CRUISE TO-M-I (SCOT) 

 il aphil ism - 20 june ism 



HICRONEKTON AT NIGHT STATIONS 



108LIOUE NAULS, 9O-0 M. 5 KHOTS ) 



IN HL PCN eSTIMATtD lOOOH* - 



FiRure 12.--Distribution of total micronekton on SCOT Expedition. 



It is of interest to compare these plots 

 with chlorophyll- zooplankton plots for the 

 same cruise, which are shown on the left in 

 figure 13. For Expedition SCOT this relation- 

 ship is significant but for TO- 59-1 it is not. 

 There is thus no evidence of a steady state 

 in the biotic part of the energy chain for 

 TO-59-1, but the data indicate the possibility 

 of such a state in the area and period of 

 TO-58-1 (SCOT). 



This may be exannined further. The lines 

 in the SCOT plots in figure 13 indicate func- 

 tional or structural relationships obtained by 

 the method of Bartlett ( 1 949), not least- squares 

 regressions. It is obvious that the slope 

 coefficients are not 1.0 and that chlorophyll a 

 and micronekton increase more than zoo- 

 plankton does between any two points on each 

 line. This, on the face of it, is no steady 

 state, but there are considerations that do 

 not exclude such a state. For instance, some 

 components of the micronekton might feed 

 directly on plant material in living or detrital 

 form (e.g., copepod faeces). Euphausiids, 

 which are commoner in night n-iicronekton 

 than in day zooplankton catches, are known 

 to do this, and so possibly do the large 

 Crustacea (pelagic crabs, etc.) that some- 

 times bulk very large in the micronekton 

 although they are seldom taken in the zoo- 

 plankton. (Large Crustacea and zooplankton 



crops are not correlated, as mentioned above.) 

 One way to test this possibility is to study the 

 relationship between micronekton and chloro- 

 phyll a at the same (night) stations; some 

 data were collected for this purpose on cruise 

 TO-59-2 and more on TO-60-1. but they have 

 not yet been analyzed. At present it appears 

 possible that a steady state is approximated 

 in certain regions and seasons. 



The question of the steady state has prac- 

 tical significance for the STOR program, 

 because its existence would warrant the use 

 of simpler models and methods for analysis 

 and prediction of, say, standing crop of tuna 

 food. For instance it would justify the belief 

 that the size of a given standing crop of tuna 

 food depended upon events in the same area 

 and not in some other, which would simplify 

 understanding and prediction. In investigations 

 by the Bureau of Commercial Fisheries in the 

 central tropical Pacific there was evidence of 

 progressive poleward displacement of organ- 

 isms at higher trophic levels (King, 1958; 

 Murphy and Shomura, 1 958), which complicated 

 the investigation. 



TUNA ECOLOGY 



(M . Blackburn) 



In this section the dependence of yellowfin 

 and skipjack tuna upon temperature and food 



36 



