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versión On-line ISSN 0718-560X
Lat. Am. J. Aquat. Res. v.37 n.3 Valparaíso 2009
Lat. Am. J. Aquat. Res., 37(3): 555-570, 200
Seamounts in the southeastern Pacific Ocean and biodiversity on Juan Fernandez seamounts, Chile
Montes submarinos en el océano Pacífico suroriental y biodiversidad en el cordón de Juan Fernández, Chile
Eleuterio Yáñez1, Claudio Silva1, Rodrigo Vega2, Fernando Espíndola3, Lorena Álvarez1, Nelson Silva1, Sergio Palma1, Sergio Salinas1, Eduardo Menschel2, Verena Häussermann4, Daniela Soto1 & Nadín Ramírez1
1Pontificia Universidad Católica de Valparaíso, P.O. Box 1020, Valparaíso, Chile
2Universidad Austral de Chile, P.O. Box 567, Valdivia, Chile
3Instituto de Fomento Pesquero, P.O. Box 8-V, Valparaíso, Chile
4Fundación Huinay, P.O. Box 462, Puerto Montt, Chile
ABSTRACT. Seamounts are vulnerable marine ecosystems. In Chile, information on these ecosystems is quite scarce; thus, a compilation of information on their geographical distribution and biodiversity is presented herein. A total of 118 seamounts distributed in the Chilean EEZ are identified and characterized. Additionally, an in situ assessment was carried out on the Juan Fernandez seamounts 1 and 2 (JF1 and JF2), which were also oceanographically characterized. Phytoplankton, zooplankton, and marine invertebrate samples were collected and an exploratory fishing survey was executed using different gears. According to the bibliographical review, a total of 82 species have been collected on the JF1 and JF2 seamounts, highlighting fmdings of black coral species caught in lobster traps at the Juan Fernandez Archipelago. Submarine images of the marine substrate at JF1 and JF2 reveal characteristics attributable to the impact of bottom dredges, coinciding with the information obtained from the trawling fleet. The fishing activity was carried out primarily at JF2 (4,667 km of trawling). The monthly fishing effort increased considerably in 2002, 2003, and 2005, reaching values above 500 km of trawling and, thus, modifying the spatial structure of the resource aggregates on the JF2 seamount.
Keywords: seamounts, identification, biodiversity, fishing impact, Juan Fernández Archipelago, southeastern Pacific.
RESUMEN. Los montes submarinos constituyen ecosistemas marinos vulnerables. Chile presenta una escasa información acerca de estos ecosistemas, por lo que este trabajo recopila información sobre distribución geográfica y biodiversidad. Se identifican y caracterizan 118 montes en la ZEE de Chile. Adicionalmente, una evaluación in situ se desarrolló sobre los montes Juan Fernández 1 y 2 (JF1, JF2), caracterizándolos oceanógraficamente. Se recolectaron muestras de fitoplancton, zooplancton e invertebrados marinos, y se realizó pesca exploratoria con diversos artes. La revisión bibliográfica establece que en JF1 y JF2, se han capturado un total de 82 especies, destacándose la presencia de corales negros en trampas langosteras en el archipiélago de Juan Fernández. Fotografías submarinas de los montes JF1 y JF2 presentan características atribuibles al impacto de artes de arrastre de fondo, concordante con información de la flota. El esfuerzo de pesca se realizó mayormente en JF2 (4.667 km arrastrados). El esfuerzo de pesca mensual se incrementó considerablemente durante el 2002, 2003 y 2005, alcanzando valores sobre 500 km arrastrados, modificando la estructura espacial de las agregaciones de recursos en el monte JF2.
Palabras clave: montes submarinos, identificación, biodiversidad, impacto pesquero, archipiélago de Juan Fernández, Pacífico suroriental.
The marine environment is currently under serious depletion as a result of overfishing, contamination, and the direct and indirect impacts of climate changes. The anthropogenic and climate impacts observed in many places have caused dramatic changes in ecosystems. This is the case of seamounts, vulnerable marine ecosystems in which a decrease of biostructure-forming species and a collapse of oceanic fisheries have been observed. The vulnerability of these ecosystems is related to the possibility that a population, community, or habitat will experience a substantial alteration, which may be irreversible or of slow restoration (FAO, 2007). The international information on seamount biodiversity and ecology is limited, especially for those at depths exceeding 300 m (Tracey et al, 2004). Therefore, although thousands of seamounts are estimated to exist around the world, only around 200 have been biologically sampled, in most cases, during commercial fishing activities (Probert et al, 1997; Gálvez et al, 2006).
In Chile, there is lack of information for an unde-termined number of seamounts in the Economic Exclusive Zone (EEZ). Research on seamount biodiversity along the Chilean coast has been carried out since 1950, mainly by the Russian government on the Nazca and Salas and Gómez ridges, beyond the EEZs of Chile and Perú (Parin et al, 1997). The information on the Juan Fernandez Archipelago (33°S-78°W) is limited to the H.M.S. Challenger scientific expedition (1873-1876), the Pacific Swedish expedition (1916-1917), and the B/I Antón Bruun expedition (1966) (Rozbaczylo & Castilla, 1987), as well as the ocean-graphic cruises MARCHILE VIII and IX of 1972 and 1973, respectively (Cerda, 1977), the CIMAR 5 and 6 Oceanic Islands cruises in 1999 and 2000 (Rojas et al, 2004), and the scientific survey of B/I Koyo Maru in 2004 (Zuleta & Hamano, 2004). Furthermore, information has been systematically collected on fauna associated with bottom dredges over Chilean seamounts (Gálvez et al, 2006).
The objective of this work, considering the international demand for information on vulnerable marine ecosystems such as seamounts (Resolution 59/25 of the ONU General Assembly), is to determine the geographical distribution of seamounts in the Chilean EEZ, including a biodiversity and fishing impact study on some seamounts of the Juan Fernandez Archipelago.
MATERIALS AND METHODS
The geographical seamount identification and distribution was determined through the analysis of images generated using 2' x 2' resolution satellite altimetry data (Smith & Sandwell, 1997) and 1' x 1' resolution sounding data (GEBCO, 2003), according to the Kitchingman & Lai methodology (2004). Furthermore, in situ assessments were carried out on two seamounts of the Juan Fernandez Archipelago - Juan Fernandez 1 (JF1) and Juan Fernandez 2 (JF2) -through two exploratory campaigns at 247 and 292 m depth, the respective depths of their tops. The first was executed aboard the PAM Portugal II in July-August 2007, and the second was carried out aboard two artisanal boats in November-December 2007: Boat No. 58 Cumberland and L/M Alborada. All the relatively fíat area accessible for fishing and sampling systems (over 700 m deep) was systematically gridded (0.5 x 0.5 tenths of degrees), and a grid was randomly selected for sampling.
Three different depth strata were analyzed: pelagic, demersal, and benthic. Different fishing systems were also used: vertical longlines (1,264 hooks), handlines (12 hooks), fishing pots (108 traps), surface longlines (440 hooks), zooplankton nets (10 haul), dredging (5 haul), submarine camera observations (4 observation periods), and oceanographic surveys of the water col-umn (CTD and Niskin Bottles). The surface oceanographic characteristics were analyzed using satellite information (NOAA, TOPEX, SeaWins, SeaWifs).
Additionally, a bibliographical analysis was done to determine the different species previously collected during surveys, cruises, and commercial fishing activities carried out on these seamounts. Finally, an evalua-tion of the fishing effects index (FEI) (O'Driscoll & Clark, 2005) was done in the same area of study. This index involves data on the fishing effort executed on each seamount, the direction of the trawling, and the seamount area. On one hand, this index measures the fishing density on a seamount as a proportion of its area; on the other hand, it reflects a scale factor that is proportional to the directions the seamount was trawled. A high FEI value may be explained through a heavy effort relative to the seamount size and the fact it was trawled in all directions. The information used for this analysis corresponds to data from fishing bin-nacles of the industrial trawling fleet operating over orange roughy (Hoplostethus atlanticus) and alfonsino (Beryx splendens) between 2000 and 2006. The same data was used to analyze the spatial structure dynam-ics of the resources in 2001 and 2003 through geostatistical techniques.
A total of 118 seamounts were identified in seven areas of the Chilean EEZ (Fig. 1): 35 around Easter Island (25°-30°S, 105°-112°W) (Fig. 2), 21 near San Félix Island (24°-29°S, 76°-84°W) (Fig. 3), 21 off northern Chile (18°-30°S, 71°-75°W) (Fig. 4), 15 around the Juan Fernandez Archipelago (30°-35°S, 76°-82°W) (Fig. 5), eight in the central area of the country (30°-40°S, 71°-76°W) (Fig. 6), nine in the southern area (40°-50°S, 73°-79°W) (Fig. 7), and 10 off far-southern Chile (50°-58°S, 70°-77°W) (Fig. 8). This identification included the geographical location, surface area, and depth of these seamount tops and the designation of codified ñames (see Yañez et al. 2008 for details).
Figure 1. Areas where seamounts were identified in the southeastern Pacific Ocean. NZ: northern zone, El: eastern island, SF: San Félix island, ZC: central zone, JF: Juan Fernández Archipelago, SZ: southern zone, SAZ: far-southern zone.
Figura 1. Localización de areas donde se identificaron montes submarinos en el océano Pacífico suroriental. NZ: zona norte, El: isla de Pascua, SF: isla San Félix, ZC: zona central, JF: archipiélago de Juan Fernández, SZ: zona sur, SAZ: zona sur austral.
Figure 2. Locations and codes assigned the seamounts identified in the Easter Island area (El).
Figura 2. Localización y código asignado a los montes submarinos identificados en la zona de Isla de Pascua (El).
Figure 3. Locations and codes assigned the seamounts identified in the area of San Félix Island (SF).
Figura 3. Localización y código asignado a los montes submarinos identificados en la zona de isla San Félix (SF).
Figure 4. Locations and codes assigned the seamounts identified in the northern zone (NZ) (18°-30°S).
Figura 4. Localización y código asignado a los montes submarinos identificados en la zona norte (NZ) (18o-30°S).
Figure 5. Locations and codes assigned the seamounts identified in the area of the Juan Fernandez Archipelago (JF).
Figura 5. Localización y código asignado a los montes submarinos identificados en el cordón de Juan Fernández (JF).
Figure 6. Locations and codes assigned the seamounts identified in the central zone (CZ) (30°-40°S).
Figura 6. Localización y código asignado a los montes submarinos identificados en la zona central (CZ) (30o-40°S).
Figure 7. Locations and codes assigned the seamounts identified in the southern zone (SZ) (40°-50°S).
Figura 7. Localización y código asignado a los montes submarinos identificados en la zona sur (SZ) (40°-50°S).
Figure 8. Locations and codes assigned the seamounts identified in the far-southern zone (SAZ) (50°-58°S).
Figura 8. Localización y código asignado a los montes submarinos identificados en la zona sur-austral (SAZ) (50°-58°S).
Seamounts JF1 and JF2 have volcanic substrate, which is mainly constituted by bare rock and sand. These seamounts are influenced by several water masses: Subtropical Water (STW), Subantarctic Water (SAAW), Equatorial Subsurface Water (ESSW), and Antarctic Intermedíate Water (AAIW), but are pre-dominantly influenced by SAAW and STW (Fig. 9).
Figure 9. T-S diagram of the oceanographic stations for the seamounts a) JFl and b) JF2.
Figura 9. Diagrama T-S de estaciones oceanógraficas para los montes a) JFl y b) JF2.
The vertical distribution of dissolved oxygen showed a two-layer structure. The well-oxygenated surface structure of approximately 100 m with concentrations greater than 5 mL L-1 (90-100% saturation) is the result of oxygen-atmosphere exchange and primary production in the area. Beneath this layer and at approximately 200 to 300 m depth, the dissolved oxygen was quickly reduced to concentrations of less than 1 mL L-1 (5-20% saturation); the latter drop was caused by the presence of ESSW coming from off Perú (Fig. 10). A slight current system was observed in July-August (winter) with sea surface temperature (SST) anomalies that were negative at JF1 and posi-tive at JF2. The SST showed a typical cold condition of 10° to 17°C, surface salinity of approximately 34.3, and chlorophyll concentrations between 0.09 and 1 mg m-3. In November-December (spring), however, a greater amount of mesoscale structures such as shifts and currents were observed. The STW showed a cold condition that is typical of the season, with SST of 13 to 18°C; surface salinity cióse to 34.1, and a chlorophyll-a concentration around 4 mg m-3.
Figure 10. Vertical distribution of dissolved oxygen at eight oceanographic stations.
Figura 10. Distribución vertical de oxígeno disuelto en ocho estaciones oceanógraficas.
The phytoplankton collected on the surveyed sea-mounts involved seven classes of organisms that were classified into 31 genera, 23 species, and other non-identified species. Fifty percent of the organisms were classified as "other flagellates", another 40% corresponded to the Dinophyceae class, and the remaining 7% included the Bacillariophyceae (3.3%), Ciliata (2.1%), Cianophyceae (1.4%), Dictyochophyceae (0.15%), Chlorophyceae (0.04%), and Acantharia (0.01%) (Table 1). Meanwhile, a total of 52,309 organisms were identified as zooplankton; these were distributed among 16 taxonomic groups belonging to the phyla Cnidaria, Ctenophora, Chaetognatha, Annelida, Nemertina, Arthropoda, Tunicata, and Verte -brata. An 87.8% of the organisms were chitinous (euphausiids, mysids, amphipods, ostracods, copepods, cirripedia, decapod crustacean larvae), 11.6% were gelatinous and semi-gelatinous (jellyfish, siphonophores, ctenophores, chaetognaths, salps, appendicularians, polychaetes, nemertins) and the remaining 0.6% corresponded to ichthyoplankton (Hygophum brunni, Sardinops sagax) (Table 2).
The fishing methods allowed catches of two pe-lagic species, blue shark (Prionace glauca) and snoek (Thyrsites atún); two demersal species, croaker (Helicolenus lengerichi) and depth conger (Pseudoxenomystax nielseni); and two crustacean species, golden crab (Chaceon chilensis) and Juan Fernandez king crab (Paromola rathbuní). A total of 409 invertebrates were collected using a dredge. These represented important groups of species such as Echinoidea (Echinacea), Polychaeta, Porifera, Actinaria, and Asteroidea (Table 3). Due to the complexity of the identification, only two taxa have been identified to this date: 1) Asteroidea new species of Smilasterias and 2) Gorgonia species Callogorgia kinoshitae (Kükenthal, 1913). Only preliminary results are available for other species.
Table 3. Invertebrate species collected with dredging.
Tabla 3. Especies de invertebrados recolectados con rastra.
The bibliographical review established that, during the 2001 to 2006 fishing activities, a total of 82 species were collected from the JF1 and JF2 seamounts; these belonged to four phyla (Chordata, Arthropoda, Mollusca, Echinodermata) and the families Macrouridae (9), Moridae (6), and Dalatiidae (4) stood out. The presence of black coral species (Parantipahes fernandenzii, Trisopathes spp., Leiopathes spp.) in lobster traps used around the Juan Fernandez Archipelago deserve mention (Arana et al, 2006).
Submarine images of the JF1 and JF2 marine sub-strate showed characteristics ascribed to the impact of bottom dredges, coinciding with the information from the trawling fleet, whose activity was primarily executed on the fiat surface area of the seamounts (Gálvez et al, 2006). When analyzed, this information revealed that the fishing activity was mainly concentrated on the JF2 seamount, reaching 4,667 km of trawling; in comparison, trawling on the JF1 and JF4 seamounts reached values of 1,526 km and 906 km, respectively. In spite of these results, the FEI showed higher values for seamounts JF4 and JF2 (10.5 km-1and 11.7 km-1, respectively) than for JF1. Although heavy fishing activity was executed on the latter, its FEI was 2.51 km-1 due to its larger area, which is es-timated to be 608 km2 (Table 4).
Table 4. Name, mean latitude and longitude, and the estimated area, effort, and relative fishmg effect mdex (FEI) of six seamounts where extractive activity was conducted between 2000 and 2006.
Tabla 4. Nombre del monte, latitud y longitud media, area estimada, esfuerzo estimado e índice relativo de pesca (FEI) de seis montes donde se efectuó actividad extractiva durante 2000-2006.
In general terms, the fishing effort, measured as the total trawling distance, increased considerably in 2002, 2003, and 2005, with values that exceeded the 500 km of trawling. Later, a considerable decrease was observed by the end of the analyzed period (2001-2006), followed by the same values observed at the beginning of the fishing activity. The high level of observed fishing effort seems to have modified the spatial structure of the resource aggregates exploited at the JF2 seamount. In 2001, the aggregates at this seamount showed a symmetrical spatial distribution up to 4 km; however, that value that did not exceed 1 km in 2003 (Fig. 11). The spatial variability was affected by a decrease in the relative abundance of the resources exploited on this seamount (orange roughy and alfonsino) (Fig. 12).
Figure 11. Theoretical and adjusted spherical model for the catch rate variogram on seamount JF2 in 2001 and 2003.
Figura 11. Modelo esférico teórico y ajustado para el variograma de las tasas de captura en el monte submarino JF2 en 2001 y 2003.
Figure 12. Distribution of the catch rates for the seamount JF2 in 2001 and 2003; maps were generated by ordinary punc-tual kriging.
Figura 12. Distribución de las tasas de captura para el monte submarino JF2 en 2001 y 2003; mapas generados mediante estimación espacial krigging puntual ordinario.
A total of 118 seamounts were identified in the continental and insular EEZ of Chile. A method similar to that used by Kitchingman & Lai (2004) was put into practice, considering statistical (standard deviation, filters, hillshading) and visual (judgment, 3D cartography) analyses for the identification of potential seamounts. The number of identified seamounts is influenced by the depth standard deviation as well as filter size and type (kernel 5*5 nearest-neighbor) and visual analysis criteria. Furthermore, the identification sensitivity is directly affected by the spatial resolution of the bathymetric data.
The information on the diversity of the phytoplank-ton organisms collected in the area, along with the data analyzed by Pizarro et al. (2006), allow the preliminary inference that the nano- and microplankton structure detected with the analysis of the water samples collected in late winter 2007 indicate the presence of a clearly oligotrophic environment. Small organisms predomínate such environments and the systems are mainly supported by regenerated production and the probable entry of allochthonous nutrients from adjacent islands or elements advected from the seamounts or the coastal areas of Chile through large upwelling plumes that are generally observed on satellite images. Regarding the diversity of zooplankton organisms, most species and/or genera identified around the seamounts corresponded to organisms that are characteristic of the oceanic waters of the Humboldt Current System, which are found in low densities off the coast. The taxonomic composition of the zooplankton in this area is characterized by the presence of copepods (84.4% zooplankton), which coincides with results for oceanic waters in similar ecosystems of other oceans (Schnack-Schiel & Mizdalski, 2002). The quantity of zooplankton was quite scarce, in agreement with the low densities reported around the Juan Fernandez Archipelago (Palma, 1985) and the oceanic waters along the Chilean coast (Palma & Silva, 2006), and with other studies that have shown low densities on seamounts with abrupt topographies. This contradicts the results of Schwartz (2005) for seamounts from the Eastern Central Pacific. In fact, the biomass values were quite low compared to those detected in Chile's coastal waters.
The diversity of pelagic, demersal, and benthic organisms from this area was restricted to four fish species and two crustacean species. This was basically due to the fishing systems used in the surveys, which prioritized direct, non-intrusive sampling methods such as submarine images and gears like traps and longlines. One fish was the blue shark (Prionace glauca), a species considered to be epipelagic and of circumpolar distribution (Compagno, 1984). This shark is abundant in the southeastern Pacific and is captured by multiple fleets using surface longlines. The sawfish (Thyrsites atún), on the other hand, is considered to be a benthopelagic fish with a well-known distribution on continental shelves or around islands (Nakamura & Parin, 1993). Among demersal fish, the croaker (Helicolenus lengerichi) has been cited as one of the five species of the Scorpaenidae family present around the Juan Fernandez Archipelago (Pequeño & Sáez, 2000), whereas the conger Bassanago albescens has been caught with a low incidence (Lillo et al, 1999) as part of the by-catch of orange roughy fishing activities on Juan Fernandez seamounts.
The golden crab (Chaceon chilensis) and the Juan Fernandez king crab (Paromola rathbuni) have been cited as two of the five decapod crustacean species captured during surveys and experimental trap fishing activities around Robinson Crusoe and Santa Clara islands (Retamal & Arana, 2000). The presence of the Juan Fernandez king crab was originally reported for the Juan Fernandez Archipelago (Retamal, 1981) and the Desventuradas Islands (Báez & Ruiz, 1985) and is considered to be endemic to this area of the southeastern Pacific. This decapod is distributed between 100 and 300 m depth, with a greater abundance at 200 m around Robinson Crusoe and Santa Clara islands (Retamal & Arana, 2000). Furthermore, the golden crab has been reported off Zapallar and Quintero, along the central coast of continental Chile (Báez & Andrade, 1977; Andrade & Báez, 1980; Andrade, 1987), the Juan Fernandez Archipelago and San Félix and San Ambrosio islands (Retamal, 1981; Chirino-Gálvez & Manning, 1989), and along the undersea Nazca Ridge mainly at 90°W (Parin et al, 1997). The golden crab is generally distributed between 200 m and 2,000 m of depth (Dawson & Webber, 1991). It was found at depths of 400 and 800 m along the undersea Nazca Ridge (Parin et al, 1997) and was caught at 100 and 1,000 m around Robinson Crusoe and Santa Clara islands, with a greater abundance at 300 m and between 500 and 600 m (Arana, 2000).
The submarine images of the plains of seamounts JF1 and JF2 (up to 600 m approximately) suggest the presence of a marine substrate with similar characteistics to those reported in the literature for places that have been strongly impacted by trawling gears (FAO, 2007; Clark & Koslow, 2007).
Johnston & Santillo (2004) have suggested that sustainable seamount fisheries require good knowledge of the biology and ecology of the species to be exploited. Regarding the orange roughy fisheries on seamounts within the Chilean EEZ, there has been a trend towards increased global quotas in spite of the ignorance regarding the stock abundance at the Juan Fernandez Archipelago (Young et al., 2000; Gálvez et al, 2006). Despite this increase, the quota has never been totally extracted and the landing proportion has been observed to decrease.
The FEI provides a measure of relative intensity of the trawling fishing activities on a seamount, thereby allowing the categorization of the seamounts according to trawling density and direction. Due to the fact that the trawling was reported to last cióse to a minute and the trawling velocity is generally constant, then the trawling length estimation offers an adequate indicator of the scanned area. The distribution of the trawling direction on the studied seamounts was not random, suggesting that the fishermen have some degree of knowledge and, thus, prefer certain areas (trawling routes), whereas other adjacent areas do not seem to be affected by fishing activities. O'Driscoll & Clark (2005) have suggested that the FEI cannot directly assess the fishing impact on a seamount. Therefore, it should be necessarily related to other ecological indexes in order to obtain an ecological impact index of the trawling fishing over the substrate and associated fauna that could vary according to the substrate and fishing intensity.
Furthermore, strong spatial variability of the relative densities of the fishing resources associated with seamount JF2 in 2001 and 2003 was observed. This spatial variability was associated with a decrease in the relative abundance of the two main fishing resources exploited on this seamount (orange roughy and alfonsino) and a strong spatial contraction of said resources, which was represented by a significant change in the variogram range. The effect of the commercial exploitation on seamount JF2 caused an 85% reduction in the range of values between 2001 and 2003. Pankhurst (1998) indicated that orange roughy aggregates in the same period and place on the seamounts of New Zealand, which makes it quite predictable. These dense aggregations cause an elevated backscattered acoustic amplitude that is easily identified. Thus, the resource is highly vulnerable to commercial fishing. Besides, it has also been suggested that, during productive periods, orange roughy aggregations tend to remain still during certain periods or even for many days (Bull et al, 2001).
One of the objectives of the current international approach for marine biodiversity conservation is the identification and protection of the discrete areas that are defined from the representativeness of the existing ecosystems and/or their role as an essential habitat for the conservation of vulnerable or threatened species. Therefore, the demand for the identification and prioritization of possible protected marine areas in the Chilean seamounts requires some knowledge of the structure and singularity of its communities and the role such areas play in the Ufe cycle of the species identified as special conservation subjects. In this sense, the extent of the knowledge necessary for the adequate conservation of biodiversity on seamounts in the Chilean EEZ is huge and this study is just one step towards an increase in the available information. Obviously, most attention is directed towards those areas currently under fishing exploitation, where it is crucial to take conservation measures for the development of sustainable activities.
The authors would like to thank the crews of PAM Portugal II, the L/M Alborada, and the boat Cumberland for their great disposition and assistance with the works carried out on board. Furthermore, we wish to thank the Fondo de Investigación Pesquera de Chile for their support of FIP project No. 2006-57.
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Received: 11 May 2009; Accepted: 1 October 2009