Experimental Collection of Pearl Oyster, Pinctada mazatlanica and Pteria sterna, Spat on a Filament Substrate

Juveniles of Pinctada mazatlanica and Pteria sterna were collected with artificial collectors from Falsa Bay, Baja California Sur, Mexico during a 12 month experimental period. Filament substrate artificial collectors contained in 2 mm plastic mesh bags (25 ± 25 cm) were deployed from the surface to 17 m of depth, and replaced monthly. Pinctada mazatlanica had the greatest recruitment (12 juveniles/cm²) in late summer and P. sterna (5 juveniles/cm²) in winter. Maximum spat collection from September 1986 to April 1987 occurred at 10 m depth for P. mazatlanica and at 4–7 m depth for P. sterna . However, peak spatfall under 11m depth occurred from late July to August 1987. The mean prodissoconch shell height was 254 μ m (SE = 0.003; N = 50) for P. mazatlanica and 313 μm (SE = 0.004; N = 50) for P. sterna . The growth equations for the first five weeks of both species, based on the prodissoconch shell height and the maximum spat height (measured from the umbo to distal edge) are presented.     

Spat availability of commercial bivalve species recruited on artificial collectors from the northern Gulf of California. Seasonal changes in species composition

This study reports a year‐round recruitment of spat of four commercial bivalve species; Pteria sterna, Euvola vogdesi, Pinctada mazatlanica and Pinna rugosa collected in the region of Puerto Peñasco, north‐eastern coast of the Gulf of California. Bimonthly recruitment of commercial bivalve spat on netlon^® collectors was evaluated for six sites from June 2007 to August 2008. To describe spat recruitment abundances with environmental parameters, sea surface temperature (°C) and surface chlorophyll a concentration (mg m^?3) were characterized by means of monthly Aqua/MODIS satellite data. For each species a repeated measures anova was used to evaluate differences in the number of spat between months, sites and depths. Maximum sea surface temperature was recorded in August–September (~31.5°C) and the minimum in January–February (~15°C), while the minimum surface chlorophyll a was observed in June–September (mean range = 1.5–2 mg m^?3) and the maximum in January–March (mean range = 2–5 mg m^?3). Spat recruitment showed distinct patterns; P. sterna can be characterized as having a Winter–Spring pattern, E. vogdesi a winter pattern, while P. mazatlanica and P. rugosa a summer spat recruitment pattern. This information constitutes part of the fundamental data needed for the development of aquaculture and conservation initiatives in the region based on wild spat supply.     

Growth and survival of the winged pearl oyster Pteria sterna (Gould, 1851) in suspended culture in the tropical Eastern Pacific: Influence of environmental factors

The growth, survival and influence of environmental factors were analysed in two cohorts of cultured Pteria sterna in Ayangue Bay, Province of Santa Elena, Ecuador (tropical Eastern Pacific). Juveniles representing cohorts I and II (8.4 ± 0.54 and 5.0 ± 0.17 mm in dorso‐ventral axis) were deployed in November 2015 and February 2016, and grown in pearl nets suspended in a long line for 12 and 10 months respectively. The stocking density was monthly and bi‐monthly reduced during sampling of individuals to determine growth in dorso‐ventral shell axis, dry mass of shell, soft tissues and dry mass of fouling on shell. Water temperature, salinity, total seston and phytoplankton biomass (chlorophyll a) were determined at the culture site. Results showed that P. sterna reached ~100 mm in length during the first year of culture. Although little negative influence of environmental factors was detected, high temperatures during the reproduction period can be the most negative influential trait. The highest tissue mass (6 g), which occurred at the 10th month of cultivation, as well as a high availability of spat by artificial collectors in the coastal waters, showed that the species can be considered a good candidate for aquaculture in the tropical eastern Pacific.     

Pacific oyster (Crassostrea gigas) spatfall prediction at Hiroshima,Japan, 1977

The spatfall prediction techniques used in Hiroshima Bay, Japan, are described. Data are given for the 1977 season. Plankton hauls from seven stations showed successive high peaks of small, medium and large larvae during early August. Small larvae (< 150 μm diameter) peaked at an average of 1,782 larvae per tonne of sea water (m³) on 10 August; medium larvae (151–250 μm) at 1,258/m³ peaked on 12 August as did large settling larvae (251–300 μm) at 350/m³. A small spatfall occurred on 14, 16 and 18 August when an average of 65, 64 and 65 spat per shell, respectively, attached on collectors during 2 days' immersion.A second, much bigger peak of small larvae built up from 16 August to reach an average maximum of 4,702 larvae/m³ on 24 August. Medium larvae peaked at 754 larvae/m³ on 28 August. A red tide then appeared consisting of vast numbers of a dinoflagellate tentatively identified as Gymnodinium simplex, and the anticipated main spatfall did not occur. The effects of red tides are discussed. By 17 September water conditions had improved and an estimated 50–100 spat were reported attached per shell on the collectors. This is about half the 200 spat per shell considered by the industry to be a good set.     

Spat Collection and Growth to Commercial Size of the Tehuelche Scallop Aequipecten tehuelchus (D'Orb.) in the San Matias Gulf, Patagonia, Argentina

Studies on larval settlement and growth of the commercial scallop Aequipecten tehuelchus were carried out over a 2-yr period in San Matias Gulf, Argentina. Gonadal index was used to indicate spawning and spat collectors were deployed when spawning began. Artificial spat collectors (mono-filament bags filled with thin shrub branches) were placed at a depth of 25 m in two areas of the Gulf during two seasons (1989–1990 and 1991–1992). Maximum settlement occurred by mid-February during the first season and by mid-January in the second season. Larger numbers of spat were found in collectors placed near the sea bottom. After settlement, spat were removed and placed in cages for growout. Scallops reached the average commercial size (60 mm shell height) 16 mo later. Mortality rate during the entire period was 10%.     

In situ growth of pearl oysters Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851) under repopulation conditions at Bahia de La Paz, Baja California Sur, Mexico

Pearl oysters Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851) were studied for an annual cycle of in situ growth from May 1992 to April 1993. Organisms generated from extensive culture were kept under repopulation conditions at Caleta El Merito. Growth measurements of shell height and length were taken monthly. Data were used to build the annual growth curve of both species, to test the temporal relationship between shell height and length, to calculate monthly and total growth rate, to follow the modal progression with the ELEFAN software, and to fit the growth curve to the Von Bertalanffy equation. Growth dimensions increased steadily during the annual cycle, from 7 to 18 months old for P. mazatlanica and from 11 to 22 months for P. sterna. No significant differences were detected between shell height and length during growth, although length seemed to grow faster. The ELEFAN program identified two modes in P. mazatlanica (Rn= 0.205) and a single one for P. sterna (Rn= 0.557). A positive correlation to the Von Bertalanffy equation was seen for both species (r²= 0.97 for both species).     

Effect of immersion time of cultch on spatfall of the scallop Argopecten purpuratus (Lamarck 1819) in the Marine Reserve at La Riconada, Antofagasta, Chile

A pilot program to evaluate the feasibility of collecting juvenile (seed) scallops using Japanese technology was carried out from October 2001 to April 2002 in the Marine Reserve at La Rinconada, Antofagasta, Chile. The continuous presence of larvae in waters in the reserve allowed for collection of 400–15,340 spat per collector and showed the high reproductive capability of local scallops and the relationship between numbers of larvae in the water and amount of spatfall. Highest rates of settlement were proportional to high numbers of umbone larvae in the water at >5000 larvae m⁻³ when collectors were first immersed. Absence of a relationship between larval numbers and postlarval settlement with trophic factors such as chlorophyll and particulate organic matter in the water suggests that productivity was not limited by these factors. Harvest of spat from collectors immersed for four and five months had recovery efficiencies of 5.5% and 59.4% compared with settlement in collectors after immersion for one month. Cohort analyses of recovered spat suggested that settlement occurred over the lengthy immersion period and was due to the continuous presence of larvae in the water. The loss of a high percentage of spat over the 4–5 immersion period compared with settlement in the first month can be attributed to intraspecific competition of spat density and growth as well as clogging of the collectors by sediment and marine fouling that impeded a flow of water through the nets.     

Changes in shell dimensions of pearl oysters, Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851), during growth as criteria for Mabé pearl implants

The relationship between the shell dimensions of pearl oysters. Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851). was studied to determine the possible change of form of the shell during growth. The intention was to determine the number, size and location of nuclei that could be implanted in oysters used for Mabé pearl production. Using the database of our Pearl Culture Research Programme developed in Bahía de La Paz, México, we obtained measurements of 500 shells of P. mazatlanica and 500 shells of P. sterna, representing 3 years of continuous growth under extensive culture conditions. The height-length, height-thickness and the height-weight relationships of both species were analysed, as was the height-wing length relationship for P. sterna. There was isometric growth up to 100 mm shell height, and negative-allometric growth after 120-125 mm for P. mazatlanica. The height-thickness relationship followed a linear model, whereas the height-weight relationship was exponential. No clear allometric pattern was found in P. sterna and all relationships fitted the power equation.     

Experimental collection of great scallop postlarvae and other benthic species in the Bay of Brest: settlement patterns in relation to spatio-temporal variability of environmental factors

Settlement patterns of great scallop (Pecten maximus) postlarvae and other benthic species in the Bay of Brest were studied from 2-D and 3-D collectors to clarify biotic interactions at the postlarval stage. Plane tiles became colonized mainly by epifaunal suspension feeders, while the 3-D substrata collected a more diverse fauna. Both species diversity and total abundance were higher in Netlon bags, compared with sandstone tiles. However, hydroids, bryozoans, tubicolous polychaetes, a number of epifaunal molluscs and macroalgae were more abundant on tiles. Between-sites differences in taxonomic group abundances mostly reflected the benthic fauna and flora beneath the collectors and would be explained by differential settlement and survival, according to local environmental conditions. Sediment type, depth, salinity, water turbulence, food and biotic interactions would be the factors regulating settlement. Bryozoans, hydrozoans, Anomia ephippium, Crepidula fornicata, mussels, tubicolous polychaetes, Pisidia longicornis, Hiatella arctica, Aequipecten opercularis and Chlamys varia were the main potential competitors of Pecten maximus collected. Crabs and Nassaridae would account for most of the potential scallop predators. Possible ways of improving scallop spat collection and cultivation are discussed with reference to the efficiency and placement of collectors, to environmental characteristics and to the intensity of biotic interactions at the postlarval stage.     

大钦岛海区虾夷扇贝采苗试验

2010年在山东长岛县大钦岛南部海区进行虾夷扇贝采苗试验。采用规格为35cm×50cm的12目聚乙烯网袋组成的采苗器,垂挂于浮筏上,第一组网袋距离水面约3m,采苗器下端绑系质量约4kg坠石。试验结果表明,5月26日至6月1日投放采苗器平均采苗量40～50个/袋,6月6日投放采苗器平均采苗量10个/袋。3m、5m、8m采苗水层分别为30个/袋、48个/袋、71个/袋。远岸区平均采苗46个/袋,近岸区平均采苗24个/袋。     

Settlement of the commercial scallop,Pecten fumatus (Reeve) 1855, on artificial collectors in eastern Tasmania

The settlement of the commercial scallop, Pecten fumatus (Reeve) 1855, in artificial collectors was monitored on the east coast of Tasmania over a 4-year period using spat collection techniques similar to those practised in Japan. Major spat settlement occurred in mid-late September but small irregular settlements were observed in late spring and early summer. Information on settlement obtained in the first 2 years of the study was successfully applied in the collection of large quantities of scallop spat during the later years of the study.The number of settled scallop spat and growth of the spat varied with depth. Maximum settlement occurred at depths of 16–22 m, with a decrease in numbers towards the surface and the seabed (depth, 31 m). Growth of scallop spat also varied with depth. Scallops in collectors near the surface grew faster than those in deeper water, the most noticeable change in growth occurring at depths between 16 and 20 m.A considerable percentage (up to 62%) of settled spat were lost from the larger-mesh collectors and most losses occurred when spat detached their byssal threads in late November-mid-December. Further losses are attributed to fish predation and competition with colonising ascidians. Major colonising groups apart from scallops included brown and filamentous algae, ascidians, bryozoans, crabs, shrimps, gastropods, bivalves and fish.     

Reproductive condition of the pearl oyster, Pinctada imbricata, Röding, in Port Stephens, New South Wales, Australia

In an investigation of the potential for pearl production in New South Wales (NSW), Australia, changes in the physical and reproductive condition of the pearl oyster, Pinctada imbricata, were monitored for over 2 years. Using wild oysters gathered from close to the southern extent of the species' range in Port Stephens, NSW, a series of macroscopic and histological observations were made. Reproductive activity in P. imbricata was greatest from late spring to early autumn with oysters in poor reproductive condition during winter. Peaks in reproductive indices occurred in November 1998, March 1999, December 1999 and April 2000. Four indices of physiological condition were used: shell growth, byssal attachment, mantle thickness and mucoprotien layer. With the exception of the thickness and extent of the mucoprotein layer, these indices either showed little variation or the variation that occurred was not related to seasonal or reproductive changes. Changes in the mucoprotein layer were correlated with water temperature and suggest that this layer is metabolized during periods of high demand such as during gonadogenesis. Collectors deployed at two sites in Port Stephens demonstrated that spatfall occurs largely in the months of December and January following the spring and early summer peaks in reproductive activity (November 1998 and December 1999). Spatfall was not observed following the autumnal peaks (March 1999 and April 2000) in reproductive activity. Overall, reproductive patterns in P. imbricata are poorly suited to spat supply in Port Stephens. Farmers require spat in early spring (September) to allow maximum use of the ‘growing’ season (September–May). Reproductively capable oysters are not available from the wild until September and quantity of natural spatfall is too variable and occurs too late in the season (December–January). As a result, oysters are being conditioned in the hatchery in July, spawned in August and spat are supplied to farmers in mid September.     

Growth of the Pearl Oysters Pinctada mazatlanica and Pteria sterna in Different Culture Structures at La Paz Bay, Baja California Sur, México

A growth study of Pinctada mazatlanica and Pteria sterna was conducted to explain the basic steps required for the development of a pearl culture program in México. Seed for both species was collected using onion bags filled with black polyethylene sheets (40 ± 80 cm) and 5 g of vexar filament. The spatfall was July-August 1987 for P. mazatlanica and December 1987-February 1988 for P. sterna . The seed (12.8 ± 1.2 and 13.0 ± 0.6 mm respectively) was placed in pearl-nets for intermediate culture (to attain 30 mm height). Populations were subsequently divided into three groups, two groups at 10 m depth in lantern and pocket nets and a third placed over a submerged shelf at 10 m depth in plastic net cages. Growth in height, survival and temperature were monitored. After 22 mo P. mazatlanica showed no significant differences in growth between culture structures. Nevertheless, the survival obtained in cages (99%) was larger than that obtained in hanging structures (65%). After 18 mo of culture, significant differences (F = 5.199 P = 0.05) in growth were observed for P. sterna . Larger animals were found in pockets (106.6 ± 0.8 mm) followed by lanterns (104.0 ± 0.7 mm) and finally in cages (103.5 ± 0.6 mm). Survival in pockets was 99%, 84% in lanterns and 98% in cages. With the operation of the different culture structures used in this study, the bottom cage system seems optimal to begin a culture program to obtain pearl-oysters for nucleus implantation.     

Growth and survival of the Calafia mother-of-pearl oyster Pinctada mazatlanica (Hanley 1856) under different sequences of nursery culture–late culture at Bahía de La Paz, Baja California Sur, México

The Calafia mother‐of‐pearl oyster, Pinctada mazatlanica (Hanley), and the Rainbow nacre shell, Pteria sterna (Gould), represent an important resource for México because of their potential in pearl production. The present work deals with the effect of different sequences of nursery culture‐late culture on growth and survival of P. mazatlanica, from September 1993 to October 1994. The collected spat presented two main size groups: small (mean shell height of 7 mm), and large (13 mm). They were arranged into four experimental batches for each size group at a constant stocking density of 40–45 juvenile pearl oysters per Nestier cage. Three batches remained in nursery culture for 2, 4 and 6 months respectively, after which they were transferred to late culture in rail cages. A control group remained in nursery culture for 12 months. Growth was evaluated monthly and compared through anova and HSD Tukey tests. In addition to the shell height, width, depth (mm) and weight (g), data of shell volume (height × width × depth, in mm³) was also introduced to estimate and compare growth among the experimental groups. Mortality was estimated by counting the dead specimens every month and obtaining the percentage from a 100% initial survival at the start of the experiment. The juveniles showed different responses to the change from nursery culture to late culture; the level of each response varied significantly among the experimental groups at the end of the study. It seemed that a 6‐month period for nursery culture was propitious for P. mazatlanica.     

Repopulation and culture of the Pacific Calico scallops in Bahia Concepcion, Baja California Sur, Mexico

The Pacific Calico scallop, Argopecten ventricosus (Sowerby), is the most important commercial species in Bahia Concepcion. Catches declined steadily from 1991 to 1993 as a result of overexploitation, forcing the adoption of management measures. The Government has now established regulations for exploitation and scallop culture development. In 1994, Centro Interdisciplinario de Ciencias Marinas (CICIMAR) and the Fisheries Department of the Mexican Government initiated research on the feasibility of increasing scallop biomass through a reseeding programme to protect artisanal fishing. The use of onion bags to collect spat in Bahia Concepcion (1988-1994) demonstrated that settlement was cumulative from January to March. At Punta Coloradito, there were two peaks, in January and early March. Commercial collectors were deployed in February at El Indio and in April at El Remate. In June, about one million juvenile scallops were placed in an enclosure, held until mid-August and then released. Mass mortality (>80%) of the scallops was observed in September, increasing to 99% in October. The high water temperature and predators may be responsible for the mortalities.     

The recruitment of scallops (and beyond) by two different artificial collectors (Gulf of Taranto,Mediterranean Sea)

This study provides for the first time an evaluation of the natural availability of scallop seeds along the coastal area of Taranto (Mediterranean Sea, Southern Italy). To select the best artificial collectors to harvest scallop seeds in this area, cylindrical collectors (Cyl) were compared to traditional ‘Japanese‐style onion bags’ (Bag) across three sites. Scallops represented 26.6% of total bivalve recruitment among all collectors (782 ± 331 ind. m^?2). The most recruited scallops were Flexopecten glaber and Mimachlamys varia. The white (F. glaber) and black scallops (M. varia) were abundant at all three sites, while the queen scallop, Aequipecten opercularis, was only found at one site. Beyond the recruitment of scallops, numerous other potential commercial bivalve species were collected, including Limaria tuberculata, which was the most abundant bivalve species (33.3% of total recruitment). At all sites, Bag collectors had higher recruitment than Cyl collectors. Scallops recruited in artificial collectors exhibited a multicohort size distribution at most sites, suggesting potentially continuous reproductive activity in the scallop populations. F. glaber, M. varia and L. tuberculata could be good candidates to diversify the aquaculture production because of the availability of seed and their growth rate. Moreover, the farming of these bivalves integrates well with other forms of aquaculture (e.g. mussels), thus potentially offering farmers an additional source of income.     

Experimental suspended culture of mussels (Mytilus edulis L.) in Wales using spat transplanted from a distant settlement ground

Spat of Mytilus edulis L. were transferred 300 km by road on collectors from an area of high and regular spatfall, but unfavourable culture conditions, to a raft at a site deficient in mussel settlement. Spat were collected on coir ropes and fibrous rubberized matting staked to intertidal settlement grounds in Morecambe Bay, northwest England. During January to April, 80 mm circumference ropes could collect 3 000–7 000 spat/m/week, with smaller numbers in other months, and fibrous matting sometimes also caught many spat.Spatted collectors were suspended in the Menai Straits, North Wales. Despite heavy losses from overcrowding, fast currents and turbulence, growth was sufficiently good for some rope populations to produce marketable crops after about 16 months. Mean lengths increased from 1.5–5.0 mm to 47.5 mm in the first year, and to 60 mm after 1.5–2 years. At about 55 mm, attained at ca 16 months, the best crops yielded 10–15 kg/m live weight, corresponding to 2–3 kg of cooked meat/m. Percentage meat yields from 40–50 mm mussels were equally good, suggesting that crops could be harvested below the present marketable size.Economic systems for collecting spat and for on-growing at controlled densities remain to be developed for different hydrographic conditions and scales of commercial operation in Britain.     

Effect of Stocking Density on Growth and Survival of the Rainbow Pearl Oyster <Emphasis Type="Italic">Pteria sterna</Emphasis> (Gould 1852) during Nursery and Late Culture in Bahía de La Paz,Baja California Sur,México

Growth and survival of the rainbow pearl oyster, Pteria sterna (Gould 1852), was evaluated in field culture at Bahía de La Paz, México. Mexican made Nestier^TM trays were used in nursery culture from March to July 1999 at four different stocking densities (25, 50, 75 and 100 individuals/tray). Late culture proceeded from July 1999 to March 2000 in sandwich nets and rail cages. Each artifact received 70 to 75 individuals. We studied the long-term effect of nursery culture stocking treatments. Growth patterns were examined using shell volume (height × width × depth, in cm³). Survival was estimated monthly. Growth and survival were acceptable regarding routine operations, but variations in this experiment depended on stocking density and type of late culture device. The interaction of density and culture device was significant for shell volume at the end of the experiment (F = 3614.14; p < 0.0001). Final shell volume depended on stocking density in nursery culture (F = 8.09, p < 0.001), but culture device had no influence (F = 0.76; p = 0.3). The results indicated that growth and survival in nursery culture were not proportionally related with stocking density. The change to late culture improved overall response. Advantages in growth were favorable for D50 C only. Rail cages promoted better survival than sandwich nets. Based on the natural behavior of P. sterna, the Optimal Stocking Density may be higher than the ranges tested in the present study. We recommend new strategies to improve the actual culture technology for P. sterna. A 3-dimensional culture unit might be an important advantage for this species regarding territorial exploitation and efficiency of spatial management in the production cycle.     

Distribution patterns of larval myctophid fish assemblages in the subtropical–tropical waters of the western North Pacific

We examined larval myctophid fish assemblages and their distribution patterns, based on discrete depth sampling. Samples were collected at 19 stations along a transect that crossed the subtropical–tropical waters of the western North Pacific. In total, we collected 27 189 larvae of 40 myctophid species or types, belonging to 15 genera. Three assemblages were recognized, based on their species composition: Kuroshio Axis (KuA), Kuroshio Countercurrent (KCC), and Subtropical Countercurrent–North Equatorial Current (SCC–NEC) assemblages. The distributions of these assemblages were well defined by the positions of the KuA and the Subtropical Convergence. Each species had a specific distribution depth, and none showed diel vertical migration. Larvae of the subfamily Lampanyctinae were distributed in shallower waters (0–50 m) than larvae of the subfamily Myctophinae (50–150 m). Larvae of the same species were distributed at lower depths in the SCC–NEC area than in the KCC area. This corresponded to the abundance of chlorophyll a, which would reflect abundance of prey organisms such as copepod nauplii and copepodites.     

Effects of water depth on survival and growth of <Emphasis Type="Italic">Argopecten purpuratus</Emphasis> (Lamarck, 1819) spat in northern Chile

Collection and suspended culture of Argopecten purpuratus spat in Japanese-type collectors was undertaken in the Rinconada Marine Reserve (Antofagasta, Chile) to determine growth variations between surface and bottom waters. Scallop spat was collected at 16-m depth and grown at 1- and 16-m depths. An initial settlement of ca. 13,000 post-larvae per bottom collector (2 cohorts) was observed on 3 February 2001. Two new cohorts settled in bottom collectors on 3 March, while no spat settlement occurred in surface collectors. The four cohorts exhibited substantial and different mortality rates over the study period, depending on the cohort and on-growing depth. The first and second cohorts exhibited mortality rates of 80.3 and 53.1% in bottom collectors, respectively, versus 29 and 43.6% in surface structures. The third and fourth cohorts exhibited mortality rates of 21.4 and 59.7% in bottom collectors, respectively. Mean shell height of scallop spat after 88 days of culture was 6.46 mm for the first cohort and 4.37 mm for the second cohort in bottom collectors, versus 10.33 and 7.31 mm in surface collectors, respectively. Mean post-larval growth rate in bottom collectors (86 μm day⁻¹) was significantly lower than growth rate in surface collectors (146 μm day⁻¹). Factors explaining the depth-related mortality and growth rates are discussed to improve scallop culture in the Reserve. It was concluded from the results that culture improvement in Antofagasta Bay would require collecting spat in bottom waters and raising it near the surface during initial cultivation stages.