CCAMLR

This report summarizes the satellite ocean color (chlorophyll) data that are currently available, from missions beginning with the Coastal Zone Color Scanner in the late 1970s through to the SeaWiFS and MODIS sensors that have been providing data for the last ten years. The characteristics of these data and limitations such as cloud cover and high solar zenith angle are discussed with regard to their use in the Southern Ocean. A brief history of algorithms linking ocean color to primary productivity is presented, focusing on the vertically generalized production model (VGPM) and more recent regional, carbon-based approaches. Using monthly climatologies of SeaWiFS chlorophyll, a phenology of phytoplankton blooms is presented for the major provinces surrounding Antarctica. Some of the published information regarding phytoplankton species composition and succession is summarized. Finally, a review of ecosystem and biogeochemical models for the Southern Ocean is presented, with a focus on those models that have been validated using satellite ocean color data.

Krill (Euphausia superba) distribution and abundance data are available from a number of sources: from net surveys (the longest historical series of available date), from acoustic surveys, from fisheries data and from the distribution of krill predators. Each of these forms of data collection has its own biases and limitations and our current understanding of krill distribution and abundance comes from utilising the various forms of data to the maximum extent possible. Time series data are really only available from the South Atlantic where scientific netting programs and annual acoustic surveys have been carried out annually. The South Atlantic is also the area where the fishery has concentrated for the last 20 years. There have been suggestions of changes in the distribution and abundance of Antarctic krill, based mainly on analysis of available scientific net data. There is also evidence of intense inter- and intra-annual variability of krill abundance within regions. These fluctuations in abundance make detection of long-term trends difficult to detect. This review examines the main types of data available for Antarctic krill and will present an indication of the extent and limitations of the available datasets and will present the currently accepted state of knowledge concerning krill distribution, abundance and trends.

First attempts were made in the early 1980’s to estimate the krill and pelagic food consumption by Antarctic demersal fish. These estimates were extended to the mesopelagic realm and the high-Antarctic Zone in the late 1980’s and early 1990’s when these areas were exploited commercially and a larger number of food studies were conducted. Currently, the best estimates of krill consumption by fish are 23 – 29 . 106 tonnes of krill and other pelagic prey taken annually by demersal fish and 7 – 44 . 106 tonnes taken by mesopelagic fish in the Atlantic Ocean sector only. However, these estimates still have wide confidence limits. Major shortcomings of the consumption estimated for mesopelagic fish are the validity of hydro-acoustic biomass estimates conducted in the late 1980’s and the lack of quantitative food consumption data in some abundant myctophid species. Major shortcomings of the consumption estimates of demersal fish are the inaccurracy of biomass estimates for some species, the shortness of most food studies which do not adequately grasp the opportunistic feeding habits of many demersal fish and the scarcity of quantitative winter food studies. However, it is evident from this review that the importance of krill in fish diets varies with time and location, and with the suite of prey types available in different regions in the Southern Ocean. Models of food web and ecosystem dynamics need to account for the role important taxa, such as myctophids, Champsocephalus gunnari, and other abundant channichthyids and nototheniids play as predators of krill and other pelagic resources. Furthermore, the effects of large changes in abundance and community structure of fishes brought about by industrial fishing needs to be considered.