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The short‐tail yellownose skate, Zearaja brevicaudata, occurs off southern Brazil and along the Argentine continental shelf, including waters surrounding the Islas Malvinas and the upper slope, and is very frequently caught by trawl fisheries throughout its range. The age, growth, and maturity of Z. brevicaudata were investigated using 204 individuals collected by commercial fishing vessels from northern Argentina, between March 2016 and September 2019. Age was determined on a sample comprising vertebrae from 151 individuals, 60 males, ranging in size from 391 to 956 mm total length (TL), and 91 females, ranging in size from 324 to 1060 mm TL. Maximum ages determined for males and females were 22 and 29 years, respectively. A Bayesian framework was employed with a set of three candidate models to estimate growth parameters (von Bertalanffy, Gompertz, and Logistic). The von Bertalanffy model had the best fit, and the sexes showed undistinguishable growth parameters. For sexes combined, derived growth mean parameters (± S.D.) were L∞ = 1081 mm ± 64.34 mm, k = 0.09 ± 0.01 years−1, and L0 = 248 mm ± 23.52 mm. The age at maturity was estimated at 13.15 and 14.66 years for males and females, respectively. [ABSTRACT FROM AUTHOR]

Context. Rioraja agassizii is a vulnerable species endemic to the Southwest Atlantic. It is caught by trawl fisheries throughout its range. Aims. To determine the age, estimate growth parameters, and age and size at maturity. Methods. Ages were determined using vertebrae readings. To fit growth models, a Bayesian framework was employed with the von Bertalanffy, Gompertz and Logistic candidate models. To estimate age and size at maturity, a logistical ogive was fitted to binomial maturity data. Key results. Maximum ages determined for males and females were 12 and 11 years respectively. The von Bertalanffy model was selected as the best one and there were no differences between sexes (mean parameters: L∞ = 684.8 mm, k = 0.33 years-1 and L0 = 105.5 mm). Age and size at maturity were estimated at 3.31 and 4.55 years, and 485.02 and 544.55 mm TL for males and females respectively. Conclusions. Rioraja agassizii has a moderate growth rate and age at maturity was similar to those of skate species with a similar body size. Implications. Because skate species have different maximum ages, growth rates and maturity parameters, we strongly recommend urgent species-specific management measures for the pool of skate species exploited in Argentina. [ABSTRACT FROM AUTHOR]

Determining the extinction risk of poorly known species is difficult, as data on both their biological traits and the threats to which they are exposed are often not available. Neotropical freshwater stingrays (potamotrygonins) represent such a challenge, as limited ecological data prevent formal assessments. Geographic range size (GRS) was computed for the first time for potamotrygonins (as a longitudinal extent of occurrence measured in km of river length) and, together with two other traits correlated with intrinsic susceptibility to extinction—body size, biological productivity (rmax)—was used to rank potamotrygonins according to their intrinsic susceptibility to extinction. Potamotrygonin GRS was only 6%–7% of that of marine elasmobranchs and is likely to be a significant driver of potamotrygonin extinction risk. The relationship between potamotrygonin GRS and body size differed from the expected triangular theoretical pattern; probably a result of the fragmented nature of freshwater habitats. Using K‐medoids clustering, we identified seven groups of species; the most susceptible groups comprised the biggest species such as Potamotrygon brachyura and Paratrygon spp. Intrinsic susceptibility was also highest in the largest hydrographic basins, likely as a result of species with low rmax being more common there. Exposure to anthropogenic threats is highest for the species most intrinsically susceptible to extinction, which consequently have a high‐extinction risk. We recommend the use of longitudinal extents of occurrence as standardized measurements of freshwater taxa GRS. Our ranking method, combining observed and predicted traits, may be a useful tool to assess poorly known taxa to assist conservation prioritization. [ABSTRACT FROM AUTHOR]

Egg capsules of the multispine skate, Bathyraja multispinis (Norman, 1937), described here for the first time, are larger (180 mm in length without horns) than those of any Bathyraja species from the South-west Atlantic Ocean (SWA). The capsule’s surface texture is relatively smooth by the presence of woven-like fibres. However, below the fibres, it is rough to the touch by the presence of longitudinal ridges and prickles of different shapes and sizes, ending in two or more digitiform projections. An identification key to all described Bathyraja egg capsules occurring in the SWA from 34° to 55°S is provided. [ABSTRACT FROM AUTHOR]

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase rmax of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°–42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404–1300 mm total length, TL; males: n = 60, size range 400–1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non‐linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size‐at‐age) models were fitted: three‐parameter von Bertalanffy, two‐parameter von Bertalanffy with fixed L0, Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non‐linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D.: L∞ = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years−1; L0 = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase rmax was estimated as 0.252 years−1. Life‐history traits and rmax provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure. [ABSTRACT FROM AUTHOR]

The La Plata basin is the second largest basin of South America and has supported important river fisheries for more than a century. In this paper, we evaluate for the first time the historical trends of landings of 21 fish taxa and the recent population trends of 27 species of commercial fishes in the lower La Plata basin (Argentina). We compiled three kinds of data sets: Total fishery landings (between 1934 and 1986) and exports (1994‒2019), fisheries monitoring programs of Chaco and Santa Fe provinces in the Paraná River (2009‒2019), and surveys of fish populations in the Upper (Corrientes, 1993‒2020) and Middle (EBIPES, 2005‒2020) Paraná River. The analysis of the historical landings showed more species declining in the lower portion of the basin than in the upper basin. Regarding recent population trends, Pimelodus spp., Hoplias spp., Salminus brasiliensis, Luciopimelodus pati, and Ageneiosus spp. declined in more than one region, while Megaleporinus spp., Pterodoras granulosus, and Oxydoras kneri showed stable to positive trends, with the other species varying in their trends between regions. These tendencies could be associated to a combination of factors such as overfishing and environmental changes that would require an ecosystem approach for their adequate management. [ABSTRACT FROM AUTHOR]

Aim: We assessed the validity of the division of the Magellanic Province into the four provinces as proposed by Briggs & Bowen (J Biogeogr39 12–30, 2012): Southern Chile, Tierra del Fuego, Southern Argentina and Falkland (Malvinas) Islands. We aimed to (a) present an updated list of the fishes from the region known as 'Magellanic Province', (b) analyse the specific richness of fishes in the Atlantic and Pacific sectors and their degree of endemism and (c) evaluate statistically the validity of the three Provinces proposed for the Atlantic sector. Location: Southern tip of the American continent at latitudes higher than 40° S in the Atlantic as well as in the Pacific Oceans. Taxon: 348 South American marine fish species. Methods: The list of fishes was prepared by consulting more than 140 sources, many related to observations resulting from research cruises, although two ichthyological collections and two ichthyological websites were also used. The South American species with distributions extending outside of the area corresponding to the Magellanic Province, and all cosmopolitan species, were excluded of endemism analyses. For analysing fish distributions in the Atlantic sector, the data employed are from eight research cruises carried out from 1978 to 2006 from 37° to 55° south. A total of 523 fishing trawls have been analysed, grouped into cell of 1° × 1° cells. The species composition of each cell was evaluated by multivariate analysis (non‐metric multidimensional scaling, cluster and similarity analyses). Results: The percentage of endemism in each sector (Atlantic 2.87% and Pacific 2.87%) is smaller than the endemism common to both sectors (9.2%). The total of endemic species in the Province is 14.94%, which is bigger than the 10% indicated as the lower limit for defining a biogeographic province suggested by Briggs (Marine Zoogeography, 1974). In addition, multivariate analyses do not show differences in the species composition, neither between Falkland (Malvinas) Islands and 'Southern Argentina' nor between the latter and Tierra del Fuego. Main conclusions: The ichthyological data indicate only one biogeographic province in the region not four as previously posited. [ABSTRACT FROM AUTHOR]

Many myliobatoid rays are important mesopredators, having significant effects on coastal benthic communities. In tropical and subtropical high-diversity oligotrophic ecosystems, they partition their trophic resources, which results in high ecological singularity. However, it is unknown whether this is true for temperate low-diversity eutrophic ecosystems. In the present study, we tested, for the first time, the hypothesis that myliobatoid mesopredators are ecologically redundant in a temperate low-diversity eutrophic ecosystem. We quantified diet and measured intra- and interspecific trophic overlap in the three species that regularly occur off Uruguay and northern Argentina, namely Myliobatis goodei, Myliobatis ridens and Dasyatis hypostigma. M. ridens had a typical durophagic diet composed of bivalves and gastropods, M. goodei fed primarily on polychaetes and decapods, diverging from the durophagic diet typical of its genus, and D. hypostigma preyed primarily on amphipods and decapods. There were ontogenetic and seasonal dietary differences in all three species. It is concluded that ecological singularity is present in this temperate myliobatoid assemblage, with each species having a different trophic niche. The practice of pooling together myliobatoid mesopredators in trophic models must be abandoned unless there is evidence of ecological redundancy. [ABSTRACT FROM AUTHOR]

Freshwater elasmobranchs are threatened but little is known about them. Potamotrygon brachyura is the world's largest obligate freshwater elasmobranch. This makes it popular among fishermen and suggests a susceptibility to anthropogenic threats. We collected records of P. brachyura (n = 70) from media, fishermen and scientific sampling, to estimate its global geographic distribution (using both generalised additive and MaxLike models). Then, we estimated the species' exposure to habitat modification and fishing pressure, by applying multinomial ordinal models with threat levels as response and the presence or absence of P. brachyura as an independent variable. Distance to coast, depth, water temperature range, salinity range and mean water temperature were the main determinants of the distribution in the Río de la Plata. This resulted in a narrow coastal distribution. In the Uruguay and Paraná River basins, the probability of occurrence was positively associated with flow accumulation, percentage of open water and submerged vegetation, and lowland ecoregions, and negatively to wetness index and altitude. This limited the distribution to large lowland rivers. Approximately 41% of the range of P. brachyura in the Río de la Plata was subject to high habitat modification. In the Uruguay and Paraná River basins, this percentage reached 7%; however, the overlap with high fishing pressure was 59%. For conservation purposes, P. brachyura may function as an umbrella species. [ABSTRACT FROM AUTHOR]

The eyespot skate, Atlantoraja cyclophora, is an endemic species from the southwestern Atlantic, occurring from Rio de Janeiro, Brazil, to northern Patagonia, Argentina. The feeding habits of this species, from off Uruguay and north Argentina, were evaluated using a multiple hypothesis modelling approach. In general, the diet was composed mainly of decapod crustaceans, followed by teleost fishes. Molluscs, mysidaceans, amphipods, isopods, lancelets and elasmobranchs were consumed in lower proportion. The consumption of shrimps drecreased with increasing body size of A. cyclophora. On the other hand, the consumption of teleosts increased with body size. Mature individuals preyed more heavily on crabs than immature individuals. Teleosts were consumed more in the south region (34° - 38°S) and crabs in the north region (38° - 41°S). Shrimps were eaten more in the warm season than in the cold season. Prey size increased with increasing body size of A. cyclophora, but large individuals also consumed small teleosts and crabs. Atlantoraja cyclophora has demersal-benthic feeding habits, shifts its diet with increasing body size and in response to seasonal and regional changes in prey availability and distribution. [ABSTRACT FROM AUTHOR]

The bignose fanskate, Sympterygia acuta, is a small-to-medium-sized species endemic to shallow coastal waters of the Southwest Atlantic. Sympterygia acuta displays a clear seasonal reproductive cycle, characterized by maximum egg-laying activity in spring and hatching in summer. We hypothesized that diet and feeding activity change with maturity stage and season and that, given its smallish size, the trophic level is low. Using a multiple-hypothesis modeling approach, the diet of S. acuta in relation to sex, body size, maturity stage, region ( i.e. north and south) and season was analysed; and a potential relationship between feeding activity and the seasonal reproductive cycle was assessed. Sympterygia acuta fed on a broad spectrum of prey, but teleosts were more important (47.97% index of relative importance, % IRI), followed by decapods (39.84% IRI), cumaceans (8.31% IRI) and isopods (1.89% IRI). Maturity stage was a strong determinant of the ontogenetic diet shift of S. acuta, and relationships between number of prey consumed with season and region were found.. Feeding activity was higher in the cold season than in the warm season, and was less important in the south region than in the north region. Unexpectedly, the specific trophic level was high (3.87). Sympterygia acuta shifts its diet with maturity stage, possibly by a combination of an improved ability to capture prey and a change in energy demand of mature individuals. Despite being a small-to-medium-sized skate, S. acuta showed a trophic level similar to that of large-bodied marine predators. It reduces its feeding activity seasonally because in the warm season this species may experience an increased predation risk from large sharks. [ABSTRACT FROM AUTHOR]

Detecting and determining changes in the occurrence and abundance of species is a priority for effective management of resources and for conservation of biodiversity. In the absence of long-term monitoring data, potential population declines may be very difficult to establish. Therefore, alternative information on occurrence of species to infer population trends is highly valued. Records of sharks (i.e., Notorynchus cepedianus, Carcharias taurus, Galeorhinus galeus, and Carcharhinus brachyurus) off northern Argentina from a recreational fishing magazine (Weekend), between 1973 and 2008, were reviewed with the aim of evaluating population trends with opportunistic data sources. For each shark species, the number of occurrences per year in the magazine was registered. Our analyses were based on a nonprobabilistic method (McPherson and Myers' approach) designed to determine population trends with opportunistic sighting records. In this approach we included the number of classified ads offering fishing guide services published per year in the magazine as a measure of observation effort. For each species, we fitted generalized linear models with a Poisson error structure and a log link, where the response variable was the number of occurrences per year, the explanatory variable was the year, and the logarithm of the number of fishing guide ads was specified as an offset in each model. For both approaches, the models estimated that populations of the four shark species have suffered declines. Estimates produced by these models will help to determine the magnitude of population changes where a paucity of data prevents more precise analysis. [ABSTRACT FROM AUTHOR]

1. From a biodiversity conservation viewpoint it is crucial to estimate the sensitivity of species and populations to climate change, especially of key species such as top predators. 2. Here, the El Niño-Southern Oscillation phenomenon (ENSO) was used as a natural experiment to estimate the sensitivity of a population of the rainforest-dwelling broad-snouted caiman, Caiman latirostris, to extreme floods. 3. Caiman abundance declined by 35% annually between 1996 and 1998, and then increased, without reaching 1996 levels, indicating a marked effect of the 1997 El Niño. Accordingly, the Southern Oscillation Index was positively correlated with caiman abundance, indicating lower caiman abundance with warm ENSO events. 4. The relationship between the relative annual mean abundance of caimans and the maximum daily annual discharge of the Iguazú River was analysed. This relationship was parabolic, with caiman abundance increasing at discharges from 500 to 1500m³ s-1 and then decreasing at discharges from 1500 to 2500m³ s-1, indicating an adverse effect of both extreme low and high river discharge. No effect of illegal hunting was measurable. 5. This study evaluated whether the negative effect of extremely high water levels on caiman abundance could be due to a decrease in the availability of the habitat more commonly used by small (<60 cm total length, TL) and medium (60-120 cm TL) caimans. Small and medium-sized caimans used herbaceous/shrub habitats more frequently than large caimans (>120 cm TL), i.e. the type of habitat flooded during extreme floods. 6. An increase in extreme floods, as forecast for the Atlantic rainforest owing to climate change, may seriously affect the population of rainforest caimans through the reduction of adequate habitat for juveniles. This counterintuitive result, in which an excess of water reduces the abundance of an aquatic top predator, should be considered in conservation plans of rainforest-dwelling crocodilians. [ABSTRACT FROM AUTHOR]

The distribution of the planktivorous basking shark Cetorhinus maximus is influenced by zooplankton abundance at small scales and temperature at medium scales in the North Atlantic. Here, we estimate the distribution of basking sharks on South Atlantic continental shelves, and the relative importance of chlorophyll concentration, as a proxy for zooplankton abundance, and temperature in determining habitat suitability for basking sharks at large scales. We used maximum entropy (MaxEnt) and maximum likelihood (MaxLike) species distribution modelling to test three hypotheses: the distribution of basking sharks is determined by (1) temperature, (2) chlorophyll concentration, or (3) both chlorophyll and temperature, while considering other factors, such as oxygen and salinity. Off South America, basking shark habitat included subtropical, temperate and cool-temperate waters between approximately 20°S and 55°S. Off Africa, basking shark habitat was limited to cool-temperate waters off Namibia and southern South Africa. MaxLike models had a better fit than MaxEnt models. The best model included minimum chlorophyll concentration, dissolved oxygen concentration, and sea surface temperature range, supporting hypothesis 3. However, of all variables included in the best model, minimum chlorophyll concentration had the highest influence on basking shark distribution. Unlike the North Atlantic distribution, the South Atlantic distribution of basking sharks includes subtropical and cool-temperate waters. This difference is explained by high minimum chlorophyll concentration off southern Brazil as compared to North Atlantic subtropical areas. Observations in other regions of the world support this conclusion. The highest habitat suitability for basking sharks is located close to nearshore areas that experience high anthropogenic impact. [ABSTRACT FROM AUTHOR]

This article presents a study which combined both morphological and molecular identification approaches to describe the new species of eagle ray Myliobatis from Buenos Aires Province, Argentina. The southern eagle ray Myliobatis goodei Garman and the bullnose eagle ray Myliobatis freminvilii Le Sueur have long been recognized to occur in coastal Argentinean waters. Researchers discovered the new eagle ray species Myliobatis ridens sp. nov. from the Southwest Atlantic Ocean after combining both traditional taxonomy and DNA barcoding.

Competition for food could be a major force driving changes in the community structure of skates (Rajidae) subjected to fishing exploitation. Under this hypothesis, small skates are released from competition with larger skates after fishing has depleted the larger species. Here, we compare the abundance patterns of two sympatric skates with similar niches but different life histories, Bathyraja albomaculata (larger and slow-reproducing) and Bathyraja macloviana (smaller and faster-reproducing), before (1971, 1978) and after (1998-2004) a 108% increase in industrial bottom trawling on the southeastern South American shelf in order to test the prediction that B. macloviana should competitively exclude B. albomaculata after the increase in fishing mortality. In 1971 and 1978, there was no relationship between the abundance of both species, indicating that they coexisted over large scales. In 1998-2004, the relationship between the abundances of these skates was bell-shaped, indicating that both species increased in abundance at low densities until peaking, after which B. albomaculata decreased when B. macloviana became more abundant, consistent with resource competition. We tested whether food may be a potential limiting resource by comparing the diet of both species. The two species consumed mostly polychaetes, differing only in the consumption of polychaetes from the family Nephthyidae, which was much higher for B. macloviana. Bathyraja macloviana could replace B. albomaculata at high densities when food resources may become scarce. These results support the hypothesis that competition release is an important factor explaining the changes in skate communities in overexploited areas. [ABSTRACT FROM AUTHOR]

Elasmobranch predation has important effects on marine ecosystems. Identifying the main correlates of the feeding habits of skates is of paramount importance for determining their ecological role. We tested the hypotheses that the diet of the spotback skate, Atlantoraja castelnaui, off Uruguay and northern Argentina, changes with increasing body size, between seasons and regions and that prey size increased with predator's size using a multiple-hypothesis modelling approach. A. castelnaui preyed mainly on teleosts, followed by cephalopods, elasmobranchs and decapods. Small individuals of A. castelnaui consumed decapods and large individuals ate elasmobranchs and cephalopods. The consumption of teleosts was constant along the ontogeny but differed between seasons; more demersal-benthic teleosts were consumed in the cold season, whereas more benthic teleosts were eaten in the warm season. Also, A. castelnaui consumed more cephalopods in the warm season than in the cold season. Benthic teleosts were consumed more in the south region, whereas decapods were eaten more in the north region. A. castelnaui is able to consume larger teleosts as it grows. We conclude that A. castelnaui is a versatile, mainly piscivorous, consumer that shifts its diet with increasing body size and in response to seasonal and regional changes in prey abundance or distribution. We tested the hypotheses that the diet of the Atlantoraja castelnaui changes with increasing body size, between seasons and regions and that prey size increased with predator's size. A. castelnaui is a versatile, mainly piscivorous, consumer that shifts its diet with increasing body size and in response to seasonal and regional changes in prey abundance or distribution. [ABSTRACT FROM AUTHOR]

The feeding habits of the Rio skate, Rioraja agassizi, from off Uruguay and north Argentina were evaluated using a multiple-hypothesis modelling approach. Relationships between number of preys and sex, maturity stage, body size, season and region were assessed by building generalized linear models. Rioraja agassizi fed mainly upon crustaceans (shrimps, crabs and amphipods) and teleosts, but also upon isopods, cumaceans, lancelets and polychaetes. Ontogenetic diet shifts were found: small R. agassizi consumed amphipods, cumaceans and isopods and large individuals on shrimps, crabs and teleosts. The consumption of crustaceans (amphipods, shrimps, crabs, isopods and cumaceans) was higher in the northern (34°–38°S) than in the southern area (38°–41°S). Rioraja agassizi consumed more teleosts in the cold season and preyed more on lancelets in the warm season. Prey size increased with increasing body size of R. agassizi, but large individuals also consumed small prey. Ontogenetic shifts may be related to body size rather than other life-history traits. Rioraja agassizi adapts its feeding habits in response to regional and seasonal changes. [ABSTRACT FROM PUBLISHER]

Sharks are one of the most threatened groups of marine animals, as high exploitation rates coupled with low resilience to fishing pressure have resulted in population declines worldwide. Designing conservation strategies for this group depends on basic knowledge of the geographic distribution and diversity of known species. So far, this information has been fragmented and incomplete. Here, we have synthesized the first global shark diversity pattern from a new database of published sources, including all 507 species described at present, and have identified hotspots of shark species richness, functional diversity and endemicity from these data. We have evaluated the congruence of these diversity measures and demonstrate their potential use in setting priority areas for shark conservation. Our results show that shark diversity across all species peaks on the continental shelves and at mid-latitudes (30-40 degrees N and S). Global hotspots of species richness, functional diversity and endemicity were found off Japan, Taiwan, the East and West coasts of Australia, Southeast Africa, Southeast Brazil and Southeast USA. Moreover, some areas with low to moderate species richness such as Southern Australia, Angola, North Chile and Western Continental Europe stood out as places of high functional diversity. Finally, species affected by shark finning showed different patterns of diversity, with peaks closer to the Equator and a more oceanic distribution overall. Our results show that the global pattern of shark diversity is uniquely different from land, and other well-studied marine taxa, and may provide guidance for spatial approaches to shark conservation. However, similar to terrestrial ecosystems, protected areas based on hotspots of diversity and endemism alone would provide insufficient means for safeguarding the diverse functional roles that sharks play in marine ecosystems. [ABSTRACT FROM AUTHOR]

Colonello, J. H., Lucifora, L. O., and Massa, A. M. 2007. Reproduction of the angular angel shark (Squatina guggenheim): geographic differences, reproductive cycle, and sexual dimorphism. – ICES Journal of Marine Science, 64: 131–140. The reproductive ecology of Squatina guggenheim from two coastal areas in South America is analysed. In both sexes, individuals from ER (El Rincón coastal system, the more southern area) attained a larger maximum total length (LT) and a heavier weight at a given length than those from LP (La Plata River estuary). Females from ER mature at a significantly larger LT than females from LP. These patterns could be explained by an advantage of larger body size at higher latitudes in providing more reserves for winter, because individuals from ER have a larger liver than those from LP. Spines in the outer part of the pectoral fins were observed only in adult males. Fecundity increased with female total length. Females have a 3-y reproductive cycle, consisting of 10–12 months of gestation and 2 y of oocyte maturation. The embryonic growth fits the Gompertz model. Birth is in November or December, as inferred from embryo size and the presence of neonates and young of the year. Densities of S. guggenheim in LP peaked in spring and summer along the Uruguayan coast, suggesting a seasonal movement perpendicular to the shore. The reproductive pattern found suggests a population with low productivity. [ABSTRACT FROM PUBLISHER]

Size at maturity, sexual dimorphism, gonad development, and abundance of white-dotted skate, Bathyraja albomaculata, were assessed along its geographic range in the Southwest Atlantic, from Uruguay to Tierra del Fuego (Argentina). In all, 291 specimens from eight research cruises conducted between 1998 and 2003 were examined. Length–mass relationships were sexually dimorphic, adult females being significantly heavier than males of the same length. The largest female observed was 762mm total length (LT), and 50% maturity (LT50) was attained at 653mm LT. The largest male was 732mm LT, and male LT50 was 628mm LT. Female and male LT50 were not significantly different and were about 86% of observed maximum size, similar to other Bathyraja species. The lack of sexual dimorphism in size at maturity and the slight difference in maximum size between sexes support the hypothesis of relaxation of selection for large female size in oviparous elasmobranchs. Liver size was not sexually dimorphic. Mature female gonads were symmetrical in terms of mass, and similar in ovarian follicle number and size. Females carried egg cases in April, September, and October, consistent with previous observations around the Islas Malvinas and suggesting year-round egg laying. Bathyraja albomaculata was most abundant on the outer continental shelf and slope between 36°30′S and 45°S (northern area). In contrast, it was generally absent between 48°S and 52°S (southern area), a region where it was formerly reported as abundant. These differences are coincident with the development of a fishery targeting skates in the southern area, whereas in the north B. albomaculata taken as bycatch are mostly discarded alive. [Copyright &y& Elsevier]

The copper shark, Carcharhinus brachyurus, is the only member of its genus with a preferred habitat in temperate waters, and it usually gives birth in the cooler extremes of its range. Maturation patterns, reproductive condition, monthly sex ratios, and seasonal occurrence of copper sharks were analysed, mostly from Anegada Bay (Argentina), a presumed nursery area for the species. Males mature between 200 and 220 cm total length (LT), with a 50% size at maturity (L50) of 216.18 cm LT. Females mature between 215 and 223 cm LT (with an L50 of 222.16 cm LT). Maturity off Argentina is at a slightly smaller size than off South Africa and Australia. There is no sexual dimorphism in size at maturity. Only two pregnant females, each carrying 16 advanced embryos, were caught. The hepatosomatic index (IH) of adult males showed significant monthly changes, related possibly to an increase in the gonadosomatic index (IG). IH and IG of adult females showed no significant trend throughout the fishing season. The IH of adult females was significantly correlated with maximum diameter of ovarian follicles. Small translucent ovarian follicles in two gravid females indicated that ovarian and gestation cycles run sequentially, with maturation of oocytes subsequent to parturition. Neither newborns nor significant numbers of females bearing term embryos were recorded, and there was no evidence of a copper shark primary nursery area in Anegada Bay. However, most copper sharks in Anegada Bay were large juveniles and sub-adults. The species is found off Argentina from October to late March, but they do not move southwards to Anegada Bay until December, and they leave the bay again by April. These movements appear to be related more to water temperature rather than to migration of potential prey. Monthly variation in sex ratios is associated mainly with fluctuations in the sex ratios of juveniles. [ABSTRACT FROM PUBLISHER]

This study analyses the sexual activity and segregation of sand tiger sharks, Carcharias taurus, from Anegada Bay (Argentina). Reproduction-linked movements along the South American Atlantic coast were inferred from data from several SW Atlantic localities. Male sand tigers (n=162) matured at 193 cm total length (LT). Females (n=77) matured between 218 and 235 cm LT. These figures are similar to those from other populations, although size-at-maturity of males was slightly different from South African and Australian populations. In females, the size of ovarian follicles was positively correlated with gonadosomatic index and negatively correlated with hepatosomatic index, while the liver was significantly larger than in males. Sand tiger sharks were present in Anegada Bay from December to April. Males were significantly more abundant than females (2:1). Significant differences in reproductive condition through time were observed in males. During January and February males had seminal vesicles full of spermatozeugmata but by March and April the vesicles were empty. As the proportion of males with a lighter colouration peaked from January to March, it is very likely that mating takes place during January and February. The skewed sex-ratio during the mating season indicates a possible strong competition for mates among males, as observed in captivity. Males, females and some juveniles occur in Argentinean and Uruguayan waters, where mating takes place. Pregnant females occur in subtropical waters of southern Brazil, where they give birth. Given that pregnant and non-pregnant females occur at the same time in different zones, we suggest that the female reproductive cycle is biennial. Striking differences among migratory patterns of sand tiger sharks from the SW and NW Atlantic and South Africa were observed. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

The diet of Dipturus chilensis was composed mainly of the nototheniid fish Patagonotothen ramsayi, squid Illex argentinus, hake Merluccius hubbsi, serolid isopods, and crustaceans. Our results suggest that D. chilensis feeds selectively on some teleosts and rejects eel-like fishes. Total length of consumed P. ramsayi was significantly correlated with the skate's mouth width. [ABSTRACT FROM PUBLISHER]