Waterfall Bluff Rock Shelter (WB) (Eastern Cape Province (ECP), South Africa) contains archaeological deposits demonstrating persistent and continuous human occupation spanning from Late Marine Isotope Stage 3 (~39ka–29ka) to the mid-Holocene (~8ka). It is at this site that the first leopard seal (Hydrurga leptonyx) specimen was recently recovered from a Pleistocene and Holocene zooarchaeological assemblage along South Africa’s coast.
Our paper is published in the South African Journal of Science.
Leopard seal ecology
Leopard seals are apex marine predators whose habitats are usually restricted to the pack ice in the Antarctic and sub-Antarctic islands. They require pack ice to ambush their prey, the majority of which is made up of krill; however, they are also known to hunt penguins, pinnipeds, fish, and cephalopods.
In modern times, there have been only a handful of sightings from South Africa, both dead and alive, of leopard seals, with one of the earliest being in 1946 in East London in the Eastern Cape Province (ECP). A second sighting was made over 20 years later at Hout Bay in 1969.
A dead leopard seal was reported to the East London Museum (ECP) in 1994, and more recently, a living specimen was sighted at Cove Rock (ECP) in 2014. The most recent sighting was in 2021, where a living individual was spotted twice, once in Cape Town and again in Yzerfontein (Western Cape Province), before sightings ceased.
Recently, we discovered a leopard seal tooth from a deposit dating to the Last Glacial Maximum (LGM) (22,560–19,340 cal. BP) at WB. This makes it the first leopard seal to be recovered from a Pleistocene and Holocene zooarchaeological assemblage along South Africa’s coast.
Understanding the site and the discovery
WB is located around 24m above the modern coastline next to the Mlambomkulu River waterfall, ECP. It has been divided into two continuous layers of sediment, namely the Light Brown Coarse Sands (LBCS) dated to between 37,6±4,2ka and the Shell-Rich Clayey Sands (SRCS) dated by Bayesian 14C accelerator mass spectrometry model from ~11ka cal BP to 10,5ka cal BP.
What makes this site particularly significant is its consistent proximity to the shoreline during both glacial and interglacial periods.
Southern Africa currently has few coastal archaeological sites dating to the Terminal Pleistocene; although humans occupied such sites at the time, many have been destroyed or remain undiscovered. This scarcity is due to constant sea-level fluctuations, which resulted in a bias towards preserving coastal archaeological records during glacial periods.
However, owing to WB’s positioning adjacent to an exceptionally narrow continental shelf, it has survived and preserves records documenting repetitive human occupation spanning millennia. This site would have been especially desirable to humans due to its nearness to the coast, providing marine food and access to multiple terrestrial resources.
It has been hypothesized that such sites would have been occupied elsewhere in southern Africa by humans, such as by the Palaeo Agulhas Plain. However, these records are now underwater, making WB one of only a few sites providing insights into human occupation and behavior during glacial and inter-glacial periods.
We report on our preliminary results on faunal analyses undertaken in 2021 and their implications for the paleoenvironment at WB. Although our sample size is small, the interpretations provide compelling insights into local paleoenvironments and human exploitation behavior.
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The paleoenvironment at WB and its implications
The site shows evidence of a persistent mosaic environment able to support all major vegetation types and systematically exploiting both marine and terrestrial resources by hunter–gatherers throughout.
The site’s location and stable environment would have made it especially desirable to live in, as hunter–gatherers would have had various resources at their disposal regardless of the surrounding environment.
The presence of various terrestrial mammals in both SRCS and LBCS layers that require different habitats to survive, such as Eland (Taurotragus oryx), duiker (Sylvicapra grimmia), and African giant buffalo (Syncerus afer), indicate the existence of mixed, bushy and grassland environments throughout the occupation of the site.
Additionally, the presence of fish, seals, shellfish, and possible barnacle remains in the earliest deposit (LBCS) indicates that people were actively harvesting from the coast even when it was possibly ~8km away during glacial times. This persistent use of marine resources demonstrates the importance of coastal environments to early human communities, even during periods when the coast was further away, and it would have possibly required more effort to travel to the coast to acquire resources.
We identified a leopard seal tooth from this LBCS deposit. The tooth was identified by its distinctive triple-cusped crown, which is used for sieving krill, distinguishing it from the teeth of the more common fur seal usually found in the region.
Leopard seals are incredibly dependent on the frigid waters surrounded by pack ice for their survival, not only for hunting but also for breeding and food purposes. Individuals who stray too far from their home ranges are usually lost juveniles or starving and ill.
While it is possible that this leopard seal was one such lost individual, considering that local sea surface temperatures were, on average, 3°C lower than current levels, the conditions may have been suitable for these Antarctic predators to extend their range northward.
The increased pack ice resulting from such low temperatures in northerly ranges and the cutting off of specific krill spawning sites in Antarctica may have forced and enabled some leopard seals to occur much closer to the South African coast than today. Additionally, the site’s proximity to a river mouth would have washed inland nutrients into the ocean and could have helped maintain ocean nutrients that supported the marine animals upon which leopard seals preyed.
Considering that during these glacial times, WB would have been around 8km from the coast, the leopard seal tooth would have had to be brought into the shelter by humans. The presence of the leopard seal tooth indicated a much colder climate and may also indicate that humans were much more familiar with these animals during the LGM, enough to procure it and transport it, possibly as sustenance to their shelter.
The procurement of all the above animals also may hint at how adaptable and diverse the subsistence behaviors of early hunter–gatherers were, using the resources offered by predator and prey species.
This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.
More information:
Sandee Oster et al, Late Pleistocene and Holocene fauna from Waterfall Bluff Rock Shelter, Mpondoland, South Africa, South African Journal of Science (2024). DOI: 10.17159/sajs.2024/17449
I am a Ph.D. candidate at the University of the Witwatersrand; since 2018, I have been studying archaeology with a focus on zooarcheology, rock art, and isotopes. My interests lie in uncovering the interplay between humans & animals throughout history. I seek to advance current research on the 8.2k event in South Africa and contribute to filling a substantial knowledge gap with my work. I am actively working towards publishing my doctoral research findings & presenting my work at academic conferences in the hopes of becoming a well-rounded and internationally recognized archaeological researcher.
Citation:
Paleoenvironmental study at Waterfall Bluff reveals leopard seal far from Antarctic waters (2024, December 14)
