CCAMLR

A method of surveying incidental mortality of seabirds during longlining operations and the effectiveness of mitigation measures is described. An alternative design of streamer line for use with the 'Spanish' method of longlining (separate hauling and fishing lines) is described. The results of observations of incidental mortality of seabirds made during the fishing operations of the Korean longliner lhn Sung 66 are presented. Preliminary findings suggest that the phase of daylight during which the longline is set is more important than the use of a streamer line in the mitigation of incidental mortality. The use of a streamer line during setting of longlines during the day reduced the observed rate of bird deaths from snagging and drowning by 79%. More data are required to develop the investigation further.

This paper is a revision of the assessment of the competition between the Japanese krill (Euphausia superba) fishery and penguins (WG-Krill-93/7). Main fishing areas were confined to the slope and shelf to the north of either Livingston or Elephant Islands. In contrast, main foraging areas of penguins are considered to be formed in areas to the north of King George, Nelson and Robert Islands, and around Low, Clarence and Deception Islands. This little overlap between the main fishing and foraging areas is resulted from that large colonies of the dominant penguin (chinstrap penguins, Pygoscelis antarctica) are closely associated with areas where sea-ice disappears earlier in spring, not necessarily with areas of high krill abundance. The overlap between trawling depth and foraging dive depth of penguins was also insignificant. Furthermore, less similarity between krill caught by trawlers and those captured by penguins was observed. The above mentioned results imply a low level of competition between the fishery and penguins. Krill biomass was estimated to be as large as 200-1500 xl03 tonnes within the preferred fishing areas during the breeding season. Compared with the level of biomass (≥200 xl03 tonnes) and its variability (the order of 100 xl03 tonnes/half-month period), the present catch rate (≤13 xl0 3 tonnes/half-month period) is smaller by one or more orders of magnitude within the localized areas. Thus, the present fishery is very unlikely to have an adverse impact on the local krill biomass and hence on penguins,. when catch levels are also taken into account.

The consumption of food by the four species of breeding penguins at the Prince Edward Islands is assessed on an annual and seasonal basis. Total annual food consumption was estimated at 880 000 t, of which king penguins accounted for 74%, macaroni penguins 21%, rockhopper penguins 5% and gentoo penguins

Predator-prey interactions play an important role in determining the dynamics of pelagic ecosystems. Human intervention in such interactions can have effects that cascade throughout these ecosystems. Recently, concerns have arisen due to the commercial harvesting of Euphausia superba, the Antarctic krill, a keystone prey species in the Southern Ocean food web. It has been difficult to evaluate these concerns because of problems associated with determining the availability of krill to their natural predators. Here, we report a novel method for assessing prey availability to an important krill predator, Pygoscelis antarctica, the chinstrap penguin. Acoustic techniques were used to analyze the three-dimensional distribution of krill within a 1852 X 1852 X 100 m volume of ocean. Our study revealed the presence of at least six, distinct krill aggregations and substantial vertical and horizontal patchiness at scales of 10s to 100s of metres. Monte Carlo simulations revealed significant spatial concordance between the surface distribution of penguins and krill distributed in the 30 - 40 m depth layer; no spatial concordance was detected in shallower layers. We conclude that fine-scale, depth-dependent patterns of kill patchiness must be incorporated into analyses of krill availability to predator populations if we hope to predict predator responses to a changing food environment.

Since penguins rely on the main planktonic resources of the Southern Ocean, knowledge of their diet may be used for monitoring these resources. During winter and spring of 1987 and 1989, we investigated the composition of the diet of gentoo penguins, Pygoscelis papua, in relation to changes in the availability of two prey species, Euphausia vallentini and Themisto gaudichaudii, sampled during plankton surveys in the Kerguelen Islands. The comparison between plankton surveys and diet analysis was performed on samples taken 2–4 km from the studied colonies. Data on the abundance of zooplankton derived from penguins' diet matched closely those from net hauls during a year of high plankton availability (1987). On the other hand, a weaker correspondence was found during a year of restricted availability (1989). The mean sizes of amphipods caught by penguins and net hauls were very similar but the size distribution showed comparatively fewer small and large individuals in net-hauls than in penguin stomachs. Detailed studies on the feeding range and foraging effort of penguins are therefore needed in the near future to validate the potential of penguin diet as a measure of plankton abundance.