Coral Reefs Part 3: Sustainable fishing and it’s importance

For the last instalment I wanted to focus on something that has taken place for years; is not in the news, blogs or hype among social media and to the general population is not that important. I don’t know why, probably because its old news, and no one likes to hear old news. The film Finding Nemo did raise the profile of the ocean and consequences of trapping fish for aquariums, but that has long calmed down. Fish and their importance in a reefs ecosystem as well as the entire ocean is one of the most important elements for any reefs and our survival. I am not simply referring to fish, but all marine life found within them. There are different aspects from over fishing, foreign invaders and in-balances caused by ourselves.

What makes a healthy reef ecosystem?

Whenever I have dived on a reef I have always had a high level of anticipation, hoping to see a wide variety of fish. Seeing videos on television as a child gave me high expectations. To my disappointment and dismay this hasn’t always fulfilled me. I have dived in Cuba, Barbados and Thailand and none but the last really amazed me, but still wasnt pristine. Why do I say this? Simply there were no fish. The Caribbean had dwindling numbers, largely related to the large bleaching event in 1998 decimating corals and the coral forests that were the home to thousands of fish. When added with over fishing stocks have plummeted. This was the same in Thailand, however instead of bleaching there were significant varieties of beautiful corals, but again due to over fishing only smaller trigger fish and grouper existed, with no sharks seen at all. This was an immediate alarm in my brain, seeing only small fish meant the reef system couldn’t maintain the balances within as all the large fish had were lost to the huge numbers of fishing boats just offshore.

Fishing for food

Fishing is an important industry for many ports, and I am certainly not advocating its practise full stop, however with limited fish stocks, it ultimately leads to less fish. Within a reef, when certain species are targeted, often the largest because they fetch the most money, causes in-balances. The example of sharks is a good one, because when removed its usually the first indicator that the reef is under threat, because it directly affects its health. Sharks maintain levels of fish, meaning certain species never dominate, while also removing diseased, injured fish, keeping the remaining fish stocks healthy. Most reach maturity after a certain age and if removed by fishing means they cant breed. Trigger fish are another important example as they predate on troublesome species such as sea urchins.  The urchins over graze coralline algae, which is important in binding the carbonate needed for reef building.  The trigger fish keep their levels low, however in Thailand, in near shore areas there was little or no coral cover. Instead there were high concentrations of sea urchins, most likely due to the lack of larger predatory fish.

The methods used are also damaging  with nets and dynamite having devastating effects. Nets are often lost or get caught on corals, causing damage and cause significant by catch. Larger animals, such as turtles, and other species that are not targeted end up trapped, drowning in the discarded nets. Dynamite, which obviously when used can cause complete destruction of the reef, killing fish and everything found on the reef, with the targeted fish collected after. There are drives towards using pole and line only, which I only buy if and when I buy fish, obviously a good thing, but with the recent controversy associated with John west, how much we can trust this I cannot say.


Dynamite Fishing destroying an entire reef

Fishing for tanks

Not only are fish extracted for food, but also for the aquarium industry. This is a more sinister and darker side from my point of view. Fish are caught either in nets, but more often than not using poison. Cyanide is scattered over the reef, paralysing fish and other marine animals. They are then collected and soon recover, however it can cause complications when transporting the fish, and often end up dead shortly after getting them into your tanks at home. The wider impact on the reef is more severe as it can cause local bleaching events as it prevents the corals from photosynthesising and can potentially cause the large areas to die.

Foreign species

Not only is extracting fish an issue, but adding them can also cause complications. A severe problem in the Caribbean is the aggressive and non native lionfish, a native predator from the pacific region. Due to the high number of poisonous spines, large grouper and sharks tend to avoid them, however there are instances where they hunt juvenile or injured lionfish. With numbers of sharks dwindling it only exaggerates the situation allowing this new predator to roam free. It devours huge swathes of smaller juveniles, leaving little for other species, and removing the next generation acting like a ´Terminator´.


Hungry invasive lionfish looking for its next meal


In Part 1 and 2 I discussed external impacts from sediment influx and climate change. There is another external impact from human developments not related to temperature or acidity, but the amount of nutrients reefs receive. Coral reefs survive because they are naturally low in nutrients compared to colder waters. Seaweed do not dominate around the equator, but corals do. Grazing fish species maintain these levels of algae in a reef area, keeping it clean, making sure it doesn’t ever dominate. Even with small levels of seaweed, it can begin to take control and with the overfishing of grazers, with time the corals become dominated by the algae.


Image from New York times. Top shows a reef with no fishing. Bottom shows where fishing takes place meaning there are less fish to remove algae. The corals can’t compete and don’t grow as well because the grazers don’t remove the algae

Not only does nutrient loading cause seaweed explosions, it can also have the same impact from certain species specifically the crown of thorns star fish. A natural predator of corals, its numbers have spiked over the past 50 years. This is the direct result of nitrogen and phosphorous run off from farmland. In normal circumstances natural predators would keep numbers stable, but with the extra nutrients from the land, it has caused this natural robot to slowly eat the reef alive.

The dilemmas we face to save coral reefs is a real one. Each of the different parts of these articles is precursor of the latter, it easily makes it more difficult. With development comes forest removal and increased run off from the land to the sea. This requires large transportation of materials, coal for instance, coupled with increased run off causes the sedimentation and the choking of reefs (part 1). These actions lead to climate change and ocean acidification (part 2) as a direct repercussion of burning fossil fuels. Finally reefs have dynamite thrown on them, fish removed and nutrients added which completely flips the ecosystem on its head. We attempt to remove invasive species such as the lionfish and crown of thorns starfish, but when joined together its a pretty dramatic and a very depressing picture. We need to control fishing and attempt to keep a natural balance species and sizes in a reef to try to reverse this ever worsening picture.

Coral Reefs Part 1

Coral Reefs Part 2

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I am a trained geologist who has a passion for conservation and working with wildlife. I write articles that interest me and that I am passionate about using skills and knowledge to highlight issues related to climate change. I don’t write articles for views, I write them to change views.

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  1. 21st December 2015

    […] sad state of affairs is tragic for many reasons. Coral reefs (Coral Reefs Part 3) provide homes and habitats for a huge proportion of the ocean’s fish and wildlife and are an […]

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