No abstract

A pod of seven killer whales (Orcinus orca) was seen to attack a lone crabeater seal (Lobodon carcinophagus) which was lying on an ice floe. The whale located the seal, moved away from the floating ice, then swam as a group close to the floe. This caused a wave which tipped up the ice floe and broke over it, causing the seal to be thrown into the water. The whales swam immediately to the vicinity of where the seal disappeared but it was not possible to ascertain if a kill was made.

No abstract

A series of laboratory experiments was designed to investigate the influence of nitrogen, phosphorus and photon irradiance on the protein to carbohydrate ratio and growth rate of Scenedesmus quadricauda. These parameters responded to nutrient additions and depletions in a predictable manner. As nutrients were added the ratio rose to a maximum of 5, but as nutrients were depleted from the medium the ratio fell to < 1 during long-term experiments. The ratio also showed that diurnal fluctuations in cultures grown under a 12 h light : 12 h dark cycle were similar in magnitude to the long-term changes. The extent of these diurnal changes was dependent upon the nutrient status of the cells. In nutrient-saturated medium the ratio showed maximum change (4.2 to 1.1), but in nutrient-depleted medium the change was small (0.98 to 0.81). In addition to these responses to nutrients, the ratio was also influenced by photon flux. At high photon fluxes the ratio showed a marked diurnal change (0.91 to 4.05), but this change decreased with decreasing photon fluxes. A general relationship existed between growth rate and the protein to carbohydrate ratio for ratios >2. Below this value, however, growth rate was independent of the protein to carbohydrate ratio. Criteria based upon these laboratory experiments were derived to determine the nutrient status of field populations of phytoplankton. Using these criteria, the phytoplankton of Mount Bold Reservoir were shown to pass from a condition indicating nutrient sufficiency in November to a condition that implied varying degrees of nutrient deficiency for the period December to March. This pattern of nutrient sufficiency based upon protein to carbohydrate ratios agreed well with the results of nutrient-enrichment trials. This pattern would not have been discernible by the rigid application of previously determined critical protein to carbohydrate ratios.

This article describes the natural history of a large colony of emperor penguins Aptenodytesforsteri, its size, dispersal pattern of chicks, and associations with other bird and mammal species. A mid-season count of 19,364 chicks indicated that about 20-25,000 breeding pairs had been present in June and July. The colony was fragmented into several sub-groups which showed different mean sizes of chicks and survival to fledging. Other species observed included leopard seals Hydrurga leptonyx, the only major predators, which preyed heavily on both adults and fledging chicks. Fledgelings left the colony over a period of about 10 days; departure was an active process in which the chicks walked to the ice edge and dispersed in groups, swimming consistently southward. At this time they were still in about 60% down and weighed about 10 kg, having lost some 30% of the heaviest mass achieved during parental feeding.