the 2 sites sampled in each area at the end of each sampling period. In only

2 cases, the majority of the abalone were no longer within 1 m from the release point. In 1 case, the recovery rate was 30% after 60 days; in another, the recovery rate was a mere 10% after 90 days. Although no significant correlations were established between distance dispersed and percent recovered, it appears that, over the short term (30-90 days), the greater recovery rates correspond to sites where recovered abalone did not move farther than 1 m after seeding. Dispersal patterns or evidence of dispersal are difficult to interpret because consistent, 24-h monitoring of multiple sites is not realistic and was not done. Although we do not know what happened to the juveniles we did not recover (Prince & Peeters 2010), we do know that those that did survive and grew during the 30-90-day periods have survived long enough to be considered established as part of the natural biota, prone to natural mortality.

Growth Rates

Juveniles were seeded during December (winter), when water temperatures average around 25[degrees]C. The 18 sites sampled in this series of experiments ranged in depth from approximately 1.55 m. The shallowest area was at Haat, with an average depth of 2.92 m. Average depth for the other 2 areas was slightly deeper: Hassila was 3.7 m and Raha, 3.8 m. Average growth rates varied considerably between sites, with the shallower sites showing greater growth rates in general (Table 5). Both linear regression and Spearman's rank correlation analyses were conducted to test the relationship between average seed size per site and percent recovered per site (Fig. 6); both tests were significant (P = 0.015 and P = 0.01, respectively). Linear regression analyses showed that a significant but weak negative correlation existed between average depth and growth in recovered abalone ([R.sup.2] = 0.133, P = 0.001). These growth rates are seasonal, and continued monitoring of tagged juveniles showed a marked increase in May to June, after the last sites were sampled. As a result, they are comparable with those for the same species reared in the Mirbat hatchery, where juveniles have been shown to grow up to 4.1 mm/mo (Al-Rashdi & Iwao 2008). Growth rates were considered important because of the potential relationship between seed size and survival (Fig. 6).

Ten-Meter Sites

Initial results from the deeper sites looked promising. After 30 days, Raha yielded a recovery rate of 30% and Hassila, 50%. After 60 days, Raha yielded 20% and Hassila, 0%. After 90 days, both sites yielded 0%. No shells were found at the sites and extensive searches in the area surrounding the seeding sites yielded nothing. We consider these experiments outside the normal recruitment depth for this species and did not conduct further tests at this depth.

Larger Scale Sites

In both of the larger scale seeding experiments, only the 4 x 4 m (16 [m.sup.2]) areas were searched. At Haat, 52% of the juveniles were recovered after a period of 72 days (seeded with the PVC tube; average depth, 2.5 m); at Ras Arian, 38% of the juveniles were recovered after a period of 99 days (hand seeded; average depth, 5.5 m). The exposed areas at the Ras Arian site comprised less sand than those at the Haat site. This type of stable substratum allows juveniles and adults to move more securely, and we expected more dispersal as a result. However, the time period and depth may also have impacted recovery rates.

PVC Tube Seeding Mechanism Versus Hand Seeding

When comparing recovery rates from the small-scale experiments the 2 different seeding methods yielded very similar recovery rates: 45% of the abalone seeded by hand were recovered and 47% seeded using the tube were recovered. However, on a larger scale, the use of the PVC pipe seeding mechanism did result in a relatively greater recovery rate--52% compared with 38%.

All the seeding and sampling during the experiments was conducted by the same 2 divers. The results reflect not only the abilities and decisions made by the these divers but also the environmental conditions at the time of and between seeding and sampling, including visibility, current and surge strengths, sand movement, and possible interference by other divers or fishermen who disturbed experimental sites.


The most westerly site, Raha, incidentally yielded the lowest recovery rates, had the lowest average growth rates, and, on average, the deepest sites. Raha also had the greatest concentration of wild juveniles. Haat, the central area, had the shallowest sites on average, the greatest average growth rates, and average recovery rates among the other 2 sites. Hassila, the most easterly area, had, on average, slightly shallower sites than Raha, but more than double its growth rate, and the greatest recovery rates on average.

We are using recovery rates as the primary indicator of successful site selection in which to seed hatchery-reared juveniles. The assumption is that if these juveniles survive in relatively high percentages after the short-term negative effects of seeding-induced mortality, those that survive will live to become part of the wild fishery. A recovery rate is a measure of the number of abalone found by divers; it indicates minimum survival at that time. The recovery rates found in this study are comparable with those found in studies conducted on other abalone species in similar size classes and over similar timescales (James et al. 2007, Goodsell et al. 2006, Huchette et al. 2005). What this research has shown clearly is that, regardless of seeding methodology, in sites with similar characteristics, recovery rates are site specific. Comparisons among sites, geographical areas, and species must be done with some caution.

In reality, a recovery rate is only one of a number of factors--both ecological and physical--that determine the suitability of a site for seeding juvenile abalone. A host of other factors, some we quantified, may play a major role in actual recovery rates, and therefore influence this indicator. Quantified factors are seed size, seeding density, distance moved, depth, and available physical shelter. Factors we may be aware of but have not measured and that could affect recovery rates include small- (between sites) and large- (between areas) scale ocean and environmental conditions at the time of seeding and between seeding and sampling, including (1) availability and quality of food (algal species), seasonal growth rates; (2) substratum type (dispersal on sand is not as safe as dispersal on reef); (3) predation on juveniles between seeding and sampling; and (4) human error in exact placement of juveniles.

It is important to note that site selection and optimization of seeding survival is the goal here. As a result, interpreting results on a site-specific scale is important, because abalone will be seeded according to the criteria developed and evaluated through this series of experiments. We are considering those factors measured in our experiments as a whole to evaluate the potential viability of translocating and seeding juvenile Haliotis mariae, either wild or hatchery bred.

We next discuss the results by addressing a series of questions to evaluate the potential of seeding juvenile Haliotis mariae (wild or hatchery bred) as a management tool.

What Are the Characteristics of Good Seeding Sites and How Are They Reflected in Our Results?

The most important fact that drives short-term survival is the fact that juvenile abalone are photosensitive, and they attempt to move into shade as soon as possible (de Waal 2002, de Waal 2005, Schoonbee 2007, Prince & Peeters 2010). If that shade is provided by habitat that can protect the abalone from predation, it is an added benefit. On average, 30% of the total area seeded was comprised of habitat that has the potential to shelter and protect juveniles (boulder diameter, <50 cm). This type of habitat typically comprises layers of small boulders; the more physically complex the site, the more habitat there is for juvenile abalone (Huchette et al. 2005, Dixon et al. 2006, Heasman et al. 2007). In total, 56% of the juveniles recovered used this habitat. Abundance of suitable physical habitat is important, but only a basis of what is required for survival. We have shown that only on a small scale are the physical characteristics significantly different among sites (Table 2), but that specific habitat selection made by recovered juveniles is not consistent among areas (Fig. 5), which may indicate some measure of quality in addition to mere physical suitability. This measure of quality could include availability of food, specific predator species, and unmeasured small-scale (the scale at which an individual abalone lives) microhabitat effects. An assumption is made that if the site is not suitable, dispersal would be evident. In the most successful sites, the juveniles used the smaller categories of habitat more. This could reflect the availability of surface area on which microalgae settles and grows, and therefore grazing can take place. Those sites with an abundance of smaller boulders appear to be more effective for survival.

What Is the Relationship Between Dispersal and Recovery?

High recovery rates in conjunction with low dispersal rates may indicate suitable habitat: if they persist over time and growth is evident, the quality of the habitat can be considered good. Evidence of dispersal indicates that low recovery rates may not be a result of mortality, but a result of dispersal (de Waal et al. 2003, Prince & Peeters 2010). Without evidence of dispersal, no inference can be made about whether mortality or dispersal has taken place. At the majority of our sites, dispersal was limited, so we accept that--over the short timescale of this series of experiments--low recovery rates indicate low survival. Over longer timescales, we would expect potential dispersal associated with growth and transformation from juvenile to adult, and a change in habitat selection that may require movement.

How Do Growth Rates Affect Potential Survival?

The correlation between recovery (hence, survival) and juvenile seed size has been shown to be positive in our study, as it has in many other abalone species (de Waal & Cook 2001, Goodsell et al. 2006, Roberts et al. 2007, Prince & Peeters 2010). We have also shown a positive correlation between decreasing depth and increased growth rates. The faster juveniles grow, the faster they become more resilient and capable of surviving over the long term. In this regard, seasonal growth rates need to be taken into account when seeding is being planned. The larger the seed size, the greater potential survival.

To What Extent Do Urchins Affect the Survival of Seeded Juvenile Haliotis mariae in This (30 to 40 mm SL) Size Class?

Urchins played an insignificant role in the survival of seeded juveniles. Although there is much evidence that urchins do shelter many wild juvenile species (Day & Branch 2000, Day & Branch 2002), the relationship between seeded juveniles and urchins is not that significant with Haliotis midae in South Africa (de Waal 2005), or in Australia with Haliotis rubra (Goodsell et al. 2006).

Tube Seeding Mechanism with P VC Pipe or Hand Seeding,: Which Is Better?

Transition from small-scale single-area seeding to larger scale seeding will require more time and runs the risk of decreased attention being given compared with hand seeding. The tube mechanism may be better when time constraints may limit the amount of attention given to the handling of juvenile abalone and to seed smaller juveniles (Heasman et al. 2007, James et al. 2007). A biodegradable alternative to PVC piping, however, needs to be found.

How Do You Take the Relatively Successful Small-Scale Seeding Experiments to the Next Large-Scale Level Successfully?

Few data exist that shows the transition between these 2 levels of seeding. However, there are indications that that large-scale seeding results in decreased survival when compared with small-scale experiments, mainly as a result of the effect of high stocking rates (Heasman et al. 2004, Roberts et al. 2007). In this series of experiments, we have shown that if the same methodology is used, if sites are selected using the right criteria, and if seeding densities are maintained, then moving from small scale to larger scale is feasible.


Reseeding and translocation of Haliotis mariae juveniles 3040 mm in SL has been shown to be successful over the short term along the Dhofar coast. Site selection is absolutely crucial, and within the context of suitable habitat, seeding should be done as shallow as possible. Although an initial methodology has been developed, it needs to be refined to achieve similar results with hatchery-bred juveniles and to increase the scale of seeding. The human aspect of stock enhancement, expertise in site selection, handling and seeding techniques, and identifying suitable ocean and seasonal environmental conditions are vital to the implementation of this technology. These initial results do suggest that stock enhancement through seeding juvenile abalone may be a feasible management option for Haliotis mariae in Oman.


This study was financed by the Oman Agricultural and Fisheries Development Fund, Sultanate of Oman. We appreciate the support given by the Directorate General of Fisheries in Dhofar. We thank Abdullah Bashwan and Abu Bakar Maharoos for collecting wild juveniles, the personnel at the Mirbat abalone hatchery facility, and Valiyakath Kunhimon Basheer and Pattanmar for feeding and tagging juveniles, and maintaining diving equipment.


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Fisheries Research Centre-Salalah, Ministry of Agriculture and Fisheries Wealth, PO Box 33, Salalah City, PC 217, Sultanate of Oman

* Corresponding author. E-mail: sdewaal@

DOI: 10.2983/035.032.0210

Testing the physical similarities between experimental areas
according to substratum categories.

Category               Chi square   df         P value

Exposed                    12       2    0.002 * ([dagger])
>50 cm [empty set]        7.48      2    0.024 *
30-50 cm [empty set]      0.55      2    0.758
<30 cm [empty set]        9.33      2    0.009 * ([dagger])
Average                   6.7       3    0.08

* Significance at 95% confidence limits using the Mood median test.

([dagger]) Significance at 95% confidence limits using the
Kruskal-Wallis test.

Testing relationships between recovery rates and: the abundance
of specific habitat categories, middle column, and selection
by juvenile abalone of specific habitat categories for
shelter, last column, using Spearman's Rank
Correlation analyses.

                       P values for habitat   P values for habitat
Habitat category           description             selection

Exposed                       0.411                 0.37
>50 cm in diameter            0.560                 0.08
30-50 cm in diameter          0.946                 0.002 *
<30 cm in diameter            0.249                 0.005 *

* Significance at 95% confidence limits.

Average percent of habitat substrate categories for seeded
areas pooled and percent use of substrate categories by seeded
juveniles from all sites pooled.

                           Substrate category    Substrate category
                           in seeded habitat    selected by juveniles
Substrate category                (%)                    (%)

Exposed                           35.9                   3.2
>50 cm in diameter                34.4                  37.9
30-50 cm in diameter              21.1                  32.6
<30 cm in diameter                 8.5                  24.2
Cracks and crevices                                      2.1
Urchins                                                   0

Cracks and crevices were not quantified prior to seeding. Urchin
numbers were determined but not quantified as part of available
substrate prior to seeding.

Percentage frequency dispersal in 1-m distance categories
for all abalone recovered.

                                  Distance moved (m)

Area         Period (days)     1           2         3

Raha              30          72.7       18.2        9
                  60          28.6       57.1       14.3
                  90           0          0        100
Haat              30          91.7        8.3        0
                  60          55.6       44.4        0
                  90          100         0          0
Hassila           30           81         19         0
                  60          92.9        7.1        0
                  90           86         14         0
Average                        68         19         14
Chi square         9.621       df = 2   P = 0.008 *

* Significance at 95% confidence limits, Kruskal-Wallis test.

Average depth and monthly growth rates for abalone from
each geographical area.

                    Raha   Haat   Hassila

Growth rate (mm)    0.74   2.15    1.44
Average depth (m)   4      2.77    3.76

Results from all sites from each area pooled.
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Article Details
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Author:de Waal, Schalk; Balkhair, Mohammed; Mashikhi, Ali Al-; Khoom, Salem
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:7OMAN
Date:Aug 1, 2013
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