A historic rapid climate change event led to whale beaching

Mannino, M. A. et al. Climate-driven environmental changes around 8,200 years ago favoured increases in cetacean strandings and Mediterranean hunter-gatherers exploited them. Sci. Rep. 5, 16288; doi: 10.1038/srep16288(2015).

Background 

Whales and humans have a shared history that spans many centuries. Before whale hunting became the popular means of acquiring whale meat, bone, blubber (oil), and baleen, humans took advantage of whale strandings. Whale stranding defines intentional stranding of whales along coasts (Guinet, 1990), which typically results in their death due to dehydration. A recent stranding that resulted in the death of 150 whales in Australia made headlines worldwide (Wang, 2018). Although scientists are actively learning about what triggers strandings, they have acknowledged that whale strandings have occurred for a very long time. A recent study by Mannino et al. (2015) suggests that rapid changes in the climate around 8,000 years ago led to an increase in cetacean strandings that were opportunistically used by the Mediterranean hunter-gatherers. The results from this study has wide reaching implications for how whale behavior might be impacted by future climate change.

Methods: caves, geochemistry, and palaeontology

The authors conducted paleontological identification on multiple bones excavated from Grotta dell’Uzzo in Sicily, Italy. They also carried out geochemical tests on human and faunal bone collagens found in the cave, in order to reconstruct the diet of the hunter-gatherers inhabiting it.

Figure 1: Grotta dell’Uzzo is located along the Sicilian coast in the Mediterranean Sea. The numbers indicate other caves that are spread along the coast. The red circle suggests the hypothesized location of the stranding that occurred around 8000 years ago. The bottom picture shows the cave entrance from the north. Source: Mannino et al. 2015.

The cave itself (Figure 1) is located in North West Sicily (Italy) and was sporadically occupied from the Late Pleistocene (~0.13 million years ago) through the early Holocene (~7,000 years ago). Multiple excavations in Grotta dell’Uzzo have made it a valuable site to study changes in human culture at that time in the Mediterranean. The results for this paper specifically focused on the Mesolithic-Neolithic transition (~8,700 – 7,850 B.P) during which the rapid 8.2 kya climate change occurred.

Mannino et al., investigated the zooarchaeology of the site with a focus on whale bone assemblage. The study also used the isotope ratios (chemical signatures) of carbon, nitrogen, and sulphur on collagen extracted from human and animal bones from Grotta dell’Uzzo to study the diet of the cave inhabitants. Carbon isotopes are reflective of the type of vegetation consumed and/or ecosystem of origin (terrestrial, freshwater or marine). Nitrogen isotope ratios reflect the trophic level differences between plant- and meat- eating organisms. Sulphur isotope ratios provide data on the biome from which protein was acquired.

Paleodiet and bone structures

The authors found a total of 224 identified specimens attributable to the order Cetacea that were recovered almost exclusively in areas of the cave where Mesolithic-Neolithic transition deposits had occurred. However, it was hard to identify the species as the majority of the bones were in fragments. An investigation of the process of fossilization of the bone surfaces lead to the observation of tool butchering cut-marks (Figure 2). The position of these cut-marks suggests that they were produced in the process of disjointing the carcasses for meat.

Figure 2: A) Cut-marks on cetacean neck bone, zoom in (B) shows multiple, short (~2mm), straight and sub-parallel marks indicative of human alterations. (C, D) Images under a scanning electron microscope (SEM) display oblique orientation of the cut marks, further suggesting lithic tool used during cutting of the carcass. Source: Mannino et al. 2015.

Isotope analysis (research that investigates the chemical composition of substances) on fox and hunter-gatherer fossilized bone collagen revealed that they had large intakes of marine substance during the Mesolithic-Neolithic transition. The marine substance coinciding with the whale strandings that occurred 8,000 years ago. Taken together the authors propose this is proof that whales were exploited during the Mesolithic-Neolithic transition. Lastly, Mannino et al., 2015 suggest that around 8,000 ago, the sea level stand around Grotta dell’Uzzo resembled acoustical dead zones where cetaceans got trapped making it impossible for them to navigate. The research has great implications for anticipating and understanding whale strandings that future rapid climate change events might bring.

 

Citations

Guinet, C. (1991). Intentional stranding apprenticeship and social play in killer whales (Orcinus orca)Canadian Journal of Zoology69(11), 2712-2716.

Mannino, M. A., Talamo, S., Tagliacozzo, A., Fiore, I., Nehlich, O., Piperno, M., & Richards, M. P. (2015). Climate-driven environmental changes around 8,200 years ago favoured increases in cetacean strandings and Mediterranean hunter-gatherers exploited themScientific reports5, 16288.

Wang, AB. (2018, March 23). Nearly 150 beached whales die after mass stranding in Australia. The Washington Post. Retrieved from https://www.washingtonpost.com/news/speaking-of-science/wp/2018/03/23/nearly-150-beached-whales-die-after-mass-stranding-in-australia/?utm_term=.68d8182cd6dc

 

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