This study describes the seasonal and annual changes in the diet of non-breeding male Antarctic fur seals (Arctocephalus gazella) through the analysis of faeces collected on shore during four summer seasons (1993/94-1996/97) in the area of Admiralty Bay (King George Island, South Shetlands). Krill was the most frequent prey, found in 88.3% of the 473 samples. Fish was present in 84.7% of the samples, cephalopods and penguins in 12.5% each. Of the 3832 isolated otoliths, 3737 were identified as belonging to 17 fish species. The most numerous species were: Gymnoscopelus nicholsi, Electrona antarctica , Chionodraco rastrospinosus, Pleuragramma antarcticum, and Notolepis coatsi. In January, almost exclusively, were taken pelagic Myctophidae constituting up to 90% of the total consumed fish biomass. However, in February and March, the number of bentho-pelagic Channichthyidae and Nototheniidae as well as pelagic Paralepididae increased significantly, up to 45% of the biomass. In April the biomass of Myctophidae increased again. The frequency of squid and penguin occurrence was similar and low, but considering the greater individual body mass of penguins, their role as a food item may be much greater. In March and April, penguins could be as important prey item as fish. The amount of krill in the diet of Antarctic fur seals declined with a concomitant decrease in the mature krill availability. This appears to have been compensated by an increased frequency of the fur seal to eat fish and penguins.
The diet of the unsexed breeding Adélie penguin (Pygoscelis adeliae Hombron et Jacquinot, 1841) was investigated during three consecutive chick rearing periods, from 199697 to 199899, on Laurie Island, South Orkney Islands (60°46S, 44°42W), Antarctica. This analysis showed that during the whole sampling period, Antarctic krill (Euphausia superba Dana, 1852) represented the predominant prey in terms of frequency of occurrence, mass, and number. The hyperiid amphipod Themisto gaudichaudii (Guerin-Méneville, 1825) was present in small amounts. Electrona antarctica (Gunter, 1878), Trematomus newnesi (Boulenger, 1902) and larval stages of Nototheniidae constituted the bulk of the fish portion, particularly during the 1997/98 and 1998/99 breeding periods. This study is the first examination of the Adélie penguin diet at Laurie Island. It is important to recognize, however, the importance of knowing the sex of the penguins being sampled and that prey composition may vary during the breeding season and from one year to the next.
Round goby (Neogobius melanostomus (Pallas, 1814)) is an invasive species in the Oder River. In this study, age of 147 fish was determined using scales and otoliths, and the Fraser-Lee back-calculation method was used for population structure and theoretical length growth rates with 3 mathematical models of growth: von Bertalanffy, Ford–Walford and 2nd degree polynomial. Fish condition was determined using Fulton, Le Cren and Clark equations. Average total length and weight of fish was 162.00 mm and 83.00 g, respectively. Males were more abundant than females, representing 70% of the fish caught, and achieved greater total lengths and weights. Age 2+ dominated females and 3+ males age groups. Of the three mathematical models used to estimate fish growth, the 2nd degree polynomial model had the best fit to back-calculated lengths. Males had slightly higher growth rates than females in the first two years of life but comparable in subsequent years. The diet consisted of various benthic organisms that varied with fish age. The most frequently occurring food com-ponent was Dreissena polymorpha, which accounted for approximately 70% in the diet of fish with a body length greater than 191 mm.
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