This is an amazing resource put together by the Monterey Bay Aquarium called "Seafood Watch". You can look up any type of seafood on their website, and they will tell you whether that seafood is good for your body and for the environment!
Even better, you can print out a pocket guide that you can carry with you when you go grocery shop. The guides are made for specific regions, so you can print one out for Southern California! I use this all the time at the grocery store.
Below is their rating system for seafood:
Best Choices: Seafood in this category is abundant, well-managed and caught or farmed in environmentally friendly ways.
Good Alternatives: These items are an option, but there are concerns with how they're caught or farmed-or with the health of their habitat due to other human impacts.
Avoid: Take a pass on these items for now. They are caught or farmed in ways that harm other marine life or the environment.
The Super Green List: A list of wild and farmed seafood that's healthy for people and the oceans.