CCAMLR

We develop a new approach to quantifying habitat use within the foraging ranges of satellite-tracked seabirds. We applied kernel estimation techniques to 167 days (3738 locations) of data from black-browed and grey-headed albatrosses Diomedea melanophris and D. chrysostoma during the chick-rearing period of the breeding cycle at South Georgia. At this time the activity range of these two species covers an estimated 440 000 and 640 000 km², respectively, with very substantial overlap. In contrast, kernel estimation reveals that the main foraging areas of these two sympatric, congeneric species are very distinct. Based on location density categories accounting for 50% of locations, the foraging areas cover c. 81 500 and c. 119 700 km², respectively, with 42% and 50% of the range of one species overlapping with that of the other.

In terms of the convention governing the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), management advice for the Antarctic krill (Euphausia superba) fishery should take the needs of the predators of krill into account in order to reduce the risk of deleterious impacts on such predators (e.g., baleen whales and numerous fish, seal, penguin and flying bird species). A single species yield model is currently being used by the CCAMLR Scientific Committee to recommend an annual krill catch limit, which is expressed as a proportion (??= 0.116) of a survey biomass estimate. This approach takes the needs of predators into account in only a crude way by assuming that a median krill escapement of 75% of its unexploited biomass would be sufficient to meet the needs of predators. A krill-predator modeling procedure is presented that could be used to directly assess the impact of krill harvesting on krill predator populations and therefore to revise this recommended harvesting level (?) for Antarctic krill. Application of a deterministic form of this model to an Antarctic fur seal (Arctocephalus gazella) data set from Bird Island, South Georgia, Antarctica, indicates that the level of krill fishing intensity (?) that would reduce this population to half the equilibrium size in the absence of krill fishing (?half) lies between 0.03 and 0.18, which includes the level recommended by CCAMLR. This large range results primarily from the sensitivity of the model to the maximum growth rate parameter, for which a range of 5-15% yr is investigated. A plausible range of values for this parameter (5-15% yr) results is estimated ?half values from 0.04 to 0.23. Stochastic calculations (which take account of interannual fluctuations in the abundance of the krill population due to recruitment variability) yield higher estimated ?half values than the less realistic deterministic calculations. However, simulation tests indicate that the estimated ?half values are biased upward; this modeling approach is therefore likely to yield ?half values that would lead to a depletion of the Antarctic fur seal population to more than half its pristine size.

Euphausia superba Dana (Antarctic Krill) has been recognized as a key forage species in the Antarctic ecosystem. This species serves as prey for many organisms in the ecosystem and has also been the target of an small industrial fishery since the mid 1970s. New quotas have recently been set but there is concern that the reduction in krill biomass due tome fishery may have impacts on other krill predators such as penguins, seals and whales.
In order to evaluate the effects of krill fishing on the trophic web, it is necessary to have better knowledge of the ecosystem structure and dynamics. This can be achieved by studying community interactions, such as those between predators and preys, as well as competitors for a common resource. In this context we aim to investigate whether the krill fishery and the top predators are competing for krill biomass. This is a cooperative pilot project led by University of Concepcion, Chile with the Fisheries Centre at University of British Columbia, Canada.
In a pilot study Ecopath with Ecosim 4.0 is being used to develop two mass-balance models of the Antarctic ecosystem, one for CCAMLR area 48.1 and another for areas 48.2 and 48.3 combined. Organisms in the system were combined into groups (of one or more species) on the basis of their feeding behavior, growth rate and their present or potential fishing importance, in order to simulate the trophic interactions of the system. Both models are being constructed with the same structure to allow comparisons between the two. Although this modeling tool has some limitations and several assumptions, the construction of these models is a step towards investigating and identifying major gaps in knowledge and potential impacts of krill fishing upon the ecosystem.

The paper submits the design of the acoustic survey that should be carried out in the next Italian expedition to the Ross Sea (2002), for eventual changes, improvements and suggestions.

Euphausia superba and Euphausia crystallorophias dominate the biomass and play a key role in the Ross Sea pelagic ecosystem (Marr, 1962; Azzali et al., 1999). To estimate the abundance of each stock it is necessary to discriminate E. superba from E. crystallorophias aggregations and to obtain information about the mean size (length) of the organisms in each aggregation.
In principle the abundance of the two populations can be estimated by single-frequency acoustics, using the standard echo integration method. This implies that species can be identified indirectly, from visual analysis of echograms, and directly from net samplings. The mean size of the crustaceans can be estimated from “in situ” target strength measurements, using the relationship between target strength and size, and from the catches . Unfortunately the precision and credibility of this method are often insufficient when applied in complex environmental and biological conditions, as in the Ross Sea.
Both crustaceans can create aggregations with similar shape, therefore visual separation of their echograms is difficult. The possibility of net samplings depends on the environmental conditions. In the Ross Sea such a limitation is due mostly to the presence of ice-cover. Moreover uncertainties of net samplings arise due to the selectivity of the net and to the net avoidance (Wiebe, 1972; Everson and Bone, 1986). This last bias affects particularity the hauls carried out in “day-time” when the light is intense. Ross Sea was investigated during the austral summer, in absence of darkness. There are two methods for “in situ” target strength measurements “split beam” and “dual beam”. The fundamental condition to apply both methods is the detection of an echo coming from an isolated organism, with no interference from noise or other targets. It means that organisms must occur in low concentrations and echo level from a single organism must be greater by the detection threshold than the total level noise. For small organisms as the Euphausiids, living in a noisy environment (storms, ice) and in dense concentrations, the detection of single targets from a ship hardly ever can be done. Therefore, in the Ross Sea the standard echo integration method can be applied sporadically, only in particularly favorable conditions.
In order to solve the above problems, since the first Italian expedition to the Ross Sea (1989-90), a two – frequency method for the recognition of E. superba aggregations have been applied (Azzali et al., 1999). In the last two expeditions of 1997-98 and 1999-2000, a three-frequency method for euphausiids discrimination and size estimation has been developed .
This paper explores applications of the multi-frequency method using data from three expeditions to the Ross Sea (1980-90; 1997-98 and 1999-2000), where the environmental conditions, the sampled areas, the instrumental and the sampling strategies varied.
First, on the basis of the echo-integrations, made simultaneously either at two or at three frequency, and of the results of net samplings, the thresholds and the decision criteria to recognize the two species are established. Next the acoustic estimates of euphausiid lengths, derived from the fluid sphere model, are compared with lengths collected from net samplings.
Finally, the developed criteria and algorithms are effectively applied to estimate E. superba biomass found in the area of the Ross Sea investigated in December 1997 and in January-February 2001. The results are compared with those obtained from the standard method.

This report summarises the results of krill studies from a large-scale surveys of the Italian Antarctic Oceanographic Cruises conducted in December 1997-January 1998 and January-February 2000. A midwater sampler-trawl (Hamburg Plankton Net) was used to collect zooplankton and fish larvae. Net samples data on Euphasiids were analysed at the aim of: 1) obtain a general picture of interannual and seasonal variability of distribution pattern and abundance of Euphausia superba and Euphausia crystallorophias in the western Ross Sea (Antarctica) in relation to ice cover. 2) Explore the population structure of E. superba and its possible spatial and temporal variations across the investigated area.
The present paper has demonstrated that, in the Ross Sea, during the late spring (1997-98), E. superba and E. crystallorophias had common spatial distribution. Juveniles of E. superba were concentrated in a delimited area in Shelf waters and in general, the maturity stage of this species increased with decreasing of latitude (from 76° to 71°S). On the contrary, during the summer period, the two species inhabited different areas and there weren’t particular spatial distribution patterns in the biological characteristics of E. superba.
For both the periods, the analysis of the biological parameters seems to indicate statistically significant differences in biological characteristics among the hauls (aggregations), while within each haul the parameters are homogeneous.

In the paper these have been discussed the results of acoustic estimation of distribution nectonic organisms, non-krill zooplanctonic fraction and krill as detected my multi-frequency echosounder in 48.4 Subarea.
It has been shown that myctophid fish species are dominated in nectonic fraction backscattering. Nectonic organism distributional pattern is evidently attributed, to a greater degree, to myctophid fish species.
There have been obtained differences between spatial distribution of different groups of pelagic organisms. One can reveal, basing on the results of surveying , the influence of water mass type on distribution of different pelagic organisms groups that form antarctic backscattering layers as follows: krill predominatingly contributes to the antarctic pelagic community within proving ground locations occupied by the Weddell Sea waters and Frontal Zone of Weddell Gyral waters; myctophid fishes prevail in northern proving ground within the Antarctic Curcumpolar Current waters; zooplankton is distributed in the Weddell Sea waters. Though krill and zooplankton major biomasses are concentrated in upper 80-90m layer, high densities of myctophid fish are observed within the whole depth range of 0-350m. At the depth of more than 90m principle backscattering recorders can be pertained to myctophid fish species.
A comparative analysis of mean stratum Sa values obtained for krill and myctophid fishes indicated that biomass of myctophid fish species could be considerable. The estimate of myctophid fish biomass which can be a part of alternative trophic chain in relation to krill is evidently of practical interest .

This paper presents a summary of the recent workshop held in Cambridge, UK, which was convened by Dr JL Watkins to assess the status of papers arising from the CCAMLR-2000 Survey of the Area 48. Key actions and target dates for the publication process are highlighted. An outline of the proposed special volume content is given and synopses of the proposed papers are provided.

This paper describes evidence of antibodies against a virus related with Alphaherpesvirinae sub-family, potentially a phocine herpesvirus (PhHV-1) that affect Antarctic Fur Seals (Arctocephalus gazella) from Cape Shirreff, Livingston Island, Antarctica.
Body fluid samples of 54 A. gazella were collected from 48 live animals and 6 from dead ones during December 1999-February 2000 fieldwork.
Blood, pleural, pericardic and peritoneal fluid samples were tested by microneutralization test using bovine herpesvirus-1 (BHV-1) strain.
Antibodies against BHV-1 were detected in four (7.4%) samples. The utility of the extra vascular fluid for serological research in this matter is suggested. It is also recognized the microneutralization test as sensitive method for this search. This finding also contribute with the knowledge confirming the extended distribution range of herpesvirus, affecting a large number of hosts including A. gazella.
It is strongly trusted the necessary to develop the scientific research on diseases in Antarctic wildlife, considering it interesting to be discussed in the WG-EMM agenda, as an important factor which may affect the population success. This also may provide information to be considered in the Antarctic Treaty System, in order to provide control tasks for regulate the possible disease transmission from or into the Antarctic environment.

Between november and february of the years 1993/94, 1995/96, 1996/97, 1997/98, 1998/99 and 1999/2000, one hundred and fifty three specimens of southern elephant seals, Mirounga leonina, were stomach lavaged at King George Island in order to analyse their diet. The two major prey types were cephalopods and fish which ocurred respectively in 98,1% and 14% of stomachs containing prey remains. The aim of the present paper was to report data on fish prey obtained from seal stomachs throughout the whole study period. One hundred and forty five sagittal otoliths were removed from 16 stomachs containing fish remains. Of these stomachs, 9 belonged to adult females, 6 to juvenile males and 1 to a subadult male. The identification of otoliths revealed the predominance of myctophids as fish prey of seals, representing 76,5% of the fish predated. The most frequent (75%) and abundant prey species was Gymnoscopelus nicholsi which constituted in number 69% of the otoliths found. This species was followed by the nototheniid Pleuragramma antarcticum which represented 11,7% in number and 31,3% in frequency of occurrence. Based on the great distances travelled by seals from their foraging grounds to their hauling sites and the differential rate of passage of fish and cephalopod remains through their gastrointestinal tract, an underrepresentation of the consumption of fish is highly probable. Moreover, according to the movements at sea of southern elephant seals tracked from King George Island we suggest that while myctophids may be their dominant fish prey in areas close to their hauling sites, they are probably replaced by the Antarctic silverfish P. antarcticum as seals migrate southward towards higher latitudes where this species is highly abundant.