Distribution and abundance of the ichthyofauna of surf zone in sandy beaches of the Rio de Janeiro Municipality, Brazil, were studied aiming to detect seasonal and wave exposure gradient influences on the fish community structure. Quarterly samplings were performed at 10 sites according to the exposure degree (sheltered, exposed and very exposed) between January and November 2004, by using beach seines with hauls carried out perpendicular to the coastline. A total of 6,464 fishes in 38 species and 22 families were identified, mainly juveniles or small sized individuals. The families Clupeidae, Carangidae and Sciaenidae amounted to 79% of the total fish number and 61% of the total biomass. The following species amounted to 81% of the total weight were: Harengula clupeola (36%), Orthopristis ruber (14%), Mugil liza (10%), Trachinotus goodei (8%), Trachinotus carolinus (7%) and Umbrina coroides (6%). Three species showed the highest relative abundance, contributing each one more than 10% of the total number (Harengula clupeola, Umbrina coroides, e Trachinotus carolinus); but only T. carolinus showed a clear pattern, being more abundant in the sheltered beaches. The highest CPUEs (number of individuals and biomass) and number of species values occurred in the sheltered beaches (p < 0.05); none of these indicators showed significant seasonal differences (p > 0.05), although some trends were detected. The wave exposure degree was confirmed as a primary factor influencing the fish community structure, with sheltered sites probably associated to higher plankton availability, lesser turbulence and more substrate stability. A distribuição e abundância da ictiofauna na zona de arrebentação de praias arenosas do Município do Rio de Janeiro, Brasil, foram estudadas objetivando detectar variações sazonais ou influências do grau de exposição na estrutura da comunidade de peixes jovens. Amostras trimestrais foram realizadas em 10 praias sendo agrupadas de acordo com o nível de exposição (abrigada, exposta e muito exposta), entre Janeiro e Novembro de 2004, com os arrastos tendo sido efetuados perpendiculares à linha de costa. Foram registrados 6.464 peixes, distribuídos em 38 espécies e 22 famílias, com o predomínio de formas juvenis ou de pequeno porte. As famílias Clupeidae, Carangidae e Sciaenidae representaram 79% do número total de indivíduos e 61% da biomassa total. As espécies de maior participação na biomassa, representando 81% do peso total, foram Harengula clupeola (36%), Orthopristis ruber (14%), Mugil liza (10%), Trachinotus goodei (8%), Trachinotus carolinus (7%) e Umbrina coroides (6%). Três espécies apresentaram maior abundância relativa, tendo cada uma, contribuído acima de 10% do número total (Harengula clupeola, Umbrina coroides e Trachinotus carolinus), mas somente T. carolinus apresentou um padrão bem definido, sendo mais abundante nas zonas abrigadas. As maiores CPUEs (número de indivíduos e biomassa) e o número de espécies foram encontradas nas zonas abrigadas (p < 0,05); sazonalmente nenhum destes indicad...
Diel fluctuations in nearshore fish communities were studied at a sandy beach in south-eastern Brazil. A total of 192 samples were performed by beach seines, during 3-hour intervals throughout 48-hour periods, between spring 2005 and winter 2006. Mean biomass and number of species were significantly higher at night, while number of individuals did not differ between day and night. Major disruptions in the fish community occurred during the winter when the assemblages underwent restructuring. Harengula clupeola, Sardinella janeiro, Anchoa lyoleps and Umbrina coroides were the predominant species at night, while Atherinella brasiliensis, Pomatomus saltatrix and Trachinotus carolinus peaked during the day, although significant diel changes in community structure were recorded only in the summer. Biological interactions, behavioural variations and local constraints might explain diel differences in the fish distribution. This study confirms that changes in diel activity in juvenile fish species can differ in similar areas, even for a given species, and the causes of these changes needs to be investigated.
Short‐term dynamics in juvenile fish assemblage structure were studied to test whether the most abundant species show temporal segregation, in order to assess whether selected environmental variables could predict species groupings, and to examine the stability of sunset–day–sunrise–night differences. Samplings were collected at 3‐h intervals over 48 h on a seasonal basis between spring 2005 and winter 2006. Fish species richness and abundance were higher in spring, and the lowest values occurred in winter. Harengula clupeola occurred mainly in spring, whereas Atherinella brasiliensis peaked in summer and autumn. On the other hand, Trachinotus carolinus, Umbrina coroides and Mugil liza were abundant in winter. Although temperature, salinity and dissolved oxygen were not found to have a strong effect on the abundance patterns of most species, they did appear to have a significant influence on assemblage groupings, according to canonical correspondence analysis and Spearman rank correlation. There is no consistency of diel usage patterns by a given species across seasons. The relative abundance differed between the time of day, which differed among the seasons; this further complicates an understanding of the dynamics of an assemblage. Studies of diel changes that pooled the sampling period as day or night can miss important changes that occur in a short time scale, such as a 3‐h period.
The study area is in the western Brazilian Amazon and is the Brazilian site of the Alternatives to Slash and Burn Agriculture (ASB) Programme. Firstly, the area's land use systems are described and entry points for agricultural intensification strategies are suggested. Secondly, the relative scarcity of land and labour is examined. Third, there is a presentation of evaluations of pairs of land-use system alternatives (traditional systems versus proposed more intensive alternatives), regarding adaptability, agronomic sustainability and broader environmental impacts, as well as tradeoffs between intensification and adaptability, plant biodiversity and carbon stocks. Finally the constraints involved in promoting successful intensification are outlined.
The role of sandy beaches as nursery areas for 0-group anchovies (Teleostei: Engraulidae) was investigated in a tropical bay, south-eastern Brazil. Spatial and temporal (diel and seasonal) changes in fish abundance and environmental influences at two beaches were assessed, one located in the outer zone, and the other in the inner zone of Sepetiba Bay. The two sites were sampled quarterly at the same time (0800, 1100, 1400, 1700, 2000, 2300, 0200 and 0500 hours) over a 24 h cycle by beach seine with three replicates, between winter 1998 and autumn 1999. Environmental variables of water temperature, salinity, and transparency (as % depth) were taken at each fish-sampling occasion. Five species in three genera (Anchoa tricolor, A. januaria, A. lyolepis, Cetengraulis edentulus, and Lycengraulis grossidens) were identified. Anchoa tricolor and A. januaria were the most abundant species and indications of spatial separation were detected, with A. tricolor being more abundant in the outer bay (higher salinity and lower temperature), while A. januaria, in the inner bay (lower salinity and higher temperature). Overall, young-of-the-year Engraulidae peaked during the day, perhaps an adaptation to avoid competition with other abundant species which peak at night. Maximum densities of anchovies due to 0-group influxes were found in spring and paucity in summer. Spatial segregation to optimize resource uses and daily habits adapted to take advantage of the rich planktonic bay waters seems to be the strategy developed by these closely related species to use the area during early life cycle. Their high abundances suggest the suitability of the sandy beaches as nursery areas.
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