New theory on fish ecology, evolution and exploitation

DTU researcher launches a new theory to model fish stocks and fish communities and applies it to current problems in fisheries science.

In his new book “Fish Ecology, Evolution and Exploitation—A new theoretical synthesis”, Professor Ken H. Andersen synthesizes his work during more than a decade at DTU Aqua.

The book conveys a new theory for describing the demography of fish stocks, the structure of fish communities and the evolutionary ecology of fish. Throughout the book, the theory is applied to current challenges in fisheries science and management.

“We need a new theory because fisheries management faces several challenges. First of all, management struggles to implement the ecosystem approach laid down internationally in 2001, which mandates the current single-stock-oriented management to be extended towards managing the entire ecosystem. Furthermore, there is a strong need for models for managing data-poor stocks and the evolutionary impact of fisheries”, explains Ken H. Andersen, DTU Aqua.

Two fundamental assumptions

The new theory is based on two assumptions on the level of individual organisms. The first one is the organisms’ standard metabolic rate needed to sustain life, also known as Kleiber’s law. This rate scales to the weight of any organism to three quarters. The second assumption is that big fish eat small fish. Together, these two assumptions describe the mass flows in marine ecosystems.

“Traditionally fish stock are described by the abundance of fish of different ages. The new theory instead uses the body size of fish. Using size works much better because a fish’s size determines its physiology, it determines whether it is caught in the mesh of a fish gear, and it ultimately defines who eats who, as larger fish eat smaller fish”, says Ken H. Andersen.

The theory has demonstrated how fishing on small fish species influences the production of large species—and vice versa—and it has been used to calculate the rates of fisheries induced evolution, how much a fish stock can be fished, and how fast it can recover from overfishing.

Strong tradition of theoretical fisheries science

With the new theory, Ken H. Andersen carries on DTU Aqua’s strong rooting in theory and quantitative analysis.

“The new theory represents an important achievement of what makes DTU Aqua unique and known globally and Ken’s book demonstrates that DTU Aqua is still setting the direction of modern theoretical fisheries science”, says Institute Director Fritz Köster, DTU Aqua.

He illustrates this with two lines of work at DTU Aqua. One line goes back to the 1970ies when the pioneering North Sea Model was developed at the Institute. This model is the foundation of the multispecies assessment models, which DTU Aqua is known for today. The second line is the development of a solid statistical foundation for stock assessment models, which has put DTU Aqua on—what Fritz Köster describes as—the international forefront of designing and implementing stock assessment methods.

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