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Friday, December 14, 2012

Modeling the Whale Pump

Trying to model the whale pump will probably be horribly complex but for all of that, very worthwhile to do.  It could effect the fisheries of the world and the policies we adopt.  So what is the Whale Pump.

Many whales feed in deep water and defecate and excrete (pee) in surface waters.  They are pumping nutrients from deep dark waters into the photic zone where algae, utilizing the energy from the sun, can  rebuild these mineralized compounds back into energy rich fats, proteins etc.  Many whales also feed on the surface and equally, defecate on the surface, circulating nutrients to power the web of life.  I don't know where to start so I'll just plunge in, in the middle and see where we get to.

Let's suppose we are in the Antarctic and, for the sake of the argument, that the upwhelling that occurs there is bringing up all the nutrients needed.  Nutrients are not  limiting  primary production and hence not limiting secondary, tertiary etc. production.  A bunch of whales now add their nutrients to the photic zone.   We are already at the sun limit (all the primary production that the sun can power is already taking place) so primary production does not increase.  That is the "first approximation" but here comes the first wrinkle.

Some algae can use more complex molecules such as amino acids in addition to the fully mineralized nutrients such as nitrates, phosphates and all the other 'ates' they require.   In a previous blog, I discuss the detritus cycle. In the detritus cycle bacteria which secrete the enzyme, cellulase use the chemical energy from the cellulose rather than sun energy to build their bodies.  This forms the base of a food chain that is independent of sun light.  It is likely that the algae which can utilize amino acids and perhaps a range of other energy rich compounds also get at least part of their energy from these energy rich molecules.  Here we have a likely way around the limit to primary productivity set by the sun.  Whale poo is likely to be rich in such compounds.  Lets  look now at what primary productivity we could expect from whale poo in water which has less than adequate nutrients.

If you were to make a first approximation of the effect of Whale Poo, you might say that the amount of nutrient given out by the whales could support X amount of primary productivity (algae), 0.1X of secondary productivity (krill), and 0.01X of tertiary productivity (penguin)* and so on up the food chain.  However it is not that simple.  Each tropic layer, including the algae, is excreting into the water and providing nutrients for the sun to build back into more energetic compounds.  The actions of all these organisms act to lock nutrients in the surface sunlit waters and they are only slowly  lost to deep water.

*Note that about 10% of the substance (or energy if you like) from one tropic layer is transferred to the next layer.

So already, the situation is complicated.  How about when the whales migrate to oligotrophic (nutrient poor) waters.  A number of whale species migrate to the Gulf of California and other nutrient poor tropical waters to give birth to their young.  Once the Colorado river flowed into the head of this semi confined body of water.  It undoubtedly carried masses of nutrients in the form of dissolved and particulate material.  This flow has almost ceased as water extraction has increased for agriculture.  Into this sheltered water adult female whales migrate and give birth to their young. Even if the adults do not feed and therefore, do not defecate, they suckle their young and the young poop out nutrients.  If they are similar to most animals, 90% of the nutrients the young consume as milk are pooped out into the water.  Since whales are probably down to one or two percent of the population* that  existed at before the advent of whaling, you can imagine the reduction in nutrients and the potential if whales returned to their original abundance.  The Gulf of California is surrounded by desert.  It has a large number of sun hours and so the potential primary productivity is great if nutrients are made available**.

 *This site gives the population of Right Whales in 1997 compared with the historical estimates and includes the rate of growth of the population.  If you invert the growth rate and project it back to the end of industrial whaling, you realize that this species was very close to extinction when whaling ceased.

A well known migration of whales are the Humpbacks of the Southern ocean.  They migrate from the Antarctic to the warm waters of various south sea islands via New Zealand waters to give birth.  There is no food  for the adult females in the tropics (New Zealand Geographic, Jan-Feb 2013 p36) but they have gorged on two tons of krill a day over the Antarctic winter and now feed their young 200l of rich milk per day.  Nutrients are being shifted from Antarctic waters to tropical waters and as we have seen, these nutrients cycle around in surface sunlit waters only slowly being sequestered in deep water.  A little nutrient goes a long way in nutrient poor areas.  Imagine what sort of fisheries could result from whale populations restored to their former levels.

Hopefully, this sort of argument might convince the remaining few whaling countries to cease killing whales.  These same nations are also fishing nations and are reducing their own fish catches by killing whales.

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