Luiz Felipe Cestari Dumont

By-catch analysis of Argentinean prawn Artemesia longinaris (Decapoda: Penaeidae) in surrounding area of Patos Lagoon, southern Brazil: effects of different rainfall

One of the most problematic fishing methods in terms of by-catch and discarding is prawn-trawling. This paper analyses the incidental catch of an artisanal trawl fleet during two discrete Artemesia longinaris fishery seasons (2002 and 2004). The fishery season of A. longinaris operates monthly and it takes place in the surrounding area of the Barra do Rio Grande. Sampling was carried out during the fishing season (April-December) always on the same artisanal trawl boat. An observer was included on-board to avoid loss of information due to discards made by the fishermen at sea. Fifty species were caught: 38 fish and 12 crustaceans. Discrete fauna abundance and composition were recorded in analysed years, with higher by-catch ratios associated with elevated rainfall and low salinity. The overall discard ratio was 1:5.6, with values ranging from 1:11.3 in 2002 to 1:2.5 in 2004. The most striking differences between both years analysed were observed during autumn (1:75 in 2002 and 1:11.30 in 2004) and winter (1:16 in 2002 and 1:0.97 in 2004), while spring presented similar values (1:8 in 2002 and 1:4 in 2004). The discard ratio estimated in terms of number showed a different pattern, presenting overall values of 1:2.24 in 2002 and 1:0.5 in 2004. Higher estuarine runoff may have increased biomass production in the surrounding area of Patos Lagoon during 2002, sustaining higher abundance of estuarine-related and marine species in the area, as well as higher mean trophic level and abundance of top-predators. Conversely, A. longinaris production was consistently lower, since this marine species does not tolerate marked reductions in salinity. In 2004, salinity was higher, associated with low rainfall and favouring A. longinaris abundance in the area. During this dry year, the target-species was dominant in samples resulting in very low by-catch ratios, especially in winter (1:0.97). The catch was mainly composed of juvenile fish, since fishery is performed in nursery grounds.

High Connectivity among Blue Crab (Callinectes sapidus) Populations in the Western South Atlantic

Population connectivity in the blue crab Callinectes sapidus was evaluated along 740 km of the Western South Atlantic coast. Blue crabs are the most exploited portunid in Brazil. Despite their economic importance, few studies report their ecology or population structure. Here we sampled four estuarine areas in southern Brazil during winter 2013 and summer 2014 in order to evaluate diversity, gene flow and structure of these populations. Nine microsatellite markers were evaluated for 213 adult crabs, with identification of seven polymorphic loci and 183 alleles. Pairwise FST values indicated low population structure ranging from -0.00023 to 0.01755. A Mantel test revealed that the geographic distance does not influence genetic (r = -0.48), and structure/migration rates confirmed this, showing that even the populations located at the opposite extremities of our covered region presented low FST and exchanged migrants. These findings show that there is a significant amount of gene flow between blue crab populations in South Brazil, likely influenced by local current dynamics that allow the transport of a high number of larvae between estuaries. Considering the elevated gene flow, the populations can be considered a single genetic stock. However, further information on population size and dynamics, as well as fishery demands and impacts at different regions, are necessary for harvest management purposes.

Growth of Ligia exotica (Isopoda: Oniscidea: Ligiidae) in two estuarine regions of Patos Lagoon, Rio Grande do Sul, Brazil

The aim of this study was to estimate growth parameters of two populations of Ligia exotica inhabiting discrete estuarine areas of Patos Lagoon, Rio Grande do Sul, Brazil. Sampling was performed fortnightly at two different estuarine zones, named Leonideo Island and West Breakwater, to detect different growth patterns for this species by using the von Bertalanffy growth model (VBGM). The VBGM estimated were as follows: TL mm = 34 . 57 ( 1 - e ―0.012(t ― 2.93) ) (males in Leonideo Island), TL mm = 35.61 (1 ― e ―0.009(t ― 5.87) ) (males in West Breakwater), TL mm = 30.11(1 ― e ―0.009(t ― 5.84) ) (females in Leonideo Island) and TL mm = 29.65(1 ― e ―0.01(t ― 4.87) ). Significant sexual dimorphism was observed, since males reach larger TL (mm) by higher k value (day) and consequently a faster growth pattern. Different growth patterns of males were also detected comparing both populations, in such a way that the West Breakwater individuals are larger than those from the Leonideo Island. One possible explanation is the higher food availability observed in the former site, as well as favourable environmental parameters, providing better conditions for individual growth. Briefly, two different populations of L. exotica were detected in the studied area, presenting discrete growth parameters highly influenced by environmental factors.

Biologia reprodutiva de Ligia exotica (Crustacea, Isopoda, Ligiidae) em Rio Grande, Rio Grande do Sul, Brasil

Aiming to elucidate some aspects of the reproductive biology of Ligia exotica Roux, 1828, two populations inhabiting the Estuary of the Patos Lagoon (West Breakwater of Rio Grande Channel and Leonidio Island) were analyzed. Sampling was performed fortnightly, from summer/2003 to winter/2004. Animals were collected manually during one hour. The reproductive season of the species occurred from October to June. No ovigerous females were observed from July to September. In West Breakwater of Rio Grande, 5,376 individuals were captured (1,494 juvenile, 1,748 males and 2,134 females, in which 245 were ovigerous). Sex ratio estimated was 0.78 (M:F). To perform fecundity analysis, 178 ovigerous females with intact marsupium were analyzed. Total length of these females varied from 20.73 to 34.3 mm, and the number of eggs-embryos ranged from 33 to 142. The mean length of sexual maturity of females was 24.65 mm and the mean number of eggs-embryos was 88.0. In Leonidio Island, 5,519 animals were collected (510 juvenile, 1,956 males and 3,053 females, from which 129 were ovigerous). The sex ratio was 0.68 (M:F). While the lowest percentages of ovigerous females were found from September to May, the highest percentage of ovigerous female was observed at the end of March. In this location, 101 ovigerous females were analyzed, with total length varying from 17.62 to 28.61 mm, and the number egg-embryos ranged from 25 to 113. The mean length of sexual maturity of females was 21.43 mm and the mean number of eggs-embryos was 73.8.

Biometric relationships of the Argentinean prawn Artemesia longinaris (Decapoda: Penaeidae) in the south-western Atlantic

Biometric relationships of size and weight were estimated for the Argentinean prawn (Artemesia longinaris), a new commercial penaeid prawn exploited in the south-western Atlantic. Morphometric and meristic traits were used to elucidate population structure of this species along its distribution area. The morphological relationships were estimated by a simple linear regression, considering total length (TL) as the dependent variable. The males collected in southern Brazil, an area under influence of the Subtropical Convergence, presented a slightly lower TL increment than females. A marked reduction in slopes of males between populations from southern Brazil was observed in autumn and winter. Additionally, relative growth in length of males from Argentina is similar to that observed during autumn and winter in southern Brazil. The other morphometric and meristic variables used also indicated higher similarities between southern Brazil and Argentina, which may be explained by relative growth associated to water temperatures or migration during winter, taking advantage of the oceanographic systems connecting both sites. Moreover, the population from Rio de Janeiro seems morphologically apart from the others, forming a separate unit stock.

Spatial and temporal variation in juvenile size distribution of the pink shrimp (Penaeus paulensis) in the Patos Lagoon Estuary, Brazil

ABSTRACT The Patos Lagoon Estuary (PLE) is the main nursery ground for the pink shrimp Penaeus paulensis, accounting for more than 40% of its total landings in Brazil. The spatial distribution and recruitment of shrimps in estuaries are usually non-uniform and influenced by the frequency and intensity of marine water intrusions. Recruitment of penaeid shrimps in tidal-regulated estuaries often presents a pattern where smaller individuals are concentrated in the lower estuarine regions associated to the saltwater influence. Conversely, in the PLE tidal variation is negligible and mainly influenced by rainfall and wind direction, controlling the freshwater discharge and saltwater intrusion. Understanding size distribution and its relation to the ontogenetic trends in habitat use is relevant for fisheries assessment and for species conservation. Additionally, the high fishing pressure applied to this stock has led to overexploitation and its associated consequences, such as shifts in size structure by removing the larger individuals, which in turn hinders the renewal capacity of the population. Therefore, our first hypothesis is that the long-term exploitation of the shrimp stock has resulted in the erosion of large size classes. The second hypothesis of this investigation is that the size distribution of shrimps in this estuary will not present a characteristic pattern, as previously described for other penaeids in tidal-regulated environments, since the unpredictability of environmental shifts could change the life strategy during the recruitment process. Continuous sampling of pink shrimp was carried out monthly with a beach seine net at five shallow sites (PL1–PL5) for the years 1996 to 2012. Temperature, salinity and transparency data were also obtained. Sampled shrimps were measured and grouped in 10 size classes of 10 mm interval. A factorial ANOVA was used to evaluate the spatial variation of the size distribution frequency along the estuary during 16 years, and a cluster analysis was performed to identify similar sites according to size composition. Shrimps were not distributed homogeneously in the PLE (P < 0.05), and no significant pattern related to distance from the mouth of the estuary, temperature or salinity was evident. In spite of not presenting a significant difference in size composition between sites, it was possible to observe a clear tendency of higher frequency and abundance of smaller individuals in the upper estuarine areas. The dominance of small juveniles in the upper estuarine areas is probably related to the erratic pattern of saltwater penetration and freshwater discharge, resulting in a nearly unpredictable pattern of size distribution. The cluster analysis grouped two stations (PL3, PL4) with greater size diversity. These areas were identified as favourable for catching large-sized individuals. Conversely two sites (PL1, PL2) were characterized by a high frequency of small individuals and should be taken into consideration when establishing fishing restricted areas. The long-term analysis of size structure indicated that the mean size of individuals decreased approximately by 25% after the first four years of the survey, suggesting overexploitation of this species in the region, and that fishery is removing an important fraction of the population. The conservation of large individuals is vital for stock recovery, since this group represents better chances of survival and better reproductive performance.

Responses of the infaunal peracarid Monokalliapseudes schubarti (Tanaidacea: Kalliapseudidae) to a bottom trawling disturbance and seasonality in an estuary of southern Brazil

ABSTRACT The tanaid Monokalliapseudes schubarti is one of the dominant macrobenthic species in the shallow mudflats of southern Brazil. This species plays an important role in local trophic webs as a primary consumer and as a prey. This work investigated (1) the temporal variations in the population densities and structure of M. schubarti in the Patos Lagoon Estuary and (2) the potential impacts of shrimp trawling on the population densities, population structure and vertical stratification of the species in shallow areas of the estuary. The species exhibited significant temporal variability in its total densities and population structure, with a reproductive period observed during late summer and autumn, following an increase in salinity within the estuary. There were significant differences in M. schubarti densities, which appeared to be associated with variations in sediment texture and salinity. No well-defined pattern of trawling impact was identified; however, after high-impact trawling, decreases in the abundance of males and juveniles in the sediment superficial layer were recorded, and ovigerous females disappeared from the sampled area with relatively higher percentages of medium sand. Changes in the densities of different morphological categories observed after trawling were likely due to mortality, resuspension or rapid movement deeper into their tubes.