Atlantic croaker, one of the most abundant fish in the Gulf of Mexico, are starting to exhibit changes that appear to be related to the massive summer "Dead Zone." A NOAA-sponsored study found croakers exposed to low oxygen for as few as 10 weeks underwent hormonal alterations that transformed some of their female reproductive tissue into male tissue. The male tissue was incapable of fertilizing eggs, and hatching rates of successful pairings were a tenth of normal.
All of these factors are quite capable of causing a population crash in one of the Gulf's top ten important recreational fisheries. Because croaker are closely related to several species of fish in the Gulf of Mexico, scientists say there are many fish populations susceptible to crashing if the conditions are right for a large drop in croakers.
Croaker are a relatively small, $8M annual recreational fishery, but the species it's related to are amongst the largest commercial fisheries in the Gulf. A problem in one species could spell trouble in any or all of them.
See page 5 of the 2011 Hypoxia Task Force Annual Report.