Darumbal voyaging: intensifying use of central Queensland's Shoalwater Bay islands over the past 5000 years

Island archipelagos of the tropical coast of central Queensland include the most distant offshore islands used by Aboriginal Australians. Excavations on Collins, Otterbourne and High Peak Islands, located up to 40 km from the mainland, reveal evidence of offshore voyaging and marine specialisation in the Shoalwater Bay region for at least 5200 years. A time lag of up to 3000 years between island formation and systematic island use may reflect delayed development of key marine resources. Expansion of island use commencing around 3000–3500 years ago is linked to population increases sustained by synchronous increases in marine resources. Occupational hiatuses variously between 1000 and 3000 years ago are associated with increased ENSO activity. Intensified island use within the past 1000 years is primarily a social phenomenon associated with continuing demographic pressures and the development of more coastally and marine-focused mainland groups, with settlement patterns increasingly encompassing adjacent islands. The viability of risky offshore canoe voyaging was underwritten by two key high-return subsistence pursuits – hunting green turtles and collecting turtle eggs. In addition to subsistence and quartz quarrying, a key motivation for island visitation may have been socially restricted (e.g. ceremonial) practices.

Sexual niche segregation and gender-specific individual specialisation in a highly dimorphic marine mammal

While sexual segregation is expected in highly dimorphic species, the local environment is a major factor driving the degree of resource partitioning within a population. Sexual and individual niche segregation was investigated in the Australian fur seal (Arctocephalus pusillus doriferus), which is a benthic foraging species restricted to the shallow continental shelf region of south-eastern Australia. Tracking data and the isotopic values of plasma, red blood cells and whiskers were combined to document spatial and dietary niche segregation throughout the year. Tracking data indicated that, in winter, males and females overlapped in their foraging habitat. All individuals stayed within central Bass Strait, relatively close (< 220 km) to the breeding colony. Accordingly, both genders exhibited similar plasma and red cell δ13C values. However, males exhibited greater δ13C intra-individual variation along the length of their whisker than females. This suggests that males exploited a greater diversity of foraging habitats throughout the year than their female counterparts, which are restricted in their foraging grounds by the need to regularly return to the breeding colony to suckle their pup. The degree of dietary sexual segregation was also surprisingly low, both sexes exhibiting a great overlap in their δ15N values. Yet, males displayed higher δ15N values than females, suggesting they fed upon a higher proportion of higher trophic level prey. Given that males and females exploit different resources (mainly foraging habitats), the degree of individual specialisation might differ between the sexes. Higher degrees of individual specialisation would be expected in males which exploit a greater range of resources. However, comparable levels of inter-individual variation in δ15N whisker values were found in the sampled males and females, and, surprisingly, all males exhibited similar seasonal and inter-annual variation in their δ13C whisker values, suggesting they all followed the same general dispersion pattern throughout the year.