María B. Cousseau

Fish composition in a south-western Atlantic temperate coastal lagoon: spatial–temporal variation and relationships with environmental variables

Mar Chiquita, an irregularly shaped brackish-water coastal lagoon, is located in the Buenos Aires province of Argentina and considered since 1996 by the Coordination Council of the Man and Biosphere Program of UNESCO as a World Reserve of Biosphere. The present paper aims to study both the spatial and temporal variation of fish composition in this coastal lagoon and the influence of some environmental variables on the relative abundance of the main fish species. Monthly sampling surveys over a two-year period in three different areas were conducted, using a beach-seine net and three monofilament-gill nets with different mesh size. Twenty-eight species belonging to four bio-ecological categories were identified, five of them are new records for Mar Chiquita fish community. The correspondence analysis showed strong relationships between high salinity range and the abundance of Brevoortia aurea, Cynoscion guatucupa and Pomatomus saltatrix. Conversely, low salinity range corresponded to high abundance of Mugil platanus and Odontesthes argentinensis. High temperatures were corresponded with abundance of Micropogonias furnieri and Brevoortia aurea. In contrast, high abundance of both Odontesthes argentinensis and Oligosarcus jenynsii were corresponded to low temperatures. Brevoortia aurea, Mugil platanus and Odontesthes argentinensis were the most abundant species, representing more than 80% of the total capture. The group of estuarine-nondependent-marine fish presented the highest species richness. Estuarine-dependent-marine species presented for both juveniles and adults specimens the highest abundance values.

Does Mugil liza Valenciennes 1836 (Teleostei: Mugiliformes) occur in Argentinean waters?

The present paper deals with the occurrence of two nominal species of Mugil (Mugil liza Valenciennes 1836 and Mugil platanus Gunther 1880) in Argentinean waters. The investigation is necessary to clarify the distribution of these species before any regional study on the biology can be made. In Argentinean bibliographies, two members of the familiy Mugilidae are mentioned as living in Argentinean waters, M. liza Valenciennes 1836 and M. platanus Gunther 1880, while recent revisions on the southwestern Atlantic members of this family recognised M. liza as living in the Caribbean and northern Brazil and M. platanus along the southern coast of Brazil and north of Argentina. Samples from six coastal localities and from a freshwater lagoon between 36 and 42oS latitude, comprising a total of 369 individuals were examined and compared with Type specimens of both nominal species and a sample of 38 individuals of M. platanus from Rio Grande do Sul, Brazil (32oS). Morphometric and meristic data were recorded: morphometrics was analyzed by normalization of the individuals of each locality followed by principal component analysis and meristics were compared with the values from Types and fresh specimens corresponding to M. platanus and M. liza. The comparative analysis indicated that M. liza does not occur in Argentinean waters, being M. platanus the only permanent present species.

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.

Ocean–estuarine connection for ichthyoplankton through the inlet channel of a temperate choked coastal lagoon (Argentina)

We examined the fish larvae colonising pattern of the Mar Chiquita lagoon (Argentina). We hypothesised that in this microtidal lagoon, winds could regulate fish larvae dynamics. Ichthyoplankton samples were taken in marine waters, the surf zone and the estuary. Previous studies showed no reproduction by fishes with planktonic eggs inside the lagoon. However high abundance of eggs and larvae of Brevoortia aurea collected within the estuary also suggest possible spawning activity. Throughout the study period, the cumulated richness of fish larvae was slightly higher in the estuary. However, univariate analysis revealed a higher number of species per tow in marine waters than in the estuary. The lowest average values of fish density, number of species and diversity recorded in the surf zone suggest that this area is only used as a transient corridor between the sea and the lagoon. The canonical correspondence analysis (CCA) indicated that wind direction, tidal stage, temperature and rainfall contributed significantly to the fish larvae distribution patterns observed; being ‘onshore wind’ the most important variable affecting fishes. Our results show how winds, in addition to pushing seawater into the lagoon, contribute to larvae recruitment into this estuary. Finally, we discuss the role of small lagoons in the life-history of coastal fishes.

Morphological, morphometric, meristic and osteological evidence for two species of hake (Actinopterygii: Gadiformes: Merluccius) in Argentinean waters

Morphologically, both classic and landmark-based morphometry and meristic analyses of 241 specimens of Merluccius, along with the re-examination of six paratype specimens of Merluccius hubbsi, the holotype and three paratypes of Merluccius patagonicus and the syntype of Merluccius australis revealed the presence of only two species of Merluccius in Argentinean waters. Internal structures (hyomandibula, urohyal and sagitta otolith) of M. hubbsi were compared to those reported for M. patagonicus and were shown to have identical morphology. Type specimens of M. patagonicus showed a complete overlap in morphometric and meristic characters with M. hubbsi, whereas M. australis had a greater number of second dorsal and anal-fin rays, and more lateral-line scales. In addition, M. australis had a smaller eye and longer snout than M. hubbsi and M. patagonicus. The results indicate that there is no evidence for a third hake species in Argentinean waters. Merluccius patagonicus is a synonym of M. hubbsi.

Reproductive biology and abundance of the freckled sandskate Psammobatis lentiginosa McEachran,1983 in the southwest Atlantic

Abstract The reproductive biology and abundance of the freckled sandskate Psammobatis lentiginosa in the southwest Atlantic was investigated. Specimens of P. lentiginosa were captured from 35°15′S to 45°19′S with a gap between 39°20′ and 44°22′S, from 49 to 164 m depth, which was consistent with most previous studies. Major concentrations of P. lentiginosa were detected between 35° and 37°S, and between 90 and 130 m depth. Females matured at larger sizes than males; L50 (estimated size at which 50% of individuals are sexually mature) was 313 mm TL (total length) and 333 mm TL for males and females, respectively. Oviposition in P. lentiginosa occurs in winter and spring in northern areas, and in summer in the southern area. Given their relatively small size, Psammobatis spp. may be less susceptible to population depletion than other skates. Nonetheless, factors such as increasing fisheries pressure and habitat disturbance due to trawling may be impacting on those species in the study area.

Composição e abundância da ictiofauna de duas lagunas costeiras da América do Sul Austral: lagoa do Peixe (31ºS; 51ºW), Brasil e laguna Mar Chiquita (37ºS; 57ºW), Argentina

Este artigo descreve e compara a ictiofauna de zonas rasas de duas lagunas costeiras (lagoa do Peixe, no Brasil e laguna Mar Chiquita, na Argentina). A lagoa do Peixe foi amostrada entre 2000 e 2001 com rede de arrasto de praia (9 m de comprimento, malha de 5 mm entre nos 3 m centrais e de 12 mm na lateral) totalizando 125 amostras, resultando na coleta de 33.848 individuos e 32 especies. A laguna de Mar Chiquita, foi amostrada durante os anos de 1995 e 1998 com rede de arrasto de praia (20 m de comprimento, com panagem unica de 12 mm), totalizando 232 amostras, sendo coletados 31.097 individuos pertencentes a 28 especies. Das 47 especies observadas, 13 sao comuns nos dois sistemas. As especies marinhas-estuarino-relacionadas foram semelhantes e dominaram as assembleias de peixes em ambas as lagunas. As especies restantes foram similares as especies coletadas nos estuarios do sul do Brasil, Uruguai e Argentina. O numero de especies observado na lagoa do Peixe (S = 32) foi maior que em Mar Chiquita (S = 28), provavelmente associado a um forte gradiente latitudinal negativo de riqueza de especies de norte para sul. Pelo fato da lagoa do Peixe e da laguna Mar Chiquita estarem isoladas pelos grandes estuarios da lagoa dos Patos e do rio da Prata, a composicao das especies de baixa abundância e a ocorrencia ocasional foram bem distintas para cada local estudado. Esses resultados ampliam o conhecimento da fauna de ambos locais e ajudam na conservacao e manejo de ambas as lagunas. Palavras-chave: Argentina, Brasil, lagoas costeiras, peixes estuarinos, recursos pesqueiros.

The presence of southern fishes in the Argentinian continental shelf and adjacent areas

A list of Southern Ocean fishes captured in the Argentinian continental shelf and adjacent areas is presented. The list comprises a total of 41 species. They represent 15% of the ichthyofauna registered in the Southern Ocean. The geographic position of the samples was considered in order to show the northward displacement of some Antarctic species toward southwestern Atlantic waters.