Overfishing – simple word with complicated content

Whenever we are invited to give talks on fish, the topic of overfishing comes up in the discussion. Today, global overfishing is considered one of the biggest threats to the health of the oceans and the economic livelihood of fishermen.

The figures of the Food and Agriculture Organisation of the United Nations (FAO) are often used to support statements on overfishing. In its latest advice, the FAO says that around 64.6 % of the world's fish stocks are within sustainable biological limits, with 57.4 % maximally sustainbly fished and 7.2 % under-exploited. The remaining 35.4 % are considered overfished. Surprisingly, these figures are often interpreted differently in the public debate: The 57.4 % of maximally sustainably fishedstocks are lumped together with the overfished ones and this group is then described as "exploited to the limit or overfished". This quickly leads to the impression that the vast majority of our fish stocks are in the greatest danger, even though "fully exploited" denotes the internationally agreed sustainable management goal of maximum sustainable yield.  

Things become even more confusing because not only the FAO issues status assessments for fish stocks, but also the EU Commission and national authorities. However, neither the data basis nor the threshold values for overfishing have been harmonised globally, and there are fundamentally different theoretical approaches to their definition. This is where clarity is finally needed in the discussion!

When fishing leads to more fish being taken from a stock than are replaced by reproduction and immigration in the following years, fisheries biologists refer to recruitment overfishing. The ultimate consequence of recruitment overfishing would be the extinction of a fish stock. But this has so far never happened in marine fisheries, because at low stock sizes, targeted fishing is no longer profitable and is discontinued. But even above the extinction threshold, there are serious consequences for the stock, the ecosystem and the fishermen and their families who depend on the income.

According to EU rules, however, stocks are already considered overfished if they are not managed according to the principle of maximum sustainable yield. We call this form of overfishing growth overfishing: beyond this limit, yields per fishing hour cannot be increased or even decrease again, but not necessarily so much is caught that serious biological consequences occur. Less than one third  of the fish stocks in the European North Atlantic suffer from this, but  38% are currently recruitment overfished (or outside safe biological limits), as stocks recover only slowly after decades of intensive overfishing.

A closer look reveals that overfishing is always bad from an economic point of view, but not every form of overfishing leads to an ecological disaster in the oceans. Sustainable fishing and protection of the oceans are compatible through good, scientifically sound management concepts and are absolutely necessary to tackle the global challenge of food security. Unnecessary scaremongering about overfishing is of no use and makes people insensitive to the long-term threats to the oceans, such as the destruction of habitats (also through fishing), climate change including ocean acidification or the increasing littering of the seas.