The… emptying seas phenomenon will be inevitable if you don’t make an effort on reverse it.
Choosing sustainable species of fish would be one pretty good step in order to make an impact. Yes, you cannot make an impact on your own, but if you think that many others will do the same (be overcoming the «I cannot change the world» affirmation) it is a good start.
So, what do you have to do in order to get there?
First of all, try to consume a wide variety of fish than choosing just one type all the time.
Secondly, look for the «Sustainable Fisheries» label on the products you buy. Two major labels that certify sustainable fisheries are MSC (Marine Stewardship Council) and FOS (Friend of the Sea).
Read the labels. On them, you should find the trade name of the species the production method (fishery or aquaculture) and the area of production. Moreover, you should also see whether the product is fresh or not, or it has been frozen and defrosted.
Finally, it is important to buy only adult fish and always «in season» and -definitely- avoid the species that have been caught during their reproductive period.