Some thoughts on estimating change to Arctic cod populations from hypothetical oil spills in the eastern Alaska Beaufort Sea

Abstract

We describe a fecundity-hindcast model that incorporates Arctic cod (Boreogadus saida) acute toxicity data, field studies of Arctic cod larval distribution and abundance, natural mortality estimates for Arctic cod eggs and larvae, and an oil spill fate model in Alaska Beaufort Sea. Three orders of magnitude of spill events (1000, 10 000, and 100 000 tons) were evaluated for both physically and chemically dispersed oil. Using worst-case assumptions in our model, a 100 000 ton spill of crude oil treated with dispersants resulted in 266 million m3 of water that exceeded our acute toxicity threshold, compared to a volume of 71 million m3 for a 100 000 ton spill not treated with dispersants, and resulted in exposure of about 2 million Arctic cod larvae remaining from an initial 87 million eggs. This represents the reproductive output of about 7300 adult females. Adult Arctic cod populations in the Alaska Beaufort number in the tens to hundreds of millions. The results show that even with an order of magnitude variation in exposure, the effect of dispersing a large oil spill on the regional cod population is expected to be insignificant (∼0.7%). The recent hiatus in Arctic oil and gas development affords an opportunity to acquire additional data to further strengthen this conclusion.

Keywords

• alaska
• beaufort sea
• arctic cod
• oil spill impacts
• natural mortality rates
• ichthyoplankton
• boreogadus saida