- Underestimated Vulnerability: Fish Populations Facing Greater Peril Than Previously Anticipated
Various fish populations globally are under danger or have already reached their breaking point due to overfishing. As per a research published in "Science" journal, this isn't solely due to not adhering to the scientifically calculated maximum catch limits. Rather, these limits themselves have been set too high, and the size of populations and their recovery rate were earlier estimated to be much more optimistic than the actual scenario.
Fishing policies and models serve as the foundation for regulating global and regional fisheries. The primary cause behind overfishing was believed to be fishing policies setting catch limits above the recommended model levels.
Excessive Estimations
A research team led by Graham Edgar from the University of Tasmania (Australia) examined data from 230 fish stocks worldwide and made comparisons with model figures. They discovered that in numerous instances, the number of fish in a species and the rate of stock recovery were markedly overestimated, especially for overfished populations.
Even stocks categorized as recovered continued to dwindle in reality, resulting in insufficient reductions in catch limits when they should have experienced drastic reductions, as explained by Rainer Froese from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, a co-author of a commentary on the study published in "Science".
The issue is not limited to the past. "The overestimations of stock sizes from recent years are not being used to correct current stock sizes," said Froese.
Overfished instead of Sustainably Fished
According to the study, approximately one-third of the stocks categorized by the Food and Agriculture Organization (FAO) as "maximally sustainably fished" are actually overfished. For a fish population to be considered sustainable, not more fish should be caught than can replenish the population.
Additionally, many more populations than previously thought have collapsed: 85% more populations than originally estimated have collapsed, shrinking to less than 10% 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 rely on more than 40 parameters, including species' life history characteristics, fishing details, and the necessary fishing effort. This multitude of variables makes the estimates excessively complex, they argue. Moreover, modelers occasionally relied on poorly supported values for certain parameters.
Complex Models
"Why the sometimes implausible predictions of official models were and are accepted is the big question," said Froese. The fisheries science community has been providing misguiding advice to the politics for years and thus shares some responsibility for the overfished and collapsed stocks, even in Europe.
"Overfishing is a significant issue in the Mediterranean, West Africa, and Southeast Asia," explained Boris Worm from Dalhousie University (Canada), who was not involved in the study. Many coastal fisheries worldwide have already collapsed and are not even documented. The current study acts as a warning that "many stocks that are still considered well-managed – for example, even in Europe – might be in a worse state than assumed."
Baltic Sea Example: Cod
The phenomenon, such as the cod in the western Baltic Sea, has been proven for this species, explained Christian Möllmann of the University of Hamburg. "The overly optimistic biomass estimates, in my opinion, have also contributed to the overfishing of the stock."
A review of the assessment methods is necessary - towards simpler, more realistic models, conclude Froese and Pauly. Furthermore, the precautionary principle should be implemented more strongly - conservative estimates should be used in uncertain situations.
However, according to Möllmann, the quality of the models is not the primary concern. "In my opinion, the will of the fishing industry to not deplete every fish in the sea is more important." The will and comprehension to fish responsibly and conservatively is often lacking.
This is evident in the Baltic Sea, where all once-important cod and herring stocks, despite years of warnings from scientists and environmental organizations, have been overfished to such an extent that recovery is uncertain or even improbable.
Other fishing policies and models, besides the ones regulating global and regional fisheries, also play a role in some local contexts. Incorrect assumptions about fish populations and their recovery rates, often due to overly complex models, can lead to 'Other' misestimations in these local fisheries as well.
Despite the need for simpler, more realistic models, as suggested by Froese and Pauly, the primary issue often lies in the 'Other' lacking will and comprehension to fish responsibly and conservatively, as highlighted by Christian Möllmann.
