CCAMLR

This paper describes the diet and foraging behaviour of Ad6lie penguins at B6chervaise Island during 1998-99, a season of high chick mortality. One thousand nests perished in the three weeks following first hatch, when the chicks were very small. A total of 802 chicks reached crèche age from 1880 nests compared to previous "good" seasons in which between 1200 and 1800 chicks crèched on the island. Evidence from analyses of foraging location, foraging trip duration and diet led to the conclusion that the death of chicks during the guard stage resulted from decreased feeding frequency due to adult birds spending longer at sea foraging than in normal years. In most previous seasons birds have foraged both at the continental shelf edge (particularly females) as well as locally (particularly males). This season male penguins carried out fewer local trips, and both sexes spent longer at sea than in "good" years. Meal masses brought back to the chicks appeared normal, but feeding frequencies were reduced. These findings contrast with observations in 1994-95 Ca season in which all chicks starved to death) when smaller meals were delivered and birds foraged further offshore than in this or any other season studied. The significance to CEMP of these variations in foraging behaviour is discussed.

We irradiated captive juvenile Euphausia superba in the laboratory with lower than spring surface levels of ultraviolet-B, ultraviolet-A and photosynthetically active radiation, in order to examine their response in terms of mortality and generalised activity. Levels of photosynthetically active radiation 3–5 times below surface irradiance caused krill to die within a week, while animals in the dark survived. Addition of ultraviolet-B typical of depths up to 15 m were found to significantly accelerate mortality and lead to a drop in activity in all experiments. A drop in activity in krill exposed to ultraviolet-A wavelengths was evident without an increase in mortality. The protein content of animals from various treatments was found not to vary.

This background paper consists of the agenda and information for the Second International Symposium on Krill which has been partially sponsored by CCAMLR. The symposium will be held at the University of California, Santa Cruz, from 23–27 August 1999. Further information can be found on the website: http://www2.ucsc.edu/people/msmangel/Krill Symposium.html

The global abundance of krill is estimated using recent estimates of krill density from acoustic surveys and historical information on the overall range of krill. The biomass estimates fall between 64 and 137 million tonnes - at the low end of values that have been suggested in the past. The differences between our estimates and others can be explained by a number of factors such as: an underestimation of the range, or of the acoustic biomass estimates, the possibility of a large, undetected krill population, and the overestimation of the demand for krill by predators. Even if these low global krill biomass estimates are correct, regional and global precautionary limits are still likely to rise as a result of new surveys because the method used to calculate precautionary limits uses a value of 11 % of the biomass. Additionally, the current precautionary catch limits in the South Atlantic are set using the old target strength which has effectively underestimated the krill biomass by a factor of three so the new survey of the South Atlantic is likely to result in an effective biomass which is greater than that used in the past. The seasonal and local consequences of elevated catch limits will have to be taken into account when managing an expanded krill fishery and the appropriateness of using the existing statistical divisions as management areas will have to be considered.

Dual frequency (38 and 120 kHz) acoustic data from grid surveys in two boxes to the north-west and north-east of South Georgia during December/January 1998/99 were used to estimate mean krill density there. Densities (east = 11.1 g m-2 , west = 12.0 g m-2) were towards the lower end of the range observed over the past two decades, but not abnonnally low, and comprised almost entirely of large (>50 mm) adult krill.

The diet of the gentoo penguin Pygoscelis papua was investigated during three different autumn periods at Laurie Island, South Orkney Islands (60°46’S, 44º42’W), Antarctica. Stomach contents of migrant adults were sampled during 1993, 1995 and 1996. Fish were the most important prey by mass in 1995 (81.1%) and 1996 (60.5%) whereas crustaceans predominated in 1993 (70% by mass). Euphausia superba was largely the most important prey among the eleven crustacean taxa identified in the samples. Among fish, species of the family Nototheniidae predominated in the diet with G. gibberifrons as the most important prey by mass in 1993 and 1995 and N. nybelini in 1996. Other nototheniid fish such as L. nudifrons and T. newnesi were also well represented in the three sampling periods. A total of 1628 squid lower beaks were found and 1582 (97%) of them were identified as Psychroteuthis glacialis. Diet composition in terms of frequency of occurrence, mass and number is compared with results of previous studies.

The underwater vessel noise levels perceived by the echosounder EK-500 transducers of three Russian research vessels have been presented. These data have been compared to the estimate of the underwater noise level, produced by the Icelandic R/V B.Saemundsson..
Underwater noise level perceived by the echosounder transducer versus its operation frequency and vessel speed has been analyzed. It has been shown that the level of underwater noise produced by vessel is an important technical property to be taken into account in assessment of such parameters of Acoustic Sampling Protocol as TS and Sv thresholds and vessel’s speed . The interrelation between choice of TS and Sv thresholds and vessel speed when echosurveying has been emphasized.
It has been shown that a difference between the underwater noise levels of vessels participating in multiple-ship survey, cannot provide for the choice of desirable speed of the vessels with the unique given level of TS and Sv thresholds used by all vessels. The importance of the research vessel underwater noise level has been discussed when standardizing acoustic data collection from multiple-ships like during a multinational effort to synoptical survey the Area 48 .

An acoustic survey, designed to study the distribution of shore-breeding, marine predators and their pelagic prey, was carried out in 1986 around the western end of South Georgia. This paper describes how this acoustic data has been used to estimate krill biomass of part of the original survey area as part of an interannual study. The radiating transect design gave increased sampling intensity in the shallower part of the area, so a method of post hoc stratification has been devised to generate sub areas with more even sampling. The results highlight the importance of the shelf slope area for krill.

We update in this paper the previously reported model for the Antarctic fur seal Arctocephalus gazella population breeding at Cape Shirreff and San Telmo Islets (SSSI No.32), Livingston Island, South Shetland, Antarctica. We also discuss the current reliability of the model and related population parameters to an environmental index (the Southern Ocean Oscillation Index - SOI).
Two fur seal censuses were developed at Cape Shirreff during 1998/99, but we could not census the San Telmo Islets. In this regard, we had to model the population at the latter site, in order to have a complete estimate of the population. From this, we estimated an overall increase of 17% in the total population, including in this figure a 10% increase in pup production in the SSSI No.32.
Current population estimates are reaching modelled values of the carrying capacity of the environment (K). This might not be correct due to the restrictions of the simple model used, and the weighted effect of the continuos data set during these last 8 years, and the scattered historical data.
Further evidence that the breeding population of A. gazella is affected by the El Niño Southern Oscillation phenomena might be given by the intrinsic rate of population growth (r) when compared with Southern Oscillation Index (SOI) values.
The intrinsic rate of increase of a population of top predators, in this case A. gazella, can probably predict large scale environmental phenomena if the population is under a monitoring programme, and may have an interesting effect on resources management policies.