Here is an interesting blog post analyzing theories about why people are eating more shrimp than was previously the case. In short, people without training in economics seem to focus more on the demand side than people with such training.
One response that surprised me was “a rise in the number of vegetarians who will eat shrimp.” Now, if you are a vegetarian because you think it is wrong to kill cows and chickens for food, that may be a sensible position. If you are a vegetarian for general reasons of ecological sustainability, it is a lot less valid. As fisheries go, shrimp is one of the worst when it comes to bycatch. The UN Food and Agriculture Organization says that the present shrimp catch is at least 50% above the maximum sustainable level. Shrimp also tends to be collected through a process called bottom trawling: where large steel rollers smash and kill everything on the ocean floor.
Shrimp aquaculture is arguably even worse. There are all the problems attendant to all agriculture – close quarters, disease, harvesting other creatures unsustainably to turn into feed, antibiotics, etc – and then there is the fact that mangrove swamps are ideal for conversion into shrimp farms. The UN Environment Programme estimates that 1/4 of the total destruction of these important ecosystems has been brought about by shrimp farming.
From an ecological standpoint, vegetarianism (and probably veganism) remains a far preferable option, compared to eating meat.