Roberto Carlos Menni

Distribution, environment and biology of batoid fishes off Argentina, Uruguay and Brazil. A review.

Available published and unpublished information on the distribution , environment and biology of batoid fishes occurring off Brazil, Uruguay and Argentina is summarized and reviewed for sixty species. Zoogeographic provinces proposed by Lopez (1963, 1964) are considered an adequate framework to define the distribution of these species. The Magellanic fauna, which includes the Pacific Ocean coast off Chile, is a well-defined biological unit. Conversely, the northern fauna changes gradually from the temperate Bonaerensean District off northern Argentina, Uruguay and southern Brazil, to a subtropical and tropical fauna along most of the Brazilian coast. The more drastic change to a truly tropical fauna occurs off French Guiana and Surinam. Within the area studied, rajids are the dominant batoid family, with a large number of rhinobatids and myliobatoids to the north. A more detailed cluster analysis (Jaccard) of batoid distribution patterns, results in nine groups largely corresponding with biological and distributional information: Group I of Magellanic species, Group II of three Magellanic species extending into the Bonaerensean District, a small Group III formed by the deep water skates Bathyraja schroederi , Amblyraja frerichsi and Dasyatis cf . pastinaca , another small Group IV of species with uncommon distributions, Group V of Bonaerensean species, Group VI of relatively rare deep water species, Group VII of northern migrants into the Bonaerensean District, Group VIII of Brazilian species occurring in both the South Brazilian and Brazilian districts, and a completely different Group IX of Northern Brazilian species with their southern distributional limit usually at Rio de Janeiro. A large amount of information is available on many of the species, regarding depth and temperature of occurrence, patterns of distribution, and in many cases reproduction and feeding. Preliminary evaluations of abundance have been obtained for a few species only, but the risk of overfishing is clearly documented for some of them. An odd taxonomic - geographic situation is the status of D . cf. pastinaca , and a peculiar type of cloacal gestation has been described for Benthobatis (similar to that in Squatina ). Studies at community ecology level are discussed and full references provided, including many reports only published as meeting summaries.

Subtle relationships: freshwater fishes and water chemistry in southern South America

We investigated the relationships between water chemistry and the occurrence, distribution, physiology, and morphology of fish faunas. We examined 34 species (ca. 10% of the Argentinean freshwater fish fauna) from 120 localities (5 areas) situated between 26°15′ S (Trancas, Tucumán) and 38°30′ S (Sierra de la Ventana, Buenos Aires). Fourteen chemical features are described by: conductivity, total dissolved solids, temperature, pH, CO32−, CO3H−, Cl−, SO42−Ca2+, K+, Mg2+, Na+, Mg/Ca, Mg+Ca/Na+K. Three Basic Data Matrices considering the mean, maximum and minimum values of each variable for each fish species were used in a Cluster and Principal Component Analysis. Groups of species clustered in similar ways to particular water chemistries. Similarity was the common occurrence of species in a defined area and preference for a common range of the factors considered. Groups of species so defined showed patterns of distribution related to climate, environment, trophic state and hydrographic complexity. Each cluster included some eurytopic species which appeared together at extreme chemical and geographic characteristics. Twenty four species had ranges of tolerance for the 14 variables and evidence of a grouping according to these ranges. Eighteen species which occurred at maximum or minimum absolute values for more than one factor were ordered along an eurytopy — stenotopy axis. We support the statement that species with a larger tolerance range for most factors have a higher probability of being widely distributed. Astyanax fasciatus and A. bimaculatus tolerated the highest number of maximum and minimum values, followed by Jenynsia l. lineata, A. eigenmanniorum and Trichomycterus corduvensis. Groups of species based on chemical factors showed differences in the relative number of basic morphological types.

Marine biodiversity at the community level: zoogeography of sharks, skates, rays and chimaeras in the southwestern Atlantic

For more than a century, two major zoogeographic provinces have been proposed for the southwestern Atlantic: a warm water Argentinean Province from Rio de Janeiro (23°S, Brazil) to Valdés Peninsula (42°S, Argentina), and a cold water Magellanic Province from Valdés Peninsula to Cape Horn. This zoogeographic scheme has been recognized so far using data covering only parts of the whole geographic area. Here, we test the validity of this scheme by analyzing the distribution of sharks, skates, rays and chimaeras, using data from research cruises covering the entire area. We used cluster, similarity and dissimilarity analyses to identify species assemblages, and canonical correspondence analysis to identify the main environmental variables affecting the composition of the assemblages. The distribution of chondrichthyan assemblages strongly supports the current zoogeographic scheme and identifies a previously unknown and distinctive deep water zoogeographic unit off southern Brazil. Both, the Argentinean and Magellanic Provinces had extensive internal structure, with four and three subareas identified in each of them, respectively. These subareas correspond, with slight differences, to previously proposed zoogeographical districts within the Argentinean Province and confirm ecological differences within the Magellanic Province. Species composition had the highest correlation with depth and bottom water temperature. Since the distribution of anthropogenic disturbances in the region is uneven, different assemblages can be subjected to different impacts. Our results provide an objective basis to establish priority areas for the conservation of chondrichthyans in the southwestern Atlantic.

Benthic and Semidemersal Fish associations in the Argentine Sea

Abstract During a fishery research cruise aboard the R/V “Orient Maru I”;, the authors identified 65 species of benthic and semidemersal fishes captured in 96 stations between the southern part of Buenos Aires province and Magellan Strait. Data were analyzed with a combination of similarity coefficients and cluster analysis as used in numerical taxonomy. The matrix obtained by using the Jaccard coefficient was used as input in the calculation of phenograms by unweighted pair groups using arithmetic averages (UPGMA). Phenograms were calculated for both the species (R mode) and the stations (Q mode). Four associations were found, three of them consistent with known zoogeographical and ecological interpretations of the considered area, and another, unexpected one, which proved the heuristic value of the employed methodology. Each association was found within a given area with particular temperature (specially) and depth ranges. The permanence of the associations in space and time was checked against a simila...

On the habitat and isolation of Gymnocharacinus bergi (Osteichthyes: Characidae)

SynopsisGymnocharacinus bergi is a rare Paranensean fish which is the only characiform almost lacking scales in the adult. It is endemic and the only species in a peculiar spot — a tributary of the Valcheta creek — in the Somuncurá plateau in northern Patagonia, Argentina, over 300 km from the nearest place with a paranensean fish fauna. Besides its geographical isolation, G. bergi occurs within an area with climatic features drastically different from those currently associated with fishes from Neotropical temperate zones. We tested the assumption that water temperature in the naked characin habitat do not agree with the northern Patagonia climate. We also considered the isolation of G. bergi within the framework of an increasing inpoverishment of the paranensean ichthyofauna along a NE-SW axis in the Buenos Aires province. For this we applied a decrement equation used in island biogeography. Our findings demonstrate that the existence of G. bergi in its isolated habitat is possible because of the thermal traits of the water at the sources of the creeks, its temperature being independent of the climate of the area. The chemical composition of water was found to be within the range of common environments in the Buenos Aires ‘pampas’ inhabited by several species of Paranensean fishes. Geographically, G. bergi lives in the last of a series of habitats which show a decreasing number of species correlated with the increasing distance from the La Plata River. Conservation status of the species is briefly discussed.

The physical–chemical habitat of the Buenos Aires pejerrey, Odontesthes bonariensis (Teleostei, Atherinopsidae), with a proposal of a water quality index

The pejerrey, Odontesthes bonariensis (Valenciennes 1835) (Atheriniformes, Atherinopsidae) is a highly valued food and sport fish both in Argentina and abroad, and has been introduced in numerous natural and manmade environments in this country, Chile, Japan, and Italy. Considering a wide array of environments, where the pejerrey lives and somewhere it does not, we demonstrate its considerable eurytopy and define its range as water traits and chemical composition concern. Moreover, as pejerrey’s natural habitat, the pampasic lagunas (lakes of third-order) in temperate Argentina display a wider range of chemistry traits than many other environments throughout the country, we confirm its adaptability, suggested by previous introduction success. Relative influence of total conductivity and particular ions is evaluated, as well as the relationship of water traits with the fish distribution. A water quality index is provided, which allows the determination of the best conditions for pejerrey cultivation in both artificial and natural conditions. The index summarizes many traits of the realized niche of the fish.

Spatial patterns in the diversity of sharks, rays, and chimaeras (Chondrichthyes) in the Southwest Atlantic

Knowing how the diversity of sharks, rays and chimaeras (Chondrichthyes) is distributed helps us to design strategies to conserve these highly-vulnerable predators and their habitats. Here, we analyzed the spatial distribution of chondrichthyan species richness in the Southwest Atlantic (34–56ºS), and its relationship with environmental variables and marine fronts, by using a dataset obtained before the major development of industrial trawling fisheries. We also explored the relationship between richness and reported catches of chondrichthyans from commercial, demersal fisheries. Generalized linear models were used to assess the relationship of species richness with environmental variables; with marine fronts and with commercial catches. Species richness increased towards the north, particularly close inshore and on the outer shelf, with cells of highest richness found north of 48ºS. Dissolved oxygen was related negatively with richness; depth, latitude and longitude were also related with richness, but to a lesser extent. Chondrichthyan diversity hotspots, i.e. cells with richness higher than the 90% percentile of the richness distribution, were more likely to occur on marine fronts than elsewhere. High chondrichhtyan catches were significantly associated to hotspots, but low-catch areas were not related to coldspots, i.e. cells with less than the 10% percentile of the richness distribution. Areas of high richness of chondrichthyans coincide with high levels of catches and are used by other species of high conservation concern. Given the importance of these areas to multiple species in the Southwest Atlantic, any conservation strategy based on a network of protected areas should include marine fronts.

Fish ecology of a seasonal lowland stream in temperate South America

El Pescado (literally ‘the fish’) is a lowland stream in the pampean plain, entering the Rio de La Plata at 35˚55¢S,57˚45¢W, 70 km SW of the city of Buenos Aires. The stream develops as a potamon with variable flood frequency along its 36 km length. The water is slightly soft, with relatively high conductivity and dominance of HCO–3 , Na + and Cl – ions. Three fish families, Characidae (29%), Pimelodidae (14.6%) and Loricariidae (12.8%) are most abundant among 55 species. Differences in species composition among four stations with different environmental traits were observed. Flooding slightly affected the fish fauna. In open-water and rocky-bottom stations, both species number and number of individuals were correlated with conductivity, an indication of the decrease of fish density with floods. Species richness was well over worldwide means. Diversity values, higher than in small tropical streams in Venezuela and southern Brazil, ranged from 0.32 to 2.59, being higher during autumn and spring. The stream has a high persistence, with the composition of the fish community maintained or recovering as soon as flooding ends. One Synbranchus marmoratus specimen was found among rocks, the first record of this behaviour for the species.

Ontogenetic habitat preferences of the narrownose smooth-hound shark, Mustelus schmitti, in two Southwestern Atlantic coastal areas

The aim of this study was to determine the ontogenetic habitat preferences of the narrownose smooth-hound shark, Mustelus schmitti, in Río de la Plata and El Rincón coastal areas. There, canonical correspondence analyses of fishery research survey data showed that M. schmitti ontogenetic stages were differentially affected by depth, temperature and salinity. Neonates and juveniles were more abundant and remain in nearshore waters, suggesting the presence of nursery areas in which food availability and environmental conditions allow a faster growth. Adults M. schmitti presented different environmental associations mainly associated with depth and temperature. During non-reproductive season they were associated with deeper coastal waters. With the arrival of the reproductive season, adults migrate from deep to nearshore waters and show sexual segregation associated with pre- or post-mating behaviors. Hence, the year-round presence of neonates and juveniles and the seasonal occurrence of adults in nearshore waters make this habitat essential to M. schmitti population dynamics since key ontogenetic stages will be vulnerable if a direct impact occurs there.

Fish and limnology of a thermal water environment in subtropical South America

Two thermal sources with water temperatures from 51 to 59°C flow into a stream of 2 to 5 m width and about 0.5 m depth at Agua Caliente (23° 44′, 64° 38′) in Jujuy province, Argentina. Data from 3 years sampling show that the influence of the thermal sources maintains the water temperature of the stream section at a high and constant level (from 24 to 35°C), different from the thermal regime of other streams in the area. Composition of water (N=13) has the following mean values: pH 8.36, conductivity 1591 µS cm-1, dominant ions (in mg l-1) CO3-- 12.77, CO3H- 140.27, Cl- 246.86, SO4-- 460.14, Na+ 400.45, K+ 2.18, Ca++ 27.68 and Mg++ 2.14. Mean total dissolved solids: 1.3 g l-1. Large amounts of SO4--, Na+, and Cl- Sixteen fish species (2460 specimens) were captured in the warmed reach. Dominant families were Characidae, Cichlidae and Loricariidae. New geographic distribution information is provided for eight species, some of them with restricted northwestern Argentina distributions. Most abundant species were the eurytopic characid Astyanax bimaculatus, followed by the cichlid Bujurquina vittata. These species have the highest critical thermal maximum according to field experiments. Temperature of acclimatization is closer to lethal than in fishes from ‘normal’ habitats. Agua Caliente differs from other thermal habitats in the lack of isolation, its placement in a rain forest area, a high number of species, and the lack of cyprinodontoids. The fish fauna here represents an opportunistic invasion of a habitat with water parameters strongly different from those in the area, particularly temperature and salinity. Both faunistic and limnological traits make of Agua Caliente a new type of environment within the subtropics.