I’ve saved the scariest problems for the end. The status of the world’s fisheries is indeed scary.
There are different levels of destruction of fisheries around the world—some are doing worse than others. In some cases, especially those where rivers are heavily dammed, aquatic species have been exterminated or nearly gone extinct. In other cases, where fishing industries have been reined in or have had the foresight to change their ways, fish stocks have rebounded or stabilized.
But overall global wild fisheries have been in decline. The way fisheries are determined to be “overfished” is very complex; this link explains one example of this methodology. The UN FAO estimates that in 2011 almost 30% of wild fisheries were “fished at a biologically unsustainable level”, while a full 85% were fished at the “maximum sustainable yield”, were depleted, over-exploited, or close to it. An American-German research effort, finding flaws and limitations in the FAO methods for calculating overfished stocks, found 56.4% of global stocks were overfished.
These declines are caused by the overharvesting of fish, in combination with ecological factors and the economic incentives that encourage the overharvest. While small fishing operations (i.e. traditional fisher people) can contribute to reduction in a particular stock, especially in the midst of sudden ecological changes that reduce the ability of a species to recover population size, it is the corporate fishing industry and their massive fleets of massive boats with massive equipment that enable major and quick reductions in fish stocks.
Larger faster fleets with larger nets that result in lots of “bycatch”, and freezing capacities such that boats can be out farther and longer, are obviously more dangerous to particular stocks than small fisher folk.
The rise and dominance of companies with this equipment has been associated with an equivalent dispossession of small fishing communities from their traditionally available fishing areas, and thus their livelihood. In some cases, these communities have been forced out of their coastal areas for tourist development. In other cases, as their traditional fishing areas were decimated by industrialized fishing, rendering their traditional livelihoods impossible, fisher people have become workers on industrial fleets. (Meanwhile, a global surge in fish farming, or “aquaculture” has occurred with its own ecological consequences. Aquaculture is estimate to provide 40% of human consumption of fish and shellfish.)
The documentary film “Darwin’s Nightmare” tells such a story of concurrent environmental damage combined with social injustice, where traditional fishing was supplanted by industrial modes of production.
Centered on Lake Victoria and communities along its shores in Tanzania, the film depicts how one species of fish (the Nile Perch, introduced in the 1950s) has outcompeted all others in the lake, creating a monoculture of fish. Although this fish could theoretically support local fishing livelihoods, demand for its consistent filet in Europe and the economic incentives associated has meant that instead, a few local entrepreneurs have dominated the lake, and export all the fish instead of it feeding local communities.
The film’s scenes of prostitutes whose customers are the pilots of the planes that carry the frozen fish away, and of children going hungry alongside the scraps of bones and heads (the only parts of the fish left for locals from the lake’s fishing industry), are dark—and a reminder of how the environmental impacts of food systems are nearly always tied to social and economic inequalities. 
 They are also tied to challenging contradictions: as some critics (Ponte, et al) of Darwin’s Nightmare have pointed out, the impact of the existing fishing industry on local populations is not all negative, and some locals appreciate the economic engine of the export-focused Perch industry.