Manipulation of fishing patterns threatens global fisheries

Fish stock assessment is the foundation of effective fisheries management. Nevertheless, estimating fish populations in the oceans is extremely challenging due to dynamic fluctuations in their abundance. These fluctuations are the result of a number of factors, such as food availability, climate change, predator pressure and pollution. A recent study, published in the journal Science, suggests that models used to manage fisheries may overestimate the amount of fish available for sustainable harvest. This situation threatens marine ecosystems leading to their degradation.

Computer models as a tool for fisheries management

Computer models play a key role in marine resource management. They help scientists and policymakers predict changes in fish populations and set catch limits to protect these resources. These models are developed based on a wide range of data, including population dynamics, mortality, reproduction rates, fish migrations and the impact of human activities, including fishing intensity.

In theory, computer models allow for sustainable management of marine resources, minimizing the risk of overfishing and loss of biodiversity. The reality, however, is more complicated, and the models, while technologically and analytically advanced, do not reflect the full complexity of marine ecosystems after all.

Assumptions for modeling

One of the main challenges of using computer simulations in fisheries management is their susceptibility to error due to incomplete or inadequate input data. In other words, what data we input into the model – these are the results we get. Models are often based on simplistic assumptions that do not take into account the dynamic and complex interactions in marine ecosystems. An example is climate change, which is playing an increasingly important role in shaping ocean environments, and whose impact on fish populations is not sufficiently taken into account in the analyses made.

Changing water temperatures that affect species distribution, ocean acidification that hinders shellfish growth, and changes in ocean currents that affect food availability are just some of the factors that can cause actual fish population dynamics to deviate from model predictions. Underestimating these factors in models leads to erroneous decisions that result in overfishing.

Accuracy of estimates

The study, conducted by a team of scientists, aimed to analyze the accuracy of fish biomass estimates at the time of assessment and identify potential biases in those estimates. The researchers analyzed data on 230 fisheries, comparing historical biomass estimates (over an average of 47 years) with later retrospective projections for the same year derived from more recent stock assessment models. In this way, they were able to assess whether the initial estimates were accurate or whether there was a tendency to overestimate stock status.

Overestimation of catches – the norm, not the exception

The results of the study showed that historical biomass estimates were generally inflated compared to current assessments. This means that stock assessment models that were used in the past often gave overly optimistic predictions of the state of the ichthyofauna, which could lead to overly liberal setting of fishing quotas.

This overestimation was particularly evident in the assessment of resources in the last year before the report was published. The analysis showed that 66 percent of the of assessments overestimated the value of biomass compared to later retrospective estimates. Moreover, for 17 percent of the assessments the estimates were more than 1.5 times higher than the values obtained in later analyses, and in 8.5 percent. cases they were twice as high.

Consequences of overestimating catches

Overestimating the amount of fish available to be caught, is a serious problem that can lead to a drastic reduction in the abundance of certain species. The impact is particularly severe for those with long life cycles and slow reproductive rates.

In their study, the researchers showed that 29 percent of of fish stocks that the FAO considers to be sustainably exploited are in fact overfished. In addition, they calculated that 85 percent. of these stocks are likely to collapse, meaning their populations could fall below 10 percent. of their original abundance. Such low abundance makes it much more difficult for populations to regenerate and recover.

Need to revise modeling approach

In the face of these challenges, it is necessary to revise and improve the models used in fisheries management. Researchers suggest that future models should better account for environmental variability, including the effects of climate change on marine ecosystems. An important step is also to improve the accuracy of input data, for example by better monitoring fish populations and their environments, and developing data collection methods that will enable more accurate forecasts. Only through a holistic approach to fisheries management that takes into account both the complexity of marine ecosystems and the impact of human activities can we ensure that our oceans remain full of resources.