The effects of overfishing and climate change on marine life

By Naveesha Karunanayaka 

As the global population grows and the demand for food becomes ever higher, the strain on marine ecosystems increases. ‘Catching fish is not inherently bad for the ocean, except for when vessels catch fish faster than stocks can replenish, something called overfishing,’ remarks the WWF on the matter.1 While some fishing is done in an ethical and controlled manner, sometimes it is done illegally. 

Illegal fishing usually arises when fishermen experience a lack of fish in their local waters. This can lead to fishing in nationally protected areas, which in turn puts pressure on the surrounding ecosystem. Tragically, illegal fishing is still thought to account for around 30% or more of the catch for high value species. As described by the WWF, ‘Experts estimate illegal, unreported, and unregulated fishing nets criminals up to $36.4 billion each year.’1 The decline of smaller fish means less prey for their predators, potentially causing them to starve and resulting in a steep decline of marine life. Furthermore, when fishing for a certain species, other unwanted species can also be caught by accident.  Consequently, we are now seeing the regular and world-wide loss of ‘billions of fish, along with hundreds of thousands of sea turtles and cetaceans.’1

Climate-related factors are also causing damage to marine ecosystems. There is evidence, for example, that climate change is linked with the large-scale shifts in aquatic species to deeper and more northern waters.2 In combination with overfishing, this means that considerable ecological damage has already been done, eradicating a frightening number of high value fish from the ocean. Although the consequences of the damage vary, one recent study showed that dwindling shark numbers off the west coast of Australia has caused changes in the body shape of their prey, which ‘could have consequences for energy flow throughout the ecosystem, ultimately impacting the food web.’3 In the area with depleted shark populations, prey fish were observed to have smaller fin and eye sizes compared to the ones in regions with normal shark populations, indicating that the lack of predators led to fish developing usually unseen adaptations over time.3

It is crucial to replenish and maintain fish stocks in the ocean. Not only does this balance and rejuvenate marine ecosystems, but it also allows the ocean to become more effective as a carbon sink. Overall, carbon dioxide (CO2) moves between the atmosphere and the ocean via molecular diffusion, caused by the different partial pressures of COin the ocean and atmosphere. Once dissolved in the ocean, the CO2 then sinks to the underwater depths where it is stored. This is vital – over the past 200 years, ‘the oceans are thought to have been the only net sink of human CO2 emissions’2 by absorbing and storing the COthat would have otherwise contributed to further climate change. Notably, oceans can only store such large quantities of dissolved CO2because of the reaction between it and water (which produces non-gaseous products, carbonic acid, and bicarbonate and carbonate ions). This decreases the CO2 underwater and allows for more diffusion from the atmosphere.4 Unfortunately, however, CO2 uptake is also causing ocean acidification.

Further damage to the marine ecosystem cannot be allowed to happen, particularly given the current global situation of climate change. Worryingly, it is predicted that the ocean will only be able to act as such an effective carbon sink for around 50 more years. Afterwards, its storing capabilities will steadily become less effective, meaning that CO2 levels may start rising much more quickly than before.5 Researchers from the University of British Columbia, Canada, recently stated that supporting aquatic life would be key in tackling this issue. ‘Healthy fish stocks and marine ecosystems can help to mitigate global warming, which in turn protects the ocean and makes marine life more resilient, in a cyclic positive feedback loop.’2 Albeit, studies from the Scotian shelf and the Caribbean suggest that reversing such environmental damage is difficult. This is due to how, even after ending the exploitation of cod and returning normal sea temperatures, ‘the Scotian shelf system shows no signs of recovery…[and] the persistence of the new state is striking.’6

The extremely high demand for seafood leads to overfishing and disrupts the environment, which negatively impacts both marine ecosystems and the ocean’s climate. It is a vicious cycle – and one that is currently nigh-on impossible to break. It also has an impact on economies and coastal communities, as a decline in fish can leave people unemployed and (most frequently) without their only source of income. In this manner, many are pushed into poverty, consequently putting further strain on governments and the economy.

There are still steps that can be taken to decrease overfishing, of course, such as the creation and expansion of marine protected areas, or the implementation of fines for overfishing. Alas, this is hard to accomplish at a large scale and as fast as required, particularly with the difficulty of convincing fisheries to comply. Fishing authorities also lack the technology to track every boat on the ocean, only compounding the conundrum of overfishing.


  1. World Wildlife Fund (WWF). Overfishing [Internet]. n.d. [cited 2022 Oct 21] Available from:
  2. Sumaila U. R. and Tai T. C. End Overfishing and Increase the Resilience of the Ocean to Climate Change. Frontiers in Marine Science 2020;7(523):1-6. Avaliable from: doi: 10.3389/fmars.2020.00523
  3. University of Miami. Assessing the cascading ecosystem impacts of marine predator declines as a result of overfishing [Internet]. 2022 [cited 2022 Oct 21]. Available from:
  4. National Oceanic and Atmospheric Association. How the oceans absorb carbon dioxide is critical for predicting climate change [Internet]. National Ocean Service website2021 [cited 2022 Oct 19]. Available from:
  5. Rosane O. Oceans absorb almost 1/3 of global CO2 emissions, but at what cost? [Internet] World Economic forum; 2019 [cited 2022 Oct 21].Available from:
  6. Scheffer, M., Carpenter, S. & de Young, B. Cascading effects of overfishing marine systems. Trends in Ecology & Evolution; 2005 [Cited 2022 Oct 19];20(11):579-581. Avaliable from: doi:10.1016/j.tree.2005.08.018

@Karunanayaka, Naveesha  [HA1] [HA1]

Hi Naveesha,

Please find the edited version of your article below. Overall, the text definitely felt pressing and relevant to the topics explored in it, and I liked how you emphasised your points with numerical figures. Similarly, I found the sections where you referred to recent studies very interesting. That said, there are some details that I think could be improved for the future.

Besides a few grammar issues in the text, a number of sentences felt somewhat awkward and/or redundant to read (e.g., ‘When laws are broken and seafood is fished from areas that are in danger…’). A few others also didn’t feel totally complete, particularly when they were quoting other articles. In these cases, you should always make it clear to the reader who you are quoting – and not only through a citation. (Also, please note that superscript citations always go after punctuation.)

Finally, if everything’s alright with you, you can accept the changes by selecting the text and right-clicking. I will then send the article off to be published next week on Friday. Till then, let me know if you have any questions about IBR or otherwise, and have a good weekend 🙂

Kind regards,


Hi, thank you for your edits and comments. I will accept them now.  [KN2] [KN2]

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