Marcus R. da Costa

Use of a tropical bay in southeastern Brazil by juvenile and subadult Micropogonias furnieri (Perciformes, Sciaenidae)

The white croaker Micropogonias furnieri is a commercially important marine fish that uses bays and other semi-closed coastal areas early in its life. A sampling programme, using beach-seine and otter trawl, was carried out in Sepetiba Bay (22°54′-23°04′S, 43°34′-44°10′W), southern Brazil, from October 1998 to September 1999, with the objective of assessing the patterns of temporal and spatial usage of the bay by white croaker during its early life. Early recruits (total length, TL, 10-50 mm) appear off beaches of the inner bay between October and December, move away from them during late summer and early autumn (January-April), and are caught by trawl offshore from May to September at a TL of 70-150 mm. From May to August, new recruits (10-50 mm) are again found inshore. Fish grow from 10-40 to 70-150 mm during the first year of life in the shallows of the bay, before moving offshore. They cross the deeper waters of the bay as they migrate towards the open ocean. Juveniles (TL 70-150 mm) are most abundant in the inner bay, and subadults (TL 150-200 mm) in the outer and central bay. M. furnieri use semi-closed coastal areas as nursery grounds, before moving out over the continental shelf, where they spawn.

Environmental influences on distribution of four Sciaenidae species (Actinopterygii, Perciformes) in a tropical bay at Southeastern Brazil

We sampled fish and measured environmental variables in the Sepetiba Bay, a tropical embayment at Southeastern Brazil. The aim was to assess environmental influences on distribution of four abundant species of Sciaenidae Micropogonias furnieri (Desmarest, 1823), Ctenosciaena gracilicirrhus (Metzelaar, 1919), Cynoscion leiarchus (Cuvier, 1830) and Menticirrhus americanus (Linnaeus, 1758) to test the habitat partition hypothesis. Samples were taken between June 1993 and July 1996, at three bay zones (outer, central and inner). Depth was the most important environmental variable to influence fish distribution, followed by transparency. M. furnieri showed significant negative correlation to depth, transparency and salinity, while C. gracilicirrhus showed the opposite situation. The highest densities of C. leiarchus occurred in the lowest temperature, while M. americanus did not showed preferences for any of the examined environmental variables. Spatial separation, mainly between M. furnieri and C. gracilicirrhus, seems to be the strategy developed to coexist in the Sepetiba Bay, with M. furnieri being more adapted to copy with harsh environmental conditions of the inner bay. The other three species, which use mostly the outer bay zone, seem to be restricted to more stable conditions, where influences from oceanic waters are more intense.

The use of the Guaratiba magrove, Sepetiba Bay, Rio de Janeiro, by the silverside Atherinella brasiliensis (Quoy & Gaimard) (Atheriniformes, Atherinopsidae)

Fish and environmental variables were sampled in a mangrove area from Sepetiba bay to assess the role of this system in life cycle of the silverside Atherinella brasiliensis (Quoy & Gaimard, 1824). Standardized monthly sampling using beach seines were conducted at five sites, between August, 2002 and July, 2003 in daily (day/night) basis, with environmental variables being taken at each site. The highest numerical abundance was recorded in the intermediate sample area in the mangrove channel and the lowest in the innermost site. The highest weight occurred in the outermost site near to the sea connection. Numerical abundance was directly correlated with temperature and salinity, and weight with salinity and dissolved oxygen (p < 0.05). Size ranged from 10 to 160 mm TL, with modes of 40-50 mm TL occurring all over the year in all sites. Recruitment occurred all year round but peaks (TL = 30 mm) in October-December, 2002 and July, 2003 were recorded afterwards the records of larger fishes (September, 2002 and June, 2003) mainly in the outermost site. The largest fishes concentrated in the sandy substrate of the outermost sites, areas more suitable for A. brasiliensis spawning, with recruits dispersing all over the mangrove areas, which are used as rearing grounds. The affinity for highly structured habitats in mangrove and the capacity to use efficiently semi-closed systems was confirmed for A. brasiliensis in Guaratiba mangrove.

Distribution and size of the mojarra Diapterus rhombeus (Cuvier) (Actinopterygii, Gerreidae) in a Southeastern Brazilian bay

Diapterus rhombeus is one of the most abundant fish species in the Sepetiba bay, which is a 520 km2 semi-closed coastal area in Southeastern Brazil. The size and distribution of this species have been described in order to assess the use of the area as a rearing ground in both spatial and temporal (seasonal) dimensions. A fish sampling program was conducted monthly by using an otter trawl between October 1998 and September 1999, in three bay zones (outer, middle and inner), defined according to depth and salinity gradient. Highly significant differences were found for CPUEs (number and biomass) among seasons and zones. Size ranged from 50 to 230 mm TL, and three size-groups were defined according to a maturation scale (n = 1435): 1 - immature ( 100 mm TL). Immature and L50 individuals were more abundant (number and biomass) during Autumn in the inner zone, while adults (L100) predominated during Summer in the outer zone. Evidences of movements of young-of-the-year (50-90 mm TL) individuals from the inner to the outer zone were detected as they reach larger sizes (180 mm TL) in the second year of life. Condition (k) was higher in larger sized individuals in the outer zone during Spring, when they are apt to start the reproductive process. Two cohorts were detected according to modal progression: the first (smaller size) showing faster growth than the second, evidencing a slower growth rate as they reach larger size. Distinct size classes occupying different bay zones suggest that the age-groups optimize their coexistence by partitioning the available resources, avoiding intra-specific competition.

Habitat preferences of common native fishes in a tropical river in Southeastern Brazil

Determinamos neste estudo a preferencia de habitat de sete especies de peixes abundantes em um rio regulado do Sudeste do Brasil. Testamos a hipotese de que peixes diferem na preferencia de habitat e usam trechos do rio com diferentes caracteristicas hidraulicas e tipos de substratos. Realizamos amostragens de peixes, utilizando redes de espera e tarrafas em quatro trechos do rio de 1 km de extensao, compreendendo diferentes caracteristicas do habitat, onde tambem obtivemos medidas de profundidade, velocidade da agua e tipo de substrato. Quatro Siluriformes (Loricariichthys castaneus, Hoplosternum littorale, Pimelodus maculatus e Trachelyopterus striatulus) e tres Characiformes (Astyanax aff. bimaculatus, Oligosarcus hepsetus e Hoplias malabaricus) que juntos compreenderam aproximadamente 70% do numero total e 64% do peso total de peixes foram estudados. Classificamos os peixes em quatro guildas: (1) peixes que ocorrem em trechos com baixa velocidade de fluxo e substrato constituido predominantemente de lama e areia, compreendendo dois Siluriformes, um de areas rasas ( 8 m, i.e., L. castaneus); (2) peixes que utilizam rapidos de areas laterais mais profundas com substrato lamoso, representados pelos pequenos Characiformes, A. aff. bimaculatus e O. hepsetus; (3) peixes que utilizam rapidos que ocorrem em areas rasas e substrato arenoso, representado por T. striatulus; e (4) peixes de corredeiras que utilizam as margens rasas com fundo lamoso, representados por H. malabaricus e P. maculatus. As especies estudadas apresentam diferenciacao na preferencia por variaveis do habitat, corroborando a hipotese investigada.

Size distribution of the jack Chloroscombrus chrysurus (Linnaeus) (Actinopterygii, Carangidae) in a tropical bay at Southeastern Brazil

Chloroscombrus chrysurus (Linnaeus, 1766) e o representante mais abundante da familia de Carangidae na Baia de Sepetiba, uma area semi-fechada com 450 Km2, localizada no sudeste do Brasil. Foram analisadas as CPUEs de numero, peso e tamanho, alem dos dados ambientais, a fim de avaliar parte do ciclo de vida desta especie num ambiente de baia. As amostras foram realizadas mensalmente em triplicatas atraves de rede de arrasto de fundo, em tres zonas da baia (interna, central e externa), definidas de acordo com um gradiente espacial de profundidade e salinidade. Juvenis foram registrados primeiramente na zona interna da baia, medindo entre 30-90 mm de comprimento total - CT (moda = 60 mm CT) na primavera. Este mesmo grupo de tamanho desloca-se para as zonas central e externa da baia durante o verao-outono quando atingem CT = 120-180 mm, juntando-se posteriormente aos adultos no inverno. Jovens do ano nao utilizam as praias arenosas da Baia de Sepetiba como area de recrutamento, embora a desova desta especie ocorra na plataforma continental, com ovos e larvas penetrando em direcao a parte mais interna da baia. Pelo menos duas classes anuais de tamanho coexistem na baia durante os primeiros dois anos. O gradiente ambiental de temperatura, salinidade, transparencia, oxigenio dissolvido e profundidade foram pobres preditores para o numero e o peso dos peixes, e a correlacao negativa significante com salinidade e a profundidade reflete somente as altas abundâncias de jovens na parte mais interna da baia onde predominam maiores influencias de drenagem continentais e maiores deposicoes de sedimento.

Condicionantes ambientais na distribuição e no periodo reprodutivo do Orthopristis ruber (Cuvier) (Teleostei, Haemulidae) na Baía de Sepetiba, Rio de Janeiro, Brasil

Orthopristis ruber (Cuvier, 1830) is a very common species in the Brazilian coast, being found in large abundance in bays where they rank among the most numerical abundant species in bottom trawls. This work aims to assess environmental influences on spatial, temporal distribution and reproductive period of O. ruber in the Sepetiba Bay, a coastal semi-closed area in the Rio de Janeiro State. Monthly samplings were carried out using otter trawl from October 1998 to September 1999, in three Bay zones, defined according to the proximity of the sea (inner, middle and outer). Samples were taken as triplicate at each site as well as environmental measurements of water temperature, salinity, transparency and depth. Relative abundance was assessed by CPUE (capture per unit effort) in both number and weight. The reproductive period was determined by the gonadossomatic index. A total of 866 individuals was caught, with size ranging from 31 to 293 mm Total Length and sex ratio 1:1. Higher fish numbers and biomass were recorded in January/February and May, although no significant difference was found among seasons. Spatially, the highest number and biomass were recorded in the outer zone. Positive significant correlation between relative abundance and depth, salinity and transparency and negative with temperature were found. The reproductive period, indicated by the highest gonadosomatic index (IGS) occurred probably between June and September, coinciding with the lowest temperatures. This species seems to have distribution limited to outer bay zones, near to the sea influence, with the highest influxes in Summer, as a probable effect of the South Atlantic Central Waters (SACW) that compress Coastal Waters (CW) toward the bay.