Long term fish assemblages as units of management in a temperate estuary (Rio de La Plata - SW Atlantic Ocean)

Demersal fish assemblages from trawl surveys in the Rio de la Plata estuary and its inner continental shelf were analyzed from 1975 to 1995. The first two factors of Principal Component Analysis explained 48% of the variance in species distribution, and they are consistent with the results of a cluster analysis. The analysis indicated the existence of three spatially and temporally distinct fish assemblages: internal and external estuarine and inner continental shelf (Uruguayan coastal assemblages). These assemblages were persistent considering the environmental characteristics and their species composition. Despite the changes registered in the species density during the period surveyed, the fish assemblages tend to persist over time. It was demonstrated that the assemblages can be considered as open systems and that there exists a reciprocal flow of organisms between adjacent associations. However, each assemblage showed high spatial and temporal persistence in accordance with the environmental characteristics of the system analyzed. Therefore, and according to the multispecies fisheries operating in the system, each assemblage defined could be considered a unit of management.Foram analisadas as associações dos peixes demersais provenientes de arrastos de prospecção no estuário do Rio de la Plata e sua plataforma interna no período de 1975 a 1995. Os dois primeiros fatores da Análise de Componentes Principais explicaram 48% da variância na distribuição das espécies sendo consistentes com os resultados da análise de agrupamento. Os resultados mostraram a existência de três associações de peixes espacial e temporalmente distintas: uruguaia costeira, estuarina externa e estuarina interna. Essas associações foram consistentes quanto às características ambientais e de composição de espécies. A despeito das mudanças registradas na densidade das espécies ao longo do período analisado, as associações de peixes foram persistentes ao longo do tempo. No presente trabalho foi demonstrado que embora as associações sejam consideradas um sistema aberto, um fluxo recíproco de organismos acontece entre associações adjacentes. Contudo, cada associação apresenta diferentes graus de estabilidade, dependentes da estabilidade física e temporal do habitat, e das interações das espécies nas associações. No entanto, cada associação mostrou alta persistência espacial e temporal, apesar da variabilidade ambiental no sistema analisado. Nesse sentido, e de acordo com a pesca multiespecífica que opera neste sistema, cada associação poderá ser considerada como uma unidade de gestão

Reclutamiento de juveniles de peces a una pequeña laguna semi-obturada de clima templado (Argentina) y la influencia de factores ambientales durante el proceso

Juvenile fishes were sampled every 15 days from September 2009 to April 2010 along the marine-estuarine gradient (surf zone, estuary and a freshwater stream) of the Mar Chiquita lagoon, Argentina. The temporal variations of juvenile assemblages in spring-summer and the environmental variables related to the spatial and temporal patterns were analysed. Four groups of sampling stations were defined, indicating differences in fish composition among zones during the spring–early summer period (Groups I to III), while the composition of juvenile fishes was homogeneous along the marine-estuarine gradient during the late summer–early autumn period (Group IV). Platanichthys platana and Ramnogaster arcuata (Group A) and Odontesthes argentinensis and Brevoortia aureaz (Group B) contributed most to the temporal differences observed. The three first species reached this estuarine system in spring, although with lower abundances than in early summer, while B. aurea was dominant in late summer–early autumn, showing different periods of recruitment of these species into the lagoon. After factoring out variation due to shared spatial-temporal-environmental factors (4.43%), canonical correspondence analysis (CCA) showed that temporal factors had an almost five times greater contribution (15.15%) than spatial factors (2.85%) and almost twice as great as the pure environmental factors (8.11%) to explaining the variation in abundance of the juvenile fishes. From the significant environmental variables incorporated in the CCA, wind direction contributed more than water temperature, salinity or transparency in explaining data variability. Indeed, most species were related to “onshore winds” and therefore the importance of wind in the successful recruitment of juveniles into this shallow and micro-tidal estuary is discussed.Los juveniles de peces se recolectaron cada 15 días desde septiembre de 2009 a abril de 2010 a lo largo de un gradiente marino-estuarino (en una zona de rompiente, estuario y un arroyo de agua dulce) de la laguna costera Mar Chiquita (Argentina). Se analizaron las variaciones temporales de las asociaciones de juveniles durante el periodo primavera-verano y las variables ambientales que estuvieron relacionadas con los patrones espaciales y temporales. Fueron definidos cuatro grupos de estaciones de muestreo indicando diferencias en la composición de peces entre zonas durante el período de primavera-verano temprano (grupos I a III), mientras que la composición de peces juveniles fue homogénea a lo largo del gradiente marino-estuarino durante el período de verano tardío-otoño temprano (grupo IV). Platanichthys platana y Ramnogaster arcuata (Grupo A), y Odontesthes argentinensis y Brevoortia aurea (Grupo B) fueron las especies que más contribuyeron a las diferencias temporales observadas. Las tres primeras especies llegaron a este sistema estuarino durante la primavera, aunque con menor abundancia en relación a la registrada en verano temprano, mientras que B. aurea fue dominante durante el verano tardío-otoño temprano, mostrando períodos de reclutamiento a la laguna distintos. Después de factorizar la variación compartida entre el factor espacial, el temporal y las variables ambientales (4.43%), el análisis de correspondencia canónica (CCA) mostró que el componente temporal tuvo una contribución casi 5 veces mayor (15.15%) a la del componente espacial (2.85%), y casi el doble a la de los factores puramente ambientales (8.11%) para explicar la variación en la abundancia de los juveniles de peces. De las variables ambientales significativas que fueron incorporadas en el CCA, la dirección del viento contribuyó más que la temperatura, la salinidad o la transparencia del agua en explicar la variabilidad de los datos. De hecho, la mayoría de las especies estuvieron relacionadas con los “vientos marinos” y, por lo tanto, se discute la importancia del viento en el éxito del reclutamiento de juveniles de peces a este estuario poco profundo y de régimen micro-mareal

Life history traits influence in gonad composition of two sympatric species of flatfish

AbstractParalichthys orbignyanus and Paralichthys patagonicus are flatfish with different life history traits, having in common the condition of breeding in seawater. Paralichthys patagonicus remain their whole life in open seawater and Paralichthys orbignyanus are sometimes found in brackish water bodies. As marine and estuarine food webs have different fatty acid (FA) compositions, the aim of this study was to characterize the gonadal maturation of P. orbignyanus and P. patagonicus females through the analysis of lipid content and FA profile in order to understand to what extent life history traits are reflected in the ovarian composition. During gonadal maturation lipid content increased and FA profiles changed in both species, but the lipid increase was greater in P. orbignyanus. The N-3FA and n-3HUFA proportions increased in both species but were higher in P. orbignyanus. The differences between the lifestyles of these species were reflected in the ovarian FA profile mainly as a result of differences in their FA metabolism, causing a greater accumulation of n-3FA and n-3HUFA in P. orbignyanus than in P. patagonicus. The higher lipid accumulation in P. orbignyanus’ ovaries could indicate that this species, feeding in brackish water bodies, has the possibility of storing more energy than P. patagonicus

Nuevas citas para la ictiofauna argentina y comentarios sobre especies poco conocidas

El presente trabajo está vinculado con la incorporación de nuevos especímenes a la Colección Ictiológica del Instituto de Biología Marina, Mar del Plata, Argentina. En la mayor parte de los casos se trata de peces tropicales que arriban ocasionalmente durante los meses de verano, probablemente asociados con desplazamientos de la corriente cálida del Brasil. Algunos de ellos han sido registrados por primera vez para el área, incluyéndose las descripciones de las siguientes especies: Dactylopterus volitans, Vomer setapinnis, Conodon nobilis, Boridia grossidens, Paralonchurus brasiliensis, Polydactylus virginicus, P. oligodon, Centrolophus niger, Alutera monoceros, Lagocephalus laevigatus y Sphaeroides pachigaster.The present paper deals with the incorporation of new specimens to the Ichthyological Collection of the Marine Biological Institute, Mar del Plata, Argentina. In most cases, they are tropical fishes that arrive occasionally during the summer months, probably associated with the displacement of the warm Brazil current. Some of them are recorded for the first time in the area. Descriptions are given of the following species: Dactylopterus volitans, Vomer setapinnis, Conodon nobilis, Boridia grossidens, Paralonchurus brasiliensis, Polydactylus virginicus, P. oligodon, Centrolophus niger, Alutera monoceros, Lagocephalus laevigatus y Sphaeroides pachigaster

Marcación y recaptura del gatuzo (Mustelus schmitti) en el Ecosistema Costero Bonaerense (Argentina)

The present work refers to the first results obtained on tagging and recapture in the Narrownose smooth-hound, Mustelus schmitti, along the Coastal Ecosystem off Buenos Aires Province (BCE) with the aim of describing their migratory movements. This shark is relevant not only because of its high abundance throughout the BCE but also for its commercial significance for the Argentinian trawling fishing fleet. Between November 2010 and May 2011 2,483 specimens were tagged in a marine sector known as “El Rincón”, near Monte Hermoso (Buenos Aires Province), using an artisanal fishery vessel belonging to the local fleet as a platform. Fourty-three specimens were recaptured between 2010 and 2013. From the recapture data collected in this study, patterns of movement, migration, spatial and temporal distribution were established and related to the life cycle of the species. Our results evidenced that both juveniles and adults make extensive use of coastal areas, exhibiting low levels of phylopatry. This is the traditional model proposed for small sharks, such as the Narrownose smooth-hound. However, their reproductive aspects fit better with the model indicated for large sharks. Therefore, Narrownose smooth-hound behaviour would seem to include features corresponding to both modalities, i.e. with fidelity for the breeding sites albeit without evidence of phylopathy.El presente trabajo está referido a los primeros resultados obtenidos sobre marcado y recaptura en el gatuzo, Mustelus schmitti, como medio para reconocer sus desplazamientos y migraciones en el Ecosistema Costero Bonaerense (ECB). Este tiburón es relevante no sólo por su gran abundancia a lo largo del ECB sino también por su importancia comercial para la flota pesquera de arrastre argentina. Entre noviembre de 2010 y mayo 2011 se marcaron 2.483 ejemplares cerca de Monte Hermoso, dentro del sector marino conocido como “El Rincón”, utilizando como plataforma una embarcación de la flota artesanal. Se logró recuperar 43 individuos entre 2010 y 2013. A partir del análisis de los individuos recapturados se señalaron los patrones de movimientos, migración, distribución espacial y temporal en el ECB, y además se discutieron y relacionaron dichos patrones con el ciclo de vida. Los resultados pusieron en evidencia la utilización por parte del gatuzo de áreas extensas, mayoritariamente costeras, sin alta afinidad con áreas particulares. Este es el modelo tradicional propuesto para tiburones pequeños como el gatuzo. Sin embargo, la modalidad reproductiva indicaría un ajuste al modelo señalado para grandes tiburones. Por lo tanto, el gatuzo en su comportamiento parece contener aspectos correspondientes a ambas modalidades con fidelidad por los sitios de reproducción pero sin evidencias de filopatría

Population structure, distribution and abundance patterns of the patagonian smoothhound mustelus schmitti springer, 1939 (chondrichthyes, elasmobranchii, triakidae) in the Rio de la Plata and inner continental shelf, SW Atlantic Ocean (34º30’-39º30’s)

A total number of 4824 Mustelus schmitti was sampled. Females ranged from 25 to 93 cm in spring and from 28 to 90 cm in summer. Males ranged from 34 to 82 and from 28 to 77 cm, respectively. Length composition of the population showed significant differences between spring and summer being females larger than males. Total length distribution did not show significant differences between cruises. Males density varied significantly between cruises while for the females no significant variation was observed. In the spring cruise, both sexes occurred at depths lower than 50 m. Females occurred in the whole area with adult occurrence only above 35°30’S. Mature males occurred throughout the area, immature males occurring in two trawls in Samborombón Bay. The summer cruise showed a discontinuous distribution of the species along the study area resulting in spatial segregation in two groups with immature females predominating in both of them.Um total de 4824 Mustelus schmitti foi amostrado. As fêmeas apresentaram comprimento total de 25-93 cm na primavera e 28-90 cm no verão enquanto os machos apresentaram 34-82 e de 28-77 cm, respectivamente. A composição de comprimentos da população mostrou diferenças significativas entre primavera e verão sendo as fêmeas maiores do que os machos. A distribuição de comprimento total não variou significativamente entre cruzeiros. A densidade variou significativamente entre cruzeiros nos machos sendo que a variação não foi expressiva nas fêmeas. No cruzeiro da primavera, ambos os sexos ocorreram em profundidades menores do que 50 m, as fêmeas ocorrendo em toda a área de estudo, as adultas somente acima da latitude 35°30’S. Os machos adultos foram observados em toda a área sendo que os imaturos somente em dois arrastos na Bahia de Samborombón. O cruzeiro de verão mostrou uma distribuição descontínua da espécie ao longo da área de estudo, resultando na segregação espacial em dois grupos, com predominância de fêmeas imaturas em ambos

Records of selective fishing mortality of Myliobatis goodei on the Southern Brazil coast by Beach Seine

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