Over-fishing is already a concerning problem, but new research indicates that not only could it mean losing fish species, it could also contribute to global warming more than we’d previously thought.
That’s because researchers from the Marine Institute and the University of Southampton have found that fish that feed on our ocean floor and do not come to the surface actually act as carbon sinks. Other examples of naturally occurring carbon sinks include forests and, indeed, the oceans themselves. What’s more, the UK-based researchers have found that deep-sea fish might be capturing more than a million tons of carbon dioxide from UK and Irish waters.
The process starts with what are known as mid-level swimming fish, as well as jellyfish and certain cephalopods like squid. They will often venture close to the surface, feed and then, for a short time, dive to deeper waters. When they do this, they run the risk of becoming prey for larger bottom dwellers who never surface. When this happens, the carbon in the prey animals’ system transfers to the predator fish — and there it stays. True, when one of those predator fish dies it’s likely some of that carbon is released, but even then those fish are often dined on by others at the bottom of the ocean, and so the majority stays in our deep water fish.
The researchers investigated this by collecting muscle tissue samples from fish caught in fish trawls off the west coast of Ireland, at varying degrees between 500 and 1,800 meters. To look at how much carbon was present at each stage they searched the muscle samples and looked for carbon and nitrogen isotopes. By doing this, the researchers are able to see how carbon transfers through the ecosystem and thereby determine diet and the predator/prey dynamics of that area.
This is an important finding because it tells us a number of things. Chiefly, it reveals a vital carbon sink that could help us in a small but significant way to combat adding to the global warming problem. It also tells us how dangerous unregulated fishing and overfishing practices can be. For instance, many of the bottom-feeders are not caught for food but regularly get swept up in fishing trawls regardless. They are killed in this process and then usually thrown back, thus releasing that carbon (which is just one troubling aspect of this practice).
Deep sea mining operations are also threatening these fish, driving down their numbers and interrupting what we know is a very important ecological process.
On this, lead researcher Clive Trueman is quoted as saying, “As fishing, energy extraction and mining extend into deeper waters, these unfamiliar and seldom seen fishes in fact provide a valuable service to all of us. Recognizing and valuing these ecosystem services is important when we make decisions about how to exploit deep water habitats for food, energy or mineral resources.”
In fact, the researchers believe that as many as half of all bottom-feeders get their energy in this way as opposed to the presiding theory that they eat particulate matter that settles at the bottom of our oceans.
The United Nations classes illegal fishing practices and over-fishing as a major concern to biodiversity and, ultimately, to the global food supply because, once fish numbers drop below a certain level, the populations will not be able to rebound, creating a collapse that will hit the poor in under-developed nations especially hard as, often, fishing is their main food and income source.
Needless to say, it will also contribute to the loss of fascinating and oftentimes beautiful animal species. You can read more on the problem of overfishing and how we might overcome this issue here.
Photo credit: Thinkstock.
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