Marty Harris is an assistant digital editor at the Lowy Institute.

Measuring the impact of over-fishing is difficult: conducting global stock assessments is both complex and expensive, while seasonal and long-term changes in currents and water temperatures effect feeding and spawning habits, complicating results.

For example, are declining cod stocks in the Greenland Sea the result of over-fishing or climate change?

A new study published in the Marine Pollution Bulletin estimates the state of the world's fisheries based on a number of indirect measurements, such as catch estimates, fishing days per fish, and the decline of predator biomass. The 'catch only' assessment, based on Food and Agriculture Organization figures, is pretty scary:

 

...several deeper analyses of the status of the majority of world fisheries confirm the previous dismal picture: serious depletions are the norm world-wide, management quality is poor, catch per effort is still declining. The performance of stock assessment itself may stand challenged by random environmental shifts and by the need to accommodate ecosystem-level effects.

The global picture for further fisheries species extinctions, the degradation of ecosystem food webs and seafood security is indeed alarming. Moreover, marine ecosystems and their embedded fisheries are challenged in parallel by climate change, acidification, metabolic disruptors and other pollutants. Attempts to remedy the situation need to be urgent, focused, innovative and global.

(H/t Kevin Drum.)