1999 - INIDEP Documento Científico Nro 5

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    Acoustic surveys on the southern blue whiting (Micromesistius australis).
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 1999) Madirolas, A.
    Two joint Argentine-British acoustic surveys specifically targeted on the southern blue whiting (Micromesistius australis) were carried out during September 1994 and 1995. The surveys confirmed the existence of a spawning concentration area located south from San Carlos Strait, in waters south of Malvinas Islands, ASW. The obtained point estimates of blue whiting abundance were 84801 t for the 1994 survey and 140953 t for the 1995 survey. The surveys also provided information on the school structure and behavior as well as some clues about the complex migration pattern of the species.
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    Features of the reproductive biology of the southern blue whiting (Micromesistius australis).
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 1999) Macchi, G.J.; Pájaro, M.
    Different features of the reproductive biology of the southern blue whiting (Micromesistius australis) are analyzed. Samples were obtained from research cruises and from commercial catches carried out between March-November 1995, in waters near Malvinas Islands. Reproductive activity of M. australis was observed between the end of July and September, southwest of Malvinas Islands. Oocyte diameter distribution of gravid females and the histological observations show that this species is a batch spawner with determinate annual fecundity. Preliminary estimate of the potential annual fecundity was about 478,000 oocytes for a 51-cm mean total length. Size at first maturity for this species was about 31 cm total length.
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    Ichthyoplankton composition, distribution and abundance on the southern patagonian shelf and adjacent waters.
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 1999) Ehrlich, M.D.; Sánchez, R.P.; de Ciechomski, J.D.; Machinandiarena, L.; Pájaro, M.
    This paper reviews the information on pelagic and demersal fish eggs and larvae, describing the distribution and seasonality of different species and their arrangement in icthyoplankton assemblages in the Southern patagonian waters. It also reports on 11 surveys conducted by INIDEP during 1992-1995. A total of 488 ichthyoplankton samples were analyzed. Fish eggs have been recognized in 47. of all ichthyoplankton samples. They belong to three species: Coelorhynchus fasciatus, Macrourus whitsoni and Micromesistius australis. Fish larvae of 23 species and 17 families have been identified in 96. of all samples analyzed. Spawning of most species begins in autumn, and progresses through winter, when the southern blue whiting and grenadier fish contribute to more than half of all eggs present in our samples. Nototheniid and myctophiid larvae were caught during all year long. Four larval groups were detected using cluster analysis: the first group, formed exclusively by nototheniids, which occupied a vast area on the continental shelf between 100 and 200 m depth, the second formed by Agonopsis chiloensis, Eleginops maclovinus, Macruronus magellanicus and Sprattus fuegensis in coastal waters, the third formed by myctophiids, Gymnoscopelus spp. and Micromesistius australis, inhabit the outer continental shelf and slope, and the fourth included Protomyctophum spp., Krefftichthys anderssoni and Bathylagus antarcticus, species typically found in Subantarctic waters of the Malvinas Current. Comparing the distribution of eggs and larvae of blue whiting from collections obtained during the 70's and 80's, with those of recent surveys, it is evident, that a significant contraction of the spawning grounds of the species has take place, particularly to the west of the archipelago.
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    Zooplankton biomass in the reproductive area of the southern blue whiting (Micromesistius australis).
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 1999) Sabatini, M.; Álvarez Colombo, Gustavo; Ramirez, F.C.
    Total and size-fractioned zooplankton biomass (larger and smaller than 5 mm) were analyzed over two cruises conducted in the late austral winter (September 1994 and 1995) in the area surrounding Malvinas Islands at the time that massive spawning of southern blue whiting was expected to take place. Biomass was rather uniformly distributed in the area and dominated by the fraction larger than 5 mm in which euphausiids and secondarily chaetognaths were dominating in terms of both weight and number. The smaller fraction was mostly made up of copepods. From the high occurrence of euphausiids and seasonal abundance of the several species of copepods normally present within the area it was hypothesised that the feeding requirements of juvenile and adult blue whiting as well as those of larvae and postlarvae may be met during the winter spawning season. The data were also examined in conjunction with the general pattern of zooplankton biomass occurring in autumn and spring in the Southern Patagonian shelf.
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    Oceanographic conditions at the southern end of the argentine continental slope
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 1999) Guerrero, R.A.; Baldoni, A.G.; Benavides, H.R.
    The characteristics of the upper Antartic Intermediate water (AAIW) entering the Southern Atlantic are described on the base of oceanographic data collected from four late austral winters (1978-1980-1994-1995). The upper 500 meters regime along the shelf break and around Malvinas Islands (48° to 55° S) is analyzed. In particular, the 1994 horizontal distribution of temperature, salinity and density was mapped in order to show the extreme winter pattern of these parameters. Three salinity sections crossing the water flow direction in the Malvinas Channel (South to the islands) were selected to describe the vertical stratification 1995 and 1995. Horizontal and vertical distribution of chlorophyll a from the 1995 cruise is presented as reference data, considering the lack of information on this parameter for the area. Finally, the inter-annual variability of the heat content in two 5° x 5° areas (East and West to the islands) is discussed by comparing the Sea Surface Temperature (SST) data between the four sampled years. From this information, 1995 resulted in the coolest winter, presenting a temperature anomaly around -4° C respect to the other winters.