South Brazil Bight Research Articles

ESTRUTURA TERMOHALINA DO LITORAL CENTRO-NORTE CATARINENSE

This paper describes the seasonal behavior of the water masses which occur inside the South Brazilian Bight, specifically inside the Santa Catarina Center-North Inner shelf. It is located between the Itapocu river and the Tijucas Bay. Inside the area there is the Marine Reserve of Arvoredo and the Itajaí river, the most important river of the State that reachs the Atlantic Ocean. Four surveys cruises was done since November 94 to July 95 making STD measurements. Wind data was obtained at an oil platform located 100 nautical miles off Itajaí city. During spring and summer the water columns was stratified and upwelling and doweling events occur according to the northern and southern winds. During autumn-winter period the water column was homogeneous because of doweling or advection of modified subantartic water trough the area.

Priceless prices and marine food webs: Long-term patterns of change and fishing impacts in the South Brazil Bight as reflected by the seafood market

The lack of market variables in fishery systems (i.e., prices and quantities) has often been cited as one reason for the particular difficulty of understanding whole marine ecosystem change and its management under a broader ecosystem perspective. This paper shows the results of efforts to tackle this problem in the South Brazil Bight by compiling and analyzing in-depth an unprecedented 40-year database from the region’s largest wholesale seafood market, based in the megacity of São Paulo. Fishery landings and market values for the period 1968–2007 were analyzed primarily by updated trophic level classes and multispecies indicators including the (1) marine trophic index (MTI), (2) weighted price, and (3) log relative price index (LRPI) which relates prices and trophic levels. Moreover, an inferential analysis of major seafood category statistical trends in market prices and quantities and their positive and negative correlations was undertaken. In general, these market trends contributed substantially to identifying and clarifying the changes that occurred. Considerations of the behavior of demand, supply and markets are included. In particular, while the MTI did not support a “fishing down the marine food web” hypothesis, other indicators did show the continued scarcity of major high trophic level categories and fisheries target species. Overall, the results indicate that the analysis of fishery landings, or of certain other indicators alone, can mask real changes. Rather, a joint ecological–econometric analysis provides better evidence of the direction of ecosystem pressures and stock health. This method for detecting market changes across the food web may be particularly helpful for systems considered data-poor but where fish market data have been archived. This study further elucidates historical changes and fishing impacts in the South Brazil Bight ecosystem.

A comparative multi-fleet analysis of socio-economic indicators for fishery management in SE Brazil

One of the problems in an ecosystem approach to fisheries management is the lack of economic analyses which clearly define the performance of different fishing fleets within the system. We describe a comparative multi-fleet analysis of socio-economic indicators applicable for inclusion into ecosystem modeling and management. Based on a survey of different industrial fishing fleets in São Paulo, Southeastern Brazil, an inter-fleet comparison of economic attributes such as investment, fixed costs, effort, labour, sailing-related costs and profits, as well as a set of performance indicators, was conducted. Costs varied between fleets with fuel being the largest component on average, representing almost 37% of total costs. Similarities between fleets were driven by fuel costs, gross incomes and profits. In general, the best economic performance was associated with indicators of profitability and economic efficiency. Bottom-longliners and both surface and bottom-gillnet fleets showed the best economic performance per fishing trip due to their low percentage of variable costs. Purse-seiners and pink-shrimp trawlers had the lowest average rate of return and economic efficiency because of their high variable costs and relatively low catch values, and were considered economically net losers. However, in terms of jobs generated, purse-seiners had the greatest value creating about 49% of total jobs by all fleets. The sea-bob-shrimp fleet had the lowest crew size per vessel but generated the second highest total number of direct jobs (23%), with high economic viability as a whole. The inter-fleet cost and socio-economic performance analysis revealed that additional attention should be given to the poor profitability and overcapacity of fleets, fishing impacts, and open-access related issues, while social indicators may also be considered. This study provides information useful for evaluating different fisheries management scenarios and fleet size optimization in the South Brazil Bight, for ecosystem modeling policy optimization routines, and for a pragmatic ecosystem approach to fisheries management.

The relationship between multi-sensor satellite data and Bayesian estimates for skipjack tuna catches in the South Brazil Bight

In this study we tested a Bayesian model based on a conjugate gamma/Poisson pair associated with environmental variables derived from satellite data such as sea surface temperature (SST) and its derived gradient fields from Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra, chlorophyll-a concentration from Sea Viewing Wide field of View Sensor (SEAWiFS)/SeaStar and surface winds and Ekman pumping from SeaWinds/Quick Scatterometer (QuikSCAT) to predict weekly catch estimates of the skipjack tuna in the South Brazil Bight. This was achieved by confronting the fishery data with model estimates and regressing the results on the satellite data. The fishery data were expressed by an index of catch per unit effort (CPUE) calculated as the weight of fish caught (in tonnes) by fishing week, and were divided into two series, called historical series (1996–1998; 2001), and validation year (2002). The output of model CPUE estimates is in good agreement with the historical weekly CPUE and generated updated weekly estimates that explained up to 62% of weekly CPUE from 2002. In general, the best proxy for the Bayesian weekly estimates is the gradient zonal SST field. The results refined previous knowledge of the influence of SST on the occurrence of skipjack tuna.

The trophic role of the squid Loligo plei as a keystone species in the South Brazil Bight ecosystem

Abstract Gasalla, M. A., Rodrigues, A. R., and Postuma, F. A. 2010. The trophic role of the squid Loligo plei as a keystone species in the South Brazil Bight ecosystem. – ICES Journal of Marine Science, 67: 1413–1424. The issue of whether loliginid squid can influence the average structure of marine ecosystems in a keystone role, i.e. a strong effect with relatively low biomass, has not yet been examined. Here, the diet of Loligo plei in inner shelf waters of the South Brazil Bight was examined, as a first step, based on the stomach contents of 2200 squid hand-jigged in shallow water (<30 m) and taken as bycatch of shrimp trawlers in deeper water (30–100 m). Diet varied by size, season, and fishing zone. Stomachs were not empty in ∼12%, with more empty during winter. The range of mantle lengths of squid caught by jigging (101–356 mm) appeared to differ from the squid trawled (30–236 mm), and the diet also differed. Food categories recorded in deeper water did not include amphipods or polychaetes, but in both fishing areas, fish were the most common prey. The fish prey identified included Trachurus lathami, small pelagic species, trichiurids, and Merluccius hubbsi. Demersal species, such as Ctenosciaena gracilicirrhus, and flatfish were also present. An ecosystem network model is updated through which a mixed-trophic impact matrix and “keystoneness” indicators were calculated. Loligo plei represents an important link between pelagic and demersal energy pathways, with high indices of keystoneness.

Disentangling the upwelling mechanisms of the South Brazil Bight

This article presents a suite of long-term numerical simulations that investigate the dynamical mechanisms controlling the circulation in the South Brazil Bight (SBB). The overarching goal of these simulations is to quantify the relative contributions of local wind forcing and the Brazil Current (BC) to the upwelling of nutrient-rich slope water onto the shelf. The model results indicate that the water mass structure of the SBB is controlled by the synergy between wind-driven, inner-shelf upwelling and geostrophic, shelf-break upwelling. The later extends yearlong but the former peaks during the austral summer and decreases towards the winter. The interaction between the poleward flow of the BC and the bottom topography greatly influences the shelf circulation, particularly in the bottom boundary layer. Changes of the SBB coastline direction and shelf width modulate the along-shore pressure gradient and the magnitude of the shelf-break upwelling and downwelling. Thus, although the summer upwelling winds extend over large part of the SBB surface temperatures are warmer in the south because of the cooling effect of the shelf-break upwelling in the northern region. At difference with previous studies of shelf-break dynamics the shelf-break upwelling in our model is not controlled by the uplifting associated with the presence of instabilities of the boundary current or nonlinear accelerations under a variable shelf width. The proposed mechanism is relatively simple. As the boundary current flows along the continental slope, changes in the coastline orientation and along-shore bottom topography modify the along-shore pressure gradient which through geostrophy leads to inshore bottom flow and hence shelf-break upwelling. Such a mechanism can provide insight into upwellings on other western boundary current regions where similar topographic variations exist.

Distribution of common dolphins (Delphinus spp.) in the western Atlantic Ocean: a critical re-examination

Due to indications that misidentification (largely confusion among dolphins of the genera Delphinus and Stenella) in the past had led to erroneous assumptions of distribution of the two species of common dolphins (Delphinus delphis and D. capensis) in the western Atlantic Ocean, we conducted a critical re-examination of records of the genus Delphinus from this region. We compiled 460 ‘plottable’ records, required support for confirmation of genus and species identifications, and found many records lacking (and some clearly misidentified). When we plotted only the valid records (n = 364), we found evidence of populations in only three areas, and apparent absence throughout much of the tropical/subtropical regions. Off the east coast of the US and Canada, D. delphis is found from the Georgia/South Carolina border (32°N) north to about 47–50°N off Newfoundland. Since the 1960s, they have apparently been absent from Florida waters. There is no evidence that dolphins of the genus occur in the Gulf of Mexico. Reports of common dolphins from most of the Caribbean Basin are also rejected, and the only place in that region where they are confirmed to occur is off central-eastern Venezuela (a coastal D. capensis population). Off eastern South America, common dolphins appear to be restricted to south of 20°S. There is a coastal long-beaked population found in the South Brazil Bight, and one or more short-beaked populations south and offshore of this (ranging south to at least northern Argentina). The results are very different from commonly-accepted patterns of distribution for the genus in the Atlantic. Most areas of distribution coincide with moderate to strong upwelling and common dolphins appear to avoid warm, tropical waters. This study shows that great care must be taken in identification of similar-appearing long-beaked delphinids, and that uncritical acceptance of records at face value can lead to incorrect assumptions about the ranges of the species involved.

Sources of Nutrients and Seasonal Dynamics of Chlorophyll in the Inner Shelf off Paraná State—South Brazil Bight

Abstract The seasonal dynamics of phytoplankton chlorophyll and nutrients were studied between August 1997 and March 1999 along a cross-shelf section of the inner coastal of Parana State, southern Brazil. Vertical thermohaline stratifications in the rainy summer alternated with winter homogeneities. Nitrate-N varied from 0.17 to 1.13 µM, nitrite-N from 0.04 to 1.10 µM, phosphate-P from 0.37 to 0.73 µM, and silicate-Si from 2.5 to 10.2 µM, all presenting maximum concentrations at the bottom layers at the outer stations. Chlorophyll concentrations varied from <0.02 to 10.8 µg·L−1 throughout the study period, with maxima at subsurface and bottom layers depending on the season. Seasonal differences in the distributional patterns of nutrients and chlorophyll were caused by two main wind-driven physical processes: (i) onshore intrusions of South Atlantic Central Waters and (ii) remote continental runoff from La Plata River. These were considered the main sources of new nutrients in summer and winter periods, re...

Numerical simulation of M2 internal tides in the South Brazil Bight and their interaction with the Brazil Current

A fully three‐dimensional nonlinear primitive equation ocean model is applied to study the semidiurnal internal tide in the South Brazil Bight under summer conditions. Along the shelf break and upper slope of this region, the upper layer (0–600 m) is occupied by the southward flowing Brazil Current. Several numerical experiments were conducted to investigate the generation and propagation of the M2 internal tide. Using horizontally homogeneous and vertically stratified density fields, internal tides were generated over the whole Bight with a clear signal on the continental shelf. When a more realistic summer stratification was considered, a baroclinic jet, representative of the Brazil Current, developed and comparisons between current observations and modeled results were improved. This jet acts as a barrier to the coastward propagation of the internal tide generated over the slope, reflecting it back towards the open ocean. On the negative relative vorticity side of the Brazil Current, located over the shelf, internal tides are trapped, enhancing vertical current variability and, hence, tidally induced mixing. The results highlight the importance of considering background flows when investigating internal tides in regions of strong along‐slope baroclinic flows such as western boundary currents.

Cephalopods and cetaceans as indicators of offshore bioavailability of cadmium off Central South Brazil Bight

Regarding Brazilian coast, industrial and urban developments are concentrated along Central South Brazil Bight. Samples from inshore and offshore species from the concerned area were analyzed, comprising 24 cetaceans (9 species) and 32 squids (2 species). Cadmium was determined by GFAAS and our results were in agreement with certified values (DOLT-2, NRCC). Mean cadmium concentration (in μg/g, wet weight) observed in the digestive gland of sexually mature Argentine short-finned squids ( Illex argentinus) was 1002.9. To our knowledge this is the highest cadmium level ever reported for a cephalopod. Concerning cetaceans, our results include one of the highest renal cadmium concentrations described for striped dolphins (71.29 μg/g, wet weight). Anthropogenic action, upwelling and cannibalism of Argentine short-finned squid on the studied area are possible reasons for such remarkable cadmium concentrations.

First record of Fritillaria venusta Lohmann, 1896 (Tunicata: Appendicularia) in south Brazil bight (23°s - 28° 40's)

Fritillaria venusta Lohmann, 1896 was collected in South Brazil Bight in summer, autumn and spring 1976 and summer 1993 for the first time. This species occurred in 13 of 269 sampling stations, from 68 m to 200 m in depth and water temperatures between 13 °C and 26 °C. Seasonal out of size variations of F. venusta were observed, being adults significantly larger in summer 1993.

A comparison of the circulation patterns over the Southwestern Atlantic Shelf driven by different wind stress climatologies

We compare the oceanic circulation patterns over the Southwestern Atlantic Shelf (SWAS) forced by nine different wind stress climatologies. The largest differences are observed in experiments forced with the Hellerman and Rosenstein [1983, hereafter HR83] and Trenberth et al. [1990, hereafter TR90] winds. HR83 shows a general northeastward flow near the shelf break. The TR90 results shows a bifurcating path south of ∼40°S and a poleward flow north of 35°S. The most robust circulation patterns are a broad northward flow and the generation of coastal re‐circulation cells in southern Patagonia and the development of a southward jet in the inner portion of the South Brazil Bight.

A Modelling Study of Coastal Upwelling Driven by Wind and Meanders of the Brazil Current

A numerical model is used to investigate coastal upwelling in the South Brazil Bight. The wind in the area is predominantly from the northeast, especially in summer, which is upwelling favorable. Reversals of the wind direction are frequent and intense during the winter, due to the passage of frontal systems. The offshore circulation is dominated by the Brazil Current, which flows southward meandering around the 200 m isobath. Significant shelf-break upwelling has being associated with Brazil Current cyclonic meanders. To assess the relative importance of the two processes in the pumping of South Atlantic Central Water (SACW) onto the continental shelf, three cases are analyzed: (1) wind-driven upwelling; (2) upwelling induced by Brazil Current meanders and (3) both effects acting together. The results show that in the coastal area upwelling/downwelling is mainly caused by the wind, whereas the cyclonic meanders of the Brazil Current are the dominant mechanism in the generation of vertical velocities over the shelf break and slope. This meander-induced upward motion brings the SACW to shallower depths, where it is influenced by the wind. In this situation, when both effects act together, the SACW penetrates all the way to the coast.

Contribution of ecosystem analysis to investigating the effects of changes in fishing strategies in the South Brazil Bight coastal ecosystem

Ecosystem effects of recent changes in fishing strategies in the South Brazil Bight (SBB) area, including increasing squid catches by shrimp bottom trawlers and fishing for young sardines as bait, for the skipjack tuna pole-and-line fishery were investigated by modelling the SBB coastal ecosystem for the 1998–1999 fisheries period, using the mass-balance modelling software, Ecopath with Ecosim. Based on fisheries information and on previous models, 25 species groups were defined. The mean trophic level of all fisheries was 2.99 with small trawlers and the live baitfish fleet occupying the lowest trophic levels. The change in squid fishing rate and the most important squid predators fishing rate were simulated by increasing fishing mortality ( F) from 0 to 1 per year, while maintaining F constant for other exploited groups. Also, the impact of fishing pressure by trawlers on squids and by the live baitfish fleet on young sardines were simulated. Different hypotheses of flow control were tested by setting the maximum instantaneous mortality rate that consumers could exert on food resources by (a) “top-down” control by predators (predator control); (b) all interactions of mixed control type; and (c) “bottom-up” control of predators by their prey (donor control). For squid, predicted biomass changes were more pronounced under top-down control that under bottom-up. Biomass of the weakfish, which are important squid predators, were the most affected under all hypotheses. A similar pattern of decrease in other squid predators was seen. The ecosystem consequence of overexploiting weakfish and large pelagic fish biomass was speculated regarding the increasing squid catches. Simulations of increasing live-baitfish fleet did not show prominent impact in the inner shelf, where present F values are low. Given young sardines concentrate in shallow waters, where the conflicts converge, a complementary model of the adjacent coastal system and artisanal fisheries could better address fleet’s impact. Nevertheless, it was noted a decrease of sharks and rays reflecting their vulnerability in the system. A precautionary measure for fisheries management in the region would be to assume that top-down control is a dominant force in energy flows, differing from the custom emphasis placed only in environmental forces and productivity. The ecosystem approach will require the integration of information from a wide range of disciplines, levels of ecological organization and temporal and spatial scales, as well as concrete management measures.

Oceanographic Characteristics of a Multi‐Specific Fishing Ground of the Central South Brazil Bight

In the Central South Brazil Bight, a multispecific demersal trawl fishery is conducted by trawlers licensed for the industrial pink shrimp (Penaeus paulensis and Penaeus brasiliensis) fishery. In addition to the pink shrimp, many by‐catch species have become increasingly valued in the last two decades. In spite of the importance of this multispecific fishery, the oceanographic characteristics of the inner continental shelf, onshore the 100 m isobath, are poorly known. In this paper we present, for the fist time, monthly oceanographic records taken from December 1995 to May 1997 with the R/V ‘Diadorim’ at two of the main fishing grounds of this region. Water temperature data showed the formation of a strong thermocline during summer, from November to April. This thermal gradient, due to the South Atlantic central water (SACW) intrusion that reaches these shallow waters, disappeared with the homogenization of the water column during autumn and winter, from May to September. This cold and low salinity water does not originate from local river discharges, but also represents an advection of sub‐Antartic water mass. After this and during spring, a new thermocline develops, reaching its maximal expression from February to March. A maximal gradient was registered in February 1997, when the temperature dropped from 26°C at 7 m to 16°C at 14 m depth. This result shows that the SACW intrusion is a large‐scale phenomenon that regularly influences the whole inner continental shelf up to 20 m. Demersal fishing grounds located in this area were covered during summer by a cold and nutrient‐rich mass of water that resulted in an unusual maximum of chlorophyll a values near the bottom (30 m). The homogenization of the water column and the presence of another cold water mass during winter resulted in a strong semi‐annual thermal cycle on the bottom. The role of this important oceanographic process in fishery production and dynamics deserves further investigation, but the data presented here show evidence for the importance of this phenomenon.

Interannual variability of the sea surface temperature in the South Brazil Bight

In the austral winter of 1993, during a COROAS hydrographic cruise in the South Brazil Bight (SBB), an unexpected mass of cold and fresh water was observed on the continental shelf near 23°S. Subsequent analyses of different data sets suggested that the origin of that water was probably the Argentine continental shelf, near the Rio de la Plata mouth. In this article, a 13‐year time series of AVHRR Sea Surface Temperature anomalies is analyzed to investigate the occurrence of this phenomenon in other periods. The results of these analyses and a good correlation with the Southern Oscillation Index suggest that the penetration of these waters into the SBB occurs in a frequency that may be associated with ENSO events.

Effects of seasonal variations in meteorology and oceanography on the Brazilian sardine fishery

Seasonal variations in meteorological and oceanographic processes in the South Brazil Bight were studied to assess their influence on the Brazilian sardine Sardinella brasiliensis fishery. According to its environmental characteristics, the South Brazil Bight was divided into three sectors. The northern and southern sectors were similar during the spring and summer, showing areas of coastal upwelling and low rainfall rates. The middle sector was characterized by the presence of low‐salinity coastal waters in the inner shelf and by high rainfall. During autumn and winter, the middle and southern sectors were similar, both being under the influence of sub‐Antarctic waters. Multiple regression analyses showed significant correlation between environmental data and catches, although at a lower level in the northern sector (r2 = 0.57). In the middle and southern sectors, environmental data were highly correlated with the catches (r2 = 0.90 and 0.84). The sardine landings in the middle sector are principally affected by meteorological parameters, and in the south by oceanographic ones. In the middle sector, an inverse correlation between landings and rainfall is shown, while in the south, landings are positively correlated with salinity and sea temperature. The conclusion is that the seasonal landings of the Brazilian sardine within the South Brazil Bight are influenced by the distribution of less saline waters, the coastal waters and sub‐Antarctic waters.

Experiment studies circulation in the western South Atlantic

Observations in the Brazil Current region between 20° and 30°S are revealing many interesting oceanographic features. In the austral winter of 1993, what appears to be an anomalous northward penetration of waters from the Brazil/Malvinas confluence region into the South Brazil Bight was observed (Figure 1).

Numerical diagnostic of the circulation in the Santos Bight with COROAS hydrographic data

This work represents part of the analyses of the data generated during the first two mesoscale hydrographic cruises of COROAS Project: one during the Summer and the other during the Winter of 1993. The area surveyed during these cruises is the region of the South Brazil Bight (or Santos Bight) limited at the coast by the cities of Ubatuba and Iguape, extending from the 50 m isobath to oceanic regions with depths greater than 2500 m. The main goal of this work consisted of the adaptation of the Princeton Ocean Model to the area of study, including realistic topography, observed thermohaline structure and open boundaries. Using this model, a set of diagnostic experiments was realized using density structures based on the COROAS hydrographic data. The baroclinic velocity fields obtained, as expected from preliminary analyses of the thermohaline structures, showed similar features for the Brazil Current in bOla seasonal cruises. The results show an intrusion of Tropical Water over the continental shelf in the region between Ubatuba and Santos, both during the Summer and the Winter cruises. The results also suggest the penetration of the South Atlantic Central Water, underneath the Tropical Water, to the external part of the continental shelf in both occasions.

Numerical diagnostic of the circulation in the Santos Bight with COROAS hydrographic data

This work represents part of the analyses of the data generated during the first two mesoscale hydrographic cruises of COROAS Project: one during the Summer and the other during the Winter of 1993. The area surveyed during these cruises is the region of the South Brazil Bight (or Santos Bight) limited at the coast by the cities of Ubatuba and Iguape, extending from the 50 m isobath to oceanic regions with depths greater than 2500 m. The main goal of this work consisted of the adaptation of the Princeton Ocean Model to the area of study, including realistic topography, observed thermohaline structure and open boundaries. Using this model, a set of diagnostic experiments was realized using density structures based on the COROAS hydrographic data. The baroclinic velocity fields obtained, as expected from preliminary analyses of the thermohaline structures, showed similar features for the Brazil Current in bOla seasonal cruises. The results show an intrusion of Tropical Water over the continental shelf in the region between Ubatuba and Santos, both during the Summer and the Winter cruises. The results also suggest the penetration of the South Atlantic Central Water, underneath the Tropical Water, to the external part of the continental shelf in both occasions.