PERU CURRENT 



90° W. Bottom contours at great depth may assist the course of 

 convergence. These are physical boundaries and can be detected 

 with a thermometer by the sharp change in temperature. They can 

 be as easily detected by the distinction of life within the water. 



Within the Antarctic Zone, surface water temperatures 30° F. to 

 38° F., the food of birds, as well as of whales and some seals, consists 

 mostly of "krill", the Norwegian whaleman's name for the euphau- 

 sian crustaceans or oppossum shrimps. Although there are many 

 kinds of euphausid, the species Eupkausia superba has been found 

 most abundant in the stomachs of penguins, petrels, seals and whales 

 of the far south. The exclusive food of penguins is swarms of this 

 form of "krill" which in turn subsist largely on diatoms, the predom- 

 inant microplankton of the area. The body growth of the birds and 

 whales are thus only one step removed from the organic fixation of 

 the radiant energy of the sun by the phytoplankton. 



ANTARCTIC CONVERGENCE 



The Sub-Antarctic Zone, surface water temperatures 38° F. to 

 58° F. is almost entirely within the belt of westerly winds and is an 

 area of much deeper and warmer surface water. Salinity and temp- 

 erature decrease with depth in this area and there is a constant tend- 

 ency toward upwelling and vertical mixing. The unstable conditions 

 of rough weather tend toward less production of phytoplankton. 

 Munida, known by the southern whalemen as "lobster krill", make up 

 the predominant bird-whale-feed in this zone. These creatures occur 

 in enormous abundance. Munida gregaria sometimes color the sur- 

 face of the ocean a bright red. They appear in vast numbers far north 

 in Peru Current waters and form a substantial part of the food of gulls, 

 cormorants, petrels and penguins. 



An impressive description of marine life in profusion living in 

 nearly perfect conditions in the Peru Current has been recorded by 

 R. E. Coker as follows: 



"In contrast to the barrenness of the coast [of Peru] there is a 

 peculiar wealth of certain forms in the open ocean. The great 

 red seas, formed sometimes, at least, of myriads of microscopic 



dinoflagellates, are of common occurrence Sometimes, 



too, great areas of the surface of the sea are reddened by the 

 vast numbers of small Crustacea (Munida) which then play a 

 part of great importance as food for the fishes and for the 

 guano-producing birds. More striking still are the immense 

 schools of small fishes, the "anchobetas" (Engraulis ringens 

 Jenyns ), which are followed by numbers of bonitos and other 

 fishes and by sea lions, while at the same time they are preyed 

 upon by the flocks of cormorants, pelicans, gannets, and other 

 abundant sea birds. It is these birds, however, that offer the 



most impressive sight. The long files of pelicans, the low mov- 

 ing black clouds of cormorants, or the rainstorms of plunging 

 gannets probably cannot be equaled in any other part of the 

 world. These birds feed chiefly, almost exclusively, upon the 

 anchobetas. The anchobeta, then, is not only , . the food of 

 the larger fishes, but, as the food of the birds, it is the source 

 from which is derived each year probably a score of thousands 

 of tons of high-grade bird guano . . . No more forcible testimony 

 to its abundance could be offered than the estimate, made 

 roughly, but with not wide inaccuracy, that a single flock of 

 cormorants observed at the Chincha Islands would consume 

 each year a weight of these fish equal to one-fourth of the en- 

 tire catch of the fisheries of the United States." 

 The Sub-Tropical Zone, surface water temperature 58° F. to 

 73° F., show an increase in salinity and a striking decrease in nutrients. 

 Oxygen in the surface layers decreases from about 80 percent of satu- 

 ration in 28° S. to about 40 percent at the Equator. These waters are 

 not favorable for diatom growth except where replenished by up- 

 welling such as exist along the Peruvian Coast where conditions remain 

 constantly favorable. The volume of plankton diminishes under these 

 adverse conditions in the Sub-Tropical Zone and the collective popu- 

 lation of surface organisms may be no more than ten to each quart. 

 The diatoms are replaced by less well known varieties and likewise 

 the pelagic Crustacea, so important to life in the southern zones, are 

 replaced by copepods. Therefore the abundance, if available, becomes 

 sporadic. The Portuguese man-o-war appears in this zone. Flying 

 fishes and dolphins replace the immense schools of small fishes of the 

 colder waters. The numbers and types of sea life near the surface 

 diminish greatly. 



The Tropical Zone of surface waters, temperatures 74° F. to 

 84° F., differs little with that of the Sub-Tropical.' Salinity is at a 

 minimum because of heavy rainfall and low evaporation. Waters 

 of greater density and salinity are observable below the surface layer. 

 There are no detectable phosphates and but minute quantities of 

 nitrate nitrogen. Bird life in these climes is regarded as land bound 

 rather than pelagic except for flock or single migrations. 



Next to the extraordinary abundance of marine life in low south- 

 ern latitudes, the most evident characteristic of the Peru Current is 

 the unequalled northward distribution of Antarctic and Sub-Antarc- 

 tic types of birds and mammals. Examples in this category are many 

 Peruvian species with distinctly subpolar affinities such as: 



(a) The Southern Kelp Gull (Larus dominicanus), a Sub- 

 Antarctic sea bird of circumpolar range, which breeds in 

 numbers on Tierra del Fuego and upon other heavily-glaciated 

 ice-covered islands, such as South Georgia and Kerguelen. 

 This bird also extends its breeding range along the tropical 

 western coast of South America practically as far as the Peru 

 Current is in contact with the land . Its northernmost breed- 

 ing station, on Lobos de Tierra (Lat. 6° 25' S.) is one of its cen- 

 ters of maximum abundance. 



(b) The White -breasted Cormorant, or Guanay (Phalacroco- 

 rax bougainvillei), first in importance as the Peruvian guano 

 bird, is a member of the well-defined Antarctic branch of the 

 cormorant family. Its closest kin are the cormorants of the 

 Strait of Magellan, New Zealand, Sub-Antarctic islands, and 

 the shores of the Antarctic Continent, but its relationship with 

 the other cormorants of South America or with those of the 

 Northern Hemisphere is distant. The range of the Guanay 

 extends along the west coast of South America from central 

 Chile to within six degrees of the Equator. 



(c) Diving Petrels ( Pelicanoididae ) are representatives of a 

 typical Sub-Antarctic family of marine birds. They breed 

 along the western coast of South America from Cape Horn to 

 the northern islands off Peru (Lat. 6°25'S.). Diving Petrels 

 do not breed north of about latitude 37° S. in any other 

 part of the world. 



(d) Penguins (genus Spheniscus) are found along the west 

 coast of South America southward of latitude 6° S., and also an 

 endemic species (S. mendieulus) resides on the Galapagos 

 Islands at the Equator. 



(e) The Southern Sea Lion (Olaria byronia) is a permanent 

 resident along the west coast from Cape Horn to northern Peru, 

 and again a representative of the same genus occurs at the 

 Galapagos Islands. 



(f) The rare Southern Fur Seal ( Arclocephalus australis), 

 sometimes sighted at Independencia Bay (Lat. 14°10'S.), 



64 



