[OANNES Foro] An 11, 500-year analysis of human coexistence with clams in British Columbia, Canada

[Mario Cabrejos]

Research points to traditional custodians for clues to sustainable
practices. Natalie Parletta reports.

Insights from historical human-clam coexistence 

16 October 2019 

https://cosmosmagazine.com/biology/human-clam-co-history

 

 



Researchers in British Columbia, Canada excavate ancient shells from the
beach of a "clam garden" -- a constructed rock-face terrace where Indigenous
People cultivated clams. Mark Wunsch (Greencoast Media, British Columbia,
Canada).

Coastal ecosystems are not only threatened by habitat loss and climate
change; a breakdown of traditional aquaculture practices could also have
significantly contributed to their deterioration.

This has been illustrated by an 11,500-year analysis of human coexistence
with clams in British Columbia, Canada,
<https://www.pnas.org/content/early/2019/10/09/1905921116> published in the
Proceedings of the National Academy of Sciences.

Ginevra Toniello, from Simon Fraser University, Canada, and colleagues
gathered paleoecological, archaeological and modern records of
<https://www.centralcoastbiodiversity.org/butter-clam-bull-saxidomus-gigante
a.html> butter clams (Saxidomus gigantea) in the northern Salish Sea to
understand their relationship with humans throughout the Holocene.

The cultural significance of these bivalves is revealed by stories, rituals,
language and the deep piles of ancient shell middens that line kilometres of
coastlines. Archaeological and ethnographic analyses suggest clams were
popular food sources harvested seasonally and all year round and enjoyed
both fresh and preserved. 



Butter clams from 11,500-11,000 years ago (left) and 10,900-9,500 years ago
(right) showing the sometimes dramatic differences in size through time.
Ginevra Toniello

Archaeological records can also provide insights into the ecological impacts
of interactions between humans and fauna, while palaeoecological information
can reveal the ecology of species without human interference.

"Taken together," Toniello and coauthors write, "these two records can offer
a powerful lens through which to assess coupled social-ecological systems
over broad spatial and temporal scales and can help establish ecological
baselines for modern management."

To peek into the past, the researchers gathered clam shells from middens at
five coastal sites and measured the size and width of growth rings in the
mollusc's shells. They put these into context according to their historical
location, before, during and after evidence of management by indigenous
people and were able to group the samples into seven time periods.

Together, these data allowed them to analyse predictors of clam size
throughout the Holocene.

They found the mollusc shells' size and growth was limited in early
postglacial times, but then flourished over the next few millennia until the
early-Late Holocene, likely reflecting more favourable habitat conditions.

Middens showed evidence that humans then harvested them around 9000 years
ago, and about 5500 years later started constructing clam gardens -
"intertidal rock-walled terraces" - as a form of aquaculture management.

The gardens made the bivalves more accessible to harvesters by reducing the
beach slope, exposing more beach during low tide, and bringing them closer
to human settlements.

The researchers believe the gardens' construction reflected population
growth and increased complexity of social structures, necessitating measures
to preserve the clams for food and trade.

By around 2700 years ago, harvesting intensified, yet evidence suggests the
clam populations flourished throughout the Late Holocene.

The clam habitats were likely preserved by the gardens built by generations
of Indigenous peoples, the team suggests. Along with cultivation methods
such as tilling, removing non-human predators, removing rocks, modifying the
substrate and monitoring access, the Indigenous people were able to maintain
a sustainable harvest. 

Toniello and colleagues speculate that the course sediment garden terrace
and rock wall also facilitated abundant growth and access to other marine
foods like crabs, sea cucumbers and seaweeds.

Sadly, modern records indicate that growing conditions declined since
European settlement replaced traditional management practices with
industrial activities, with an impact comparable to the ice age.

"It is striking that the growth patterns of clams living in the beach today
are most similar to the clams that lived and died in the unstable and
relatively unproductive habitats of the Early Holocene," the group writes.

"As in the Early Historic Period, we propose that the current low
productivity is due to the decline in traditional management, including
ongoing tilling through harvesting."

They note it could also be attributed to deposition of fine silts on the
clam beaches - less favourable for clam growth than the coarse grains used
as garden substrates - as a result of logging, along with warmer ocean
temperatures and associated declines in productivity. 

Nonetheless, they suggest modern humans could learn much from traditional
practices for aquaculture management, which also has broader ecological and
ethical implications.

"Examining the deep and specific history of human-species relationships,
such as that between people and clams, is requisite for understanding and
better managing our resources and ecosystems today," they write.

"Documenting these interactions between humans and coastal ecosystems, such
as we have done here, also counteracts the erasure of the long-term
connections of Indigenous peoples to their lands and seas."

 



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