CCAMLR

To validate the timing of annuli in otoliths of immature Notothenia coriiceps Richardson. a time-series of samples were taken over a complete year. Light and scanning electron microscopy (SEM) techniques were used to examine the structure of sectioned otoliths. Six growth regions were identified in the otolith sections and micro-increments were also evident. The timing of growth and annual nature of annuli revealed by SEM were demonstrated. Annuli revealed by SEM and light microscopy techniques were shown to correspond, supporting the hypothesis that annuli visible by using light microscopy represent one year. Using SEM the potential errors due to light illumination artefacts and the pseudo-hyaline features could be avoided.

Observations on abundance of by-catch fishes were made during the austral winter months of 1992 (from July 9 to August 3) on board F/V No.3 and No.5 Chiyo Maru in the vicinity of the South Georgia Island. Among 74 net hauls examined, a total of 66 specimens of fishes belonging to 3 species were found in 20 trawl catches.
Among by-catch fishes, juvenile Lepidonotothen larseni was the most abundant (62 specimens; 93.9% in number; 58.9% of total weight of by-catch fish). Standard length (SL) of L. larseni varies from 32.4 to 52.1mm (average 44.5mm; mean 45.3mm). Three specimens of juvenile Champsocephalus gunnari ranging 80.5 to 88.3mm of SL and one adult specimen of Electrona antarctica (72.1mm of SL) were also found, but no other fish species was recognized in our by-catch samples. The abundance of fish in our krill catches was relatively low (less than 52 individuals and 43.68g per 100kg of krill) in comparison with some data reported previously.

During the 6th Antarctic Expedition of R/V Kaiyo Maru (1990/1991), observations on the occurrence and abundance of fishes in a total of 102 pelagic hauls for the Antarctic krill were made.
Of the 102 net hauls, a total of 104 fishes belonging to 4 families and 16 species were captured in 25 tows. Juvenile Lepidonotothen larseni was the most abundant (46 individuals; 44.2% in number) and post-larval Cryodraco antarcticus was the next (14 individuals; 13.5% in number). The standard length of L. larseni ranged from 41.4 to 50.9ram (average 46.8mm; mean 46.6mm). Among the notothenioid fishes collected, only two adults (one specimen of Gobionotothen gibberifrons and one channichthyid fish - specimen lost on board) were included. Bottom depths of the stations where notothenioid post-larvae and juveniles were caught were less than 1000m deep. On the contrary, bathypelagic groups of the Myctophidae and Paralepididae were collected at the 11 offshore stations which bottom depths were deeper than 2000m.
In contrast with other previous data, present results (less than 36 individuals per 0.5 hour haul) show relative low abundance in pelagic catches for this region.

Acoustic estimates of krill biomass in the vicinity of Elephant Island for the years 1981-1993 (with the exception of 1982 and 1986) are presented. Estimates for 1981-1991 are based on previous reports adjusted for the recently proposed definition of krill target strength. Biomass estimates range from 81 xl03 t (March/April 1985) to 4,880 xl03 t (January 1993) and areal biomass densities range from 2.5 g/m2 to 134.5 g/m2 Average biomass and average areal density over the 13-year period was 1,692 xl03 t and 52.8 g/m2.

The diel vertical migration of Antarctic krill (Euphausia superba) can greatly bias the results of qualitative and quantitative hydroacoustic surveys which are conducted with a down-looking sonar and independent of the time of day. To demonstrate and quantify these negative biases on both the estimates of biomass distribution and abundance, a time-depth-density analysis was performed. Data for this study was collected in the vicinity of Elephant Island, Antarctica during the Austral Summer of 1992. The data includes five surveys conducted from mid-January to mid March. The first and fourth surveys covered a 105 by 105 n.mile study area centered on Elephant Island; the second and third surveys covered a 60 by 35 n.mile area immediately north of Elephant Island; the fifth survey covered a 1 n.mi.2 area centered on a large krill swarm to the west of Seal Island. Average krill volume densities were calculated for each hour as well as for three daily time periods; day, twilight and night; these data were normalized and presented as a probability of daily average density. A function was fit to the probability of average daily biomass versus local apparent time. This function was used to create a temporal compensation function(TCF), for upwardly adjusting acoustic biomass estimates due to diel vertical migration. The TCF was then applied to the original survey data; the resulting biomass estimates are 2.3 to 99.6% higher than those calculated disregarding biases due to diel vertical migration.