Andrés J. Jaureguizar

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.

Distribution of Micropogonias furnieri at different maturity stages along an estuarine gradient and in relation to environmental factors

Whitemouth croaker ( Micropogonias furnieri ) maturity stages distribution and its relation to environmental factors was evaluated from 166 stations sampled within the Rio de la Plata estuary (36°S–56°W) during spring 1994–1999 and 2003. A canonical correspondence analysis was used to explain whitemouth croaker distribution and estimate its relation to environmental factors (depth, surface and bottom waters temperature and salinity, bottom salinity and temperature horizontal gradients and vertical stratification). Results indicate that bottom salinity horizontal gradient (BSHG) and depth have a major influence on M. furnieri maturity stages spatial distribution; bottom salinity and temperature play a significant although secondary role. Spent and resting adult stages were associated to low BSHG, high salinity and low temperature while immature, gravid (with hydrated oocytes) and running stages to low salinity and high temperature. Although immature, gravid and running stages were clearly linked to similar bottom salinity they were segregated, with gravid and running stages associated to a strong BSHG. The distinct preferences of the different spawning stages result in a segregated distribution pattern along the main axis of the Rio de la Plata estuary. The area with low salinity and high horizontal bottom salinity gradient (habitat for gravid and running stages) was located at the river head. The horizontal retention mechanism associated to BSHG within the spawning habitat favours growth and survival of fish larvae and the subsequent transport to nursery habitats.

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.

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

Drepanopus forcipatus e Calanus australis sao copepodos planctonicos relevantes na plataforma da Patagonia Austral. Seus padroes de alimentacao, reproducao e status populacional foram investigados durante o fim do verao, quando as condicoes ambientais podem ser criticas. A presenca de alimento no abdomen e o tamanho das pelotas alimentares foram registados em femeas adultas e nos estagios mais abundantes de copepodito. A composicao da dieta tambem foi estudada em femeas adultas. O status reprodutivo das femeas foi avaliado atraves do estagio gonadal. De modo geral, apesar das baixas condicoes alimentares e diminuicao sazonal da temperatura, ambos os copepodos se alimentaram. Os copepoditos mais numerosos e as femeas adultas de ambas especies mostraram baixa atividade alimentar. Cerca de metade das femeas adultas das duas especies e C5s de C. australis apresentaram alimento em seu intestino, porem a proporcao de femeas D. forcipatus C4 alimentadas foi consideravelmente menor. De modo geral, todos os copepodos se alimentaram entre niveis baixo e intermediario. A distribuicao do estagio gonadal e a estrutura populacional apresentaram reproducao baixa, mas continua para ambas as especies. Os alimentos encontrados no intestino sugerem uma preferencia por particulas nanoplanctonicas, especialmente dinoflagelatos em D. forcipatus, e por presas autotroficas, particularmente grandes diatomaceas em C. australis. Os padroes de alimentacao e reproducao dos dois copepodos foram provavelmente influenciados pela distribuicao de recursos alimentares e temperatura.

Environmental factors that define the spawning and nursery areas for Percophis brasiliensis (Teleostei: Percophididae) in a multispecific reproductive coastal zone, El Rincón (39°–41°S), Argentina

The spatial distribution of Percophis brasiliensis at different maturity stages and its relationship to environmental factors was evaluated in the El Rincon area (39°–41°S) between 1994 and 2008 during eight cruises carried out in spring. For this, a canonical correspondence analysis was used. Results indicate that bottom temperature and bottom salinity horizontal gradient (BSHG) were the most important variables affecting the spatial distribution of P. brasiliensis maturity stages. Juveniles were mainly located in shallow waters with low salinity, high temperatures and vertical stratification. Conversely, gravid and running individuals were found in high BSHG and low temperatures. This link suggests that adults spawn in a well-defined area of hydrographic conditions that would tend to retain pelagic eggs and larvae, thus minimizing dispersal, and ensuring their transport from the spawning to nursery areas. On the coastal shelf of El Rincon, the water mass circulation shows an anti-cyclonic gyre whose recirculation cell during spring and summer is more constrained to inshore areas than during winter. Maximum reproductive activity of P. brasiliensis coincides with the highest retention period; therefore, dispersal of early-life stages (eggs) depends on the circulation pattern and transport pathway which would contribute importantly to its recruitment variability.

Aggregations and reproductive events of the narrownose smooth-hound shark (Mustelus schmitti) in relation to temperature and depth in coastal waters of the south-western Atlantic Ocean (38–42°S)

Knowledge of environmental influence on reproductive dynamics in chondrichthyans is critical for effective management. The present study assessed the potential influences of temperature and depth on aggregations and reproductive events of the narrownose smooth-hound shark (Mustelus schmitti), using an analysis criterion based on the co-occurrence of different reproductive stages. Data were collected from 363 sample sites during six research surveys, covering an area of ~47744km2 along the coast (38–42°S, depth of <50m). Aggregations of M. schmitti adults were mostly associated with the warmer spring surveys, with the aggregation sites being significantly warmer than those of non-aggregation. Evidence of pupping and ovulation was observed, almost simultaneously, during all spring surveys. However, the occurrence of these reproductive events showed a clear interannual variability pattern that was significantly explained by water temperature. Particularly, the occurrence of ovulation was associated with temperatures above 16–17°C. These results suggest that M. schmitti adults may follow the warming gradient along the environment and, thus, they aggregate in shallow and productive waters during the course of spring. Their reproductive events could be induced by temperature increase. This scenario suggests that changes in the patterns of bottom temperature may be important drivers of the reproductive dynamics of M. schmitti.

Length-weight relationships of 29 species of teleost fish from shallow estuarine environment of Samborombon Bay (Río De la Plata, Argentina)

The length–weight relationships (LWR) of 29 teleost fish species from the shallow estuarine environments of the Samborombón Bay wetland (Río de la Plata, Argentina) were estimated. A total of 6,376 individuals belonging to 19 families were measured and weighed. The best represented family was Sciaenidae with 6 species, followed by Clupeidae (n = 3), and Heptapteridae and Characidae with 2 species each. Significant length–weight relationships with high correlation coefficients were found for all species, which mostly presented positive allometric growth. This study reports the first findings regarding the LWR of 29 species in the Samborombón Bay waters. New maximum sizes and geographic distribution records of certain species are also commented.

Relações peso-comprimento de 29 espécies de peixes teleósteos dos ambientes estuarinos pouco profundos da Baía Samborombón (Rio da Prata, Argentina)

The length–weight relationships (LWR) of 29 teleost fish species from the shallow estuarine environments of the Samborombon Bay wetland (Rio de la Plata, Argentina) were estimated. A total of 6,376 individuals belonging to 19 families were measured and weighed. The best represented family was Sciaenidae with 6 species, followed by Clupeidae (n = 3), and Heptapteridae and Characidae with 2 species each. Significant length–weight relationships with high correlation coefficients were found for all species, which mostly presented positive allometric growth. This study reports the first findings regarding the LWR of 29 species in the Samborombon Bay waters. New maximum sizes and geographic distribution records of certain species are also commented.