They are very slow to grow and reproduce and their numbers are very low. Southern right whales may number just a few thousand worldwide. They only produce one calf every three years and take about ten years to reach breeding age. We need to minimise all the threats to their survival. Threats include things like collisions with boats, entanglement in drift nets, swallowing of marine debris such as plastics and oil spills.
Marine pollution is a long term threat.
Another is whale watching. It is important to know and follow whale watching guidelines, so that you do not put yourself or the whales at risk. Watson L. 1981. To Whales of the World.