At first thought most of us tend to think of the oceans really only getting massively depleted of fish with the dawn of industrial fishing in the latter half of the last century. But as Fred Pearce points out in a new article for New Scientist, that's not the case—humans have had a major impact on the world's fisheries going back at least 1000 years:Overfishing a Problem Long Before Modern Technology
Pearce quotes Poul Holm, an environmental historian at Trinity College Dublin:
We are discovering that human pressure on marine life was much earlier, much larger and much more significant than previously though. We know that there was major commercial exploitation of fisheries, doing huge damage to fish populations, back in medieval times and even before. The idea that it is only modern fishing technology that has done damage turns out to be completely wrong.
Backing up all this is work presented at the Ocean Past II conference, just concluded in Vancouver, British Columbia: The gist of which says even before industrial fishing techniques made the situation even worse, humans were already doing a job on fish.
1000 years ago in Europe freshwater fish were already in decline, which led people in the region to take up marine fishing. Five hundred years later, with coastal fish stocks disappearing around Italy, deep-sea trawling began. The early 1800s saw the collapse of the European herring fishery, which in turn led to an increase in the jellyfish population, seriously altering the food web.
Overfishing Impact Seen in Decline in Fish Size
That's the abstract, but in very concrete terms other work presented at the same conference (via Science Daily lays out the effect of overfishing and poor fisheries management in modern times on the average size of fish caught.
Loren McClenachan of the Scripps Institute of Oceanography presented research that shows from 1956 to 2007 the average fish size of fish caught in the water off Key West, Florida to have shrank from an estimated 20 kg at the start of the period to 2.3 kg at the end of the period.
More: Science Daily, New Scientist
Overfishing Means Marine Animals Are Starving: Report
Oceans in the Old Days Had Way Bigger and More Fish Than We Thought
Atlantic Bluefin Tuna Will Be Gone in 3 Years at Current Fishing Rates