CCAMLR

Quickly studied and quantified were sources of uncertainty in the CCAMLR 2000 acoustical estimate of krill abundance in FAO statistical area 48. The variance in system calibration was evaluated in relation to the effects of variant water temperature and salinity on sound speed, sound absorption, and beam characteristics. Uncertainty in krill target strength (TS) was estimated using a distorted wave born approximation model of krill TS, fitted with measured distributions of animal lengths and orientations. The uncertainty in species delineation was also investigated through the same scattering model. The combined measurement and sampling variance was estimated from a simulation which assumed the three frequency measurements provided independent estimates of the krill biomass. The overall variance (1 1.33%) was little different from the sampling variance (1 1.38%). That is, the measurement variance may be negligible relative to the sampling variance due to the large number of measurements averaged to derive the ultimate biomass estimate. Some potential sources of bias were also explored. The latter (ie. stemming from uncertainties in target strength, species delineation, bubble attenuation, thresholding, area definition, etc.), may be more appreciable components of measurement uncertainty. Further studies are warranted.

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is it’s aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.5 times longer than the cADL, while New Zealand sea lions on average dove 1.4 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P

Spawning by Antarctic fish is generally considered to be seasonal and restricted to a brief period during the autumn and winter. Arising from this it has been assumed that the gonadal maturation cycle is also closely tracked to the time of year. The gonad maturation cycle of the mackerel icefish, Champsocephalus gunnari, was investigated using data collected during research surveys and from sampling the commercial fishery. Spawning appears to occur at the same time each year, but the timing of gonadal development is subject to a considerable inter-annual variation. The implications of this variation are discussed with respect to feeding conditions.

Mackerel icefish are widespread on the South Georgia shelf, Antarctica and have been subject to commercial fishing since the early 1970s. They are known to feed predominantly on krill. An index of condition which uses the ratio of the measured total mass to the estimated mass is show to provide a good indicator of local krill density. The index is likely to be little affected by the reproductive cycle unless there is high krill availability during the months around the spawning time and even then the effect is much less than the highest observed values The condition index responds rapidly to changes in hill density and therefore can provide indications of short term variations in krill availability. Condition index provides a useful proxy for krill density that is likely to be of considerable value in interpreting the results from ecosystem assessments such as that in progress under the auspices of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

The relationship between krill abundance and predator performance is fundamental to an ecosystem based approach to resource management. We propose a method using krill sampled from the diet of predators to provide a length-frequency distribution of krill at times when it is possible to run automated ship-board acoustic systems but not to conduct scientific netting, i.e during logistic/re-supply operations. This will allow a robust estimate of krill abundance to be estimated from acoustic data. Changes in the length-frequency distribution of krill over a period of few weeks produced a 10 % difference in TS whereas simultaneous samples from predators and nets produced only a 1 % difference, illustrating the need for simultaneous length-frequency data. By integrating data from land-based predators directly with automated on board data collection systems it will be possible to gain important estimates of krill biomass at times of the season hitherto unavailable from ship-board scientific surveys.

This paper examines the foraging behaviour of Adélie penguin parents and the provisioning of their chicks during the guard and crèche stages of chick development. The differences, observed in three poor breeding seasons compared with six seasons where a higher fledging success was achieved, are highlighted. A continuous collection of data on foraging trip duration and meal mass (arrival weight minus departure weight) from birds of known breeding status and sex was obtained using an automated monitoring system. It is concluded that chicks during the guard stage are most vulnerable to a decreased availability of food and thus most susceptible to competition from a fishery.