Evaluando el origen del proceso ‘fishing down marine food web’ en la Zona Común de Pesca Argentino-Uruguaya

The temporal trend in the mean trophic level (mTL), fisheries-in-balance index (FIB), trophic categories landing (TrC) and landing profile (LP) of the exploited marine community (82 species) in the Argentinean-Uruguayan Common Fishing Zone (AUCFZ) were examined from 1989 to 2003. The total landings (Yt) (rs=-0.561; P< 0.05) and the Yt of carnivores and top predators has declined, while the Yt of herbivores, detritivores and omnivores has increased. Consequently, the mTL significantly decreased (rs =-0.88; P< 0.01) at a rate of 0.41 from 1991 (mTL =3.81) to 2003 (mTL =3.4), and the FIB index has declined in the last 6 years. The LP temporal pattern showed four periods with significant differences in their species composition and Primary Production Required, which shows a strong decline in the traditional fishery resources (i.e. Merluccius hubbsi, Micropogonias furnieri), and increases in crustacean (Chaceon notilis), molluscs (Zygochlamys patagonica) and some fishes (Macrodon ancylodon, Macruronus magallanicus, Rajidae). The mTL trend reflects the changes in the AUCFZ landing structure. This was characterized by large, slow-growing and late-maturing species during the early 1990s, while during recent years, early 2000s, it was mainly characterized by medium-sized fishes, crustaceans and molluscs. The examination of the mTL, FBI, TrC trajectories and LP temporal pattern suggests that new fishery resources are developing or that the fishing effort has been redistributed from overexploited resources to lightly exploited resources. In addition, the examination of discriminator and common species, and the fact that traditional resources are being over-fished support the hypothesis that the mTL trend has been influenced more by the impacts of new fishing technologies than the changes in market-driven exploitation and environmental fluctuation. These results provide evidence of the fishing down process along AUCFZ.La tendencia temporal en el nivel trófico medio (mTL), índice de balance de las pesquerías (FIB), desembarques de categorías tróficas (TrC) y perfiles de desembarque (LP) de la comunidad marina explotada (82 especies) en la Zona Común de Pesca Argentino-Uruguaya (ZCPAU) fue examinada entre 1989 y 2003. Los desembarques totales (Yt) (rs=-0.561; P< 0.05) y los desembarques de carnívoros y predadores tope disminuyó, mientras que los desembarques de herbívoros, detritívoros y omnívoros se incrementaron. Consecuentemente, el mTL decreció significativamente (rs =-0.88; P< 0.01) a una tasa de 0.41 desde 1991 (mTL =3.81) a 2003 (mTL =3.4), por su parte el índice FIB disminuyó en los últimos 6 años. El patrón temporal de LP presentó cuatro periodos significativamente diferentes en su composición específica y la Producción Primaria Requerida (PPR), con una fuerte caída en los recursos pesqueros tradicionales (i.e. Merluccius hubbsi, Micropogonias furnieri), y el incremento en crustáceos (Chaceon notilis), moluscos (Zygochlamys patagonica) y algunos peces (Macrodon ancylodon, Macruronus magallanicus, Rajidae). La tendencia en el mTL refleja cambios en la estructura de los desembarques de la ZCPAU, que fue discriminada por especies grandes, de lento crecimiento y tardía maduración en los inicios de los 90’, mientras que durante los años recientes, inicios de los 2000, ellos fueron principalmente discriminados por peces de tallas medianas, crustáceos y moluscos. Las trayectorias de mTL, FIB, TrC y el patrón de LP sugieren el desarrollo de nuevos recursos pesqueros o la redistribución del esfuerzo de recursos sobreexplotados a recursos explotados o poco explotados. Asimismo, el análisis de las especies discriminantes y comunes, junto con la sobrepesca de recursos tradicionales, soportan la hipótesis de que la tendencia en el mTL ha sido mayormente influenciada por el impacto de nuevas tecnologías de pesca que por cambios en el mercado o fluctuaciones ambientales. Estos resultados evidencian el proceso “Fishing Down” en la ZCPAU

Fish assemblages in a small temperate estuary on the argentinian coast: spatial variation, environmental influence and relevance as nursery area

The effects of different environmental variables on the fish community structure were evaluated in a small temperate estuary. The biological and environmental data were collected bimonthly between 2007 and 2009 along the main estuarine axis. Multivariate analyses were applied (CLUSTER, SIMPER, CCA) to determine the spatial structure of fish community and to estimate the environmental influence on it. A total of 48 species of “teleost” fishes were observed, with the families Characidae and Sciaenidae presenting the largest number of species, 90% of the catches being juveniles. The fish community was overwhelmingly dominated by one species (Micropogonias furnieri, 88.9%), and only four species contributed more than 1% of total catch (Odontesthes argentinensis 5.4%, Brevoortia aurea 1.1%, Paralonchurus brasiliensis 1.1%, and Mugil platanus 1.0%). Estuarine and freshwater stragglers dominated in number of species, followed by freshwater migrants and marine migrants. Three areas with different fish assemblages, with distinctive species and functional guilds, were defined along the main axis. The occurrence and spatial spread of these areas were linked to spatial variation in salinity, which was consistently influenced by discharge from the Río de la Plata and local precipitation. The results highlight the importance of shallow environments as nursery areas and permit emphasis on their susceptibility to environmental changes.Foram avaliados os efeitos das diferentes variáveis ambientais na estrutura da comunidade de peixes em um pequeno estuário temperado. Dados biológicos e ambientais foram obtidos bimestralmente entre 2007 e 2009, ao longo do eixo principal do estuário. Análises multivariadas foram aplicadas (CLUSTER, SIMPER, CCA) para determinar a estrutura espacial da comunidade de peixes e para estimar a influência ambiental sobre ela. Um total de 48 espécies de "teleósteos" foi observado, com as famílias Characidae e Sciaenidae apresentando o maior número de espécies e sendo 90% das capturas formada por juvenis. A comunidade de peixes foi altamente dominada por uma só espécie (Micropogonias furnieri, 88,9%) e quatro espécies contribuiram com pouco mais de 1% cada para o total das capturas (Odontesthes argentinensis 5,4%, Brevoortia aurea 1,1%, Paralonchurus brasiliensis 1,1% e Mugil platanus 1,0%). Retardatários estuarinos e de água doce dominaram em número de espécies, seguidos por migrantes de água doce e marinhos. Ao longo do eixo principal foram definidas três áreas distintas, cada uma apresentando assembleias de peixes com espécies e guildas funcionais distintas. A ocorrência e abrangência espacial dessas áreas estiveram ligadas à variação espacial na salinidade, que consistentemente foi influenciada pela descarga do Rio da Prata e pela precipitação local. Os resultados destacam a importância dos ambientes rasos como áreas de berçário e permitem enfatizar sua susceptibilidade às mudanças ambientais.Facultad de Ciencias Naturales y Muse

Desde el agua dulce hasta el talud: ecología de comunidades de peces en el Río de la Plata y el mar adyacente

The spatial pattern of fish assemblages and its relationship with factors along an environment gradient, from fresh to marine water environment along the Río de la Plata estuary (36°S, 56°W) the shelf and part of the slope, was examined using data from 22 sampling stations. Fish were sampled from all station with an Engel type trawl (200 mm stretched mesh in the wings, 120 mm stretched mesh in the cod ends, 4 m vertical opening and 15 m horizontal aperture) towed at 4 knots for 20 to 30 min per set. Cluster analysis and ordination analysis MDS were used to define spatial distribution of fish assemblages based on fish composition (abundance and biomass). BIO-ENV process was used to estimate assemblage association with depth, temperature and salinity of surface and bottom waters. The results of these analyses showed that the fish community along the riverine-marine gradient was structured in four assemblages: riverine, estuarine, shelf and slope. These assemblages were found to differ significantly in their species composition. Each assemblage was characterized by several common and discriminator species and characterized by differing environmental conditions. Bottom salinity and bottom temperature were the environmental variables most strongly associated with differences in assemblage structure across the various areas. The changes in assemblage structure between areas were gradual, with no sharp boundaries.Facultad de Ciencias Naturales y Muse

Desde el agua dulce hasta el talud: ecología de comunidades de peces en el Río de la Plata y el mar adyacente

The spatial pattern of fish assemblages and its relationship with factors along an environment gradient, from fresh to marine water environment along the Río de la Plata estuary (36°S, 56°W) the shelf and part of the slope, was examined using data from 22 sampling stations. Fish were sampled from all station with an Engel type trawl (200 mm stretched mesh in the wings, 120 mm stretched mesh in the cod ends, 4 m vertical opening and 15 m horizontal aperture) towed at 4 knots for 20 to 30 min per set. Cluster analysis and ordination analysis MDS were used to define spatial distribution of fish assemblages based on fish composition (abundance and biomass). BIO-ENV process was used to estimate assemblage association with depth, temperature and salinity of surface and bottom waters. The results of these analyses showed that the fish community along the riverine-marine gradient was structured in four assemblages: riverine, estuarine, shelf and slope. These assemblages were found to differ significantly in their species composition. Each assemblage was characterized by several common and discriminator species and characterized by differing environmental conditions. Bottom salinity and bottom temperature were the environmental variables most strongly associated with differences in assemblage structure across the various areas. The changes in assemblage structure between areas were gradual, with no sharp boundaries.Facultad de Ciencias Naturales y Muse

Fish assemblages in a small temperate estuary on the argentinian coast: spatial variation, environmental influence and relevance as nursery area

The effects of different environmental variables on the fish community structure were evaluated in a small temperate estuary. The biological and environmental data were collected bimonthly between 2007 and 2009 along the main estuarine axis. Multivariate analyses were applied (CLUSTER, SIMPER, CCA) to determine the spatial structure of fish community and to estimate the environmental influence on it. A total of 48 species of “teleost” fishes were observed, with the families Characidae and Sciaenidae presenting the largest number of species, 90% of the catches being juveniles. The fish community was overwhelmingly dominated by one species (Micropogonias furnieri, 88.9%), and only four species contributed more than 1% of total catch (Odontesthes argentinensis 5.4%, Brevoortia aurea 1.1%, Paralonchurus brasiliensis 1.1%, and Mugil platanus 1.0%). Estuarine and freshwater stragglers dominated in number of species, followed by freshwater migrants and marine migrants. Three areas with different fish assemblages, with distinctive species and functional guilds, were defined along the main axis. The occurrence and spatial spread of these areas were linked to spatial variation in salinity, which was consistently influenced by discharge from the Río de la Plata and local precipitation. The results highlight the importance of shallow environments as nursery areas and permit emphasis on their susceptibility to environmental changes.Foram avaliados os efeitos das diferentes variáveis ambientais na estrutura da comunidade de peixes em um pequeno estuário temperado. Dados biológicos e ambientais foram obtidos bimestralmente entre 2007 e 2009, ao longo do eixo principal do estuário. Análises multivariadas foram aplicadas (CLUSTER, SIMPER, CCA) para determinar a estrutura espacial da comunidade de peixes e para estimar a influência ambiental sobre ela. Um total de 48 espécies de "teleósteos" foi observado, com as famílias Characidae e Sciaenidae apresentando o maior número de espécies e sendo 90% das capturas formada por juvenis. A comunidade de peixes foi altamente dominada por uma só espécie (Micropogonias furnieri, 88,9%) e quatro espécies contribuiram com pouco mais de 1% cada para o total das capturas (Odontesthes argentinensis 5,4%, Brevoortia aurea 1,1%, Paralonchurus brasiliensis 1,1% e Mugil platanus 1,0%). Retardatários estuarinos e de água doce dominaram em número de espécies, seguidos por migrantes de água doce e marinhos. Ao longo do eixo principal foram definidas três áreas distintas, cada uma apresentando assembleias de peixes com espécies e guildas funcionais distintas. A ocorrência e abrangência espacial dessas áreas estiveram ligadas à variação espacial na salinidade, que consistentemente foi influenciada pela descarga do Rio da Prata e pela precipitação local. Os resultados destacam a importância dos ambientes rasos como áreas de berçário e permitem enfatizar sua susceptibilidade às mudanças ambientais.Facultad de Ciencias Naturales y Muse

Desde el agua dulce hasta el talud: ecología de comunidades de peces en el Río de la Plata y el mar adyacente

The spatial pattern of fish assemblages and its relationship with factors along an environment gradient, from fresh to marine water environment along the Río de la Plata estuary (36°S, 56°W) the shelf and part of the slope, was examined using data from 22 sampling stations. Fish were sampled from all station with an Engel type trawl (200 mm stretched mesh in the wings, 120 mm stretched mesh in the cod ends, 4 m vertical opening and 15 m horizontal aperture) towed at 4 knots for 20 to 30 min per set. Cluster analysis and ordination analysis MDS were used to define spatial distribution of fish assemblages based on fish composition (abundance and biomass). BIO-ENV process was used to estimate assemblage association with depth, temperature and salinity of surface and bottom waters. The results of these analyses showed that the fish community along the riverine-marine gradient was structured in four assemblages: riverine, estuarine, shelf and slope. These assemblages were found to differ significantly in their species composition. Each assemblage was characterized by several common and discriminator species and characterized by differing environmental conditions. Bottom salinity and bottom temperature were the environmental variables most strongly associated with differences in assemblage structure across the various areas. The changes in assemblage structure between areas were gradual, with no sharp boundaries.Facultad de Ciencias Naturales y Muse

Fish assemblages in a small temperate estuary on the Argentinian coast: spatial variation, environmental influence and relevance as nursery area

AbstractThe effects of different environmental variables on the fish community structure were evaluated in a small temperate estuary. The biological and environmental data were collected bimonthly between 2007 and 2009 along the main estuarine axis. Multivariate analyses were applied (CLUSTER, SIMPER, CCA) to determine the spatial structure of fish community and to estimate the environmental influence on it. A total of 48 species of "teleost" fishes were observed, with the families Characidae and Sciaenidae presenting the largest number of species, 90% of the catches being juveniles. The fish community was overwhelmingly dominated by one species (Micropogonias furnieri, 88.9%), and only four species contributed more than 1% of total catch (Odontesthes argentinensis5.4%, Brevoortia aurea 1.1%, Paralonchurus brasiliensis 1.1%, and Mugil platanus 1.0%). Estuarine and freshwater stragglers dominated in number of species, followed by freshwater migrants and marine migrants. Three areas with different fish assemblages, with distinctive species and functional guilds, were defined along the main axis. The occurrence and spatial spread of these areas were linked to spatial variation in salinity, which was consistently influenced by discharge from the Río de la Plata and local precipitation. The results highlight the importance of shallow environments as nursery areas and permit emphasis on their susceptibility to environmental changes

From fresh water to the slope: fish community ecology in the Río de la Plata and the sea beyond Desde el agua dulce hasta el talud: ecología de comunidades de peces en el Río de la Plata y el mar adyacente

The spatial pattern of fish assemblages and its relationship with factors along an environment gradient, from fresh to marine water environment along the Río de la Plata estuary (36ºS, 56ºW) the shelf and part of the slope, was examined using data from 22 sampling stations. Fish were sampled from all station with an Engel type trawl (200 mm stretched mesh in the wings, 120 mm stretched mesh in the cod ends, 4 m vertical opening and 15 m horizontal aperture) towed at 4 knots for 20 to 30 min per set. Cluster analysis and ordination analysis MDS were used to define spatial distribution of fish assemblages based on fish composition (abundance and biomass). BIO-ENV process was used to estimate assemblage association with depth, temperature and salinity of surface and bottom waters. The results of these analyses showed that the fish community along the riverine-marine gradient was structured in four assemblages: riverine, estuarine, shelf and slope. These assemblages were found to differ significantly in their species composition. Each assemblage was characterized by several common and discriminator species and characterized by differing environmental conditions. Bottom salinity and bottom temperature were the environmental variables most strongly associated with differences in assemblage structure across the various areas. The changes in assemblage structure between areas were gradual, with no sharp boundaries.Se analizó el patrón espacial de las asociaciones de peces y su relación con los factores ambientales a lo largo del gradiente desde el agua dulce en el Río de la Plata hasta la parte superior del talud. Los peces fueron muestreados en 22 estaciones con una red de arrastre de fondo tipo Engel (200 mm de abertura de malla en las alas, 120 en el copo, 4 m de abertura vertical y 15 m de abertura horizontal) con una velocidad de arrastre de 4 nudos durante 20 a 30 min. Para definir la distribución espacial de las asociaciones de peces basadas en la composición de la ictiofauna (abundancia y biomasa) se aplicó el análisis de agrupamiento jerárquico y el análisis de ordenación MDS y para estimar la relación entre estas asociaciones con la profundidad, la temperatura y la salinidad del agua en la superficie y el fondo, se utilizó el proceso BIO-ENV. Los resultados obtenidos demuestran que en la comunidad de peces a lo largo de este gradiente riverino-marino se pueden establecer cuatro asociaciones: riverina, estuarial, plataforma y talud. Estas asociaciones fueron significativamente diferentes en la composición de especies, cada una de ellas fue caracterizada por varias especies comunes y discriminantes y presentó diferentes condiciones ambientales. Concluimos que la salinidad y temperatura de fondo fueron las variables ambientales determinantes de la estructura de las asociaciones a través de las áreas. El cambio en la estructura entre las áreas fue gradual y con limites flexibles

Variabilidad anual de la temperatura superficial del mar en la Plataforma Continental Argentina Norte

Twelve years of daily satellite data (0.1° spatial resolution) were used to study the seasonal variability of the sea surface temperature (SST) over the Northern Argentinean Continental Shelf (NACS; between 33°- 45° S and 52°- 66° W). The seasonal cycle, which includes the annual and semi-annual signals, was assessed using harmonic analysis. The annual cycle explained more than 90% of the total variance in the NACS, with SST amplitudes varying from 3.4 to 7.6° C. Largest variances values for this timescale were observed along the Argentinean coast and the inner shelf; particularly in the El Rincón region (exceeding 96%). Empirical Orthogonal Function Analysis (EOF) in S-Mode was applied to daily SST anomalies in the annual timescale, indicating that nearly 94% of its variance was explained by the first two modes, which accounted for 70 and 24% of the variance, respectively. Mode 1 prevailed most of the year with its positive phase occurring in autumn/winter and the negative in spring/summer. This mode revealed the seasonal radiative warming/cooling, related to the heating/cooling in summer/winter in most of the NACS; the shallow waters of the Río de la Plata and El Rincón were heated and cooled more and faster than deeper waters. The weakest seasonal heating/cooling occurred around Península Valdés, where vertical mixing maximizes due to tidal action. Mode 2 corresponded to early spring and early fall in their positive and negative phases, respectively. This mode was related to a transition during the early intermediate seasons when the cooling/heating of an extended coastal region connecting Península Valdés and the Río de la Plata occur.La variabilidad estacional de la temperatura superficial del mar (TSM) en la Plataforma Continental Argentina Norte (PCAN, entre 33º- 45º S y 52º- 66º O) fue estudiada a partir de doce años de datos satelitales de resolución diaria y 0,1° de resolución espacial. El ciclo estacional, que incluye las señales anuales y semianuales, fue evaluado mediante análisis armónico. El ciclo anual explicó más del 90% de la varianza total en la PCAN, con amplitudes de TSM que variaron entre 3,4 y 7,6 ºC. Los mayores valores de varianza para esta escala temporal se observaron a lo largo de la costa argentina y la plataforma continental interna, particularmente en la región de El Rincón (excediendo el 96%). Un análisis de funciones ortogonales empíricas (EOFs) en modo-S aplicado a las anomalías diarias de TSM en la escala anual indicó que casi el 94% de la varianza fue explicada por los primeros dos modos, que representaron el 70 y el 24% de la varianza, respectivamente. El Modo 1 prevaleció la mayor parte del año con su fase positiva en otoño/invierno y la negativa en primavera/verano. Este modo reveló el calentamiento/enfriamiento radiativo estacional, relacionado con el aumento/disminución de las temperaturas en verano/invierno en gran parte de la PCAN; las aguas poco profundas del Río de la Plata y El Rincón se calientan/enfrían más y más rápido que las aguas más profundas. El calentamiento/enfriamiento estacional más débil se produjo alrededor de Península Valdés, donde la mezcla vertical por acción de las mareas es intensa. El Modo 2 corresponde a principios de primavera y principios de otoño en sus fases positiva y negativa, respectivamente. Este modo se encontró relacionado con una transición durante el inicio de las temporadas intermedias, cuando se produce el enfriamiento/calentamiento de una larga región costera que conecta Península Valdés y el Río de la Plata.Asociación Argentina de Geofísicos y Geodesta

FEEDING AND REPRODUCTIVE ACTIVITY OF THE COPEPODS Drepanopus forcipatus AND Calanus australis DURING LATE SUMMER ON THE SOUTHERN PATAGONIAN SHELF (ARGENTINA, 47&#176;-55&#176;S)

Drepanopus forcipatus and Calanus australis are key planktonic copepods on the southern Patagonian shelf. Their feeding and reproductive patterns and population status were investigated during late summer, when environmental conditions may be critical. The presence of food in the gut and food-pellet length were recorded in adult females and the most abundant copepodite stages. Diet composition was also studied in adult females. Female reproductive status was evaluated by gonad staging. Despite generally low feeding conditions and decreasing seasonal temperature, both copepods fed to some degree. The most numerous copepodites and adult females of both species showed similarly low feeding activity. About half of the adult females of the two species and C5s of C. australis contained food in their guts, but the proportion of fed C4-females of D. forcipatus was much lower. All copepods were generally feeding at low or intermediate levels. Gonad stage distribution and population structure showed low but still ongoing reproduction in both species. Gut content findings suggest a preference for smaller nanoplanktonic particles, especially dinoflagellates by D. forcipatus, and for autotrophic prey, particularly large diatoms by C. australis. The feeding and reproduction patterns of the two copepods were likely influenced by the distributions of potential food resources and temperature