Age determination of the Antarctic fishes Champsocephalus gunnari and Notothenia rossii from South Georgia

Foremost in the elucidation of accurate population dynamics parameters in fish is a necessity for an errorless estimation of age. Age determination can provide basic life history information, including mortality, population age structure, and changes in individual growth. Most investigations have used annual rhythmic deposition in calcified tissues as time marks but, due ts the lack of distinct periodicity in Antarctic hydrographic conditions, age determination of Antarctic fish has proven to be difficult. It is now possible to determine the age of fish through the utilization of daily increments in otoliths, calcified tissues which may contain a large amount of biological and ecological information about a fish's past history. As part of an effort to study Antarctic fish growth and population dynamics, investigations were performed on otoliths from the Antarctic fish Champsocephalus gunnari and Notothenia rossii. External and internal examination of otoliths from by Scanning Electron Microscope (SEM) methodology revealed internal rhythmic patterns which make it possible to estimate the age of these species. Multivariate mathematical models relating age to otolith morphometrics and fish size demonstrated that age could be reliably determined from body measurements and otolith measurements. These techniques allowed us to determine that the Champsocephalus gunnari grew 55cm in 17 years and the Notothenia rossii grew 55 cm in 7 years. The lack of: the large size groups for Notothenia rossii may be indicative of over fishing and that only the younger age groups are available for harvest. It appears that length at age data determined a yearly basis for these species would provide valuable management data.