How many fish are in the ocean?

Great reality check on the current state of our oceans (earlier post here). We always being relativists assume the vastness of the ocean directly corresponds abundance of fish and develop this delusion,  leading to an unquenchable appetite for sea food.

"Ryther’s approach to this complex problem is actually quite simple- any introductory biology student could understand the scientific principles behind his solution. Although it is impossible to count all the fish in the ocean, it IS possible to measure the primary productivity (how much energy is produced by photosynthesis at the base of a food chain). By knowing how much food is out there and knowing how efficiently energy from food is transmitted up the food chain, you can indirectly calculate how many fish the oceans can support.

Ryther used measurements of primary productivity from the 1950-1952 expedition of the Galathea, which had taken measurements of only 194 locations in the world’s oceans. He had access to one measurement for every 2 million square kilometers of ocean, and most of the measurements were taken in tropical waters.

The data from the Galathea expedition is startling. The overwhelming majority of the oceans (approximately 90 %) have extremely low primary productivity. The average is 50 grams of carbon per meter per year. In comparison, coastal regions (approximately 7.5% of the total area of the oceans) produce around 100 grams of carbon per meter per year, and upwelling regions (approximately 2.5% of the total area of the oceans) produce over 1,000 grams of carbon per meter per year. In other words, while there are a few incredibly rich fisheries in the world, most of the ocean simply doesn’t have enough food at the base of the food chain to support a lot of fish.

Now that Ryther knew (approximately) how much food was at the base of the food chain, he could start to solve the problem. The next step required a knowledge of trophic transfer efficiency, which is a measure of how much energy from organisms on one step of the food chain is usable by organisms that eat them. Not all the energy that a given organism has can be gained by its predator, since some of an organism’s energy goes into things like growth and reproduction.

Though trophic efficiency varies by ecosystem and organism, ecologists usually use 10% as an estimate. In other words, one hundred pounds of plant (primary producer) biomass at the base of a food chain can only support ten pounds of herbivore biomass, which can only support one pound of primary carnivore biomass.

Trophic efficiency becomes important when you consider where on the food chain humans get their food. On land, we tend to eat animals such as cows, which are only one step up from the base of the food chain. In the ocean, however, we eat animals much higher up the food chain- phytoplankton are eaten by zooplankton, which are eaten by small fish, which are eaten by medium sized fish, which are eaten by the large fish like tuna that we eat. Keep in mind that 90% of the oceans don’t have very much energy at the base of the food chain- the trophic level we get most our seafood from can support 10% of 10% of 10% of 10% of relatively little biomass. The “bounty of the oceans” is far from inexhaustible.

The final estimate from all of these calculations was as follows: the ocean can support a total of approximately 240 million tons of fish. However, humans can’t harvest all of the fish that are out there- we need to leave some to reproduce, and some to feed the ocean’s other carnivores. Ryther estimated that we couldn’t remove more than 100 million tons of fish before we run into serious problems.

As it turns out, the 2008 “State of World Fisheries” report stated that we harvested 95 million tons of fish in 2008. That makes the technical term for Ryther’s estimate from 40 years ago “pretty darn close”

I am a big fan of Nassim Nicolas Taleb, check out his "hobby":
" "My major hobby is teasing people who take themselves & the quality of their knowledge too seriously & those who don’t have the courage to sometimes say: I don’t know...." (You may not be able to change the world but can at least get some entertainment & make a living out of the epistemic arrogance of the human race)."

This arrogance of human's can be entertaining  but some of them are self destructive. Not everything which looks and seems obvious can be self-evident and not all which looks and seems self-evident can be obvious. Not everything that's both obvious and self evident are true. To get to the truth we need to look beyond obviousness and self-evidence and yes, we need to develop a sense of epistemological modesty and reduce that inflated self-esteem. That's the only way out for a solipsist.