Ecosystem enhancements? Ancient aquaculture practices in British Columbia provide insights and baselines for today’s management

Background/Question/Methods

Over one billion depend on marine resources for 20 % of their protein and nearly half of the world’s population live on the coast.  Today’s coastal fisheries are heavily impacted by habitat disturbance, climate change, sea level rise and pollution, as well as the basic challenge of feeding a global population that is expected to top 9 billion by 2050.  This has global, regional and local impacts and solutions cross sectors and cultures.  In an effort to find ecologically sound solutions for shellfish harvest, we use an integrated approach (ecological, archaeological, and traditional knowledge) to examine ecological effects of First Nations’ ancient aquaculture practices to inform today’s management.  We examine the effect of building rock-walled beach terraces, “clam gardens”, on of bivalve productivity.  We hypothesize that clam gardens (CG) are engineered to maximize optimal habitat, thus increasing growth rates and harvest of clams. This study tests if CG increase yields (density, biomass, and survivorship), and secondary productivity (growth rates). We conducted ecological surveys on 11 CG and 10 non-walled beaches (NB) on Quadra Island, BC, Canada. In addition, we experimentally out-planted 90 native Leukoma staminea per site at 6 tidal heights in 6 CG and 5 NB in 2011.

Results/Conclusions

Within and across both bays, clam gardens had significantly shallower slopes (Dy/Dx) than unaltered non-walled clam beaches (F1,19=6.914, p=0.017).  The greatest abundance and highest growth rates of L. staminea in non-walled beaches ranged between 0.5-1.5m above chart datum, and clam garden terraces tended to be built to extend between 0.5-1.2m intertidal height. Our survey results found clam gardens to have insignificant differences in L. staminea biomass (p=0.37), but significantly higher L. staminea densities (p=0.01). Results from the experimental transplants did not detect a significant difference in total L. staminea survivorship between clam gardens and non-walled beaches, (p=0.563), but growth rates for L. staminea planted in clam gardens terraces were significantly higher than those transplanted to non-walled beaches (p=0.011).  Smaller individuals (class sizes <39mm) seem to be especially sensitive to improved habitat conditions of clam gardens.  Our survey and experiment results suggest that by altering the slope of non-walled beaches, clam garden walls increase optimum habitat and growing potential for bivalves, an important subsistence food resource. This research reveals important insights into traditional methods of ensuring food security and sustainable harvest techniques that can enlighten contemporary conservation strategies.