Ichthyoplankton composition, distribution and abundance on the southern patagonian shelf and adjacent waters.

Abstract

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.