Preliminary archaeological survey and remote-sensing of shell mounds at Kwokkunum, Albatross Bay, Cape York Peninsula, Australia

Shell mounds are a prominent part of the Cape York Peninsula archaeological record. A short period of fieldwork allowed initial assessment of their presence, size, and shape in the Kwokkunum region, Albatross Bay. Shell mounds found in this area vary in size with some examples amongst the largest found in the Cape York Peninsula. Comparison of terrestrial and airborne LiDAR data suggests that shell mounds in areas like Kwokkunum may be identified remotely where mound slopes exceed 5–10°. However, vegetation provides significant challenges for shell mound recording and vegetation on the mounds impacts on their form and preservation. Some of the challenges the largest mounds pose for investigation are reviewed.

Decommissioning impacts on biotic assemblages associated with shell mounds beneath southern California offshore oil and gas platforms

The decommissioning of southern California offshore oil and gas platforms will create major economic, engineering, and environmental challenges in the next decade. Platform jackets, conductors, and shell mounds often host a diverse and productive marine community, and among the myriad considerations associated with decommissioning planning, platform operators and federal and state regulatory agencies will consider the ecological value of existing underwater structures as artificial reefs. In the event of partial removal of platform structure, fish assemblages on decommissioned platforms may remain unchanged in areas where structure is left intact. However, on the seafloor beneath the platforms, a mound of debris often called the shell mound will likely change over time if the supply of falling mussels and other organisms from the productive surface part of the structure is removed. In this study, we review shell mound research relevant to decommissioning, including mound formation, contaminant loads, associated biological communities, and transitions following the removal of platform structures at four sites. To address the gap in knowledge of shell mound fish community structure, we used manned submersible and remotely operated vehicle surveys from 1997 to 2013 to estimate the biomass, density, species composition and similarity between shell mounds at 22 southern California platforms. We found a wide range of variability in fish density and shell mound areal extent. Species composition also varied among sites, with three significant community clusters primarily distinguished by species depth preferences. These results will help inform a comprehensive net environmental benefit analysis of southern California offshore platform decommissioning alternatives.

An analysis of the fish assemblages around 23 oil and gas platforms off California with comparisons with natural habitats

Between 1995 and 2013, we surveyed fishes living around 23 California offshore oil and gas platforms (midwaters, bases, and shell mounds) and 70 natural habitats. These platforms were distributed between about Point Arguello, central California, and Huntington Beach, southern California, had seafloor depths between 49 and 363 m, and were surveyed between one and 16 times. A total of 1,526,437 fishes were observed. Fish densities were highest around platform bases, followed by platform midwaters, shell mounds, and natural habitats. Of all fishes observed, 90.4% were in the genus Sebastes. Water depth was the strongest driver of the fish species assemblages, although habitat type and geographic location were also important. Most of the fishes living around platforms and natural habitats were relatively small, primarily ≤20 cm in length. Many of these individuals were the juveniles of larger taxa or the juveniles and adults of dwarf species. Larger fishes were less common and these were most often found around platform bases and on natural habitats. Most young-of-the-year (YOY) fishes occurred at water depths of ≤150 m at all four habitats. At platforms, YOY densities were highest in platform midwaters and bases. On average, densities of these young fishes were somewhat higher compared to natural habitats and it is likely that many, although not all, California platforms play a significant role as nursery grounds for a variety of fishes, particularly for a number of Sebastes species.

Flaked stone assemblage variability across the Weipa region of western Cape York Peninsula, Queensland

Shell mounds located on the coastal and estuarine fringes are the best-known archaeological feature in the Weipa region, northwestern Cape York Peninsula, Australia. Other archaeological deposits have received less attention, with stone artefacts thought to be all but absent reflecting the lack of raw material suitable for flaking in the region. Cultural heritage surveys on the bauxite plateau in the Weipa region undertaken since 2003 have changed this view. Here we report on stone artefacts manufactured from quartz, quartzite, silcrete, and mudstone. Surprisingly, flakes and cores in assemblages from across the surveyed region retain a relatively large proportion of cortex, indicating limited lithic reduction despite the lack of local raw material. Comparisons made with assemblage characteristics from other regions in Australia indicate that this lack of core reduction may reflect use of the Albatross Bay landscape by people who were confident of being able to access the lithic sources outside the region to replenish their tool kits.