Fish evolution takes place in decades - not millions of years

Codfish have been telling a story of rapid fish evolution, reshaped by human activity more swiftly than previously assumed, reveals a cutting-edge study led by Rutgers University.

This evolutionary tale, illuminated during the latter half of the twentieth century, signifies the impact of human-driven overfishing. The findings suggest that evolutionary changes, once thought to span millions of years, can be catalyzed within mere decades. 

The report, sharing the first genomic evidence of such accelerated evolution in Atlantic cod, has recently been published in the journal Philosophical Transactions of the Royal Society B: Biological Sciences.

Breaking new ground with modern technology

“We broke new ground,” explained study senior author Malin Pinsky. Leveraging modern technology, the researchers unearthed the genetic code of codfish caught over a century ago, unveiling subtle genetic shifts. 

Pinsky, an associate professor in the Department of Ecology, Evolution and Natural Resources at Rutgers School of Environmental and Biological Sciences (SEBS), emphasizes that these new techniques played a pivotal role in the discovery.

By the turn of the 20th century, many overfished cod seemed to have cultivated a survival edge. They matured at a younger age, and their smaller size made them less noticeable to fishing efforts, thus increasing their chances of reproducing before capture. The researchers, in their quest to understand this apparent new fish evolution, searched for key gene mutations, but this proved fruitless.

Small setback spawned a new approach

Undaunted by initial setbacks, the team adopted a different approach. They theorized that if changes were spread across a multitude of genes, rather than confined to a select few, their analysis might yield different results. Driven by this hypothesis, and empowered by novel technology, the team discovered the intricate genetic dance of the codfish.

“We have now been able to demonstrate that many genes throughout the genome did shift in the same way in cod from both sides of the Atlantic Ocean over the past 100 years,” said study first author Brendan Reid.

This indicates that, rather than an isolated genetic aberration, small changes in many of the cod genes triggered the fish evolution. Reid, a postdoctoral associate at SEBS, considers this finding a first of its kind for any overfished species.

Renowned for their mild flavor and flaky flesh, Atlantic cod inhabit the deep-sea regions of the North Atlantic. They have been a staple ingredient in traditional dishes like fish and chips, and their livers are used to produce vitamin-rich cod liver oil. However, during the 1990s, decades of unrelenting overfishing pushed their population down to just 1% of historical levels.

A new hope in the fight against overfishing

Commercial fishing practices underwent a radical transformation in the 1970s, with powerful trawlers equipped with sophisticated radar and sonar systems. These technologies expanded fishing reach, both in terms of depth and duration. 

Unfortunately, this resulted in accelerated depletion of cod stocks, culminating in the fishery’s collapse and, as the Rutgers research suggests, the cod’s swift evolution.

This research brings not just fascinating insights into fish evolution, but also glimmers of hope for the beleaguered codfish. Their population, which has been slowly recovering since fishing pressure lessened, could potentially regain its former glory.

“Since evolution in response to fishing happened through lots of small changes in many genes rather than large changes in one or two genes, and cod have maintained most of their genetic diversity, it will be easier for cod to evolve back towards their previous pattern of slower growth at large sizes,” said Reid.

The scientist also notes encouraging signs in the cod population, suggesting the possibility of a return to previous growth patterns and, with proper management, the restoration of a sustainable fishery.

This research, a testament to international collaboration, also included contributions from Bastiaan Star of the University of Oslo in Norway.

More about overfishing

Overfishing, or the practice of depleting a fish population to below its natural ability to reproduce and replenish, has far-reaching implications for both the environment and humanity. Its impacts are numerous and interconnected, affecting ecosystems, economies, and global food security.

Ecosystem Disruption

Overfishing is one of the primary threats to ocean biodiversity. The removal of a significant number of a particular fish species can unbalance the marine ecosystem and fish evolution.

Predatory fish like sharks, tuna, and cod, which are often targeted by commercial fishing, play crucial roles in maintaining the balance of marine life. Their decline can trigger a cascading effect through the food chain, allowing other species to become overly abundant and destabilizing the marine ecosystem. 

For instance, the decline in large predator fish can lead to an overabundance of smaller fish or invertebrates, which can then over-consume vegetation and other smaller organisms, disrupting the balance of the ecosystem.

Loss of Livelihood

Overfishing not only affects the health of our oceans but also the livelihood of millions of people. According to the United Nations, over 3 billion people depend on marine and coastal biodiversity for their livelihoods. 

When fish stocks collapse, the fishing industry – including all those involved in the supply chain, such as boat operators, processors, sellers, and other associated jobs – can be severely impacted. In many developing countries, where alternatives for income are limited, the effects can be particularly devastating.

Threat to Food Security

Fish is a crucial source of protein and nutrition for billions of people around the world. Overfishing threatens this vital food source, particularly in poorer countries where people are more dependent on fish for dietary needs. 

As per the Food and Agriculture Organization, fish provide more than 20 percent of animal protein for about 3.2 billion people. Depleting fish stocks can thus pose a serious risk to global food security.

Harm to Coral Reefs

Overfishing can also harm coral reefs, which are critical habitats for many fish species. Certain types of fishing, such as blast or cyanide fishing, directly destroy coral habitats. Also, the removal of herbivorous fish can lead to the unchecked growth of algae, which can smother coral reefs and disrupt the ecosystem’s balance.

Economic Implications

Overfishing can have significant economic repercussions. The World Bank estimates that the mismanagement of fisheries results in an annual loss of $83 billion globally. Ensuring sustainable fishing practices can thus lead to economic benefits as well as ecological ones.

In summary, overfishing is a pressing global issue that extends beyond just the depletion of fish stocks. It has wide-reaching impacts on the marine ecosystem, global economies, and human livelihoods and food security. 

Addressing overfishing requires coordinated global efforts to implement sustainable fishing practices, enforce regulatory measures, and raise awareness about the importance of preserving marine biodiversity. Hopefully, this new discovery about rapid fish evolution will lead to further scientific breakthroughs.

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