How anglers benefit from cod reverse evolution

Intensive fishing and overexploitation have led to evolutionary changes in fish stocks such as cod, reducing both their productivity and market value. These changes can be reversed by more sustainable and forward-thinking fisheries management.

The new study by researchers from the German Center for Integrative Biodiversity Research (iDiv), the University of Leipzig and the Institute for Marine Research in Tromsø, which was published in Nature Sustainabilityshows that reversing the evolutionary change would only slightly reduce fishing profit but help restore and maintain natural genetic diversity.

The impact of global fishing on marine ecosystems is severe: fish stocks have declined and marine habitat degradation and biodiversity loss have accelerated.

Less visible, intensive fishing has also affected the age and size structure of fish stocks and caused evolutionary changes, often towards lower growth rates, smaller mature sizes and earlier reproductive ages. For example, North Sea cod, which has been heavily exploited in the past, matures at sizes just over 50 cm, compared to more than 70 cm expected in an unfished population.

Early reproduction can increase the resilience of stocks in the short term, but over time it leads to populations with smaller fish that have fewer offspring. “At the end of the day, this can reduce both a stock’s productivity and market value,” says first author Hanna Schenk from iDiv and the University of Leipzig. “Furthermore, we don’t know much about potential consequences such as trophic cascades and other ecosystem changes that feed back on harvested species and may interfere with critical ecological functions.”

Only long-term planning can reverse evolutionary decline

But evolution is not a one-way street. That’s why researchers from iDiv, the University of Leipzig and the Institute of Marine Research in Tromsø, Norway, set out to find out what it takes to reverse evolutionary decline after decades of intensive exploitation, particularly in horizon planning. in fisheries management.

For this, they developed a model that took into account several processes: biological growth and reproduction as well as economic harvesting costs and consumer preferences. The researchers also analyzed potential trade-offs between economic profit and conservation goals.

They found that evolutionary decline is profitable to reverse under one-century planning horizons. With a more typical short-term design, stock recovery in terms of biomass is achieved, but evolutionary decline continues, albeit at much slower rates.

“Fisheries usually look at short planning horizons of a few years. This conflicts with long-term sustainability and biodiversity goals,” says Hanna Schenk. The researchers found that more forward-looking planning horizons would help rebuild the stock, but the evolutionary decline continues. According to Schenk, reversing this process takes much longer than biomass recovery and is only achievable with century-long planning horizons.

Appropriate conservation goals only slightly reduce profit

The researchers also show that setting conservation goals to restore not only fish stocks, but also their genetic makeup would only slightly reduce profits. The cost and time of evolutionary reversal could be further reduced if fisheries can select fish according to their genes, which may be possible to some extent by choosing when and where to harvest.

However, current conservation agendas do not include the restoration of genetic diversity, for example target 14 of the Sustainable Development Goals (SGDs), which calls for an end to overfishing.

“More selective fishing could reverse the evolutionary decline in the long term,” says senior author Professor Martin Quaas from iDiv and the University of Leipzig. Economic incentives alone may not be sufficient to achieve these sustainability goals, so genetic diversity and conservation must be explicitly included in the UN’s Sustainable Development Goals and Biodiversity Goals.

“From an economist’s point of view, fisheries should have largely avoided unwanted evolutionary changes. Now that these changes have taken place, it is costly to reverse them in the short term, but in the long term, it will pay off in economic terms.”