Browne T.,University of Otago |
Lalas C.,PO Box 31 |
Mattern T.,University of Otago |
Van Heezik Y.,University of Otago
Austral Ecology | Year: 2011
The link between poor reproductive success and diet was investigated in yellow-eyed penguins Megadyptes antipodes, by assessing diet at two localities separated by about 30km: the north coast of Stewart Island where breeding success is low (0.38-0.67 chicks per pair in recent years), and Codfish Island where breeding success is higher (0.96-1.51 chicks per pair), and relating this to published data from South Island localities, where average breeding success was 1.1 chicks per pair. Diet composition, meal sizes and energetic content of meals and prey were determined from stomach contents, and stable isotope analyses of chick down, fledgling feathers and adult blood provided information on diet throughout the fledging period. The high proportion of stomachs that were empty or lacked diagnostic remains reduced sample size considerably, and variability between samples reduced the power to detect significant differences in meal size, proportions of empty stomachs and prey diversity of meals. Energetic content of Stewart Island meals was less than Codfish Island meals, and there was a non-significant trend for smaller meal sizes and reduced prey diversity among Stewart Island samples. Both localities had lower prey diversity and smaller meals than South Island penguins. Blue cod Parapercis colias accounted for 99% of prey biomass in Stewart Island and 70% in Codfish Island stomach samples, where 27% of prey biomass was opalfish Hemerocoetes monopterygius. Isotopic mixing models carried out on larger sample sizes indicated that opalfish comprised a large proportion of the diet at both locations, with adults selectively provisioning chicks with opalfish while feeding mainly on blue cod themselves. We suggest the large blue cod consumed by Codfish Island and Stewart Island penguins, larger than those consumed by South Island penguins, is difficult to transfer to chicks by regurgitation. Oyster dredging around Stewart Island may have reduced the availability and abundance of alternative prey to Stewart Island penguins. © 2010 The Authors. Journal compilation © 2010 Ecological Society of Australia.
Miller E.,University of Otago |
Lalas C.,PO Box 31 |
Dawson S.,University of Otago |
Ratz H.,PO Box 31 |
Slooten E.,University of Otago
Marine Mammal Science | Year: 2013
Stomach contents of 63 Hector's dolphins (Cephalorhynchus hectori) were collected between 1984 and 2006 from throughout New Zealand to provide the first quantitative assessment of prey composition. Twenty-nine taxa were identified. Those most commonly consumed were red cod (Pseudophycis bachus), ahuru (Auchenoceros punctatus), arrow squid (Nototodarus sp.), sprat (Sprattus sp.), sole (Peltorhamphus sp.), and stargazer (Crapatalus sp.). By mass, these six species contributed 77% of total diet. Red cod contributed the most in terms of mass (37%), while ahuru and Hector's lanternfish (Lampanyctodes hectoris) were consumed in large numbers. Prey ranged from <1 cm to >60 cm in total length, but the majority of prey items were <10 cm long, indicating that for some species, juveniles were targeted. Diets of dolphins from South Island east and west coasts were significantly different, due largely to javelinfish (Lepidorhynchus denticulatus) being of greater importance in west coast stomachs, and a greater consumption of demersal prey species in the east. The feeding ecology of Hector's dolphin is broadly similar to that of other Cephalorhynchus species. Hector's dolphin is shown to feed on species from throughout the water column, and differences in diet between populations are thought to reflect prey availability. © 2012 by the Society for Marine Mammalogy.
Dai H.J.,University of Leicester |
D'Souza N.,PO Box 31 |
Dong H.B.,University of Leicester
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011
Spiral grain selectors are used to grow single-crystal (SX) turbine blades during investment casting. Competitive growth in the spiral selectors leads to the selection of a single grain that subsequently grows to form the blade. In this study, the effect of spiral design on grain selection during investment casting was investigated through a series of experiments. It is found that the spiral design can effectively reduce the grain number but is not able to optimize axial grain orientations during solidification, the effectiveness of grain selection is strongly dependent on the spiral "take-off" angle, and spirals with smaller take-off angles are most potent. It is proposed that grain selection in the spiral is controlled by the geometry of the spiral via a "geometrical blocking" mechanism. © 2011 The Minerals, Metals & Materials Society and ASM International.