Climate change

Fish fecal carbon sequestering likely halved over past century

WRITTEN BY Oceanographic Staff

An international team of researchers created a new model that shows the effects of fish and their excrement on the world’s oceans over the past century.

The model found that fish fecal carbon sequestering has most likely declined by half during the past century. The paper, published in the journal Science Advances, looked at the human impact of commercialising fishing around 1900. Commercialised fishing activities led to an increasing number of fish getting caught every year, which also translated into a decreased number of fish in the oceans. At the same time, fish are known to digest phytoplankton which, in turn, gets pushed out as a near constant stream of excrement which holds some amount of carbon.

Fish excrement tends to collect at the ocean floor where it builds up and is a form of carbon sequestration. Due to the decreasing number of fish in the oceans, the researchers wanted to find out how the decline directly affects the amount of carbon sequestered by the ocean.

As part of the study, the researchers studied historical documents to find out how many fish used to call the ocean home and tried to estimate the current amount of fish living in the oceans. Other estimates included the changing amount of phytoplankton eaten by fish. Some of the findings: a century ago, fish ate around 2 per cent of total organic material globally and the entire global biomass of fish has dropped by approximately 47 per cent over the past century.

The study is an important indication on how decreasing fish numbers ultimately affect climate change. As the biomass and biogeochemical roles of fish are still very undiscovered, the findings can help develop better understanding of how fish alter biogeochemistry.

Ultimately, the model suggested that today’s amount of fecal matter dropped by fish globally is around half of what it once was. This, in turn, means that only half as much carbon is being sequestered with that the remainder ending up in the atmosphere and exacerbating climate change.

For more from our Ocean Newsroom, click here.

Photography courtesy of Unsplash.

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