Isotopic records on the massive death of sea scallops in Vancouver Island of Canada

Carbonate shells can be used in the detection of climate change and ocean acidification in fisheries science and aquaculture. In this study, we reported stable carbon and oxygen isotope ratios (δ13C and δ18O) in sea scallop (Patinopecten caurinus) shells from the Island Scallop Limited (ISL) in Vancouver Island, British Columbia, Canada, where approximately ten million sea scallops died in 2013. The δ13C values of the harvested scallop shells from 1993 ranged from −0.58 to +0.66‰, whereas δ18O values from the same samples ranged from −3.05 to −0.32‰. The harvested scallop shells from 2014 showed similar variation in δ13C but significantly higher δ18O values in the summer of 2013. As compared with the otoliths of Atlantic bluefin tuna and the Zhikong scallop (Chlamys farreri) shells from the northern Yellow Sea of China, our data did not show a steady δ13C decrease in the 2014 samples and thus do not support the hypothesis that ocean acidification led to the massive death of the ISL scallops. Hatchery observations on incoming seawater in 2014 showed normal and stable profiles in temperature, salinity, and pH; thus, the significant increase of δ18O values in the summer of 2013 suggests that an unusually cold-water mass from upwelling might have occurred in the ISL grow-out site.