Sharks, tuna, billfish, and other top marine predators have generally been considered the most vulnerable to population collapse, having experienced massive declines in the past decades due to overfishing. But a recent study done at Stanford university suggests that smaller fish are just as vulnerable:
"Analyzing over 200 scientific assessments of fisheries around the globe, the team found that populations of small fish such as sardines and anchovies were at least as likely to have collapsed at some point in the last 50 years as stocks of large fish."
Small fish like sardines reproduce and mature more rapidly than large fish, so, theoretically, their populations can recover from collapse more quickly. But one of the study’s researchers cites the collapse of the sardine fishery in Monterey bay, which took decades to recover, as an example of this not always being the case. To their surprise, researchers found that in the last 50 years, small species "were almost twice as likely to have suffered a major decline."
The conclusion is hardly surprising: "all species of fishes can collapse once humans decide to eat or use them."