1. Evolution
2. Human behaviour
3. Climate change

Last September, a research article in the journal Science reported a study of body-size trends in plants and animals since 1960 using data from BioTIME. This global open-access biodiversity time-series database includes 361 studies from 374 contributors.

BioTIME data comes from terrestrial, freshwater and marine environments with a time range dating from before the Industrial Revolution to the present day. Most of the studies focus on areas of the planet undergoing rapid environmental change of which the oceans and freshwater environments of the world are two.

The article assessed body size changes in six species from 1960 to 2020. Within those species, the research looked at compositional changes and trends. The data showed that reduced body size within the general fish population was increasing in abundance.

Dino Grandoni of the Washington Post, who writes a column called Animalia, published an article describing what is happening to fish species around the world on May 4, 2024, entitled “Fish are shrinking around the world. Here’s why scientists are worried.”  He writes “Fish are shrinking and no one can agree why.”

He describes research from the University of Massachusetts, Australia’s University of Tasmania and Deakin University, the University of British Columbia, and the U.K.’s University of York that confirm that smaller fish sizes have become widespread.

How does evolution play a role in fish size? 

Fish evolve smaller adult body sizes because environmental pressures cause genetic traits to smallness emerge as dominant in the species gene pool. What environmental stresses are we talking about? Competition for less food is another. Predation is a second. A third is water temperature.

To compete for resources, smaller fish can be more successful in reaching their reproductive phase because they need less food, they can avoid being eaten by humans and other predators, and they can better adapt to warmer temperatures. Asta Audzijonyte at the University of Tasmania notes that the shrinking fish phenomenon is changing ecosystems because size is an environmental determiner.

How has human behaviour impacted adult fish size?

The polluting of fresh and saltwater sources has impacted fish enormously. The unknown future impacts of microplastics in the water on fish populations will play out in the next few decades. But, one surefire impact on fish is human overfishing. It is affecting the size of fish in the wild.

Fisheries harvest 200 million tons of fish annually with a decreasing amount coming from the wild. Aquaculture, the factory farming of fish, is from where the majority of the fish we eat today comes. Harvesting of wild fish is selective with only the larger ones caught. That in itself is leaving smaller fish behind. They are the survivors who spawn and pass along their genetic characteristics to offspring. Hence wild fish species are getting smaller.

Aquaculture is about turning fish into the water equivalent of chickens. It also, however, is about producing engineered superfish that grow faster and bigger. These DNA-enhanced species have yet to escape to interbreed with wild populations. So as of yet, their presence is not yet altering wild fish shrinkage trends.

What is climate change’s role in making fish smaller?

The atmosphere and oceans, rivers and lakes of the world are warming. This is the third likely cause to explain fish getting smaller. The reasoning goes as follows: Fish are cold-blooded meaning they do not regulate their body temperatures. The environment around them does. When water temperatures rise, a theory states that fish have an oxygen-absorption limit established by the area of their gill membranes. This gill oxygen limit theory could explain why the demand for oxygen in warming conditions doesn’t favour large fish. Whether the oxygen limit theory is right or not, scientists have observed consistently smaller fish in warmer waters when compared to those in colder environments.

Is there a positive to shrinking fish size?

University of York researcher, Inês Martins has observed that almost 75% of marine fish are getting smaller. She notes that there is a win to shrinking with many species increasing in numbers as average body size declines. Then there is the challenge for anglers who have to change their nets because where smaller fish predominate, they now can escape through the holes that are too big for humans to catch them.

Recently I came across “The Meaning of the 21st Century,”  in which he outlines 16 challenges that humanity faces in 21st century. I’ve added comments of my own in Italics.

1. GLOBAL WARMING Global warming will lead to severe climate change. Unless stopped, it will upset the basic control mechanisms of planet Earth.
2. EXCESSIVE POPULATION GROWTH World population may grow to 8.9 billion people, with a growing demand for consumer goods and carbon-based energy, far exceeding what the planet can handle. Forecasts of population growth indicate human population will start to peak around mid-century, level out and then slowly decline. Peak variable projections indicate a population as little as 9 billion or as high as 12 billion.
3. WATER SHORTAGES Rivers and aquifers are drying up. Many farmers will not have the water essential for food growing. There will be wars over water. Freshwater is one of the most challenging issues we face.
4. DESTRUCTION OF LIFE IN THE OCEANS Only 10% of edible fish remain in the oceans, and this percentage is rapidly declining. Aquaculture is only a partial solution to the problem of the collapse of fish stocks. Climate change influencers like CO2 are acidifying the ocean changing impacting krill, coral and shellfish, principal food sources for most marine life.
5. MASS FAMINE IN ILL-ORGANIZED COUNTRIES Farm productivity is declining. Grain will rise in cost. This will harm the poorest countries. Agricultural production in the Developing World needs to reach the same yield levels as in the factory farms of the Developed World replacing subsistence agriculture.
6. THE SPREAD OF DESERTS Soil is being eroded. Deserts are spreading in areas that used to have good soil and grassland. Grazing and improper land use including deforestation continue to impact soils in the Developing World contributing to desertification.
7. PANDEMICS AIDS is continuing to spread. Infectious pandemics could spread at unstoppable rates, as they have in the past, but now with the capability to kill enormous numbers of people. Although pandemics will always put humans at risk we have the means today to contain outbreaks and develop rapid response to them when they occur.
8. EXTREME POVERTY 2 to 3 billion people live in conditions of extreme poverty, with lack of sanitation. The difference between rich and poor is becoming ever more extreme. This is even a problem in the Developed World as indicated by the recent Wall Street protest movement and Arab Spring.
9. GROWTH OF SHANTYCITIES Shantytowns (shantycities) with extreme violence and poverty are growing in many parts of the world. Youth there have no hope. We need a global commitment to addressing informal urban environments and the poverty and despair associated with these areas.
10. UNSTOPPABLE GLOBAL MIGRATIONS Large numbers of people are leaving the poorest countries and shantycities, wanting to find a life in countries with opportunity. Migration from rural to urban is happening today at the rate of 80,000 per day. Migration from the Developing World to the Developed is increasingly more difficult although illegal immigration continues at a steady if not increasing pace.
11. NON-STATE ACTORS WITH EXTREME WEAPONS Nuclear or biological weapons are becoming easier to build by terrorist organizations, political groups or individuals, who are not acting for a given state. The evidence of this development frames the beginning of the 21st century and may be with us for a long time to come.
12. VIOLENT RELIGIOUS EXTREMISM Religious extremism and jihad may become widespread, leading to large numbers of suicide terrorists, and religious war between Muslims and Christians. This is nothing new. Religion, nationalism, and tribalism have been a part of the human condition and will continue. The real challenge will be to overcome our baser nature.
13. RUNAWAY COMPUTER INTELLIGENCE Computers will acquire the capability to increase their own intelligence until a chain reaction happens of machines becoming more intelligent at electronic speed. Artificial intelligence and humanity will experience convergence throughout the century. The question will become can we distinguish one from the other?
14. WAR THAT COULD END CIVILIZATION A global war like World War I or II, conducted with today’s vast number of nuclear weapons and new biological weapons, could end civilization. War in the 21st century will be fought in entirely new ways. Cyberattacks, militarization of space and new weapon technology (robotics, lasers) will change war just as the first atomic bomb altered the rules of warfare in the 20th century leading to the disappearance of global conflicts only to be replaced by regional wars.
15. RISKS TO HOMO SAPIEN’S EXISTENCE We are heading in the direction of scientific experiments (described by Lord Martin Rees) that have a low probability of wiping out Homo sapiens. The combination of risks gives a relatively high probability of not surviving the century. Humanity will survive the century. This is just too pessimistic.
16. A NEW DARK AGE A global cocktail of intolerable poverty and outrageous wealth, starvation, mass terrorism with nuclear/biological weapons, world war, deliberate pandemics and religious insanity, might plunge humanity into a worldwide pattern of unending hatred and violence – a new Dark Age. We are just as likely to emerge at the end of the 21st century with entirely new purpose as we look outward bound beyond our planet while using technology to restore much of what the Industrial Age has wrought.

In my blog I don’t just point out the problems but show how our human inventiveness is finding solutions. Nonetheless, James Martin has pointed out challenges we must face and overcome for humanity and the other travellers on our planet.