Environment Fish are even more endangered than previously thought

Many fish stocks around the world are threatened by overfishing or have already collapsed. According to a study, this is not only due to the fact that scientifically calculated maximum catches have not been adhered to.

Rather, these recommendations are already set too high, researchers report in the journal "Science". The size of stocks and the dynamics of their recovery have so far been estimated far too optimistically.

Fisheries models provide the basis for regulating global and regional fisheries and are considered an important tool against overfishing. Until now, the main cause of this overfishing has been that fisheries policy has set catch levels higher than recommended on the basis of the models.

Significant overestimates

A team led by Graham Edgar from the University of Tasmania (Australia) has now examined data from 230 fishing grounds worldwide and compared the values with those from models. According to the results, the recommendations often significantly overestimated how many fish of a species are still around and how quickly a stock can recover. The deviation of the models used is particularly serious in the case of populations that are already overfished.

However, even stocks classified as recovered often continued to shrink in reality, according to the analysis. "As a result, catches were not reduced sufficiently, although this would have been urgently necessary," explained Rainer Froese from the Geomar Helmholtz Center for Ocean Research in Kiel, co-author of a commentary on the study published in the journal Science.

The problem is by no means limited to the past. "The known overestimates of stock sizes from recent years are not being used to correct the current stock sizes," says Froese.

Overfished instead of sustainably fished

According to the study, almost a third of the stocks classified by the Food and Agriculture Organization (FAO) as "maximally sustainably fished" are actually overfished. Fishing is considered sustainable if no more fish is taken than will grow back.

In addition, far more stocks than assumed have already collapsed, the report continues: 85 percent more populations than previously estimated have collapsed, i.e. shrunk to below 10 percent of their historical maximum.

Froese and his co-author Daniel Pauly from the University of British Columbia (Canada) explain in their commentary that the models use more than 40 parameters in some cases. These include characteristics of the species' way of life, catch details and the fishing effort required in each case. According to Froese and Pauly, this large number of variables makes the estimates unnecessarily complex. What's more, modelers rely on hardly any reliable values for some parameters.

Highly complex models

"Why the sometimes very unlikely predictions of the official models were and are accepted is the big question," says Froese. Fisheries science has been giving the wrong advice to politicians for years and therefore bears part of the responsibility for the overfished and collapsed stocks, including in Europe.

"Overfishing is a particular problem in the Mediterranean, West Africa and South Asia," explained Boris Worm from Dalhousie University (Canada), who was not involved in the study. Many coastal fisheries around the world have long since collapsed and are no longer even recorded. The current study is a warning "that a number of stocks that are still considered to be well managed - for example in Europe - could actually be worse off than expected".

Baltic Sea example: cod

Christian Möllmann from the University of Hamburg explained that this phenomenon has been demonstrated for cod in the western Baltic Sea, for example. "In my opinion, the often overly positive estimation of biomass has also contributed to overfishing of the stock."

Froese and Pauly conclude that the assessment procedures need to be revised - towards simpler, more realistic models. In addition, the precautionary principle should apply to a greater extent - conservative estimates should be used in cases of uncertainty.

Möllmann, on the other hand, does not consider the quality of the models to be decisive. "In my opinion, what is more important is the fishing industry's willingness not to pull every fish out of the sea." The will and understanding to fish prudently and cautiously is often not recognizable.

This can be clearly seen in the Baltic Sea, where all the once important cod and herring stocks have been so overfished, despite years of warnings from scientists and environmental protection associations, that recovery is largely uncertain or even unlikely.

SDA