Friday, 18 September 2015

Sperm whales, global warming and fish population

Sperm whales, featured in the novel Moby Dick,  are at the top of the marine food chain, above that of the giant squid and the colossal squid. It used to be thought that they were a threat to the available fish stocks but in fact they seem to be beneficial and it shows just how complex and full of surprises the biosphere can be.

Sperm whale clicks carry for 6 miles and are as loud as a jumbo jet (230db)

 Although sperm whales eat a lot of marine fauna their main diet is squid, which contain a lot of iron (Fe). They dive to as much as 3 km for 30-90 minutes, spending about 8 minutes resting  near the surface, where they excrete over 80% of the Fe they have ingested from the squid prey. The iron enters the ocean as Fe salts. 

This is the key to the replenishment of fish stocks because the Fe salts are highly nutritious to the phytoplankton, which is the foundation of the whole ocean food chain in the same way that ordinary green plants are the base of the land food chain. Not only does this allow the fish population to grow but, considering just the Southern Ocean, which contains 12,000 sperm whales, the phytoplankton remove 440,000 tons of carbon per year from the atmosphere.  This compares with about 176,000 tons (p.a.) breathed into the air by the sperm whales, giving a net carbon removal of 266,000 tons p.a. by the sperm whales in the Southern Ocean. Scaling up (assuming such a scaling up is valid) from 12,000 to a total of about 360,000 globally this means that in all sperm whales remove (360,000/12,000) x 266,000 =  30 x 266,000 = 7.98 million tons of carbon p.a. 

Phytoplankton,  at the bottom of the food chain, intercepts energy from the sun and converts it into plant tissue for mobile grazing sea creatures, so the sperm whale predation chain significantly increases  the number of  fish available  for food. This is despite the large consumption of sea life by the sperm whales since, as stated above, fish are only a small part of the whale's diet.

Before the Industrial Revolution there are estimated to have been 2 million sperm whales and their 6-fold decline must have had a significant effect on global warming as well as in reducing the phytoplankton biomass on which all sea life depends. So there appears to be good reason to restore the populations of these sea mammals.

 Being at the top of the chain they are highly susceptible to poisoning both by metal and plastic. (In my novel, 2077:Knights of Peace, an incidental theme is the deployment of robot plastic scavenging ships worldwide.) 

See also

John Sears