When ecological impacts of an oil spill are assessed, worst case (conservative) assumptions are commonly made. For example, it is often assumed that when exposed above a specific oil concentration all individuals will die. What are the consequences of such assumptions for estimated impacts and the evaluation of potential response options?
We focussed on this question in this project. In order to obtain more insight, mathematical population models were developed for two Arctic species that are key to the food web: the crustacean Calanus hyperboreus and the Polar cod (Boreogadus saida). These key species were selected because the Arctic is considered to be a vulnerable area, but also an area in which the interest in oil extraction increases.
A challenge for these species is that they have been studied limitedly. Hence, there is little known about their biology and their sensitivity towards oil contaminants. By applying a more theoretical approach, fed by the limited information that is available, it was possible to develop a comparison of a worst case versus more realistic approach. Depending on the magnitude of the spill, the duration and concentration of the exposure, the difference between these approaches can be considerable. In the most extreme case, a difference of a factor 300 was found in the calculated population recovery duration using worst case versus more realistic assumptions.
Although it can be useful to make worst case assumptions from a precautionary perspective, it is better to make more realistic assumptions when making relative comparisons (which is the case in oil spill response). This has to be done in order to avoid explicit weighing of the options as a result of the worst case assumptions.