Leipzig. Intensive fishing and over-exploitation have led to evolutionary changes in fish stocks such as cod, which has reduced their productivity and market value. These changes can be reversed through more sustainable and far-sighted fisheries management. The new study, conducted by researchers from the German Center for Integrative Biodiversity Research (iDiv), the University of Leipzig and the Institute for Marine Research in Tromsø, is published in nature sustainability, He explains that reversing evolutionary change will only slightly reduce hunting profits, but will help restore and maintain natural genetic diversity.
The impact of global fisheries on marine ecosystems is severe: declining fish stocks and accelerating degradation of marine habitats, as well as loss of biodiversity. Less pronounced intensive fishing has also affected the age and size structure of fish stocks and caused an evolutionary change, often towards lower growth rates, smaller maturity sizes and an earlier reproductive age. For example, North Sea cod, which has been heavily exploited in the past, matures to sizes of just over 50 cm, compared to the more than 70 cm expected in an incomplete set.
Early breeding can increase stock resilience in the short term, but over time lead to populations containing smaller fish with fewer offspring. “Ultimately, this can reduce the productivity of the stock and the value in the market,” says first author Hannah Schenk of iDiv and the University of Leipzig. “Aside from this, we don’t know much about potential consequences such as trophic succession and other ecosystem changes that feed off harvested species and may interfere with important ecological functions.”
Only long-term planning can reverse evolutionary decline
But evolution is not a one-way street. That is why researchers from iDiv, the University of Leipzig and the Institute for Marine Research in Tromsø (Norway) wanted to find out what it takes to reverse evolutionary decline after decades of intensive exploitation, particularly with regard to planning prospects in fisheries management. For this, they developed a model that took into account different processes: biological growth and reproduction as well as economic costs of harvesting and consumer preferences. The researchers also analyzed potential trade-offs between economic profit and conservation goals.
They find evolutionary decline useful for reversing under a century-long planning horizon. With the most typical short-term planning, stock recovery in terms of biomass is achieved, but evolutionary decline continues, albeit at much lower rates. “Fisheries are typically considered short planning horizons of a few years. This contrasts with long-term sustainability and biodiversity goals,” says Hannah Schenk. The researchers found that more farsighted planning horizons would help rebuild the stock but the evolutionary decline continues. According to Schenck, reversing this process takes much longer than restoring stock biomass and is only achieved through century-long planning horizons.
Appropriate preservation targets reduce profit only slightly
The researchers also showed that setting conservation goals to not only restore fish stocks, but also their genetic makeup would reduce profits slightly. The cost and time of evolutionary reversal could be further reduced if fisheries could select fish based on their genetics, which may be possible to some extent by choosing when and where to harvest. However, current conservation agendas do not include restoring genetic diversity, for example Goal 14 of the Sustainable Development Goals (SGDs), which calls for an end to poaching.
“More selective hunting could reverse evolutionary decline in the long term,” says senior author Professor Martin Coase from iDiv and the University of Leipzig. Economic incentives alone may not be sufficient to achieve these sustainability goals, which is why genetic diversity and conservation must be explicitly included in the Sustainable Development Goals and the UN Biodiversity Targets. “From an economist’s point of view, hunting should have largely avoided undesirable evolutionary changes. Now that those changes have occurred, it is costly to reverse them in the short term, but in the long term this will pay off economically.”
