1999 - INIDEP Documento Científico Nro 5

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Browsing 1999 - INIDEP Documento Científico Nro 5 by Subject "Abundance"

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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.