SPERM WHALES CAN AIDE OCEAN FISHERIES

SPERM WHALE INTERVENTION IN MARINE NUTRIENT RECYCLING

Available nitrogen is a limiting factor in marine food chains.  Nitrogen is needed by the algae at the base of open ocean food chains.  Atmospheric nitrogen can be fixed into available nitrogen by some marine microorganisms, but not in quantities needed to support a thriving food chain.  Ammonia or some other form of nitrogen can be recycled in the food chain when it is released by protein metabolism of other organisms.

The majority of the open ocean is like a biological desert because of the limiting factor of low available nitrogen.  What is there can be removed by - sea birds depositing guano on land, commercial and sport fish harvesting, and detritus and dead organisms carrying it to deep water and eventual loss to geologic deposits on the sea bed.

The first two sources of removal are somewhat balanced by return to the sea by rivers containing fertilizer and food nitrogenous components.  That makes coastal waters more productive than the open sea.  The second source of removal  can also be balanced by return due to up-welling currents producing high productivity in some localized regions in response to some cyclic weather induced currents.  Once in the deep sea deposits it is mostly trapped for long periods of geologic time.  But before it is trapped, a significant amount can be returned to surface waters by sperm whale intervention.

Sedimentation of small organic particles in the open ocean is very slow.  They can be recycled in intermediate level food chains before the component nutrients reach the seabed.  One particularly effective avenue for recycling is the intervention of ammoniacal squid that live at considerable depths in the ocean and accumulate ammonia from protein metabolism as a flotation material.  A portion of that accumulated ammonia will be returned to surface waters by sperm whales feeding on those deep water squid as well as giant squid.

The great reduction of sperm whale numbers has probably been a major factor in decline of some marine fisheries.  The reduced growth of phytoplankton diminished both the amount of food to those higher in the food chain and their ability to recover from over-fishing.

Fortunately, very little harvesting of sperm whales is occurring today.  But recovery to former numbers is very slow because so few are left, and their well-being in terms of learned culture passed on socially may have been impaired.  I tried to alert congress and our representative to the United Nations (in the 1970's) of the need to protect sperm whales to save fisheries.  About the same time there developed an international consensus to ban sperm whaling.  But Japan did not join the consensus and continued to harvest some for sperm whale research for a while.  I wrote a paper for a Japanese newspaper competition for submissions on environmental matters, but it did not get accepted.  

I thank Dr. Patrick C. Kangas, then at Eastern Michigan University, later at the University of Maryland, who alerted me to much of the quantitative contribution aspect of sperm whale intervention.  

Living giant squid have recently been shown on television for the first time.  An introduction to some of the data used above can be found in Berzin (1972) and Clarke (1977).

References

Berzin, A. A.  1972.  The Sperm Whale.  Israel Program for Scientific Translations.  374 pp.

Clarke, M. R.  1977.  Beaks, nets and numbers.  Symp. Zool. Soc. Lond., 38:89-126.

Joseph G. Engemann     August 31, 2013.