How does a vegan acquire DHA, an essential nutrient for the brain, if they don't ever consume it?

The human body has the capacity to consume some of the plant-based short-chain omega-3 known as LNA (consumed in canola/flax/soybean oils and other sources)and convert it to DHA in the liver which can then be delivered to the brain. However, this conversion is very limited such that vegan women tend to have significantly lower levels of DHA in their breast milk than non-vegans.