Skipjack tuna (Katsuwonus pelamis) sustain a large-scale fishery in the southwest Atlantic Ocean (SWA), but information about its foraging ecology in this region is still limited. Here we use carbon ...(δ13C) and nitrogen (δ15N) stable isotope analysis of muscle from individuals collected in 2017–2018 (n = 383) to quantify diet composition and characterize movement patterns. We found a relatively small degree of variation in δ13C (range: -18.9 to −16.5‰) in comparison to δ15N values (6.7–14.7‰). At higher latitudes in the southern area (30–34°S), individuals had higher mean (±SD) δ15N values (12.2 ± 1.3‰) in comparison to those collected in the northern area (9.7 ± 1.5‰) between 20–26°S. At the northern area, isotope mixing models with informative priors showed that lanternfish (median: 50%) and krill (31%) were the primary foods. In the southern area, lanternfish (53%), krill (23%) and small pelagic fish (23%) were the primary food sources. Spatial shifts in diet composition were related to warming events that likely resulted in low abundance of sardines in the northern area. The latitudinal pattern in skipjack and krill δ15N values mirrored that of regional zooplankton isoscapes, suggesting residency at the timescale of isotopic turnover for muscle (~2–4 months), and that geographical variation in the baseline isotopic composition can be exploited to characterize seasonal movements of skipjack and other top marine consumers in this region.
•Skipjack tuna diet composition and movement patterns were studied.•Key energy sources were lanternfish and krill.•Spatial shifts in diet reflected climatic anomalies during the study period.•δ15N variation suggested seasonal residency and movement between areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
As top predators in marine environments, seabirds frequently respond to the presence of their main prey, and both predators and prey are usually associated with specific environmental features. We ...investigated the variability in the presence and density of flying seabirds (mostly Procellariiformes and Charadriiformes) and Magellanic penguins Spheniscus magellanicus along the southwestern (SW) Atlantic continental shelf. Five acoustic assessment surveys were conducted to determine the biomass of the Argentine anchovy Engraulis anchoita, and seabird counts and the collection of oceanographic data were conducted simultaneously with the surveys between June and October 2010. Generalized linear mixed models (GLMMs) were fitted to test the effect of anchovy density and environmental variables on seabird density. Sea surface temperature was significant for the presence of flying seabirds. Bottom water temperature and anchovy density were key variables affecting the presence and density of penguins, while bottom water salinity was also important for penguin presence. Based on Akaike’s information criterion, the most important factor explaining the density of flying seabirds was the difference between surface and bottom salinity (ΔS), while for penguin density, the most important factor was anchovy density. These results highlight that the subtropical shelf front in the SW Atlantic Ocean is a key feature influencing the aggregation of flying seabirds and confirm the close association of penguins and anchovies. Bottom water intrusion, originating from the sub-Antarctic shelf water, is an important factor explaining the presence of penguins, which tend to aggregate in areas with high anchovy densities on the SW Atlantic continental shelf.
Skipjack tuna
Katsuwonus pelamis
sustains the largest catches among tuna species. Despite its relevance for global food security and the tuna canning industry, information about its foraging ecology ...in the southwestern Atlantic Ocean (SWAO) is limited. We combined amino acid (AA) and bulk tissue nitrogen isotope (δ
15
N) analysis with stomach content analysis (SCA) to study skipjack foraging habitat and trophic position (TP) in the SWAO. Mean (±SD) δ
15
N values of source AAs lysine (Lys: 6.5 ± 1.3‰) and phenylalanine (Phe: 10.6 ± 1.3‰) were higher at higher latitudes (30-34°S) of the southern area relative to the northern area between 20-26° S (Lys: 3.4 ± 1.1‰, Phe: 8.2 ± 1.2‰). Correlations between bulk tissue δ
15
N (δ
15
N
bulk
) and source AA δ
15
N showed that Lys is a more robust indicator of δ
15
N baseline variation in this region than Phe. Regional mixing models based on AA δ
15
N indicated spatial structure in foraging habitat: smaller individuals use the southern area and larger individuals forage at lower latitudes or in offshore areas. TP estimates using the Glx-Lys trophic-source AA pair were in much better agreement with TP estimates based on SCA (TP
SCA
) and on bulk tissue analysis (TP
bulk
) than those using Glx-Phe. Skipjack forages across multiple food webs throughout its lifecycle in the SWAO and increases its TP with ontogeny (TP
Glx-Lys
: 3.5-4.0). Stock management strategies should consider that the southern region supports dense aggregations of juvenile skipjack, which may be more vulnerable to non-selective fisheries.
•We present results from five acoustic surveys conducted to assess anchovy stocks on the South West Atlantic Continental Shelf.•Using this survey design and sequence, we identified a sharp change in ...environmental variables followed by an increase in adult anchovy biomass.•The cold subantarctic waters and low-salinity waters from the River Plate plume significantly affected the presence of anchovy on the South West Atlantic Continental Shelf.
Marine fisheries in Brazil follow a similar trend as the rest of the world, with reduced catches of most stocks. Although extensive, the Brazilian coast is poorly assessed, and marine fishery resources are not properly managed. Small pelagic fishes are secondary consumers, which feed on zooplankton and serve as foraging species for large, carnivorous fishes. The anchovy (Engraulis anchoita) is an abundant, small pelagic fish found in abundance in Brazilian waters as it migrates along the Brazilian, Uruguayan and Argentine shelves. In 2010, five acoustic assessment cruises were conducted to estimate anchovy biomass in the southernmost part of the Brazilian coast. Hydroacoustic data were obtained using a SIMRAD EK 500 echo sounder along parallel transects. CTD (conductivity temperature depth) casts and mid-water trawl hauls were used to collect environmental and biological data. Anchovy biomass was estimated using NASC values, the fish target strength by size and the dimension of the surveyed area. For each survey, a GLM binomial was fitted to anchovy presence and the following explanatory variables: surface salinity and temperature, bottom salinity and temperature, and depth. Anchovy biomass ranged between 73,000 (June) and 814,000 (August) tons. We observed a mean temperature decrease of ∼3°C during the June and August surveys. This sharp environmental change was followed by a distinct increase in adult anchovy biomass from the first to the second survey. Fitted GLM models indicated that the bottom layers of cold, saline water had a positive effect on anchovy presence in August but not in June. Furthermore, during the August survey, a sharp change in the surface layer waters was observed on the Southern Brazilian Shelf, as the result of a low-salinity water inflow to this area. This phenomena was due to the Patos Lagoon runoff and also to the coastal winds over the Argentine Shelf, which forces the northward spreading of the Plate River plume to lower latitudes. This inflow increases primary productivity and, subsequently, the occurrence of fishes within the area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Domoic acid (DA) or Amnesic Shellfish Poisoning (ASP) produced by the genus Pseudo-nitzschia diatom was investigated in two seasonal periods in fishing areas of Katsuwonus pelamis in the South ...Atlantic Ocean. Higher DA concentrations were found in spring compared to winter. Pseudo-nitzschia spp. more quantified in winter than in spring, while P. pungens, a species among the most reported for an AD toxic potential, was only found in spring.
•Two cruises during winter and spring in 2018 in the Southeast Atlantic Ocean.•We have assessed the cell abundance, environmental variables and domoic acid concentration.•Particulate domoic acid (pDA) is present in fishing areas of the Skipjack tuna.•This current study provides the first record of particulate domoic acid in southeast Atlantic Ocean.•Domoic acid could cause damage to the local biota in the Southeast Atlantic Ocean?
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Skipjack tuna (Katsuwonus pelamis) ranks third among marine resources that sustain global fisheries. This study delimits the spatiotemporal habitat of the species in the south‐western Atlantic Ocean, ...based on operational oceanography. We used generalized additive models (GAMs) and catch data from six pole‐and‐line fishing vessels operating during 2014 and 2015 fishing seasons to assess the effect of environmental variables on catch. We also analysed Modis sensor images of sea surface temperature (SST) and surface chlorophyll‐α concentration (SCC) to describe fishing ground characteristics in time and space. Catch was positively related to thermocline depth (24–45 m), SST (22–24.5°C), SCC (0.08–0.14 mg/m³) and salinity (34.9–35.8). Through SST images, we identified that thermal fronts were the main surface feature associated with a higher probability to find skipjack. Also, we state that skipjack fishery is tightly related to shelf break because bottom topography drives the position of fronts in this area. Ocean colour fronts and plankton enrichment were important proxies, accessible through SCC, used to delineate skipjack fishing grounds. Catch per unit effort (CPUE) was higher towards summer (median 14 t/fishing day) due to the oceanographic characteristics of the southern region. High productivity in this sector of the Brazilian coast defines the main skipjack feeding areas and, as a consequence, the greatest abundance and availability for fishing.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Several factors bear evidence of chemosynthetic ecosystem occurrence in the Brazilian coast; these motivated our investigation to sample three pockmarks located on the continental slope off SE Brazil ...(26°S and 46°W) at ∼700 m depth. The crater-like features were ∼1 km in diameter and 100 m in depth, and were identified with an echo-sounder (EK-500). They were sampled along two transects using a rectangular dredge. Our main objective was to identify possible evidence of a seep-related community. The surrounding sediments of the pockmarks seem to be filled with coral rubble harboring a rich fauna of metazoans including epilithic and chasmolithic organisms. A total of 9565 organisms were sampled. The most abundant group was the Ophiuroidea, followed by Cirripedia and Polychaeta. A number of new occurrences and new species were registered. The polychaete worm Amelinna was the first record for the Atlantic Ocean, which has been found in reducing habitats such as wood islands. The echo-sounder records also showed the presence of big deepwater coral mounds associated with the edge of the pockmarks. These features are ∼ 20 m in height and from 180 to 360 m wide. Records of demersal fishes were also registered right above coral mounds. The presence of deepwater coral mounds at the edge of pockmarks may be related to the flow of the cold, oxygen-rich Antarctic Intermediate Water over the bottom, or else may benefit from the fertilization of the water by the microseepage of hydrocarbons from the sediment. We suggest a more thorough survey in order to map and recognize these environments. Furthermore, our findings may shed some light on new research perspectives concerning the ecology, biogeography and evolution of reducing habitats off the Brazilian coast.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Advances in ocean observing technologies and modeling provide the capacity to revolutionize the management of living marine resources. While traditional fisheries management approaches like ...single-species stock assessments are still common, a global effort is underway to adopt ecosystem-based fisheries management (EBFM) approaches. These consider changes in the physical environment and interactions between ecosystem elements, including human uses, holistically. For example, integrated ecosystem assessments aim to synthesize a suite of observations (physical, biological, socioeconomic) and modeling platforms (ocean circulation models, ecological models, short-term forecasts, management strategy evaluations) to assess the current status and recent and future trends of ecosystem components. This information provides guidance for better management strategies. A common thread in EBFM approaches is the need for high-quality observations of ocean conditions, at scales that resolve critical physical-biological processes and are timely for management needs. Here we explore options for a future observing system that meets the needs of EBFM by i) identifying observing needs for different user groups, ii) reviewing relevant datasets and existing technologies, iii) showcasing regional case studies, and iv) recommending observational approaches required to implement EBFM. We recommend linking ocean observing within the context of GOOS and other regional ocean observing efforts with fisheries observations, new forecasting methods, and capacity development, in a comprehensive ocean observing framework.
The Mostardas Peninsula on the east coast of Rio Grande do Sul state, Southern Brazil is important for migratory shorebirds that depend upon the wetlands in the Lagoa do Peixe National Park. However, ...previous surveys have suggested that the Peninsula is bereft of terrestrial birds relative to similar habitat in Rio Grande do Sul. We used rapid assessment methods to evaluate terrestrial bird diversity and note observations of migratory birds at the western margin of Lagoa do Peixe National Park between 11 February 2007 and 25 March 2007. We recorded fourteen species not previously reported for this area, including several new breeding records, and detail the occurrence of mixed-species foraging flocks in fragmented woodland. We discuss the reasons for the discrepancy between our observations of the terrestrial avifauna and previous reports, and the possibility that the Mostardas Peninsula is a passerine migratory route that remains poorly documented.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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