Ecological Change in the Oceans and the Role of Fisheries

When I took a course with Elisabeth Mann Borgese in 1999, she reminded us that the oceans are constantly changing, both in their outer appearance, and their internal workings. Constant ecological change makes the ocean fascinating to observe and study, but challenging to understand and manage. Long-term changes are brought about by geological processes such as sediment transport, volcanism, and plate tectonics that affect the very shape of ocean basins and the extent of habitat features such as shallow shelf seas conducive to biological productivity. On intermediate time scales, climate-driven changes in ocean temperature, circulation, and chemistry can have profound ecological effects on the abundance and distribution of marine life forms, and even caused massive extinction events in the past. Over the last few thousand years, however, people have gradually become a dominant agent of change in the oceans. Initially tied to the continents where we evolved, human hunters at least 42,000 years ago started to venture out into the ocean to pursue large fish.1 Driven by changes in fishing technology, human population size, and global trade, this role has been extending to all ocean basins, and even parts of the deep sea. Over the last two decades, the profound ecological change brought about by human activities has also been studied in detail by the scientific community. Although human impacts on ocean ecosystems involve many pathways, there is little doubt that fishing— defined here as any extraction of marine animals and plants—is the activity that historically has had the most transformative ecological effects.2 Although it is not clear how much marine life has been removed over the entire history of fishing, recent total catches likely