Browsing by Subject "seals"

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    A first step towards modelling the krill–predator dynamics of the Antarctic ecosystem
    (2006) Mori, M; Butterworth, Doug S
    The history of human harvests of seals, whales, fish and krill in the Antarctic is summarised briefly, and the central role played by krill emphasised. The background to the hypothesis of a krill surplus in the mid-20th century is described, and the information on population and trend levels that has become available since the postulate was first advanced is discussed. The objective of the study is to determine whether predator–prey interactions alone can broadly explain observed population trends without the need for recourse to environmental change hypotheses. A model is developed including krill, four baleen whale (blue, fin, humpback and minke) and two seal (Antarctic fur and crabeater) species. The model commences in 1780 (the onset of fur seal harvests) and distinguishes the Atlantic/ Indian and Pacific Ocean sectors of the Southern Ocean in view of the much larger past harvests in the former. A reference case and six sensitivities are fitted to available data on predator abundances and trends, and the plausibility of the results and the assumptions on which they are based is discussed, together with suggested further areas for investigation. Amongst the key inferences of the study are that: (i) species interaction effects alone can explain observed predator abundance trends, though not without some difficulty; (ii) it is necessary to consider other species, in addition to baleen whales and krill, to explain observed trends – crabeater seals seemingly play an important role and constitute a particular priority for improved abundance and trend information; (iii) the Atlantic/ Indian Ocean sector shows major changes in species abundances, in contrast to the Pacific Ocean sector, which is much more stable; (iv) baleen whales have to be able to achieve relatively high growth rates to explain observed trends; and (v) Laws’ (1977) estimate of some 150 million tonnes for the krill surplus may be appreciably too high as a result of his calculations omitting consideration of density-dependent effects in feeding rates.
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    The role of seals in coastal hunter-gatherer lifeways at Robberg, South Africa
    (2020_) Richardson, Leesha; Sealy, Judith; Stynder, Deano
    Seals were a major dietary item for coastal hunter-gatherers and herders in South Africa. At Nelson Bay Cave (NBC), more than half of the Holocene mammal bones are from Cape Fur seals (Arctocephalus pusillus). Previous analyses of the seal assemblage from this site have studied only selected skeletal elements. This study is the first comprehensive analysis of seal remains from selected archaeological levels at Nelson Bay Cave and from the 2007/2008 excavations at nearby Hoffmans/Robberg Cave (HRC). Body part representation and frequency, age distribution and bone modification have been documented to determine the role of seals in the lifeways of hunter-gatherers and pastoralists at Robberg throughout the Holocene. The age profiles indicate that seals were obtained directly from a breeding colony throughout the Holocene. A breeding colony at Robberg would have been a rich and reliable resource for coastal foragers throughout the year. There were differences in skeletal element representation in the Early and Middle Holocene, compared with the Late Holocene. Axial skeletal elements are under-represented in earlier time periods, probably due to field butchery and the return of only parts of the seals to the living sites. In the Late Holocene, entire animals were taken back to site. Within each time period, the skeletal profiles of juveniles and adults indicate that both were processed similarly suggesting that aspects such as carcass size, weight and foraging distance were less important factors in transport decisions than the terrain of the Robberg Peninsula and the size of the hunting party. A large proportion of the bones were complete, or almost complete. There was little evidence of canid gnawing. The skeletal element representation, frequency and cut mark patterns suggest that the heads and flippers were highly sought after throughout the Holocene, as recorded in Arctic ethnography. Seals were also of spiritual significance, possibly in aiding transitions from the material into the spirit world.