One of the major threats to some populations of Orcas and other whales is starvation. Ensuring that we are practicing sustainable seafood practices so that we are leaving enough for whales to eat, while also stopping climate change so that fish and krill populations have an environment where they can thrive, are both critical for supporting whales.
Eating sustainable seafood and advocating to the government to require sustainable seafood practices are both a part of this puzzle. Identifying which seafood is sustainable can be a bit complicated, but organizations like the Monterey Bay Aquarium's seafood watch make a complicated situation much easier. You can even download an app for checking if the seafood is sustainable on the go.
When determining whether a seafood is fished sustainably or not, it's important to note what species it is, where it was caught (or in some cases farmed), and how it was caught. Once you have that information you can look it up on the seafood watch app to help you decide whether it's a good choice or not. Generally, local seafood is better if it was fished with a sustainable method because locally caught *and prepared* fish didn't have to get shipped all over the world to get to your plate.
Keep an eye on environmental legislation passing through your state or country and vocally advocate for requiring fisheries to be more sustainable. We have pulled entirely too many fish and invertebrates from the ocean, and it's critical that we ensure that future generations of both humans *and* whales can enjoy seafood like we have been able to.