Suspension-feeding aquaculture systems: Effects of phytoplankton concentration and temperature on growth of the bay scallop

The growth rate of the bay scallop Argopecten irradians was studied in relation to temperature and phytoplankton concentration. Results suggest that normal variations in phytoplankton concentration do not influence the growth rate of scallops in their natural habitat. Increasing the concentration of phytoplankton above natural levels did not result in increased growth rates while decreasing the phytoplankton concentration resulted in a decrease in growth rate of the scallops. Under extremely low phytoplankton concentrations, such as those that characterize ‘clean water’ effluent from a culture system, the animals ceased growing. A mathematical model of scallop growth rate as a function of phytoplankton concentration is proposed as a tool for comparing the functioning of different suspension feeders in aquaculture systems.     

Seasonal variations in growth and clearance rate of the Zhikong scallop <Emphasis Type="Italic">Chlamys farreri</Emphasis> suspended in the deep water of Haizhou Bay,China

The growth and survival of the Zhikong scallop Chlamys farreri suspended in deep water of Haizhou Bay were studied from July 2007 to June 2008, and the biodeposition method was used to estimate the clearance rate of C. farreri under field conditions. Results showed that the scallop grew fast during all the culture time, with the exception of summer. The condition index of the scallop increased with time and reached the highest value in spring of the second year. The survival of scallops was 60.8 ± 3.9% at the end of this study, mortality occurring mainly during the summer and autumn of the first year. The clearance rate fluctuated obviously with season,with the highest value in September 2007, and the lowest value in March 2008. Factors accounting for variations in growth and clearance rate of scallops are also discussed.     

Qualitative modelling for the development of a sustainable management strategy for the Peruvian scallop Argopecten purpuratus (Lamarck 1819)

• 1. This study is the first attempt using Levins's Theory (loop analysis) in order to develop a sustainable management for the scallop, Argopecten purpuratus, fishery in Peru during El Niño‐Southern Oscillation events (ENSO) and upwelling conditions. Based on this theoretical framework, it was possible to estimate the local stability for each of these model systems and to follow the qualitative changes of the variables in response to external factors.
• 2. Based on our results, we suggest the following management policies to be implemented: (1) during ENSO events the size at the first capture of the scallops should be >70 mm and (2) the increase in the number of fishermen during ENSO events must be prevented. Both measures increase the sustainability of fishery under ENSO and upwelling conditions. The ecological models predict that during ENSO and upwelling events, any management strategy to increase the recruitment of the scallop would not have a positive impact on the adult stock.
• 3. Finally, we suggest that more efforts must be focused on the development of extended eco‐social models, which incorporate further social and economic variables, increasing realism of the abstractions for this fishery activity.

Copyright © 2002 John Wiley & Sons, Ltd.     

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.     

Juvenile chinook salmon (Oncorhynchus tshawytscha) growth on the central California coast during the 1998 El Niño and 1999 La Niña

We assessed growth in subyearling chinook salmon (Oncorhynchus tshawytscha) during the 1998 El Niño and 1999 La Niña in the Gulf of the Farallones, a region of the continental shelf off central California seaward of the Golden Gate and the southernmost ocean entry point for the species in North America. Juvenile salmon demonstrated greater growth during this strong El Niño, when water temperature anomalies of more than +3°C were recorded at local buoys, than during the similarly strong 1999 La Niña. Slopes of regressions of weight on length, length on age, and weight on age were all significantly greater for juvenile salmon during the 1998 El Niño compared with those in the 1999 La Niña. Daily otolith increment widths, an estimator of somatic growth, corroborated population data. Between June 1 and August 9, mean increment widths for juvenile chinook salmon in 1998 were 3.54 ± 0.03 μm, significantly larger than the 3.13 ± 0.03 μm found in juveniles during the same time interval in 1999. Condition factor for juvenile chinook salmon entering the ocean at the Golden Gate was the same in both years, but became significantly greater in ocean fish during the 1998 El Niño than in ocean fish during the 1999 La Niña. Energy storage was significantly greater in ocean juvenile salmon during the 1998 El Niño as well. Mean triacylglycerol/cholesterol ratios increased following ocean entry in 1998, whereas they declined in ocean juveniles during 1999. Thus, not only was growth better in the El Niño period compared with La Niña, but lipid accumulation was also better. Oceanographic data for 1998 indicated elevated temperatures, lower salinity, greater freshwater outflow from San Francisco Bay, northerly flowing coastal currents, and positive upwelling index anomalies. This combination of environmental factors resulted in greater zooplankton productivity that, in conjunction with higher temperatures, allowed metabolic processes to enhance growth. Although El Niño events have certainly produced large-scale, and often adverse, effects on ecosystems, the results of this study emphasize the importance of local oceanographic conditions to growth and other physiological and ecological processes.     

Implications of marine environment change on Japanese scallop (Mizuhopecten yessoensis) aquaculture suitability: a comparative study in Funka and Mutsu Bays,Japan

The determination of the causes for the changes in marine environment in areas with similar oceanic climate forcing on most suitable sites for scallop aquaculture can help to ensure long‐term sustainability of the coastal ecosystem. This study assessed aquaculture suitability sites using dominant indicators of marine ecological dynamics on Japanese scallop culture in Funka and Mutsu Bays, Japan as comparative examples. Data sources comprised of Moderate Resolution Imaging Spectroradiometer (MODIS), four dimensional‐variational (4D‐VAR) data assimilation system, Advanced Land Observing Satellite (ALOS), in situ and buoy measurements. The suitable sites were ranked on a scale of 1 (least suitable) to 8 (most suitable). In the most suitable sites in aquaculture operational areas, Funka Bay had a high proportion (51.1%) than Mutsu Bay (13.7%) for the best performed model. Peaks of aquaculture suitability scores were attributed to potential effects of currents. Extreme sea temperatures (>24°C) in summer 2010 were associated with low performance of the 2010 model in Mutsu Bay and mortality of scallops based on sea temperature‐depth visualizations. Future global warming effects are likely to decrease the most suitable culture sites in Funka Bay and loss of similar areas in Mutsu Bay. Thus, change in marine environment influences scallop culture development. Such concepts could form scientific basis for aquaculture planning on designated system of larval distribution and stock management of cultured species to minimize mortality and economic losses.     

El Niño–Southern Oscillation impacts on jumbo squid habitat: Implication for fisheries management

1. Dosidicus gigas is an ecologically and economically important squid species extensively distributed in the eastern Pacific Ocean. Its habitat is extremely sensitive to climatic and environmental variability.
2. The relationship between habitat pattern of D. gigas and El Niño–Southern Oscillation (ENSO, divided into the El Niño, ENSO-neutral, and La Niña events) was assessed from 1950 to 2015, using a habitat suitability index (HSI) modelling approach including two crucial environmental variables: sea surface temperature (SST) and sea surface height anomaly (SSHA).
3. On the basis of cross-correlation analysis, it showed that both SST anomaly and SSHA were significantly positively related to the ENSO index. Moreover, a significantly negative association was found between the HSI values and the ENSO index.
4. Due to the El Niño events, SST off Peru became higher and sea level rose, resulting in contracted areas of suitable SST and SSHA; consequently, suitable habitats for D. gigas dramatically decreased. In contrast, during the ENSO-neutral and La Niña years, the extent of suitable SST and SSHA increased due to the colder water and lower sea level, and suitable habitat for D. gigas expanded.
5. Moreover, the latitudinal gravity centre of HSI was significantly positively associated with the ENSO index. Relative to the ENSO-neutral and La Niña years, a southward movement of the monthly preferred SST isotherm for D. gigas during the El Niño years could explain the occurrence of more suitable habitats in southern waters off Peru.
6. These findings suggested that the ENSO event plays an important role in regulating environmental conditions off Peru and further affected the spatio-temporal distribution of D. gigas habitat.

     

Polyculture of sea scallops (Placopecten magellanicus) suspended from salmon cages

Commercial and developmental operations for the culture of the seascallop, Placopecten magellanicus, are present in AtlanticCanada and New England. In an experiment designed to examine the commercialfeasibility of polyculture of scallops with Atlantic salmon(Salmo salar), we measured growth andsurvival of sea scallops grown in suspension at two salmon aquaculture sites innortheastern Maine (Johnson Cove (JC) and Treats Island (TI)). Sea scallop spatwere grown in pearl nets and deployed on drop lines containing ten nets inAugust 1994. One drop line of ten nets was sampled about every four months andscallops were counted, measured and weighed. Scallop tissues were also analysedfor paralytic shellfish toxins (PSP). The maximum level of PSP recorded duringthe study was 1174 g STX equiv.·100 gtissue^–1 (excluding adductor muscle weight). After one year,shell heights were 53.6 and 56.4 mm, growth rates were 0.11 and0.12 mm per day and wet adductor muscle weights were 3.3 and 4.1g (TI and JC, respectively). These growth rates were comparable tosea scallops grown in suspension culture to a nearby scallop aquaculture siteand other areas in Atlantic Canada. Reduced rates of survival were found duringthe latter part of the experiment and were attributable, in part, to heavyfouling, predators and high stocking density. The potential for supplementalincome, diversification of the salmon aquaculture industry, and feasibility ofculturing scallops at adjacent sites to salmon operations does exist.     

The significance of various environmental parameters for growth of the Iceland scallop, Chlamys islandica (Pectinidae), in hanging culture

Iceland scallops, Chlamys islandica (O.F. Müller), were grown in hanging culture at 3 different depths (2, 12 and 40 m below the sea surface) in a northern Norwegian fjord. The growth of the soft parts of the body and the shell increment were monitored throughout the growing season (March until September). At the same time, temperature, salinity, water density, current speed, chlorophyll, particulate organic matter (POM) and particulate inorganic matter (PIM) were monitored at each of the experimental depths. Analysis of the environmental data together with the growth data showed that growth differences between the experimental depths were essentially the results of differences in nutritional conditions for the scallops, defined by the relationship between PIM and POM in the water column. The results also showed that growth in Iceland scallops can be increased significantly by suspending the animals in a more favourable nutritional environment than that found on the natural scallop beds.     

El Niño effects in the Palmyra Atoll region: oceanographic changes and bigeye tuna (Thunnus obesus) catch rate variability

A generalized additive model (GAM) was constructed to separate and quantify the effects of fishery‐based (operational) and oceanographic parameters on the bigeye tuna (Thunnus obesus) catch rates at Palmyra Atoll in the central Tropical Pacific. Bigeye catch, the number of hooks per set, and set location from 4884 longline sets spanning January 1994 to December 2003 were used with a temporally corresponding El Niño‐Southern Oscillation (ENSO) indicator built from sea surface height (SSH) data. Observations of environmental data combined with the results from the GAM indicated that there is an increase in bigeye catch rates corresponding to an increase in eastward advection during the winter months of El Niño events. A seasonal pattern with higher bigeye catch rates from December to April and a spatial pattern with higher rates to the northeast and northwest of the atoll were observed during this study period. It is hypothesized that the combination of the eastward advection of the warm pool coupled with vertical changes in temperature during the winter months of El Niño events increases the availability of bigeye tuna in this region. This increase in availability may be due to a change in exploitable population size, location, or both.     

On the relationship between low winter temperatures and mortality of juvenile scallops, Pecten maximus L., cultured in western Norway

The mortality of juvenile scallops (Pecten maximus L.) cultured at two densities at 8‐ and 15‐m depth was investigated at 17 trial locations along the western Norwegian coast between latitudes 58 and 65°N. During the winter of 1995/1996, scallops suffered high mortality at many sites. The results show a clear relationship between minimum temperature recorded on the sites and scallop mortality. All the scallops died at sites where minimum temperatures were lower than 2°C, while a mortality rate below 30% was only obtained at locations where the minimum temperature was 4–5°C. At temperatures between 2 and 4°C, mortality was intermediate, ranging from 52% to 100%. There were no mortality differences between culture densities, while a significantly higher mortality at 8‐ than at 15‐m depth was shown for two of the four sites with a total mean mortality lower than 30%. The results are discussed in relation to low‐temperature conditions along the Norwegian coast to suggest risk assessments for site selection in scallop culture.     

Fluctuation in the distribution of low-salinity water in the North Equatorial Current and its effect on the larval transport of the Japanese eel

Surface water in the North Equatorial Current (NEC) is composed of southern low‐salinity water diluted by precipitation to less than 34.2 psu and northern, high‐salinity tropical water greater than 34.8 psu. Analyses of 27‐year historical data, observed in winter and summer along the longitude 137°E by the Japan Meteorological Agency, shows that an obvious salinity front (34.5 psu) generated by the two water masses was usually located around 15°N. However, the salinity front has been moving northward during the past three decades. El Niño/Southern Oscillation (ENSO) affected salinity in the surface layer, while temperature changed in the middle layer. The salinity front sometimes moved southward, mainly south of 5°N, and the movement was well correlated with the southern oscillation index (SOI). Because precipitation at Yap (9.5°N, 138.1°E) fluctuated with SOI, this spike‐like southward movement of the salinity front was probably affected by reduction of low‐salinity water during El Niño in the north‐western Pacific Ocean. However, ENSO only induced such large southward movements of the salinity front when the time lag between the low precipitation and low SOI was short (within four months). This salinity front is quite important for long‐distance migrating fish such as the Japanese eel because the eels spawn just south of the salinity front in the NEC. This behaviour suggests that the movement of the salinity front associated with ENSO may control the success of larval transport from the spawning ground in the NEC to the nursery ground in East Asia. In fact, catch of the Japanese eel larvae in Japan was well correlated with fluctuation of SOI and the location of the salinity front, and lower catch occurred during El Niño. The salinity front has moved from 13°N to 17°N during the past three decades. Considering that conditions of larval transport are worse north of 15°N, we suggest that decadal‐scale linear decrease of glass eel catch during the past three decades also can be explained by the displacement of the salinity front.     

几种养殖扇贝微卫星标记的研究进展

我国扇贝养殖规模占世界首位，栉孔扇贝( Chlamys farreri ) 、华贵栉孔扇贝( Chlamys nobilis ) 、虾夷扇贝( Patinopecten yessoensis) 和海湾扇贝( Argopecten irradians ) 是4 种主要养殖扇贝种类。本文主要概述我国4种主要养殖扇贝微卫星标记开发现状以及在遗传多样性分析、遗传图谱构建、物种鉴定等方面取得的研究成果和应用进展，为微卫星标记在扇贝类遗传学研究提供基础资料。     

流沙湾浮游植物群落特征季节变化及其与养殖活动的关系

流沙湾是中国海水珍珠“南珠”的主产区和广东省重要的贝类养殖区。为评估湾内养殖活动的环境效应,于2015~2016年对流沙湾海区进行了夏(8月)、秋(11月)、冬(2月)、春(5月) 4个季节的浮游植物和海水理化因子调查。共检出浮游植物171种,包括硅藻门43属122种、甲藻门 10属44种、蓝藻门2属2种、金藻门2属2种和裸藻门1属1种。流沙湾内湾浮游植物细胞丰度为(0.05~79.04)×104个/L,夏季>春季>秋季>冬季,且夏季丰度远大于其他三季,内湾和外湾差异不显著。春季须状角毛藻(Chaetoceros crinitus)、红海束毛藻(Trichodesmium erythraeum)和明壁圆筛藻(Coscinodiscus debilis)为主要优势种,夏季优势种主要为中肋骨条藻(Skeletonema costatum),秋季优势种主要为拟弯角毛藻(Chaetoceros pseudocurvisetus)、奇异棍形藻(Bacillaria paradoxa)、洛氏角毛藻(Chaetoceros lorenzianus),冬季主要优势种为威氏圆筛藻(Coscinodisus wailesii)、柔弱根管藻(Rhizosolenia delicatula)、岛脆杆藻(Fragilaria islandica)。其中,奇异棍形藻为春、秋、冬季的优势种,红海束毛藻为春、夏、秋季的优势种。冗余分析表明,流沙湾浮游植物优势种在春季与水温和氨氮密切相关,夏季受透明度显著影响,而在秋、冬季受亚硝酸氮含量影响显著。流沙湾不同养殖区的浮游植物多态性和丰度有明显季节差异。与2012年相比,流沙湾外湾的养殖覆盖率提高了近50%,内湾的珍珠贝养殖减少了近90%,养殖品种、规模和分布格局都发生了明显变化,目前流沙湾的浮游植物群落特征正是对其变化的一种响应。夏季鱼类网箱养殖提高了水域营养盐水平并降低了浮游植物多样性。大规模的扇贝养殖则导致了扇贝养殖区浮游植物丰度的降低。     

Genetic considerations in transfers and introductions of scallops

As the potential of scallop aquaculture becomes increasinglyrealised, transfers (movement within a species' range) andintroductions (movement outside a species' range) of scallops arebecoming more common. To predict the genetic consequences oftransfers, information on genetic differences between source andrecipient populations is vital. Morphological, allozyme and DNAbased data on genetic differentiation of scallop populations andscallop sub-species are presented and discussed. Otherconsiderations are the numbers of individuals transferred andwhether they are wild stock or hatchery product. Loss of geneticdiversity is difficult to avoid in hatchery conditions althoughthere are ecological advantages to using disease-free hatcheryseed. Mitochondrial DNA data indicating significant geneticconsequences of the introduction of Argopecten irradians fromthe USA to China are discussed and compared with data onPatinopecten yessoensis introduced from Japan to Canada.Potential risks and consequences of hybridisation should beexperimentally assessed before introductions of scallops arecarried out. Hybridisation is unpredictable and can lead to lossof genetic diversity or breakdown of co-adapted gene complexes.The use of sterile triploid scallops for introductions to avoid hybridisation and reduce ecological impact has merit butreversion to diploidy may occur.     

A BIOECONOMIC MODEL FOR CHAM SCALLOP (PATINOPECTEN YESSOENSIS) AQUACULTURE IN KOREA

A bioeconomic model of cham scallop aquaculture in Korea was used to determine an optimal farm grow-out strategy. The model used estimated cost functions for two culture methods and growth functions based on three environmental characteristics for each region (Kojin and Chumunjin). Stochastic growth was incorporated using probabilities of alternative environmental states (based on expected levels of water temperature, salinity, and dissolved oxygen) by region, culture method, and month. The model revealed a 26% potential increase in net present value from altering management of a single rotation. Optimal multiple rotations required up to four different rotations depending on the region and culture style. Farmers could increase economic returns by delaying harvest and subsequent plantings in order to market larger, more valuable scallops. Resource managers could increase resource rents by adjusting the licensing system to account for regional-style differences and by targeting the planned aquaculture investments.     

Predation risk management of sea stars (Asterias amurensis and Distolasterias nipon) by adjusting the density and size of seeded scallops (Mizuhopecten yessoensis): an improvement to local mariculture

Optimizing the release density and size of juvenile commercial species for local ecosystems is a critical issue that should be considered when countering predation impacts. To ascertain whether mariculture production of the Japanese scallop (Mizuhopecten yessoensis) could be enhanced by modifying releasing practices, we experimentally investigated the effects of density and size of scallop seeds on their survival in the presence of two sea star species, Asterias amurensis and Distolasterias nipon, with different predation capacities. Under current mariculture practices, the juveniles are briefly exposed to air just before release; therefore, we also examined how air exposure stress increased the predation risk. Scallop survival in the presence of both sea stars increased by?>?20% by increasing scallop size from 30 to 50 mm. Increasing scallop density (range: 5 to 30 scallops m^?2) increased each individual’s survival in the presence of A. amurensis but had no significant effect on predation by D. nipon. Therefore, the release of smaller quantities of large-sized scallops rather than larger quantities of small scallops is recommended to reduce D. nipon predation. In the presence of sea stars, especially by D. nipon, the predation impact on small scallops increased after just a few hours of air exposure, indicating that air exposure of juvenile scallops should be minimized. Our results will mitigate the economic cost of mariculture by facilitating the determination of optimal release conditions for juvenile scallops.

     

Physiological and biochemical responses of Zhikong scallop,Chlamys farreri,to different thermal stressors

Water temperature is a significant environmental stressor that affects physiology and biochemical activities of bivalves. Here, temporal variations in physiological and biochemical parameters of Zhikong scallop, Chlamys farreri, under three water temperature treatments were investigated. For the first treatment, scallops were transferred from rearing temperature (15°C, control temperature) to 5, 10, 20 and 25°C, respectively. The second group of scallops was gradually acclimated to above experimental temperatures at a rate of 1–2°C day^?1. The third group was transferred directly between 15 and 7°C every 12 h and for six times. Results showed that significantly higher oxygen consumption and ammonia‐N excretion together with a significant lower ingestion rate was observed for the acute temperature change treatment compared to those in the equivalent gradual temperature variation treatment (P < 0.05). In acute temperature change treatment, hepatopancreas antioxidant enzyme activities, that is, superoxide dismutase (SOD) and catalase (CAT), immune enzyme activities, that is, acid phosphatase (ACP) and lysozyme (LSZ), and heat‐shock protein 70 gene (Hsp70) expression levels of scallops increased substantially within 48 h. Significant increases in SOD, CAT, ACP and LSZ activities, and malondialdehyde content occurred under exposure to fluctuating temperatures (P < 0.01). Gill and hepatopancreatic Hsp70 expression levels also increased significantly in response to water temperature fluctuations (P < 0.05). The study provides basic knowledge about thermal stress in Zhikong scallop and may contribute to the management of scallop mortalities.     

Growth,survival and immune activity of scallops,Chlamys farreri Jones et Preston,compared between suspended and bottom culture in Haizhou Bay,China

We examined the growth, survival and immune response of the scallop, Chlamys farreri, during a 1‐year period in deep water of Haizhou Bay. Scallops were cultured using two methods: (1) in lantern nets at a 5 m depth and (2) in a bottom culture system (sleeves) on the seabed at about a 25 m depth. Shell heights, meat dry weight and immune activities in the haemolymph (superoxide dismutase and myeloperoxidase) were measured bimonthly or quarterly from July 2007 to June 2008. Survival was measured at the end of the study and environmental parameters in the experimental layers were monitored during the experiment. The growth and immune activities of scallops were lower when the water temperature was high, which was consistent with the main mortality occurring in summer. The growth and immunity of scallops were higher in the suspended culture than in the bottom culture during the experiment, with the exception of shell growth during the last study period. Survival of scallops in the suspended culture (54.6±12.3%) was significantly lower than that in the bottom culture (86.8±3.5%) at the end of this study. We conclude from our results that the high mortality of C. farreri can be prevented by culturing them in a bottom culture system before November of the first year, and then transferring them to a suspended culture to improve scallop production.     

虾夷扇贝天然苗种中间育成技术研究

自然海区采集的虾夷扇贝苗种比人工苗种晚2个月,为了实现当年采苗,当年培育成3 cm以上增养殖用苗种,2006—2008年,就虾夷扇贝中间育成技术开展了试验研究。育成密度为90~110个/层,密度对中间育成率影响不显著。密度为70~90个/层,平均壳高达到3.28 cm,群体组成中≥3 cm个体比例为83.33%;密度为120~130个/层,平均壳高3.08 cm,群体组成中≥3 cm个体比例为61%;密度为160~170个/层,平均壳高2.77 cm,群体组成中≥3 cm个体比例仅为22%,密度对苗种生长影响显著。分苗时间早晚对苗种生长有一定影响,分苗时间早,天然苗可充分利用7-8月快速生长期快速生长,提高3 cm以上个体的育成率。中间育成期间的水温对育成率有一定影响,23℃以上水温持续时间较长时,育成率下降。