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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



were found in subtropical and temperate latitudes 

 (Graham 1941). The frequently appearing con- 

 vergence at 2° to 5° N. latitude also contributes 

 to this apparent greater abundance of life in the 

 equatorial region. Floating organisms with high 

 buoyancy undoubtedly congregate here just as 

 driftwood does along a current rip or other dis- 

 continuity zone ; zooplankton capable of resisting 

 the downward currents would also tend to con- 

 centrate in the surface layers. When a strong 

 convergence has persisted for a sufficient length 

 of time, an area of relatively high-plankton abun- 

 dance should result, providing rich pasturage for 

 plankton-feeding animals. 



The unusual abundance of marine life in the 

 equatorial region has been observed by many ex- 

 peditions and world travelers while crossing the 

 Pacific. Agassiz and Mayer (1902), in their re- 

 port on observations and collections of the Alba- 

 tross in the tropical Pacific, state, 



In fact it is evident that pelagic animals are not 

 abundant in regions far from large land masses or where 

 there are no well-defined oceanic currents or counter 

 currents. As soon as one approaches the region of great 

 currents or counter currents, or the coasts of continents 

 and larger islands, the number of animals increases with 

 remarkable suddenness. 



Beebe (1926) describes masses of floating debris 

 and the associated wealth of life in a current rip 

 some 200 miles southeast (between 3° and 4° N. 

 latitude) of Cocos Island in the eastern Pacific. 

 Brooks (1934), in reporting his observations on 

 certain relationships between ocean currents and 

 birds, asks why it is that on ocean voyages day 

 after day goes by and no birds or marine life are 

 seen and then suddenly one passes into an area 

 teeming with life. He observed that, as his vessel 

 neared the Equator from the north, bird life in- 

 creased greatly, as did other marine life such as 

 flying fish, sharks, and whales ; then as he crossed 

 the Equator, the zone of abundant life was left 

 behind. 



Revelle (1944) points out the agreement be- 

 tween the southern boundary of the Countercur- 

 rent and the northern border of the Pacific Globi- 

 gerina ooze area. In reporting on results of the 

 recent Swedish Deep-Sea Expedition, Arrhenius 

 (1950) states in respect to the Pacific, 



The biogenous component and simultaneously the rate 

 of sedimentation increases strongly below the conver- 

 gence where a biolith, rich in fossils of foraminifera. 



radiolaria and diatoms is thus deposited. North of the 

 convergence of the Equatorial Counter Current, the share 

 of the biogenous component in the sedimentation de- 

 creases and the fossil-rich biolith turns into a clay, poor 

 in fossils and with a low intensity of sedimentation. 5 



As summarized by Herdman (1923), 



It is probable, on the whole, that the distribution and 

 variation of ocean currents have more than latitude or 

 temperature alone to do with any observed scantiness of 

 tropical plankton. These mighty rivers of the ocean in 

 places teem with animal and plant life, and may sweep 

 abundance of food from one region to another in the 

 open sea. 



VARIATION IN ZOOPLANKTON ABUNDANCE 



The sampling method used in the present study 

 meets the criteria for randomness in most respects, 

 allowing the use of standard methods of statistical 

 analysis. Although the stations were located in 

 systematic order, a random sample was probably 

 obtained of the zooplankton population retained 

 by a meter net with 0.65-mm. apertures from the 

 upper 200 meters of water. There is some doubt, 

 however, as to the type of distribution of the 

 plankton population. Although our results indi- 

 cate a rather uniform, but very dilute distribution 

 of zooplankton, which would perhaps conform to 

 a Poisson distribution, the majority of workers 

 have reported clumping and lack of uniformity. 

 Snedecor (1946, pp. 42 and 252) states that the re- 

 quirement of randomness must be adhered to, but 

 normal distribution of the population is a specifi- 

 cation that can be considerably relaxed. Of course, 

 there are devices appropriate for analyzing sam- 

 ples from nonnormal distributions. One com- 

 monly used method involving a transformation of 

 the data to logarithms, was employed in certain 

 initial tests of the volume data. The results and 

 conclusions obtained were the same, however, as 

 those reached through an analysis of the untrans- 

 formed data. We assumed, therefore, that the 

 degree of anormality in the zooplankton popula- 

 tion would affect our inferences but little, and in 

 this report have chosen to examine and base our 

 conclusions upon tests of the untransformed data. 

 We wish to emphasize the point that all statisti- 



5 The convergence here referred to by Arrhenius is that which 

 theoretically occurs at the southern boundary of the Counter- 

 current and, as previously stated, has not been observed by these 

 Investigations. We have found the convergence 2" to 3° south 

 of the current boundary and entirely within the South Equatorial 

 Current. 



