Tides of Trouble: Fish Populations face Challenges in Numerous Basins

As many as three thousand fish species make the Amazon basin their home, swimming through one thousand, one hundred tributaries of the great river, some of them like the Pirarucu having a length of sixteen feet, and others like the piramutaba catfish thought to migrate a distance of about two thousand and fifty miles, many of the fish species acting as an important dispersal of tree seeds.

As many as 1,045 fish species make the Gulf Of Guinea Oceanic Islands in Africa their home, surviving at the crossroad of three major ocean currents, moving through a territory covering 13 countries, making an area about 1,000 kilometers their habitat, a total of 268 coastal fish species recorded in the region, with about 12 percent endemic.

As many as 900 fish species make the Mediterranean Sea their abode, 519 of them native species, 74 species unique to this part of the world, 127 species aliens, the habitat home to seven percent of the world's marine habitat.

These geographic areas contain a combined total of over five thousand fish species, but despite the diverse locations, the population of fish species suffer from one common challenge - it appears to be declining.

In the Amazon, the population of fish species declined by 87.7 percent between 2003 and 2019, more than 70 percent of the species affected, regardless of migratory behavior, with the popular Pirarucu suffering a decline in population of 76 percent in 81 fishing communities, the same situation facing the black prochilodus, the number in catches down in a fishing community by some 40 percent in the 1980s to 20 percent today,

In the Gulf of Guinea, small fish landings showed a 59 percent decline in Ghana between 1993 and 2019, the sardinella aurita suffering a catch decline from 119,000 tonnes in 1992 to 11,834 tonnes in 2019, while a 40 percent decline in coastal catches took place in Ivory Coast between 2003 and 2022, with fish species like sardines and anchovies showing a significant drop in number in other parts of the Gulf.

In the Mediterranean Sea, fish population over the past 50 years showed more than a 33 percent decline, with almost half the species of sharks and rays threatened, with 58 percent of species overfished, and more than 40 native species faced with extinction in the next few years.

The situation with fish species in the Gulf of Guinea, Amazon basin, and the Mediterranean Sea mirrors a general problem whereby fish species in most water bodies face extinction, with the mega-fish population having declined by 94 percent since 1970, migratory freshwater species seeing a 76 percent decline.

However, a study found that fish species absorb carbon through feces, respiration and other excretions from fishes - roughly 1.65 billion tonnes annually - making up about 16 percent of the total carbon that sinks below the ocean's upper layers.

Another study found that a single great whale can absorb an average of 33 tonnes of carbon dioxide through the years, storing it until it dies, sinking to the ocean floor where the carbon remains locked away for centuries.

Another study found that fishing activities remove significant amounts of blue carbon from the ocean, releasing it into the atmosphere, while fishing fleets emit millions of tonnes of CO2 each year from burning fuel, the EU alone emitting 7.3 million tonnes per year.

These studies therefore show that since fish species absorb carbon, their decline in the population impacts on the amount of carbon absorbed in the Amazon basin, Gulf of Guinea, the Mediterranean Sea and other places.

The Amazon ecosystem absorbs about two billion tonnes of carbon dioxide per year, which represents roughly five percent of the world's total carbon emissions, but with many of the habitat's 3,000 fish species and forests declining, the ecosystem will be unable to match its carbon dioxide absorbing capacity.

The Gulf of Guinea also plays an important role as a carbon sink, but this function might come under threat with the disappearance of fish species, as the area won't be able to carry out its function of carbon sequestration, reducing the Gulf's function as a carbon sink.

The Mediterranean Sea also plays a significant role as a carbon sink, capturing 0.9 percent of global ocean carbon fluxes, but with many of its fish species under threat, the ecosystem won't be able to sequester as much carbon as before, reducing the importance of the sea as a carbon sink.

The Amazon basin, the Gulf of Guinea Oceanic Islands, the Mediterranean Sea, as well as other places act as carbon sinks, but with the declining population of fish species, these areas won't be able to efficiently carry out their function, worsening the climate crisis.

Places like the Amazon basin, the Gulf of Guinea, the Mediterranean Sea, and similar places require habitat protection, climate change mitigation, and eco-labeling to reduce overfishing as a way to halt the decline in fish populations.

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