They're good, in the sense that there are no competitors and there are relatively few predators. Unfortunately, the ocean environment and the environment in which their larvae are launched seem to be poor for them overall.
We've seen a trend for earlier spring phytoplankton blooms in the last decade or so. They're variable, but they've progressed by as much as a month in terms of timing. Most large species, such as shrimp, capelin, cod, and so on, have a hard time adjusting their spawning cycle to match the changes in the productivity of lower trophic levels.
There is a hypothesis in the scientific literature that's called the match-mismatch hypothesis. If you match up with the right food environment, you do better, and if you mismatch that environment, you do more poorly. This is basically the situation that seems to be occurring in the case of shrimp.